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CHEMISTRY AND ENVIRONMENT

Professor Chinaka Linus Ndiokwere University of Benin 21st October 2004

SYNOPSIS CHEMISTRY AND ENVIRONMENT Almost everything that happens in the world around us could come under the heading ­ Chemistry and Environment. Chemistry has contributed immensely to man's welfare and progress. It has also created problems in the management of its products ­ the chemicals. The effects of environmental pollution are exemplified by nine reported and documented episodes, which illustrate industrial chemical poisoning of the terrestrial and aquatic ecosystems. The identities and sources of the potentially toxic chemicals are established in most cases but their quantitative importance is rarely determined. The gaseous air pollutants are mainly carbon and nitrogen oxides, SO2, fluorine, ozone and sundry hydrocarbons as well as particulate matter, which includes aerosols, dusts, fly ash etc. The sources of these pollutants are fossil fuels such as coal, petroleum, natural gas and wood fuel; motor vehicular traffic; emissions from domestic and wild (forest) fires; asbestos and asphalt. Hydrocarbon emission takes part in photochemical reactions producing smog in the urban environment. More toxic and persistent contaminants are pesticides, polychlorinated biphenyls (PCBs), chlorofluorocarbons (CFCs) and polynuclear aromatic hydrocarbons (PAHs). Indeed, pesticides are considered to be the most indicted among the barrage of chemical poisons created by man for use in the control of pests. Insulations, treated wood, volatile adhesives, fabrics and carpets, especially when new, tobacco and cigarette smoking release low levels of potentially harmful chemicals, which are prevalent of indoor air contaminants. Trace metals and their ions contribute to pollution problems because of their physiological effects even at low concentrations. However, their role in human health is complex and not so well understood and so their safe levels are very difficult to determine. The anthropogenic and natural sources of the potentially toxic metals such as As, Cd, Pb and Hg from non-ferrous metal production, iron and steel production, fertilizer and cement industries are considered. The global perspectives of their (As, Cd, Hg and Pb) cycling in the environment are considered with respect to their distribution in aquatic and terrestrial ecosystems of Nigeria such as surface waters/sediments, fish/mollusks as markers of metal exposure, air-borne particulate matter, soil/vegetation/crops around industrial complexes, refuse dumps and motor ways, human tissues as indicators of industrial pollution and in crime investigations.

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Solid wastes contribute to land pollution and their disposal by incineration causes also air pollution problems. Petroleum industry is considered as major sources of air and water pollution. Pollution control measures are discussed with respect to air, solid wastes, water and waste waters as well as the significance of emission inventories such as point, line and area sources.

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INTRODUCTION

In the past few decades there has been a growing serious concern about contamination of the human environment by toxic gases, solid and chemical wastes in various forms and composition. Industrial production, energy generation, vehicular traffic, changes in the agricultural patterns, along with a desire for a higher standard of living have brought with them increasing danger of the pollution of the environment and the problems associated with it. One of the most current and interesting topics of public concern today is environmental pollution because of the public interest in the search for safety. This topic is of a multidisciplinary nature involving subject areas as widespread as medical, social, legal, physical and biological sciences. Chemistry has contributed immensely to man's welfare and progress. However, it has also created a lot of problems in the management of its products, which can comfortably come under the heading ­ chemicals, Mr. Vice-Chancellor, you will agree with me that almost everything that happens in the world around us could come under the heading "Chemistry and Environment", hence the title of my lecture. My "Doktor-Ingenieur" thesis/work in 1971/72 was in the area of Hot Atom Chemistry, - indeed, the effect of neutron irradiation involving (n, ) ­ reaction, of metal salts and complexes in organic solvents. Continuation of research in this area, as would be expected, since joining this University in 1973 was marred by lack of nuclear reactor facility and other components in Nigeria. By the nature of my training in pure and applied Chemistry and in consideration of the slogan "publish or perish" in a career in academia, it became exigent in the late seventies to move into Environmental pollution studies using nuclear and non-nuclear techniques in the measurement of trace elements levels in environmental samples. DEFINITION Environmental pollution could be seen as undesirable change in the physical, chemical or biological characteristics of the air, land and water, which may affect industrial processes, living conditions or cultural assets, or that may lead to waste or deterioration of our raw material resources. There are other forms of definition of the term Environmental Pollution considered from various perspectives, but I personally consider the definition or better the explanation of the term by the U.S. President's Science Advisory Committee, Environmental Pollution Panel on Restoring the quality of our

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Environment ­ the most appropriate. "Environmental pollution is the unfavourable alteration of our surroundings, wholly or largely as a by-product of man's actions, through direct or indirect effects of changes in energy patterns, radiation levels, chemical and physical constitution and abundance of organisms. These changes may affect man directly or through his supplies of water and of agricultural and other biological products, his physical objects or possessions, or his opportunities for recreation and appreciation of nature". The controversial question, which is not answered by the above definition is that of what constitutes an "unfavourable alteration". Any alteration of the environment due to man's activities may have unfavourable effects as far as some people's opinion are concerned and favourable effects in the opinion of others, whose livelihood may depend on the activity that produces pollution. The affluent societies of the developed nations are likely to feel more concerned about the unfavourable effects of the application of fertilizer and pesticides in agriculture than the societies in such countries in which insufficient food production leads to malnutrition and starvation. Before proceeding further to consider the pollutants and their control measures, it is necessary to consider all the three home truths of ecology, otherwise referred to as "simple laws of ecology" as suggested by Barry Commoner in his book "Making peace with the Planet", namely: (i) (ii) (iii) Everything is connected to everything else Everything has to go somewhere; and Let nature take its course.

The three laws help to explain why the earth is so vulnerable to abuse. The first law indicates that any change to one particular natural resource can lead to a chain of environmental problems. For example, deforestation has led to desertification and changes in local climate. Man continues to exploit forests as a natural resource, by cutting down trees either for firewood or for timber products. Once stripped of trees, the soils of the hill slopes are washed away by rains and so can become barren. Relatively, little is known about the interlocking parts of the vast ecosystem ­ the problem may not be identified or noticed until severe damage has been done. This is surely true in the case of waste disposal, illustrating the second law ­ Everything has to go somewhere. We can only imagine what our homes would look like if there was no disposal of wastes and domestic garbage. The earth is a closed system and so all the wastes must end up somewhere around the earthly home. Examples abound. We are all aware of the partial destruction or depletion of the ozone layer, very widely reported in scientific journals, seminars and conferences and even in newspapers and magazines. Excessive use of even apparently harmless gases such as chlorofluorocarbons (CFCs) is causing this problem ­ such gases and other potentially hazardous gaseous substances are being released into the air, rivers and other water bodies. Even some products which are considered biodegradable can in time be broken down and absorbed by natural processes but others may not. The land and waterways are littered with plastic wastes that will be left lying

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around for decades. We should also think of the less visible industrial toxic wastes usually buried somewhere. These wastes are out of sight but certainly will not always be out of mind. These buried wastes, sometimes chemical and biological, can still seep into underground water supplies and pose grave health risks to man and animals. There are so many examples of such episodes. One outstanding case is the clean up of toxic liquid wastes buried at the Hyde Park Landfill in Niagara, New York, by the Occidental Chemical Company, formerly Hooker Chemical, the firm that used the site for waste disposal for nearly 22 years. Another example is the high toxic chemical levels of the Great Lakes. Scientists often admit that they don't even know what to do with all the chemicals produced by the industries. They can't even keep track of them. The most menacing waste of greatest concern is radioactive waste, which is the by-product of nuclear power stations and nuclear research reactors. Some nuclear wastes are secretly dumped in oceans while others are stored in temporary sites waiting for exportation to some developing countries. The Koko port episode in our country is well known and documented. So far, several years of scientific research has not proffered any solution for safe and permanent storage or disposal of solid or liquid nuclear wastes. There is yet none in the offing (at least known to me at present). Who knows when the ecological time bomb might explode? Man's disregard for the aspect of waste disposal reminds us of the third law of ecology ­ let nature take its course. This means that man needs to co-operate with natural systems rather than attempt to bypass them with something he considers better. A good example here is the use of some pesticides. Farmers and gardeners have been engaged in a never-ending struggle to avoid the ravages of insects for bumper crops and vegetables and the ravages of other pests that damage vegetation. Public health officials are also struggling to control numerous pests and insects that are vectors of human diseases. The number and quantities of chemical compounds used in these campaigns have increased in the past few decades. Flaws have been found in the use of these compounds and now there is great controversy about whether or not the benefits produced by various uses of some pesticides and insecticides outweigh the disadvantages and possible long-term risks. Weeds and insects in some cases proved resistant to one pesticide after another and it became apparent that the pesticides were poisoning the insects' natural predators, the wildlife and even man himself. There is growing evidence that pesticides may not improve crop yields in the long run. For example, in the U.S.A., insects eat up a greater share of the harvest than they did before the introduction of pesticides. The International Rice Research Institute in the Philippines has established that pesticides do not improve rice yields in Southeast Asia any longer. However, these do not show that the world's farmers have stopped using pesticides. The laws outlined above have tried to explain why things are going wrong ­ in the words of Chinua Achebe; "things are falling apart". Chemical reactions of all kinds take place continuously in the atmosphere, in oceans and rivers, in all living things and even below the earth's crust. These reactions occur quite freely and independent of man's activities, but very frequently, man's activities help to complicate this already complex subject. To understand most problems associated with environmental pollution, the knowledge of the materials being deliberately and/or inadvertently released into the environment and the processes, which they undergo, is

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required. Even more than this, one needs to understand the general principles underlying the processes in order to make reasonable predictions about the effects of related substances arising from them. Pollutants which meet the criteria of the above definition are numerous including toxic gases such as SO2, CO and nitrogen oxides; particulate matter in the atmosphere such as smoke particles, lead aerosols, tar and asbestos; pesticides and related products; radioactive isotopes in the atmosphere and waterways; sewage, organic chemicals and inorganic trace elements and phosphates in water, solid wastes on land; excessive heating (thermal pollution) of rivers and lakes. Some Documented Industrial Chemical Poisoning of the Ecosystems In the last century a growing and rapidly industrializing world has produced greater quantities of common pollutants such as household garbage and sewage, and more toxic and persistent contaminants like pesticides, polychlorinated biphenyls (PCBs), dioxin, chlorofluoro carbons (CFCs), heavy metals and radioactive wastes. Pollutants affect ecosystems in a variety of ways. Pesticides and heavy metals may harm exposed organisms by being acutely toxic or by accumulating in plants and animal tissues through repeated exposures. Pollutants such as acid rain can act at a system-wide level, disrupting soil acidity and water chemistry ­ both being the critical environmental factors which affect the nutrition and physical development of plants, crops and aquatic life. Multiple pollutants can create a toxic synergy that weakens organisms and gradually reduce an ecosystem's productivity and resilience. These effects on ecosystems are exemplified by the following recorded and well-documented episodes still illustrating some industrial chemical poisoning of the ecosystems. (i) The industrial revolution has had a profound impact on the surface waters of the world. Rivers that flow through industrial zones, like the River Rhine in Germany or River Thames in England or rivers that flow through mining zones, like the Watarase in Japan, became heavily polluted in the 19th century and part of the 20th Century. The German chemical industry poisoned the Rhine so badly that salmon fish, which had been plentiful as late as 19th century, were rare by mid-20th century. Japan's most important copper mine dumped mine tailings in the Watarase river and sulphuric acid from smelters contaminated the water and ruined thousands of hectares of forest trees and vegetation. Fish and fowl died and local residents became sick. The human birth rate dipped tremendously below the death rate in the nearby town of Ashio. The US $37b global pesticide market dispenses some 2.6b kg of pesticides excluding solvents and dilutants on the world's farms, forests, gardens, with a variety of collateral effects on wildlife and human health (Aspelin and Grube, 1999) Accidental releases of toxic substances such as mining wastes, or of oil or industrial chemicals, occur routinely and with devastating effect. In January

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(ii)

(iii)

2000, 99000 m3 of cyanide-laden wastes escaped a Romanian gold mine when an earthen tailings dam collapsed. The toxic substances wiped out virtually all aquatic life along a 400 km stretch of the Danube River and its tributaries (D'Esposito & J. Fehler, 2000). (iv) In 1997 more than 167000 tons of oil spilled from pipelines, storage vessels, tankers and other carriers and sources to contaminate the world's marine and inland environments (Etkin 1998). Air pollution from SO2, nitrogen oxides, NOx and ground-level ozone had documented effects on crops, forests and freshwater in Europe, North America and Asia (EEA, 1999). A roughly 18000 km2 ­ called "dead zone" of oxygen ­ depleted waters in the northern Gulf of Mexico stems from a tripping of the nutrient pollution ­ referred to as eutrophication, carried to the coast by the Mississippi River over the last 40 years (Rabalars & Scavia 1999, NOAA 2000). The Love Canal, USA episode of 1978 very well illustrates grave effect of improper disposal of toxic chemicals. Chemical wastes, buried some thirty years earlier overflowed its banks due to excessive rainfalls and contaminated the whole area. As a result, miscarriages, congenital malformations, higher skin cancer incidence as well as chromosomal abnormalities were rampant among Love Canal residents to the extent that the area was declared a "disaster area". More recently, 2500 persons died and over 100,000 were hospitalized in Bhopal, India due to the leakage of an estimated five tones of methylisocyanate, an intermediate in the manufacture of carbaryl (known as Sevin), a carbamate pesticide. Locally here in the Niger Delta, there have been occasions of serious and largescale crude oil spills destroying aquatic and terrestrial ecosystems. These have been reported in the national dailies.

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(vi)

(vii)

(viii)

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The identity of the sources of these potentially toxic chemicals has been established in most cases but their quantitative importance is rarely determined. In this lecture the sources of these chemical pollutants and pollution control measures will be emphasized and it is hoped that the awareness of the pollution problems is awakened and that it will possibly influence some actions by the authorities and governmental agencies towards pollution abatement procedures. 2. Gaseous Pollutants/Air Pollutants

This lecture is centred on Chemistry and environmental pollution and I will like to show how Chemistry has contributed to environmental pollution problems and how it is

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struggling to solve the problems it is creating. Most sources of air pollutants have been identified and in some cases, are well characterized. Methane is generally formed by decaying organic matter, while ammonia, hydrogen sulphide and nitrogen (I) oxide are formed from the decomposition of amino acids by bacteria. Most of the atmospheric methane is produced by anaerobic bacteria in swampy areas. In swamps and bogs excess of decaying organic matter derived from marsh plants and dead vegetation remove oxygen from large volumes of water. Carbon monoxide and carbon dioxide are released into the atmosphere by the burning of fossil fuels in forms of coal, petroleum and natural gas and also by volcanic and biological activities as well as woodfuel. A large percentage of CO comes from motor vehicles. The worldwide concentration of CO is estimated at between 0.1 and 0.5 pm but its concentration in air over cities can be well over 50 times as great. The toxic effects of CO on humans are known. Airborne chemical contaminants include also such gases as SO2, fluorine, ozone, nitrogen oxides and sundry hydrocarbons. Quantities of SO2 are emitted into the atmosphere from smelters, use of fossil fuels and burning of wastes and refuse of various composition such as cloth, natural and synthetic fibers. Many sulphur compounds, after undergoing further oxidation processes in the atmosphere, come back to earth in form of sulphuric acid, dissolved in rain water (acid rain). SO2 is an unpleasant gas and is formed by the combustion of sulphur, sulphides and various organic sulphur compounds. Sometimes high levels of SO2 are found in the neighbourhood of coal-fired power stations and ore smelters. Other chemicals are emitted into the air by combustion engines, industrial mills, forest fires and agricultural burning. These burnings produce tremendous quantities of smoke including hydrocarbons, other gases, soot, fly ash and sometimeshorrible odour. Most of solid wastes in our urban and rural areas are disposed of by open incineration. It is therefore expected that open burning contributes largely to air pollution. In some areas the hydrocarbons produced can become serious, being converted to photochemical toxicants. Hydrogen fluoride is sometimes another serious contaminant emitted from brickworks, glass factories and iron smelters. It is very toxic and corrosive. High concentrations of HF have been correlated with an increase in lung cancer. Heavy industries such as fertilizers are significant sources of fluorine in the atmosphere. The main source of chlorine in both gaseous and particulate forms is seawater, which can form aerosols or droplets after the evaporation of water. The aerosols contain gaseous chlorine and hydrogen chloride, formed by the action of any available sulphuric acid on the chloride ions. The incineration of chlorinated organic materials such as polymers, for example, polyvinyl chloride and other various solid waste materials at refuse dumps is an important source of chlorine and/or hydrogen chloride gas. Vehicular Traffic is an important source of hydrocarbons and carbon monoxide as well as nitrogen oxides in the atmosphere. Hydrocarbons also evaporate into the atmosphere from petroleum refineries. Some hydrocarbons interact with oxides of nitrogen in sunlight producing smog, ozone, eye irritation and damage to vegetation. The main concern with hydrocarbon emission is their participation in photochemical reactions

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producing smog. In the polluted lower atmosphere, particularly in the urban environment, a number of complex photochemical reactions can occur producing a variety of eye and throat irritants (such as peroxyacylnitrates) aerosols and reduced visibility. Most of the aerosol burden in the air is caused by whirls of wind and moving motor vehicles. The liquid and solid particles in the atmosphere often act as carriers for other pollutants and can then produce more serious health effects. Emissions from transport vehicles and industries primarily contribute to pollution problems of urban cities in Nigeria. Pollutants like NO2 and CO from automobile traffic are considered important in the assessment of air quality of urban environments. Nitrogen dioxide is the most abundant oxidized nitrogen compound in background air and its role in the formation of photochemical oxidants and smog has attracted the attention of several scientific researchers in recent years. Ukpebor & Ahonkhai (2000) monitored the NO2 levels in Benin City. They recorded the highest concentration of NO2 13.53 g/m3 in dry season and lowest of 3.02 g/m3 in wet season and observed a positive relationship between NO2 levels and traffic density. The effects of NO2 on humans and vegetation are known. For example, at a concentration of 25-250 g/g NO2 causes defoliation and it has been reported that at a level of 0.3-5 pm for 10 to 20 days it inhibits the growth of tomato and bean seedlings. In another study, NO2 levels were monitored in an operating theatre, where N2O, a potential source of NO2 is used as an anesthetics agent. The results showed that the use of N2O in an operating room does not contribute significantly to the concentration of NO2; measured maximum value was 6.22 g/m3 (Ukpebor and Imareugiaye, 2002). In the assessment of air quality in Benin City Ukpebor and Ahonkhai (2000) also studied the levels of tropospheric ozone. The highest and lowest ozone levels were recorded at the Ring Road location and University of Benin campus respectively. The monthly mean concentrations varied spatially. Differences in traffic volume or density and industrial activities seem to be responsible for this observation. It is known that tropospheric ozone is a "greenhouse" gas and that NO2 is the limiting precursor for the formation of ozone in the free troposphere. Benin City can still be seen as relatively safe in terms of ozone pollution. Other world cities record higher ozone concentrations. For example, about a decade ago, the state of California, U.S.A. reached a crisis point concerning its air pollution levels. With the population of California exceeding 30m in 1990 there were 23m registered vehicles in the state, and the total vehicle miles traveled were 242 billion. The state-wide average for NOx emissions per vehicle was 3.0g/mile; 2.7g/mile per vehicle for hydrocarbons. The cumulative California vehicle emissions for nitrogen oxides and hydrocarbons totaled about 1.4m tons/year. The South Coast Air Basin's maximum one-hour ozone concentration recorded was 0.33 pm and the area exceeded the stage I Smog Alerts (0.20 pm ozone) on 42 days of the year. This crisis led California to tackle the problem head-on to monitor and restrict pollution levels (Jody Clark, 2004). These statistics are important to us here in Nigeria living in big cities. The vehicles are increasing in large numbers, of all makes without regulations as to maximum allowable emissions. Emissions from every-day domestic fire practices and wild fires Plant biomass provides about 14% of the world's demand of primary energy. Half of the global population covers an average of 35% of its energy needs by domestic biomass

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burning. In Africa, the biomass contribution alone to the total energy use typically ranges from 80-90% in poor, 55-65% in middle and 30-40% in high-income groups. Unlike the occurrence of free-burning vegetation fires, which is usually restricted to several months during the dry season, domestic biofuel combustion takes place during the whole year. To assess emissions from these domestic fire practices G. Helas and co-workers of Max Planck Institute for Chemistry and Biogeochemistry, Mainz Germany (1999) investigated both consumption of biofuels and related emissions. They studied patterns of biofuel use and carried out measurements of emissions of CO2, CO, NO and occasionally organic compounds and aerosols in the lodgings of rural and urban Zimbabwe (wood and maize residues), Nigeria (wood) and Kenya (wood). The fuel mass consumed was determined and the emissions from the domestic sources were quantified. In this study consumption rates were distinguished between urban and rural as they differ considerably. Together with population statistics and the emission figures the CO2, CO and NO emissions from domestic combustion processes could be assessed. The results show that for average biofuel consumption rates CO2 and CO dominantly stem from domestic cooking practices, whereas for NO the emissions from oil and industrial processes are more important. The proportions of the different sources vary from region to region. Included with particulate matter are some substances, which are potential health hazards even at low concentrations. Asbestos and asphalt are good examples. Asbestos, which has long been recognized as an occupational hazard (carcinogenic asbestos dust) is increasingly present in ambient air because of its use in construction and building materials, brake linings, etc. Asbestos is a general term that applies to a number of naturally occurring, hydrated mineral silicates. Asphalt is another material, which is frequently used on roads and highways and which can pose some health hazard, particularly the fumes and particulates. Another aspect of air pollution, which needs mentioning, is indoor pollution by smoke with all forms of oxides of carbon, nitrogen and sulphur and fumes from insecticides. A good example of an indoor pollution source is a furnace or fire place or kerosene-gas stoves used very extensively in homes for cooking. The levels of the product gases depend on the type of fuel used. Tobacco and cigarette smoking also provides other source of indoor pollutants including CO and some organic particulates. Insulations, treated wood, volatile adhesives, synthetic fabrics and carpets are often incorporated into buildings and their furnishings. Especially when new, many of these products release low levels of potentially harmful chemicals, such as formaldehyde, into the recycled air. Carpets and rugs add to the problem by absorbing various cleaners and solvents and then releasing them over a long period of time. Vapours from various solvents are sometimes the most prevalent of indoor air contaminants. The concentration of the pollutants in this case is normally quite high because of the limited volume of indoor air into which they are released. Another important airborne aerosols are the insecticides, used in homes to fight swarms of mosquitoes and other insects. The discharge of these chemicals into confined environs is increasingly causing serious problems to their users in homes. The

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fumes are sometimes inhaled. The chemical residues degrade very slowly and can be very injurious to health. The scope of the environmental problems associated with the extensive use of slowly degrading insecticides is not being appreciated by the general public and public health authorities. There is need to discuss these pesticides and other halogenated hydrocarbons in some detail because of their significance in environmental problems. 3. PESTICIDES

Pesticides are chemical compounds designed for the control of insects, fungi, weeds, rodents and other organisms regarded as pests. The most frequently used pesticides structurally fall into three main groups: (i) The organochlorine pesticides (OCPs) exemplified by DDT (1,1,1-trichloro-2,2bis(p-chlorophenyl) ethane and its relatives. The organophosphorus pesticides which are esters of phosphoric acid ­ examples are parathion, Malathion and diazinon. The carbonates. These are derivatives of carbamic acid and examples are carbonyl, aldicarb and baygon.

(ii)

(iii)

Other synthetic pesticides include the thiocyanates, dinitrophenols and the organosulphurs. Inorganic pesticides, which contain toxic elements like mercury, arsenic and phosphorus are also in use. Since the beginning of the last century, man has used a great number of pesticides both in agriculture and in the control of endemic and epidemic diseases. Some pesticides are also used in forestry, horticulture and in the preservation and storage of food products. Over these years pesticides have prevented untold miseries all over the world, especially in the tropical and sub-tropical developing countries, through the control of vector-borne diseases and in the maximization of crop yields. (WHO/FAO 1980) On the other hand, pesticides have also been responsible for many unprecedented disturbances of the world's ecological balance. This is particularly true of the organochlorines, which have such characteristics as non-biodegradability and insolubility in water. These make them ubiquitous and persistent in nature, resulting in their bioaccumulation and biomagnification along the food chain. Their use over the years has witnessed a number of hitherto unpredictable deleterious effects on fish, birds, wildlife, and other non-target organisms including man and his environment. Examples of these abound in the literature. To mention a few ­ (i) reduction and/or total extermination of some species of fish, birds, insects and soil fauna necessary for soil fertility. (ii) Tragedies involving man include those of Love Canal in the USA, a death toll of 2500 persons in Bhopal, India 1984. (iii) Agricultural pollution of the Great Lakes Basin. An estimated 375,000 cases of pesticide poisoning occur annually in the developing

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countries with about 10,000 deaths and more (Aldemar Almeida 1984). These episodes precipitated a series of public reactions and over reactions culminating in the ban or restricted use of certain organochlorines and polychlorinated biphenyls (PCBs) in most parts of the developed countries during the past few years. These have been replaced with less persistent but more toxic organophosphorus and carbonates. These are however more expensive and certainly not readily affordable in the developing countries. So, the use of organochlorine pesticides is likely to continue in the developing countries especially in vector control programmes. The distribution and fate of pesticides are determined by a number of variables that include the nature of pesticides and the factors that control the environment in which they are found. Pesticide residues have been detected in almost every soil, waterway, air and in all life forms the world over. Pesticides residues arrive at their different destinations in a variety of ways ­ planned and unplanned. Intentional application can easily leave the residues directly on soil, waterways and vegetation during the aerial spraying or treatment of agricultural land, gardens, rivers and lakes. Such direct applications result in relatively high residue levels. Most organochlorines that get into aquatic environment settle to the bottom sediment, which constitutes a reservoir for pesticides in water. As a result, sediments contain higher residue levels than the overlying surface waters. Thus, organisms in both aquatic and terrestrial environments derive their pesticide contamination by inhalation, dermal absorption or contact and by ingestion directly or indirectly through the food they eat. Pesticide Usage in Nigeria Pesticides have been used in Nigeria since the early part of the last century. By 1970 about 21 different types of organochlorine, organophosphorus and carbonate pesticides were in use in Nigeria against household pests and insects of veterinary and medical importance as well as for the protection of stored agricultural products and ornamental plants. As at today over 200 different brands of pesticides are marketed in Nigeria. It is difficult to obtain the exact number and types of pesticides currently in use because of the manner in which they are imported or manufactured locally. The agricultural sector takes up the bulk of the pesticides. The National Herbicide Use Committee (NHUC) established in 1980, recommended about 46 different brands of herbicide formulations for use in Nigeria (NHUC, 1983). The WHO malaria eradication programme brought in substantial amounts of DDT and dieldrin into Nigeria since 1955. Aerial spraying of these chemicals has been employed in the programmes to eradicate mosquitoes, tsetse flies and blackflies ­ a vector of river blindness (Onchocerciasis). Not too long ago, a number of pest control companies, which undertake the spraying of homes and surroundings against cockroaches, rats, termites, biting midges and crawlers like snakes have emerged. Many of these companies still use the chemicals like aldrin, dieldrin and even DDT due to their relative cheapness. About mid-eighties Dr. (Mrs.) Okor and Professor S.S. Atuma, then of our Chemistry Department carried out baseline studies of organochlorine pesticide residues in Nigerian

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aquatic and terrestrial environments. They measured levels of these chemical residues, most specifically DDT complex, HCH isomers, HCBs in imported fish from some countries and fish from River Niger using GC ­ equipped with 63Ni electron capture detector. Levels of these contaminants were also determined in vegetables, mother's milk and cord blood plasma. Pentachlorophenol (PCP) was measured in human blood and urine. (Okor & Atuma, 1986). The results indicate appreciable contamination of all fish samples (local and imported) as well as in humans (mother's milk and cord blood) with p,p1-DDT and its metabolites. Elevated residue levels in fish from River Niger (at Kainji) was indicative of direct local contamination from industrial and agricultural activities. High levels in vegetables from the northern part indicate more use of the pesticides in the northern than in the southern part of Nigeria. Pentachlorophenol was measured in all blood and urine samples. The body burden of organochlorine pesticides in Nigeria was reported appreciable and was largely derived from the injudicious use of pesticides especially among the lower socio-economic group. Large-scale indiscriminate use and misuse of these pesticides are factors significantly contributing to contamination of food, air, land and humans by these chemicals. An average rural dweller regards gammalin 20 (gamma HCH) as a universal insecticide which can be used to kill not only insects, but also fish and other organisms. It is known that fishermen in various parts of the country willfully release gammalin 20 into rivers for the purpose of killing fish. Market women use it to control pests of dried fish and kolanuts. Hunters use it and other chemical poisons to kill antelopes and giant rats (well known bush meat ­ a delicacy). Some people use it to kill headlice and sometimes it is orally taken as a worm expeller. In the control of malaria in many rural and urban homes pesticides are sprayed in sleeping areas with windows and doors closed to prevent any escape. The levels of these chemicals recorded in breast milk and cord blood plasma of lactating mothers by Okor & Atuma are not surprising. These women also have fish and vegetables in their diet. A lot of scientific information is available on the short- and long-term effects of a large number of pesticides on all forms of life ranging from bacteria to man. The potential of organochlorine pesticides for bioaccumulation and biomagnification is organisms, as they move up the food chain has made them most indicted among the barrage of chemical poisons created by man for use in the control of pests. The pesticides being fat soluble, accumulate easily in fatty tissues, sometimes over periods of time, and can be released into the blood stream, where they can exert their toxicological effects. Chlorofluorocarbons (CFCs) are a family of volatile compounds invented about 1928. Thought to be the world's first non-toxic, non- flammable refrigerants, their use grew rapidly. They also were used as industrial solvents, foaming agents and aerosol propellants. CFC production peaked in 1974, the same year researchers noted the CFC emissions could possibly damage human health and the ozone layer. In 1985, the discovery of an "ozone hole over the Antarctic coincided with a first-ever coordinated international or global effort to phase out the production of CFCs and other ozonedepleting substances. It is interesting to note that worldwide phase out of CFC production is scheduled for 2010, about 80 years after its celebrated invention.

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4.

Emission sources of some Trace elements

The contribution of trace metals and their ions toward pollution problems is of very serious concern, largely because their physiological effects may be substantial even at concentrations that are extremely low. Some trace metals may be accumulated in the body so much that dangerous levels can build up from long-term ingestion or inhalation of very small amounts. In some cases, little is known about their effects and the amounts, which actually constitute a safe level. Generally at low concentrations heavy metal pollution is very widespread. The actual role played by trace heavy metals in human health is complex and not so well understood and this makes the determination of safe levels very difficult. Because concentrations, that are significant, may be small, unexpected point sources may be important. For example, although the amounts of metals contained in coal and petroleum may be at trace levels, the amounts of these materials being burnt result in the release of appreciable total quantities of mercury, cadmium and others into the environment. There are over 90 naturally occurring elements in the environment, each with its own chemistry ­ properties and behaviours of themselves and their compounds. Some of these elements, particularly carbon, sulphur, nitrogen and the halogens have important biological roles and their contributions to pollution have already been discussed (gaseous pollutants). Others may be toxic and these even include some of the biologically essential trace elements. The effects of any element generally depend on the quantity and the chemical form in which it is present. This section will consider the anthropogenic and natural sources of trace heavy metals with particular emphasis on the potentially toxic ones, whose effects on human health have to a large extent been established, notably arsenic, cadmium, lead and mercury. These elements are either considered most toxic or have particularly high enrichment factors in ambient aerosols relative to the earth's crust. Discharges from non-ferrous metal production and other industries Non-ferrous metal industries involve primary and secondary production of some metals. For example, lead-zinc smelter is usually the largest source of Cd and Pb discharges as well as As and Hg emissions. Cd is used as protective plating for steel, in nickelcadmium batteries and in some pigments and stabilizers, used in plastics. The manufacture and subsequent disposal of the materials lead to the dispersal of these toxic metals in the environment. Lead is heavily consumed for a variety of purposes. The use of alkyl lead compounds in petrol and the manufacture and disposal of lead-acid batteries are considered to result in the largest environmental discharges. In Nigeria, battery disposal represents an important source of lead discharge to the city waste pathway. However, large percentage of lead in lead-acid batteries can be recycled ­ leading to the recovery of most of the Pb used in this sector. Also, some Pb from the petrol-derived Pb is present in the exhaust system and so all discarded exhaust systems enter the steel pathway as scrap material. The use of lead piping to plumb domestic water supplies results in considerable mobility of lead and as input to sewage system. Other sources of lead in the human environment are some older

13

paints in which lead pigments, such as basic lead carbonate and lead chromate were widely used. The environmental discharges of Hg arise from the major uses such as in chlor-alkali industry (caustic soda), battery manufacture, pesticides, catalysts and dentistry. Mercury is used as a catalyst in the manufacture of such plastics as urethane and vinylchloride (PVC). Electrical industries use large quantities of mercury annually in the manufacture of long-life batteries, which are eventually discarded as wastes. The environmental chemistry of Hg depends on both organic and inorganic forms, which differ considerably in their toxic effects. Oral ingestion of small amounts of Hg is less hazardous, for example in dental amalgams, since it is relatively inert. Hg is also an insidious hazard in the home. Mercury and some of its salts are used less intensively in medicine and more in some cosmetic materials. Some skin lightening preparations are still available in Nigerian markets such as HgI ­ containing medicated soap and its corresponding bleaching cream. The major sources of Arsenic in the environment are in the manufacture of copperchromium-arsenic (CCA) wood preservatives and the production of certain types of glass. The disposal of treated timber after use results in environmental discharge of arsenic, for example, when the wood is burnt, a large percentage of As is released to the atmosphere. The CCA-treatment of wood against insects is still very much in practice and so the amount of arsenic released from this source will certainly be on the increase in the future. Arsenic is also present in small amounts in detergents and phosphate fertilizers. Of the other uses or sources of arsenic, mention should be made of the arsenic pesticides, although it is no longer in much use today. Because of this variety of uses, arsenic and its compounds can be accumulated through inhalation and ingestion of dust and fumes. Coal and oil combustion is also another source of atmospheric arsenic as well as mercury. Iron and Steel Production The steel works use iron ores, iron and steel scraps and other metals for the production of some varieties of steel. As a result, high concentrations of some trace heavy metals would be expected in the slag and sludges. The manufacture of steel involves the basic oxygen and electric arc processes and this leads to high atmospheric emissions of the trace metals, especially lead and Cd. Steel works are also known to produce large quantities of aquatic effluents. Steel scraps contain some impurities, which can create a potential of atmospheric pollution by trace elements. Cement manufacture The raw materials used for cement manufacture, limestone, clays and shales contain relatively low levels of trace metals. However, the large quantities of materials consumed at elevated furnace operating temperatures (up to 1500oC) can result in high emissions of the elements Cd, Hg and Pb. Air pollutants from cement manufacture consist mainly of rather non-toxic dust, which is emitted in very fine particles. The emission of trace metals will depend largely on the type of production process, fuel used

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in the grinding mill, fuel-firing system and the control device employed. If coal is the fuel used in powering the grinding mills, some portions of the trace metals such as Mn, As, Cd and Zn are likely to be present in the dust from the sources. The manufacture and use of phosphate fertilizers Modern agriculture demands the use of a variety of chemicals notably fertilizers, pesticides and herbicides in pursuit of high productivity. I have already treated pesticides and their effects. The effluents from farmlands contain trace metals and chemicals, some of which are toxic and have long-lasting environmental effects, particularly when they are discharged into rivers and other water bodies. The quantities of rock phosphates used for the manufacture contain elevated levels of Cd, As and low concentration of Pb, Hg, as well as other elements. The process results in the redistribution of the trace elements from the raw material to the fertilizer product and gypsum waste. It can safely be assumed that all the trace element burden is retained in the fertilizer product, which is dispersed during the application of the fertilizer. Repeated application of fertilizers, for example, can result in the accumulation of total phosphorus in the upper soil layer and this can eventually be carried into rivers and streams. FARM ANIMAL AND HUMAN WASTES Organic wastes include materials such as sewage, animal and human wastes, crop residues, food wastes and general garbage. When these substances are carried into streams and rivers, they incur a high biochemical oxygen demand (BOD) and this can affect the aquatic life. When dry on land, some are combustible, some produce odours and some attract flies and vermin. SOLID WASTES Solid wastes normally contribute to land pollution. The process of modern living creates large quantities of solid wastes, the disposal of which can present formidable problems. The quantities and character of solid wastes vary greatly with geographical location, food patterns, public activities, etc. Solid waste materials generally result from industrial, commercial, agricultural operations and community activities. Solid wastes can be classified as: (a) Municipal wastes, including garbage, refuse, abandoned vehicles and parts, construction wastes, etc. Agricultural wastes, including food products, fruits, animal feeds, etc. Industrial wastes ­ plastic materials (bags, wrappers, floor tiles, shoes, etc), cloth, synthetic fibers, rubber materials, etc. Wood products and paper.

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(b)

(c)

(d)

(e)

Leather materials.

The list is a very long one and can hardly be exhausted. Most pollution problems associated with water and air and their implications for public health are usually linked to solid wastes and their disposal. For example, air can be polluted by poisonous and adourous gases, smoke and fly ash, when these are released into it through open burning of solid wastes. Flies, small animals, such as rats and other disease-carrying insects breed in open decomposing rubbish dumps and residential areas, where food garbage is exposed. These wastes can also be washed by floods during rain storms into rivers and other water bodies, thereby causing water pollution. Trace Heavy Metals in the Environment In the contribution to the "Global Perspective on Arsenic, lead, cadmium and mercury cycling in the environment" we carried out studies on the distribution of these heavy metals in aquatic and terrestrial ecosystems of Nigeria. (Ndiokwere, 1994 ­ Publication of Scientific Committee on Problem of the Environment SCOPE, John Wiley Publishers). The studies included: (i) (ii) (iii) (iv) (v) surface waters and sediments aquatic life such as fish and mollusks as living markers of metal exposure air-borne particulate matter soil, vegetation and crops around industrial complexes, along motorways and refuse dumps. human hair and nails as indicators of industrial exposure to toxic metal pollutants.

Heavy metals in surface waters The surface water samples were obtained from Niger, Benin and Ogba rivers as well as four rivers in Esan plateau; Lagos and Warri harbours. Elevated levels of As, Cd, Hg and Pb, which are over and above the WHO maximum allowable levels for potable water, are attributed to local pollution. Their levels, however, varied significantly for the four rivers in Esan plateau (Ndiokwere and Okojie, 1996). These rivers flow through rural and urban areas, where they receive large amounts of domestic and industrial untreated wastes. Large breweries, abattoirs and other small-scale industries are located close to the sampling sites. The exceptionally high levels of arsenic measured for Ogba River are attributed to effluents from a Wood Treatment factory located near the river. Salts of As, Cr and Cu in mixed soluble formulations (as copper-chrome-arsenate preservative) are used in the treatment of wood to prevent fungi and pests attack. This factory provides a potential source of arsenic, chromium and copper in the river by way of chemical spills and drainage from the treated wood. The Cd levels obtained for the harbour waters are also high when compared with background seawater values reported in the literature. Harbour and port activities at the sampling sites in Port Harcourt and Warri may also increase the concentrations of Cd (Ndiokwere & Guinn 1983).

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Sediment and algae samples from the Niger River and Atlantic coastal water also showed varying degrees of contamination by all the four heavy metals. Lead levels are much higher in the River Niger sediments. This may be due to deposition of Pb particulates from the heavy motor traffic on the Niger bridge at Onitsha and the high boating density in the area. There is some quantity of petroleum being discharged into the coastal water creeks and rivers; this, together with brine fluids from the oil wells add appreciable quantities of heavy metals such as Ni, V and Cd to harbour waters. The green algae generally contain lower levels of these metals than the sediments; the algae from the coastal waters record higher levels than those from the river Niger (Ndiokwere, 1984). Interaction between Contaminated water and Aquatic life In a study of interaction between contaminated water and aquatic life it was observed that the elevated concentrations of As and Hg in fish and molluscs from the Niger Delta and River Niger can be attributed to local pollution of the surface waters and sediments (Ndiokwere, 1983). The maximum mercury level is about 3 times higher than the background value reported for fish species in the literature. The high levels of Hg suggest exposure to Hg ­ contaminated freshwater and sediments ­ probably derived from the dumps of Hg ­containing waste materials, which may have been washed down to the rivers by floods. It may be interesting to report here that abnormally high concentrations of GOLD were detected and quantified in some fish species (up to 0.87 g/g wet weight ­ River Niger) (Ndiokwere, 1983). Arsenic concentrations in the molluscs (periwinkles) are considerably high. Indeed, for coastal marine waters the use of periwinkles as pollution indicators instead of the bivalve shellfish, known as "Mussel watch" in Europe and America is being encouraged and recommended for use in Nigeria to monitor the degree of pollution. Periwinkles feed mainly on marine algae. Considerable levels of As and Hg are also reported for land snails, which feed on decomposing matter such as dead vegetation and feacal wastes. For the terrestrial forested ecosystems I consider and recommend the giant African land snails instead of the use of epiphytic lichens as heavy metal sentinels. Therefore, As and Hg concentrations may be directly related to the concentrations in their food sources, suggesting contamination by wastes. Since the giant land snails, popularly known in the southern part of Nigeria as "congo meat" as well as periwinkle are consumed by local population as food, their heavy metal contents should be monitored. Heavy metals in Airborne particulate Matter The aerosol particles in Benin City are found to contain high levels of As, Cd and Pb. Air pollution by heavy metals can occur as a result of emissions from industrial sources, burning of fossil fuels, motor gasoline, forest fires and wood fuels. The combustion products are mostly adsorbed to the available aerosols and can be moved in this form over several kilometers. Dust particles, which can be potential sources of these elements in air, are generated in large quantities in the Nigerian rural and urban

17

environments by windstorm, motor vehicles, demolition and construction works. It is also likely that trace elements, such as As, Cd and Pb are enriched in the atmospheric environment by open burning of solid wastes and from the few poorly managed incinerators. These combustion processes emit smoke, some gases and fly ash, in which some volatile trace elements may be concentrated. Very recently, we carried out a more detailed study of the aerosol or particulate matter and its heavy metals content in the industrial locations of Benin City, Warri, Okpella in Etsako and Ewu, Esan. The total suspended particulate matter (TSPM) levels in the sampling locations were quite high when compared with the levels reported in the literature for various world industrial cities. The concentration levels of some ten heavy metals were determined. For example, the maximum levels of 44.00, 0.991, 12.00, 3.24, 3.80 and 4.00g/g were recorded for As, Cd, V, Cr, Ni and Pb respectively. Various methods of data analysis were used for the identification of sources, which include reentrained soil, automobile exhaust, residual oil combustion, petroleum activities, sea spary, steel/metal works, refuse incineration and wood fuel burning. The heavy metals such as Cd, V and Pb are highly enriched while Ni and Cr are moderately enriched in some of the sampling sites. Arsenic was highly enriched in Benin City and Warri. Source apportionment by chemical mass balance and factor analysis of the heavy metal pollutants reveals anthropogenic contribution of about 42-74% in the four sampling locations. Seasonal variations are also observed (Okuo and Ndiokwere, 2004). Industrial Complexes, Motor traffic and Refuse dumps as sources of heavy metal pollutants The accumulation of some trace heavy metals in soil, crops and vegetation along and close to the Benin-Onitsha highway has been investigated (Ndiokwere, 1984). As is expected, the heavy metals especially Cd and Pb show high concentrations in the samples. Pb is a component of anti-knock fluid in petrol and about 75% is emitted in particulate form from the exhausts of motor vehicles. The presence of Cd has been established in some lubrication oils as an important component of many zinc-containing additives such as the anti-oxidant zinc dithiophosphate and also in motor vehicle tyres. The Cd content of some brands of tyres has been reported to range from 20-90gg-1 and this is associated with the use of technical ZnO and organo zinc carbamate in vulcanization. This may explain the enrichment of Cd in low-growing vegetation and upper layers of the soil close to the highway. The highest arsenic levels are recorded in surface soils and vegetation samples from the chemicals preparation, treatment and drainage sites of a wood treatment factory. The As levels decreased with the soil depth and this observation is reassuring in view of the danger of ground water pollution. From the background values of the heavy metals it is evident that the soils in the factory premises are strongly contaminated with the metals especially As due to the dispersal of the chemical preservative. It should be noted that the accumulation of the toxic As and other heavy metals in surface soils may create problems in future redevelopment of the factory premises, for example, its suitability for agricultural purposes and use for residential zoning. The As levels in some crops and

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leafy vegetables such as pumpkin, tomato, cassava leaves, waterleaf and greens from within the factory premises, some distance from the storage and drainage sites, as well as from other farms outside the factory are also examined. The results show appreciable levels of As. The accumulation of Cd, Cr, Cu, Ni, Pb and Zn in soils, crops and plants as a result of industrial activities has also been studied at various locations in the vicinities of Delta Steel Complex, Aladja and NNPC Refinery, Warri (Ndiokwere & Ezihe, 1990). High concentrations of the metals were recorded in all samples from the sites close to the emission sources like the pellet plant and slag yard and the levels decreased with distance away from the sources. Considerable amounts of the heavy metals found in the crops and plants were mainly due to aerial deposition. Soil and crop contamination by the metals was generally higher in the steel complex than the refinery. Cadmium and lead levels were particularly high in all samples from both complexes. Arsenic in human tissues ­ An example of use in Industrial pollution Human tissues such as head hair and nails, as well as body fluids, are considered to be useful monitors for environmental exposure to some toxic heavy metals. Some authors (Chattopadhyay, 1977 and Fergusson et. al, 1981) have explored the quantitative analysis of Pb in scalp hair as an aid in clinical diagnosis of chronic or acute Pb poisoning. Trace metals, especially As, have been measured in human head hair, nails, liver and urine. Hair and nails, which are metabolically inert, accumulate trace metals for longer periods. These tissues can serve as important indicators for occupational exposure to heavy metal pollution, which may be toxic to humans. In a study (Ndiokwere, 1985), the frequency distribution of As levels in the head hair and nails of the four exposure groups of Wood Treatment factory employees was determined. The workers exposed to the chemicals could be distinguished by the following departures from the "normal" (non-exposed): (i) considerably high As levels in both hair and nails from the workers involved in the wood treatment processes, compatible with probable inhalation of the fumes from the chemicals and (ii) similar and significantly elevated As levels in workers, who were associated with the treated timber. The correlation of As content in hair with As content in the nails of the same workers was weak indicating that workers exhibiting high hair As levels do not necessarily show elevated As levels in nails. There was, however, a good correlation between the As levels and duration of employment for the workers with similar exposure ratings. It was observed during sampling that virtually no preventive measures were taken against direct exposure to the chemicals, such as wearing gloves and gas masks. Trace elements in Crime investigation Closely related to this environmental exposure to some heavy metals as indicators of industrial pollution is the importance or use of some metals such as antimony, copper, silver and tin in scientific crime investigations involving bullet-lead gunshots. Almost all brands of commercial bullet-lead contain antimony, alloyed with lead by manufacturers or suppliers as a hardening agent. Depending upon the manufacturer and the type of bullet, the Sb concentration usually lies in the range of 0.1-4%. Other additional metals

19

in the bullet-lead include Al, Cu, As, Ag and Sn, which are at trace levels (usually in ppm) depending on the origin and country of make. There are always very small amounts (particles) of unburnt or partially burnt gunpowder, deposited on the back of the gun hand when a handgun such as revolver or automatic pistol is fired. The presence of the primer residues ­ Sb, Ag and Cu has assisted law enforcement agents in their investigations. The best results are achieved by the method of neutron activation analysis. It has been shown that bullet-leads from different sources vary widely in their concentrations of the three elements. However, in a production run from a given melt of Pb, the composition of the bullet-lead is generally very constant ­ both within a bullet and from one bullet to the next. How does the analysis for Sb, Ag and Cu in the residue help in the investigation? The typical case involves the composition matching of the bullet fragments recovered from the body of a victim with ammunition being fired by or found in the possession of one or more suspects. Mr. Vice-Chancellor, I had the opportunity as an IAEA Fellow from 1981 to 1983 to work in V.P. Guinn's laboratory (VPG of Blessed memory ­ he died 3 years ago) at University of California, Irvine, USA. There were several cases of bullet-lead analyses referred to this laboratory and I participated actively in the NAA analyses of such residues. V.P. Guinn used the reports or results of the analyses in U.S. courts in evidence for the conviction or discharge of some suspects. It is important to mention that this laboratory has assisted law enforcement laboratories in the U.S. in the analysis of bulletlead evidence specimens in numerous criminal cases including two well-known and publicized cases namely: (i) (ii) The Argentine heavyweight boxer, Oscar Bonavena killed in 1976 at the Mustang Ranch in Nevada, USA. 1977-78 Re-investigation of the President J.F. Kennedy assassination. The results led the controversies to rest.

Both the research and case application aspects of this topic involve interesting interrelationships of the chemist, the criminalist and members of the legal profession. 5. The Petroleum Industry

Petroleum is the most predominant source of hydrocarbons, which are considered to be the parent compounds of organic materials, used for combustion and industrial processes. Crude oil production and associated industries are indeed major sources of environmental pollution. The production of this important source of liquid and gaseous hydrocarbons has its environmental effects. Various fractions in a petroleum refining process are either used directly as energy source such as petrol or converted to petro-chemicals and other compounds such as polymers and detergents. The motor vehicle hydrocarbon emissions from the gasoline fraction of crude oil and oil spills in on- and offshore drilling are major pollutants to land, sea and other water bodies. Oil spills on land can perhaps be more easily contained to small areas than in water bodies, where the oil floats and spreads over

20

large areas of the water surface, generally dispersed by natural means. The main environmental problems usually associated with petroleum spills on land are the devastating effects on vegetation and soil and in water bodies the effects of the slowly degrading petroleum residues on aquatic life and the evaporation of the lighter components into the atmosphere. Clean-up operations after petroleum spills are very tedious and expensive. The sources of these oil spill incidents are blow-ups, caused by excess pressure, vessels, pipelines, land and water-based storage tanks, on- and offshore oil drilling/production, loading and unloading terminals and other various facilities and activities. The problem of accidental spills can be further compounded by the discharges of oily waters from tankers and other vessels, which deliver oil to storage terminals. In our oil-producing areas the oil wells are connected by pipes to the flow stations, where oil and water are pumped into sedimentation tanks. The oil-water mixture is then passed through a series of interceptors to effect separation, which is never complete. The effluents are discharged into water bodies. As a result of the environmental pollution problems associated with crude oil production, the oil industry has seriously concerned itself in the recent time with establishing desirable and attainable environmental standards with government and other regulatory bodies. It has also sought to establish ways of achieving the standards at least cost to the operating companies and the community in the areas of operation. In this connection, some oil companies conduct baseline ecological studies, pre- and post impact assessment studies after oil spills and compliance monitoring of their industrial effluents. I have over the years participated and even led groups of consultants in the environmental pre- and post impact assessment studies of crude oil exploitation in the Niger Delta as well as compliance monitoring and standardization of effluents and water bodies for swamp location of `Oil Companies' operational areas. These studies involved analyses for over 30 parameters including physico-chemical characteristics, anions and metals as well as organo compounds and microbiologicals from Flowstations, recipient environment, terminals and discharge points. I am indeed sorry to state that the results returned to the clients hardly reflected the reality. For the compliance monitoring there were disagreements over the actual results of the analyses submitted especially for the recipient environment such as Forcados and Warri rivers and the terminals. There has been, there is and there will still be serious pollution by crude oil in these areas ­ whether on shore, near shore or off shore. The concentration levels of minor and trace elements in crude oils determine their quality and world rankings, especially levels of sulphur, nickel, vanadium and arsenic. In sulphur content the Nigerian crude records an average of 0.375 % S and is better (Ndiokwere & Atuma, 1987), than crudes from some other countries, but our crude records high arsenic when compared with those from other countries. Using the neutron activation analytical technique levels of minor and trace elements were determined in Nigerian crude from various locations/sources (Ndiokwere, 1983). Not long ago we carried out studies on the levels of some trace heavy metals and polynuclear aromatic hydrocarbons in fish species and molluscs (periwinkles) from the Forcados River and its petroleum business activities (Ndiokwere and Eloke, 2001).

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There are thirteen polynuclear aromatic hydrocarbons (PAHs) listed by the International Agency for Research on cancer in 1973 as carcinogenic. Examples of the commonest ones are 7,12-dimethyl-benzoanthraiene and 3-methylcholanthrene. Apart from fish certain marine organisms have been identified to accumulate PAHs from the sea environment readily without losing them rapidly over time. Molluscs, for example, are known to have low or little enzymatic activity to degrade PAHs but they readily accumulate these chemicals. (Farrington et al. 1983). The main concern here is the risk to humans, because the lipophilic nature of these hydrocarbons makes them easily accumulatable in sea food and they can be potentially passed on to man. In the study stated earlier, sixteen different polynuclear hydrocarbons were identified and quantified as total PAHs in Forcados blend crude. The Forcados river recorded a total PAHs of 0.05 mg/l, while total PAH ranged from 4.71 to 9.03 gg-1 whole body wet weight in the fish samples and 1.62 gg-1 in molluscs. From the results obtained in this study, it is obvious that there is bioaccumulation and concentrating effect of the PAHs from the crude oil in these aquatic organisms. In another study we found exceptionally high levels of some heavy metals such as As, Ni, Cr, Fe and Pb in vegetation and soil samples from petroleum drilling and gas flare sites in the swampy oil fields of the on-shore exploration area. (Ndiokwere & Otalekor, 1996). In addition we measured levels of suspended particulate matter and the gases SO2, NO2, CO and H2S at the sites during the rainy and dry seasons. The levels of the parameters were found to be generally lower than the FEPA ­ permissible levels. Seasonal variations of their levels were also observed. Relatively high levels of some of the heavy metals were recorded for vegetation due to aerial deposition. 6. RADIATION POLLUTION

It is not out of place to discuss briefly pollution by radioactive materials mentioned earlier because there are now increased activities in the area of nuclear energy and associated industries such as uranium mining, production of radioactive materials; treatment, transportation and disposal of low and high-level radioactive wastes. Nuclear power plants and other users of radioactive materials produce high radioactive wastes, which require special handling and disposal. Continuing studies on the radiation effects on the thousands of survivors of the well-documented Hiroshima and Nagasaki (all in Japan) atomic bomb of 1945 are still playing an important role in defining the hazards of radio activities, particularly as they relate to cancer diseases.. There is radioactivity around Kanawa uranium occurrences in Bauchi State. I had a collaborative research project in this area involving a PhD student in ABU. The scary problem of nuclear wastes with "nowhere to go" is a reminder that science (especially Chemistry) is not omnipotent. For several years, scientists have been searching for permanent safe sites to store high-level radioactive wastes without success and there is no hope in the near future. The reason why it is difficult is that no scientist or engineer can guarantee that

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radioactive waste will not leak someday in dangerous quantities from even the best of repositories. Cosmic rays are high-energy charged particles of extra-terrestrial origin. The sun contributes significantly to the flux of low-energy cosmic rays reaching the earth. One of the important products of cosmic rays is 14C. The radiation dose obtained from the cosmic rays generally depends on the altitude. Another aspect of man-made radiation pollution is radioactive fallout from nuclear weapons tests either in the oceans or very vast desert areas. There is need to monitor and learn more about the movement of radioactive fallout particles in the atmosphere from nuclear explosions and the consequences of the radiations. Nuclear energy is becoming more and more unpopular because of the danger of accidents and the difficulty of storing radioactive waste which is the most menacing garbage ­ a by-product of nuclear power stations. Thousands of tons of nuclear waste is stored in temporary sites, although some have been dumped in the oceans. Despite years of nuclear scientific research, no solution has yet been found for safe, permanent storage or disposal, and I must tell you frankly ­ none is in the offing. Who knows when these ecological time bombs might explode? The waste will remain radioactive for centuries to come. Other alternatives are referred to as renewable energy sources since they harness naturally occurring energy sources that are freely available and the main types include solar energy, wind power, hydroelectricity (dams), geothermal energy and Tidal power. Some of these sources are indeed proving very economical and non-pollution contributing. 7. NOISE AS POLLUTANT

Another aspect of environmental pollution, which may seem less important to our society today, but can be quite destructive, is noise. It is perhaps, a vitriolic pollutant, causing much concern to some members of the public. The effects of noise are not unknown. Noise reduces, and sometimes causes temporary loss of hearing ability, depending on the "perceived noise decibel". Since loud musical sounds can reduce hearing range very considerably, good cover for various crimes such as robberies, murder and rape can thereby be provided. In medical circles, it is known that noise produces some physiological effects which can create more burden for people with heart diseases, high blood pressure and emotional problems, if they are continuously exposed to this type of pollution.

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8.

POLLUTION CONTROL POLLUTANTS) Air Pollution Control measures

MEASURES

(MANAGEMENT

OF

i)

It is generally difficult to rid any affected area of such dangerous gases and fumes as sulphur oxides, nitrogen oxides, carbon monoxide, hydrocarbons and smoke as well as particulate matter. The setting of standards and their implementation, the establishment of air-quality-control programmes and general legislation on air pollution have indeed helped in reducing air pollution incidents in most of the industrialized countries. Various gas cleaning devices have been developed to remove low levels of these gases and particulates in atmospheric air or recirculated air within buildings. A group of air pollution abatement methods includes methods of removing the pollutant gases, as well as various techniques to collect particulate matter such as electrostatic precipitators, wet scrubbers, and fabric filters. Generally the levels of gaseous pollutants are small due to the large excess of inert flue gases. The removal methods are designed to concentrate the pollutants in a liquid (absorption) by choosing suitable liquid solvent and appropriate equipment for liquid-gas contact or on a solid (adsorption). Gases and vapours or liquids are concentrated on a solid surface as a result of surface or chemical forces. The most important adsorbents in industrial use today are Fullers earth, bauxite, activated carbon and alumina, silica gel and molecular sieves. Sometimes, direct conversion of the gases is possible by combustion. This is a very satisfactory process for the removal of organic materials as many of them can be decomposed to CO2 and H2O at high temperatures. The process can be carried out directly, indirectly or by catalytic methods. Among several applications of catalysts to remove gaseous pollutants are the oxidation of hydrocarbons and the reduction of nitrogen oxides. The removal of particulate matter, which is largely suspended particles and classified into liquid droplets and mists, fumes and dusts can be carried out using five methods depending on the principle on which the separation process is based. These include settling chambers ­ for collecting dust particles greater than 100m; inertia separators including cyclones; electrostatic precipitators; fabric filters (baghouses); and wet scrubbers ­ the collection process depends on collisions between the particles and liquid droplets in suspension in the flue gas. These air pollution control devices are very suitable for emissions from cement and phosphate fertilizer factories. However, baghouses, wet scrubbers and electrostatic precipitators are recommended for cement plants while a combined system of cyclones and bag filters is commonly installed in phosphate rock preparation plants. Petroleum refinery of today is an industrial complex, consisting of several processes that are often found in other industries such as production of heat and energy, so that the methods of reducing the level of pollution from refineries can be adopted from other

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industrial activities. Generally, there are two alternatives to reduce the sulphur emissions into the atmosphere, (a) (b) sulphur removal from the fuel before it is burnt; and sulphur removal for the stack gases through alkali scrubbing and regenerative scrubbing.

In the industry, sulphur is removed from residues, distillates and flue gases. The three main alternatives for control of nitrogen oxides emissions are catalytic conversion of NOx to nitrogen, thermal decomposition of NOx in a non-catalytic process and use of NOx burners. ii) Recycling as means of pollution control

Recycling conserves natural resources and reduces the quantity of solid wastes. It may not be economical in some cases to recycle materials compared to the exploitation of virgin resources. There are several examples of recycling in many industrialized countries ­ which is indeed the salvage of valuable products that are never allowed to become solid wastes ­ aluminium, bottles, cans, paper, iron and steel, zinc and copper, reclaimed rubber, vehicle tyres to recover carbon black, gas, oils and other products by destructive distillation of old tyres. Also lead from lead-acid batteries and mercury from mercury products. iii) Solid Waste Disposal

The management of solid wastes should be economically and technologically feasible and since solid wastes are generated by variety of sources such as individual homes and commercial establishments, refuse collection and disposal can present some difficulties. In the rural areas, where there is no provision for collection of solid wastes, the refuse is either burnt by individual homes somewhere around their homes or is collected and dumped in any nearby bush or open space. Disposal of solid wastes in open dumps is the commonest method used in this country. Open dumps produce air pollution problems when the wastes are burnt in order to reduce their volume and conserve space. They also cause public health problems by encouraging growth of population of flies, rodents and pests. Most of the towns in this country presently deal with solid wastes by transporting them beyond their own immediate city limits or boundaries and discarding them in less expensive but very unsafe way by open burning usually by the roadside or highway. (a) Incineration of solid wastes and sludges

Basically, the process of incineration produces heat, waste gases, smoke, soot, fly ash and inert residue. It can also pose some danger to humans and animals in the immediate surrounding. As practical advantages of incineration, only a small space is required for an incinerator, particularly in densely populated urban areas, it is not affected by weather conditions, volume reduction is great and the residue from a properly-operated incinerator is biologically stable and odourless. The major disadvantage of incineration

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is that such serious problems as odour, smoke, soot and fly ash can arise from this method, especially if the incinerators are poorly managed. Some constituents of solid wastes may form toxic oxides and other hazardous compounds, when combusted. It is important that provision for the disposal of the residue or end products of the incineration must be made. (b) Sanitary landfill of wastes and sludges

This is another method of solid waste disposal. It is less expensive and it does not usually create any end products. In its operation solid wastes and sludges are usually spread in thin layers, which are compacted by bulldozers before spreading another layer. These layers, which are normally about 3m deep, are finally covered by a thin layer of clean earth and then compacted again. In good landfills the fills are topped with about a meter of compacted clean earth. Indeed, the important advantage of this method is that the public health problems are greatly minimized. Insects and rodents do not breed in the covered solid wastes. There is normally no immediate danger of air and water pollution. Litter fences and earth embankments are usually erected at the disposal sites to minimize blowing away of light refuse and unsightly exterior views of the sites. Most industrial chemical solid wastes and sludges are usually landfilled. A serious disadvantage of the landfill method is that there can be danger of contamination of ground-water and surface water, if the site is not properly chosen or the fill is dug out very deep in the case of groundwater. The Love Canal episode of 1978 which I mentioned earlier in this lecture is a good example of "this advantage". It should be noted that aerobic reactions can take place in the refuse-filled regions, producing some gases such as CO2, H2S and methane. The rate of decomposition depends generally on the nature of the refuse and it is faster with wet landfills than dry landfills. iv) Treatment and Disposal of Industrial Water Wastes

The water treatment methods used by industries are the same as in town water supplies ­ namely: Primary treatment processes involving grit removal, screening, grinding, flocculation, sedimentation and skimming. Secondary treatment involves the use of biological methods such as trickling filters and activated sludge including sometimes chlorination to accomplish chemical oxidation and disinfection. Tertiary treatment (advanced methods) involves chemical coagulation and filtration, carbon adsorption of odours and tastes, chemical oxidation using strong oxidants such as ozone, hydrogen peroxide or chlorine dioxide and ion exchange using natural materials such as zeolite and synthetic materials (ion exchange resins).

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In industrial water wastes the exact pollutants are known and so the best treatment is chosen for the particular pollutants. The following examples are illustrative: (a) (b) 9. Biological treatment is suited for wastes from dairy and food industries. Chemical treatments have worked for wastes from metal plating industries. SIGNIFICANCE OF EMISSION CONTROL/MANAGEMENT INVENTORIES TO POLLUTION

Emission inventories constitute the key to effect air quality management programmes as well as control measures for land and water pollution. They provide basis for the planning of control strategies to achieve environmental quality goals. A comprehensive, reliable emission inventory requires a substantial amount of accurate, up-to-date technical data. In many countries, such basic data on emission source category, pollutant characteristics and location of industrial areas are now being collected. (I am aware such collections have been done in Nigeria by a group of scientists at the Obafemi Awolowo University (OAU), Ile-Ife ­ Obioh, Oluwole, Akeredolu, Asubiojo ­ under the auspices of EEC and Lome III). Three types of source configurations are usually considered, namely ­ point, line and area sources. (a) Point source is often defined as any facility which has the potential of annually emitting a certain amount of any named pollutant. These are mainly welldefined emission points such as stacks (e.g. stacked timber treated with CCA). Line sources include mobile sources and small sources arranged in a line (e.g. automotive machines). Area sources pertain to emissions from domestic heating and activities, industries, and small or diffuse sources distributed over a large plant area. Among toxic gases such as SO2, NOx and CO, hydrocarbons and heavy metals in particles usually receive special consideration in the preparation of emission inventories due to their significant amounts released into the atmosphere and water bodies and their toxicity. An emission inventory system includes collection, screening and refining, storage and summary, and retrieval of data related to emissions. CONCLUSION

(b)

(c)

10.

Now I have tried to show the negative aspects of Chemistry as they relate to pollution problems, which are man-made. Man has indeed benefited from Chemistry. However, it is clear now that lives of millions of people are already at risk as a result of man's neglect of the environment. Although man now understands something about what is going wrong, it is not easy to solve all the problems. The first difficulty is the huge sums of money required to implement, for example, the comprehensive proposals of the Earth

27

Summit in 1992. For the implementation, it would require sacrifices such as wasting less and recycling more, conserving water and energy, using public rather than private transport, etc. The most important and difficult one is really considering or thinking in terms of the whole world rather than one's own immediate environment. There are presently opinions that the assault on the environment by man cannot be effectively controlled, but must be prevented. Clearly, preventing pollution is much better than curing its ill effects. I have tried to highlight some principal environmental problems associated with Chemistry and its products. When loss of habitat or other factors cause the extermination of plant or an animal species, man cannot repair the damage. Two of the most important gauges of ecological damage are agriculture and fishing because their productivity depends on a healthy environment and man's life depends on a reliable good supply. Both sectors are showing signs of deterioration as observed by the United Nations Food and Agricultural Organization (FAO). There has been a steady decline in fish production world over. The main problems are overfishing, pollution of surface waters by chemicals and destruction of spawning grounds. The alarming trend is mirrored in crop production. During the sixties and seventies world grain production was boosted considerably by extensive use of chemical pesticides and fertilizers. Today, pesticides and fertilizers are losing their effectiveness, and water shortages and pollution are also contributing to leaner harvests. Clearly, lives of millions of people are already in danger as a result of man's neglect of the environment. In the fight to protect the environment, education is the outstanding environmental success in recent years. Most people today are keenly aware that our environment is being impoverished and polluted and that something must be done about it. The threat of environmental degradation now looms greater than the threat of nuclear war. World leaders are not oblivious of the problems. There was the Earth Summit in 1992 attended by some 118 heads of state, during which some steps were taken toward protecting the atmosphere and the earth's dwindling resources. Most countries signed a climate treaty to set up a system for reporting changes in carbon emissions with the goal of freezing the total output in the near future. This summit produced two documents ­ the "Rio Declaration" and "Agenda 21", which contain guidelines on how countries could achieve "sustainable development". The "1987 Montreal Protocol" involved an international agreement to phase out chlorofluoro carbons (CFCs) within a set time limit because the CFCs are contributing to the rapid depletion of the earth's protective ozone layer. Many countries are now taking steps to clean up their rivers (salmon have returned to England's Thames River), to control air pollution (Smog has declined 10% in some cities in the USA), to tap environment-friendly energy sources (such as solar and geothermal energy) and to conserve their natural heritage (conversion of the land area into national parks). It, therefore, requires nothing less than a fundamental change in human society and in the focus of business enterprises, centered on national interests. If technology does not find a quick solution to the environmental crises one cannot proffer any other solution or option except perhaps to ask for Divine Intervention.

28

ACKNOWLEDGEMENTS I would like to acknowledge first and foremost my "Diplom Arbeit" and "Doktor Arbeit" supervisor between 1969 and 1972, Professor Dr. H. Elias and co-supervisor for "Doktor Arbeit", Prof. Dr. K.H. Lieser of Edward-Zintl Institute of Inorganic and Physical Chemistry, Technical University of Darmstadt, Germany. My profound appreciation to them is for their love, guidance, encouragement, advice, patience, assistance and understanding throughout the period of my postgraduate work. Prof. Dr. Horst Elias was particularly the first at recognizing that the young black man, Linus among all whites was intelligent. He laid the solid foundation for my scientific research/training and he initiated my employment as "Wissenschaftlicher Hilfsassistent" (Graduate Assistant) and later during and after my postgraduate studies as "Wissenschaftlicher Mitarbeiter" (equivalent to Lecturer II). He and Prof. Dr. K.H. Lieser fought for my "stay- and work" permit till November 1973. I had rough times after my studies with the German Immigration Office, Darmstadt. I am indeed grateful for benefiting from the Research Grants which Prof. H. Elias obtained from the German Research Organization (DFG) and Chemical Industries. We carried out a lot of work in radio-labelling of organic compounds and radiopharmaceuticals. I wish to thank the then West German Government (DAAD) for the scholarship through the Roman Catholic Organization, "AFRIKANUM" to study in the University of Munich and later in the Technical University of Darmstadt. Special gratitude goes to Professor Vince P. Guinn (of Blessed memory) of University of California, Irvine (UCI), who made his laboratory and other research facilities available to me during my International Atomic Energy Agency (IAEA) fellowship from 1981 to 1983. Professor Guinn was a great scientist of repute and a very kind man. I thank him immensely for his advice, discussions and research collaboration. I am also very grateful to the IAEA, Vienna, for providing me with a fellowship for my research and training at UCI. There is no way I will conclude this acknowledgement without thanking the former ViceChancellor of this great institution Professor A.G. Onokerhoraye, who saw my stay at AAU, Ekpoma (for some reasons which will take too long to tell here) as "long sabbatical leave" and had to convince me to come back in January 1998. I also express my profound gratitude to Mrs. P.O. Ukwade, for the great job of typing this lecture script. To my dear wife, Ada Orlu I, Ezinne Eucharia Ugochi, retired school administrator, my children ­ Oddy Bertram, Chinyere Karin (now Mrs. Ekpe), Kemdi Niels and Chika Oscar and my grandchildren ­ Ezichi, Chidum, Odinakachi and Oddy jnr. for their unending warmth, care, love and support. Success in one's career, peace and progress largely depends on the family. I am enjoying all of you and for all our achievements, TO ALMIGHTY GOD, be the glory.

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REFERENCES Aspelin, S.L. & Grube, A.H. (1999). Pesticides Industry, Sales and Usage: 1996 & 1997 market Estimates. Washington, D.C. EPA, Nov. 1999. Chattopadhyay, A., Roberts T.M. & Jervis R.E. (1977). Scalphair as a monitor of community exposure to lead. Arch. Environ. Health 32, 226-236. Dasch (1982). Particulate and gaseous emissions from wood-burning fire places. Environ. Sci. Technol. 16, 639-645. D'Esposito & Fehler, J. (2000). Lessons from the disasters on the Danube: Is modern mining safe? Mineral Policy Centre Newsletter, Spring; 1, 4-5, 17 European Environment Agency (E.E.A. 1999). Environment in the European Union at the turn of the century ­ Environmental Assessment Report No. 2, Copenhagen: EEA. Etkin, D.S. (1998). International Oil Spill Statistics: 1997 Arlington, Massachusetts ­ Cutter, Information Corporation. FAO (1981). Tropical Forest assessment project: Forest resources of Tropical Africa. Country briefs, Part II, 359-379, Rome. Fergusson, J.E. Hibbard K.A. & Ting, R.L.H. (1981). Lead in human hair: General survey ­ Battery factory employees and their families. Environ. Pollution (B) 2, 235248. Jody Clark (2004). Pushing the Frontiers of Olefin Determination in Gasoline. Petro. Ind. News, July 5 (3) 2004. National Oceanic & Atmospheric Administration (NOAA) (2000). Hypoxia in the Gulf of Mexico. Ndiokwere, Ch. L. & Guinn, V.P. (1983). Determination of some toxic trace metals in Nigerian river and harbour water samples by neutron activation analysis. J. Radioanal. Chem. 79 (1983) 147-151. Ndiokwere, C.L. (1983). Arsenic, Gold and mercury concentration levels in Freshwater Fish by neutron activation analysis. Environ. Pollution (B) 6 (1983) 263-269. Ndiokwere, Ch. L. (1983). Analysis of Nigerian petroleum for Trace elements by neutron activation. Radiochem. Radioanal. Let. 59 (1983) 201-212.

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Ndiokwere, Chinaka L. (1983). Arsenic, Antimony, Gold and Mercury levels in the soft tissues of intertidal and terrestrial molluscs and trace element composition of their shells. Radioisotopes. 32 (3) 117-120. Ndiokwere, C.L. (1984). An investigation of the heavy metal content of sediments and algae from the River Niger and Nigerian Atlantic Coastal waters. Environ. Pollution 7 (B) 247-254. Ndiokwere, C.L. (1984). A study of heavy metal pollution from motor vehicle emissions and its effect on roadside soil, vegetation and crops in Nigeria. Environ. Pollution 7 (B) 35-42. Ndiokwere, Ch. L. (1985). A survey of arsenic levels in human hair and nails. Exposure of wood treatment factory employees in Nigeria. Environ. Pollution. 9 (B) 95-105. Ndiokwere, Ch. L. (1985). The dispersal of arsenic, chromium and copper from a wood treatment factory and their effect on soil, vegetation and crops. Int. J. Environ. Studies 24, 231-234. Ndiokwere, C.L. & Atuma, S.S. (1987). Total nitrogen and sulphur in some fossil fuels; their contribution to environmental pollution problems. Nig. J. Appl. Sci. Ndiokwere, C.L. and Ezihe, C.A. (1990). The occurrence of heavy metals in the vicinity of industrial complexes in Nigeria. Environ. International 16, 291-295. Ndiokwere, C.L. (1994). Arsenic, cadmium, lead and mercury in aquatic and terrestrial environments of Nigeria, published in: Global perspectives on Pb, Hg & Cd Cycling in the Environment (eds. Hutchison, Gordon & Heema) John Wiley & Sons. Chapter 14, 189-201. Ndiokwere, C.L. and Okojie, V.U. (2001). Physico-chemical characteristics of some rivers and streams of the Esan Plateau, Nigeria. Nig. J. Appl. Sci. Ndiokwere, C.L. and Eloke, F.O. (2001). Environmental Impact assessment of petroleum exploitation on fish and molluscs in the Niger Delta ­ Forcados River as a case study. M.Sc. thesis. Ndiokwere, C.L. & Otalekor, O.I. (1996). Effect of crude oil drilling and gas flaring on soil in the Niger Delta. M.Sc. thesis. Okor, D.I. & Atuma, S.S. (1986). Baseline study of Organochlorine pesticide residues in Nigerian aquatic and terrestrial environments. Okuo, J.M. & Ndiokwere (2004). Elemental characterization and source apportionment of air particulate in Benin City and other industrial areas. Ph.D. thesis, Univ. of Benin.

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Rabalais, N. & Scavia, D. (1999). Origin, impact and implications of the "dead zone" in the Gulf of Mexico ­ presented at the U.S. Global Change program Series, July 19. Ukpebor, E.E. & Ahonkhai, S.I. (2000). Spatial and temporal variation of Nitrogen dioxide concentration in Benin City using passive samplers. Nig. J. Appl. Sci. 18, 72-77. Ukpebor, E.E. & Ahonkhai, S.I. (2000). Trend analysis of tropospheric ozone concentration in Benin city, Nigeria. Nig. J. Appl. Sci. 18, 97-101. Ukpebor, E.E. & Imarengiaye, C.O. (2002). The use of simple diffusion tube samplers for the measurement of nitrogen dioxide in an operating room using nitrogen oxide as an anaesthetic. W. Afr. J. Med. 21, 192-194.

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