**1.1. Health and environmental effects of heavy metals**

inorganic (i.e. Cd, Pb, Cu, Hg, As etc) and organic (i.e. pesticides, dioxins, polyaromatic hydrocarbons etc) pollutants has increasingly been of global concern over the last decades, especially in Asian [6] and other developing countries, where urbanization and industrializa‐

Heavy metals continue to receive increasing attention due to a better understanding of their fate as well as toxicological relevance in ecosystems and human health [7]. Pollution of soils by heavy metals represents one of the most important ecological problems today [8]. Anthro‐ pogenic emission of heavy metals in the environment during the last century has led to increasing accumulation of metals in soils and natural waters in both urban and rural areas. Heavy metals are ecologically harmful because they tend to bio-accumulate over time in soils and plants with ability to have a negative influence on the physiological activities of plants (e.g. photosynthesis, gaseous exchange and nutrient absorption), influencing reductions in plant growth, dry matter accumulation and yield [9]. Heavy metal pollution exerts toxic effects on soil microbial biomass [10] and microbial processes such as soil respiration, nitrogen mineralization, and enzyme activities [11]. Soil contamination by heavy metals has also been shown to inhibit soil microbial activities [12], in turn reducing soil fertility and inhibiting the germination of certain seed plants [13]. Heavy metals contamination may also produce nutrient imbalance in plants with adverse effects on the synthesis and functioning of many biologically active compounds [14]. Subsequent accumulation of metals in the food chain [15]

Heavy metals transport in soil profile is a major environmental concern because even slow transport through the soil may eventually lead to deterioration of groundwater quality. Preferential flow can accelerate the movement of water and solutes through soil profile [16]. Soil pollution can lead to water pollution if toxic chemicals leach into groundwater, or if contaminated runoff reaches streams, lakes, or oceans. The decomposition of organic materials in soil can release sulphur dioxide and other sulphur compounds, causing acid rain which can leach heavy metals from soil. Thus, there is need to reduce the introduction of heavy metals into the environment from anthropogenic sources since metals are persistent, toxic and nonbiodegradable [3]. In addition, chemicals that are not water-soluble contaminate plants that grow on polluted soils, and they also tend to accumulate increasingly toward the top of the food chain. Both organic and inorganic contaminants are important in soil management. The most prominent chemical groups of organic contaminants are petroleum hydrocarbons, Polycyclic Aromatic Hydrocarbons (PAHs), Polychlorinated Biphenyls (PCBs), chlorinated aromatic compounds, detergents, and pesticides. Inorganic species include nitrates, phos‐

Organochlorine pesticides not only accumulate in animal tissues; many are extremely stable and persist in soil and plants, and if soluble enough can reach groundwater or surface waters. They can therefore enter the food chain not only via their target and non-target organisms, but also imbibed water and via plants eaten by herbivores, including cattle [17]. Their persistence in soils depends both on the nature of the soil and their own physico-chemical properties. Light soils facilitate the water-borne transport of soluble pesticides [18]. Soils with high clay and organic matter contents tend to retain both the more soluble pesticides (because of their high

phates, and heavy metals such as cadmium, chromium and lead.

tion have occured rapidly and haphazardly.

226 Environmental Risk Assessment of Soil Contamination

is detrimental to human health.

Metals are particularly toxic to the sensitive, rapidly developing systems of foetuses, infants, and young children, otherwise known as ''vulnerable group''. Some metals, such as lead and mercury, easily cross the placenta of mothers and damage the brain of foetuses. Childhood exposure to some metals such as lead and mercury can result in learning difficulties, memory impairment, damage to the nervous system, and behavioural problems such as aggressiveness and hyperactivity. At higher doses, heavy metals can cause irreversible brain damage. Children may receive higher doses of metals from food than adults, since they consume more food for their body weight than adults [24].

Exposure to manganese (Mn) is usually via inhalation, which results in the main cause of its toxicity. Mn toxicity has been reported through occupational (e.g. welder, miner) and dietary overexposure and is evidenced primarily in the central nervous system, although lung, cardiac, liver, reproductive and fetal toxicity have been noted [24]. Mn neurotoxici‐ ty results from an accumulation of the metal in brain tissue [25]. Brain permeability to manganese is higher than that to iron and zinc. Manganese is easily concentrated in the brain, especially in the basal ganglia, and can cause an irreversible neurological syn‐ drome similar to Parkinson's disease [24].

Following long-term exposure to cadmium, the main health concerns are its toxicity to the kidney and bones, arising via ingestion and inhalation, and its lung carcinogenicity seen in exposed workers following inhalation [26]. Over a period of time, cadmium accumulates in the kidney and, if the organ concentration exceeds a critical threshold, the tubule cells become damaged and renal function impaired. This cadmium build-up also affects vitamin D metab‐ olism, disturbing the calcium balance within the body, which may lead to a decrease in the mineral content within the bones, resulting in osteoporosis and osteomalacia [26,27]. Its toxicity is linked with reproduction problem because it affects sperm and reduces birth weight. It is a potential carcinogen and seems to be a causal factor in cardiovascular diseases and hypertension. Large concentrations of Cd in the soil are associated with parent material (black slates) and most are manmade (burning of fossil fuels, application of fertilizers, sewage sludge, and plastic waste) [28,29]. In humans, long-term exposure is associated with renal dysfunction. The average daily intake for humans is estimated as 0.15 µg from air and 1 µg from water. Smoking a packet of cigarettes can lead to the inhalation of around 2-4 µg of cadmium, but levels may vary widely [27].

Mercury is a toxic substance which has no known function in human biochemistry or physi‐ ology and does not occur naturally in living organisms [27]. Mercury is a toxic heavy metal and a persistent environmental pollutant. Known sources of Hg in soil e.g. mercury-in-bulb thermometers used in hospitals; alkyl mercury compounds especially methyl mercury used as fungicide in agriculture, present in coal and hydrocarbon gas etc. Exposure to mercury is associated with serious adverse health and developmental effects, especially in pregnant women, developing foetuses, and young children [24]. This heavy metal is toxic even at low concentration to a wide range of organisms including humans. The organic form of mercury can be particularly toxic, and the methyl-and ethyl-forms have been the cause of several major epidemics of poisoning in humans resulting from the ingestion of contaminated food, e.g. fish. Two major epidemics in Japan were caused by the release of methyl and other mercury compounds from an industrial site followed by accumulation of the chemicals in edible fish. The poisoning became well-known as Minamata disease [28,29]. Inorganic mercury poisoning is associated with tremors, gingivitis and/or minor psychological changes, together with spontaneous abortion and congenital malformation. Monomethylmercury causes damage to the brain and the central nervous system, while foetal and postnatal exposure have given rise to abortion, congenital malformation and developmental changes in young children [27]. The negotiations under UNEP of a new Minamata Mercury Convention is under way to underscore international concerns about the environmental and health impact of mercury and the need for coordinated global action to address the issue effectively. Average concentrations of mercury in soil are 6.6 mg/kg, 6.6 mg/kg, 24 mg/kg and 50 mg/kg in agricultural, residential/ parkland, commercial and industrial soils, respectively [30].

Lead has been known to be toxic since the 2nd century BC in Greece. It is a widespread contaminant in soils. Lead poisoning is one of the most prevalent public health problems in many parts of the world. It was the first metal to be linked with failure in reproduction. It can cross the placenta easily. It also affects the brain, causing hyperactivity and deficiency in the fine motor functions, thus, it results in damage to the brain. The nervous systems of children are especially sensitive to Pb leading to retardation. It is also cardiotoxic and contributes to cardiomyopathy (disease of the heart muscle leading to the enlargement of the heart) [28,29]. Lead affects almost every organ system in the human body. The central nervous system is particularly vulnerable in infants and children under age six. The effects are the same whether it is breathed or swallowed. Large amounts of lead exposure may lead to blood anaemia, severe stomach ache, muscle weakness, and brain damage. Lower levels of exposure, may affect a child's mental and physical growth leading to learning disabilities and seizures [24]. Major sources of human exposure to lead include old lead water pipes, tetraethyl lead from gasoline, lead in paint and improper disposal of used lead acid battery (ULAB) in dump sites. In humans, exposure to lead can result in a wide range of biological effects depending on the level and duration of exposure. Various effects occur over a broad range of doses, with the developing foetus and infant being more sensitive than the adult. High levels of exposure may result in toxic biochemical effects in humans, which in turn cause problems in the synthesis of haemo‐ globin, effects on the kidneys, gastrointestinal tract, joints and reproductive system, and acute or chronic damage to the nervous system. Lead poisoning, which is so severe as to cause evident illness, is now less common. This could be due to international efforts at phasing out lead in gasoline and paints in many parts of the world including developing countries [31] indeed. At intermediate concentrations, however, there is persuasive evidence that lead can have small, subtle, subclinical effects, particularly on neuropsychological developments in children. Some studies suggest that there may be a loss of up to 2 IQ points for a rise in blood lead levels from 10 to 20 µg/dl in young children [26]. Uncontaminated soil contains lead concentrations less than 50 ppm but soil lead levels in many urban areas exceed 200 ppm [32]. The EPA's standard for lead in bare soil in play areas is 400 ppm by weight and 1200 ppm for non-play areas [33].

and a persistent environmental pollutant. Known sources of Hg in soil e.g. mercury-in-bulb thermometers used in hospitals; alkyl mercury compounds especially methyl mercury used as fungicide in agriculture, present in coal and hydrocarbon gas etc. Exposure to mercury is associated with serious adverse health and developmental effects, especially in pregnant women, developing foetuses, and young children [24]. This heavy metal is toxic even at low concentration to a wide range of organisms including humans. The organic form of mercury can be particularly toxic, and the methyl-and ethyl-forms have been the cause of several major epidemics of poisoning in humans resulting from the ingestion of contaminated food, e.g. fish. Two major epidemics in Japan were caused by the release of methyl and other mercury compounds from an industrial site followed by accumulation of the chemicals in edible fish. The poisoning became well-known as Minamata disease [28,29]. Inorganic mercury poisoning is associated with tremors, gingivitis and/or minor psychological changes, together with spontaneous abortion and congenital malformation. Monomethylmercury causes damage to the brain and the central nervous system, while foetal and postnatal exposure have given rise to abortion, congenital malformation and developmental changes in young children [27]. The negotiations under UNEP of a new Minamata Mercury Convention is under way to underscore international concerns about the environmental and health impact of mercury and the need for coordinated global action to address the issue effectively. Average concentrations of mercury in soil are 6.6 mg/kg, 6.6 mg/kg, 24 mg/kg and 50 mg/kg in agricultural, residential/

Lead has been known to be toxic since the 2nd century BC in Greece. It is a widespread contaminant in soils. Lead poisoning is one of the most prevalent public health problems in many parts of the world. It was the first metal to be linked with failure in reproduction. It can cross the placenta easily. It also affects the brain, causing hyperactivity and deficiency in the fine motor functions, thus, it results in damage to the brain. The nervous systems of children are especially sensitive to Pb leading to retardation. It is also cardiotoxic and contributes to cardiomyopathy (disease of the heart muscle leading to the enlargement of the heart) [28,29]. Lead affects almost every organ system in the human body. The central nervous system is particularly vulnerable in infants and children under age six. The effects are the same whether it is breathed or swallowed. Large amounts of lead exposure may lead to blood anaemia, severe stomach ache, muscle weakness, and brain damage. Lower levels of exposure, may affect a child's mental and physical growth leading to learning disabilities and seizures [24]. Major sources of human exposure to lead include old lead water pipes, tetraethyl lead from gasoline, lead in paint and improper disposal of used lead acid battery (ULAB) in dump sites. In humans, exposure to lead can result in a wide range of biological effects depending on the level and duration of exposure. Various effects occur over a broad range of doses, with the developing foetus and infant being more sensitive than the adult. High levels of exposure may result in toxic biochemical effects in humans, which in turn cause problems in the synthesis of haemo‐ globin, effects on the kidneys, gastrointestinal tract, joints and reproductive system, and acute or chronic damage to the nervous system. Lead poisoning, which is so severe as to cause evident illness, is now less common. This could be due to international efforts at phasing out lead in gasoline and paints in many parts of the world including developing countries [31] indeed. At intermediate concentrations, however, there is persuasive evidence that lead can

parkland, commercial and industrial soils, respectively [30].

228 Environmental Risk Assessment of Soil Contamination

Arsenic is well-known as a poison and a carcinogen. It has an average concentration in the soil of 5 to 6 mg/kg [28]. Its amount in the soil is related to rock type and industrial activity [34]. It is used in combination with other materials in pigments, poison gases and insecticides (such as Paris green, calcium arsenate and lead arsenate) and is well known from former use as a rat poison. Arsenic has a long history of medical applications; before penicillin was developed an arsenic compound was used to treat syphilis and yaws. It is used in ammunition manufactur‐ ing, semi-conductor manufacturing, as a preservative in tanning and taxidermy, as well as on the exterior of wood such as deck and playground materials as well as by-product of copper smelting [34]. Acute (short-term) arsenic poisoning may cause nausea, vomiting, diarrhea, and weakness, loss of appetite, shaking, cough and headache while chronic (long-term) exposure may lead to a variety of symptoms including skin pigmentation, numbness, cardiovascular disease, diabetes, and vascular disease. Arsenic is also known to cause a variety of cancers including skin cancer (non-melanoma type), kidney, bladder, and lung, prostate and liver cancer.

Chromium is required for carbohydrate and lipid metabolism and the utilization of amino acids. Its biological function is also closely associated with that of insulin and most Crstimulated reactions depends on insulin. However, excessive amount of the metal can cause toxicity. Toxic levels are common in soils applied with sewage sludge [28,29]. Chromium is used in metal alloys and pigments for paints, cement, paper, rubber, and other materials. Lowlevel exposure can irritate the skin and cause ulceration. Long-term exposure can cause kidney and liver damage, and damage to circulatory and nerve tissue. Chromium often accumulates in aquatic life, adding to the danger of eating fish that may have been exposed to high levels of chromium [27].

Nickel occurs in the environment only at very low levels. Humans use nickel for many applications like the use of nickel as an ingredient of steel and other metal products [27], in the metallurgical, chemical and food processing industries, especially as catalysts and pigments [35]. Foodstuffs have low natural content of nickel but high amounts can occur in food crops growing in polluted soils. Humans may also be exposed to nickel by inhalation, drinking water, smoking, and eating contaminated food [27]. Uptake of high quantities of nickel can cause death, systemic effects, respiratory effects, cardiovascular effects, gastroin‐ testinal, haematological musculoskeletal, hepatic, renal, endocrine, metabolic, immunological and lymphoreticular, neurological, reproductive, developmental effects and cancer [36]. Nickel occurs naturally in the Earth's crust with an average concentration of 0.0086% (86 ppm). The nickel content of soil may vary depending on local geology [37].

Copper is an essential substance to human life, but in high doses it can cause anaemia, liver and kidney damage, and stomach and intestinal irritation. People with Wilson's disease are at greater risk for health effects from overexposure to copper. Copper normally occurs in drinking water from copper pipes, as well as from additives designed to control algal growth [28]. The major sources of environmental copper releases include the mining, smelting and refining of copper, industries producing products from copper such as wire, pipes and sheet metal, and fossil fuel combustion [38].

### **1.2. Health and environmental effects of some common Persistent Organic Pollutants (POPs)**

Persistent organic Pollutants (POPs) are associated with serious human health problems, including cancer, neurological damage, birth defects, sterility, and immune system defects. US Environmental Protection Agency (USEPA) and the Stockholm Convention have classified certain POPs as probable human carcinogens, including aldrin, dieldrin, chlordane, Dichlor‐ odiphenyltrichloroethane (DDT), heptachlor, Hexachlorobenzene (HBC), toxaphene, and Polychlorinatedbiphenyls (PCBs) [39,40,41]. Laboratory studies have shown that low doses of POPs may affect organ systems. Chronic exposure to low doses of certain POPs may affect the immune and reproductive systems. Exposure to high levels of certain POPs can cause serious health effects or death. The primary potential human health effects associated with POPs are cancer; immune system suppression; nervous system disorder; reproductive damage; altered sex ratio; reduced fertility; birth defects; liver, thyroid, kidney, blood, and immune system damage; endocrine disruption; developmental disorders; shortened lactation in nursing women; and chloracne and other skin disorders.

Studies have linked POPs exposure to declines, diseases, or abnormalities in a number of wildlife species, including certain kinds of fish, birds, and mammals [39,42]. Wildlife also can act as sentinels for human health: abnormalities or declines detected in wildlife populations can sound an early warning bell for people. For example, the behavioural abnormalities and birth defects in fish, birds, and mammals in and around the Great Lakes. People are mainly exposed to POPs through contaminated foods. Less common exposure routes include drinking contaminated water and direct contact with the chemicals. In people and other mammals alike, POPs can be transferred through the placenta and breast milk to developing offspring. In addition, sensitive populations, such as children, the elderly, and those with suppressed immune systems, are typically more susceptible to many kinds of pollutants, including POPs. Because POPs have been linked to reproductive impairments due to their endocrine disrupting properties, men and women of child-bearing age may also be at risk [43-47].

Organochlorine pesticides are a large class of multipurpose chlorinated hydrocarbon chemi‐ cals, some of which are POPs. They break down slowly in the environment and accumulate in the fatty tissues of animals. Thus, they stay in the environment and food web long after being applied [48]. Many organochlorine pesticides are endocrine disrupting chemicals, meaning they have subtle toxic effects on the body's hormonal systems [27]. Endocrine disrupting chemicals often mimic the body's natural hormones, disrupting normal functions and contributing to adverse health effects. Organochlorine pesticide is ubiquitous environmental contaminants because they break down very slowly. The effects that some of the most common organochlorine pesticides have on humans as well as animal's health are as follows:

Acute exposure to chlordane can possibly cause neurological effects while long-term exposure can damage the liver, kidney, and other internal organs. Significant immune system changes have also been reported in exposed workers. There is some evidence of carcinogenicity [49]. Research has also indicated that chlordane is an endocrine disruptor. The half-life of chlordane in soil has been reported to be from one to three years. Chlordane binds to aquatic sediments and bioconcentrates in the fat of organisms.

greater risk for health effects from overexposure to copper. Copper normally occurs in drinking water from copper pipes, as well as from additives designed to control algal growth [28]. The major sources of environmental copper releases include the mining, smelting and refining of copper, industries producing products from copper such as wire, pipes and sheet metal, and

**1.2. Health and environmental effects of some common Persistent Organic Pollutants**

Persistent organic Pollutants (POPs) are associated with serious human health problems, including cancer, neurological damage, birth defects, sterility, and immune system defects. US Environmental Protection Agency (USEPA) and the Stockholm Convention have classified certain POPs as probable human carcinogens, including aldrin, dieldrin, chlordane, Dichlor‐ odiphenyltrichloroethane (DDT), heptachlor, Hexachlorobenzene (HBC), toxaphene, and Polychlorinatedbiphenyls (PCBs) [39,40,41]. Laboratory studies have shown that low doses of POPs may affect organ systems. Chronic exposure to low doses of certain POPs may affect the immune and reproductive systems. Exposure to high levels of certain POPs can cause serious health effects or death. The primary potential human health effects associated with POPs are cancer; immune system suppression; nervous system disorder; reproductive damage; altered sex ratio; reduced fertility; birth defects; liver, thyroid, kidney, blood, and immune system damage; endocrine disruption; developmental disorders; shortened lactation in nursing

Studies have linked POPs exposure to declines, diseases, or abnormalities in a number of wildlife species, including certain kinds of fish, birds, and mammals [39,42]. Wildlife also can act as sentinels for human health: abnormalities or declines detected in wildlife populations can sound an early warning bell for people. For example, the behavioural abnormalities and birth defects in fish, birds, and mammals in and around the Great Lakes. People are mainly exposed to POPs through contaminated foods. Less common exposure routes include drinking contaminated water and direct contact with the chemicals. In people and other mammals alike, POPs can be transferred through the placenta and breast milk to developing offspring. In addition, sensitive populations, such as children, the elderly, and those with suppressed immune systems, are typically more susceptible to many kinds of pollutants, including POPs. Because POPs have been linked to reproductive impairments due to their endocrine disrupting

Organochlorine pesticides are a large class of multipurpose chlorinated hydrocarbon chemi‐ cals, some of which are POPs. They break down slowly in the environment and accumulate in the fatty tissues of animals. Thus, they stay in the environment and food web long after being applied [48]. Many organochlorine pesticides are endocrine disrupting chemicals, meaning they have subtle toxic effects on the body's hormonal systems [27]. Endocrine disrupting chemicals often mimic the body's natural hormones, disrupting normal functions and contributing to adverse health effects. Organochlorine pesticide is ubiquitous environmental contaminants because they break down very slowly. The effects that some of the most common

organochlorine pesticides have on humans as well as animal's health are as follows:

properties, men and women of child-bearing age may also be at risk [43-47].

fossil fuel combustion [38].

230 Environmental Risk Assessment of Soil Contamination

women; and chloracne and other skin disorders.

**(POPs)**

DDT is a possible human carcinogen; some of its metabolites Dichlorodiphenyldichloroethy‐ lene (DDE) and Dichlorodiphenyldichloroethane (DDD) are probable human carcinogens [49]. DDT and its breakdown products are thought to be endocrine disruptors. DDT is lipophilic and will both bio-concentrate and bio-magnify. It is present almost everywhere in the envi‐ ronment, and residue has been detected in the arctic. DDT breaks down into the related compounds; DDE and DDD. In the environment, DDT and its metabolites have a half life of 10 to 15 years in soil. DDT is highly toxic to birds and fish, DDE and DDD are also toxic and persistent [50]. Some DDT may evaporate from soil and enter the air, and some may be broken down by the sun or microorganisms.

Heptachlor is metabolised in animals to heptachlor epoxide, whose toxicity is similar to that of heptachlor [49]. Both binds to animal fat. Heptachlor and heptachlor epoxide are possible human carcinogens and are thought to be endocrine disruptors. At high levels or from chronic exposure, they can cause central nervous system and liver damage. The half life of heptachlor in temperate soil is up to two years. Heptachlor has been found in treated wastewater from industrial processes including coal mining, foundries, and nonferrous metals manufacturing. It has been detected in the blood of cattle in the U.S. and heptachlor has been strongly implicated in the decline of several wild bird populations [50].

Mirex is probably a carcinogen and is also thought to be an endocrine disruptor. It may cause damage to skin, liver, nervous, and reproductive systems at high levels [49]. Crustaceans may be the most sensitive organisms to mirex. It can bio-accumulate and bio-magnify and is very persistent, with a half life of up to 10 years in soil. It has been detected in arctic freshwater.

Lindane, which belongs to the class of new POPs under the Stockholm Convention may be a carcinogen and is thought to be an endocrine disruptor. It can cause nervous system effects and pulmonary oedema from short, and acute exposures. Long-term exposure can cause liver and kidney damage, as well as various blood disorders [49]. Lindane bio-concentrates slightly in fish and crustaceans, and can remain in the air for up to 17 weeks and travel long distances. It is broken down quickly in water [50]. Lindane exposure has been associated with recurrent miscarriage. Lindane also disrupts natural levels of estrogens, androgens and thyroid hor‐ mones in rodents [51]. Lindane produces behavioural and neurochemical changes in devel‐ oping rats at doses that do not produce symptoms in adults. This is significant because it suggests that lindane may have the greatest effect during development [52]. Both acute and sub-chronic exposures to lindane were found to reduce dopamine concentrations in the brains of rats by about 46%. Dopamine is an important neurotransmitter with effects on mood and behaviour [53]. Lindane exposure during postnatal development in rats was associated with alterations in levels of detoxification enzymes in the brain that lasted until adulthood. It is not known how this alteration might affect the outcome of future exposures [54]. Exposure to lindane decreased both thyroid hormones and progesterone in developing lambs [55S].

Dieldrin can cause poisoning in humans and mammals following exposure via the skin, oral intake or inhalation. It acts as a stimulant to the central nervous system and accumulates in fatty tissue causing severe damage to the liver and kidneys. Animal experiments have revealed a carcinogenic effect, but as yet no teratogenic action. Residue levels of aldrin (mostly present as dieldrin) do not accumulate indefinitely, as the result of yearly applications at a constant dosage rate, but will reach a maximum level which is, in practice, of the order of that resulting from a single annual dose [56,57]. There is virtually no leaching of aldrin into deeper soil layers and thus no contamination of groundwater, which is eventually used as drinking or irrigation water [58,59].

Endosulfan is highly toxic to the nervous system and can cause circulatory problems, head‐ ache, vomiting and diarrhea. Thus, it is one of the new POPs under the Stockholm Convention. It is also a suspected hormone disruptor [49]. Endosulfan has shown no potential to accumulate over time in animals. It is more water soluble than other organochlorine pesticides, such as DDT, and is less persistent in the body because it metabolises quickly [60].

#### **1.3. Health and environmental effects of Polycyclic Aromatic Hydrocarbons (PAHs)**

Because of combustion of fossil fuels and organic waste, PAHs are ubiquitous in the environ‐ ment. Studies show that certain PAHs metabolites interact with DNA and are genotoxic, causing malignancies and heritable genetic damage in humans. Many of these compounds have carcinogenic and mutagenic activities and present a hazard for human health [61]. In humans, heavy occupational exposure to mixtures of PAHs entails a substantial risk of lung, skin, or bladder cancer. PAHs generally have a low degree of acute toxicity to humans. The most significant endpoint of PAHs toxicity is cancer. Increased incidences of lung, skin, and bladder cancers are associated with occupational exposure to PAHs. It is difficult to ascribe observed health effects in epidemiological studies to specific PAHs because most exposures are to PAHs mixtures. Animal studies show that certain PAHs affect the hematopoietic, immune, reproductive, and neurologic systems and cause developmental effects [62].

#### **1.4. Soil contamination by cattle wastes**

Cattle manure is a major waste product of agricultural practice involving the breeding and rearing of cattle. Inappropriate disposal of manure can create environmental problems such as odours and leaching of nitrate ion and other pollutants into groundwater. Repeated annual application of manure with high salt content caused a build up of soluble salts in soils, sufficient to lower their productivity [63]. During the last three decades, dairy farm facilities have received attention from the public and regulations due to increased environmental concern. These facilities concentrate in certain regions of the USA (e.g. California, New York, Minnesota, and Pennsylvania) and generate considerable amount of manure, which can harm soil and water quality. Manure varies in mineral composition depending on the type of animal and the ration fed. It was reported that cattle (Bos Taurus) manure contains 2.7 to 9.5% N, 0.5 to 0.8% O, 1.7 to 2.9% K, 1.4 to 20% Ca, and 0.61 to 0.76% Mg (% dry waste basis) [64]. In addition, varying amounts of Al, Fe, Mn, S, Cl, Cu, Zn, and B and trace concentrations of Co, Cd, Cr, Ni, As and Se are present. Large fractions of these elements are present in a water-soluble form. With high precipitation, almost all regions where dairy farm facilities concentrate, great qualities of these elements are lost through surface runoff and leaching into groundwater. Manure contains a large amount of soluble and insoluble organic substances. Organic matter content ranges between 80% and 90% (dry weight basis) [64]. Pyrolysis field ionization mass spectroscopy (Py-FIMS) was also used to analyse cow manure samples [65]. The organic components that were identified include lignins, dimeric lignins, pesticides, lipids, monoest‐ ers, fatty acid, sterols, and heterocyclic nitrogen compounds.

The aim of this study was to determine the distribution, concentration and profiles of some ubiquitous environmental pollutants such as heavy metals, polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides in soil of a cattle market around River Ogun Basin, Isheri, Nigeria so as to ascertain the level of contamination of the soil resulting from the anthropogenic activities taking place in the area.
