Assessment of Heavy Metal Contamination of the Densu River, Weja from Leachate

TABLE OF CONTENTS

ABSTRACT

TABLE OF CONTENTS

LIST OF TABLES

LIST OF FIGURES

DEDICATION

LIST OF ABBREVIATIONS

CHAPTER ONE
1.0 INTRODUCTION
1.1 PROBLEM STATEMENT
1.2 JUSTIFICATION OF THE STUDY
1.3 OBJECTIVE OF THE STUDY

CHAPTER TWO
2.0 LITERATURE REVIEW
2.1 WATER QUALITY
2.2 ANTHROPOGENIC IMPACTS ON WATER QUALITY
2.3 PHYSICAL INDICATORS OF WATER QUALITY
2.3.1 CONDUCTIVITY
2.3.2 TOTAL DISSOLVED SOLIDS
2.3.3 TURBIDITY
2.3.4 COLOR, ODOR AND TASTE
2.4 CHEMICAL INDICATORS OF WATER QUALITY
2.4.1 pH
2.4.2 HARDNESS
2.4.3 SULPHATES
2.4.4 NITRATES
2.4.5 PHOSPHATES
2.5 BIOLOGICAL INDICATORS
2.6 HEAVY METALS
2.7 ARSENIC
2.7.1 EXPOSURE ROUTE FOR ARSENIC TO THE ENVIRONMENT
2.7.2 HEALTH EFFECTS OF ARSENIC
2.8 LEAD
2.8.1 EXPOSURE ROUTE FOR LEAD TO THE ENVIRONMENT
2.8.2 EFFECT OF LEAD ON AQUATIC LIFE
2.8.3 HEALTH EFFECTS OF LEAD
2.9 MERCURY
2.9.1 EXPOSURE ROUTE FOR MERCURY TO THE ENVIRONMENT
2.9.2 HEALTH EFFECT OF MERCURY
2.10 CADMIUM
2.10.1 EXPOSURE ROUTE FOR CADMIUM TO THE ENVIRONMENT
2.10.2 HEALTH EFFECT OF CADMIUM
2.11 SURFACE WATER IN GHANA

CHAPTER THREE
3.0 MATERIALS AND METHODS
3.1 STUDY AREA
3.1.1 SAMPLING SITES
3.1.2 SAMPLING
3.1 3 SAMPLE PREPARATION
3.1.4 MEASUREMENT OF pH, CONDUCTIVITY AND TDS
3.2 ANALYSES OF SAMPLES
3.2.1 DIGESTION PROCEDURE FOR WATER
3.2.2 DIGESTION PROCEDURE FOR SEDIMENT
3.4 CONTAMINATION FACTOR
3.3 STATISTICAL ANALYSIS

CHAPTER FOUR
4.0 RESULTS
4.1 QUALITY OF LEACHATE FROM LANDFILL
4.2 QUALITY OF RIVER DENSU UPSTREAM
4.3 QUALITY OF RIVER DENSU AT LEACHATE ENTRY POINT
4.4 QUALITY OF RIVER DENSU DOWNSTREAM
4.5 PHYSICAL PARAMETERS OF RIVER DENSU

CHAPTER FIVE
5.0 DISCUSSION
5.1 QUALITY OF RIVER DENSU UPSTREAM
5.2 QUALITY OF LEACHATE
5.3 QUALITY OF RIVER DENSU DOWNSTREAM

CHAPTER SIX
6.0 CONCLUSION
6.1 RECOMMENDATIONS

REFERENCES

APPENDIX A

APPENDIX B

ABSTRACT

The effect of leachate seepage from a landfill site on the quality of an urban river, Densu, that is the one of the main sources of water abstracted for treatment for most residents in the Accra Metropolitan area was determined by measuring the levels of heavy metals (As, Pb, Hg, and Cd) in the seepage and in the river itself using Atomic Absorption Spectrometry methods. Heavy metal concentration upstream before leachate contamination was low and within WHO limits. The mean concentrations of arsenic, lead, mercury and cadmium were 0.026mg/l, 0.957mg/l, 0.025mg/l and 0.005mg/l, respectively in the leachate. Mean heavy metal concentration, two hundred metres downstream from the leachate discharge point (where water is drawn for domestic and drinking purpose) was 0.008mg/l for arsenic, 0.393mg/l for lead, 0.001mg/l for mercury while cadmium was not detected. Lead exceeded the WHO acceptable limit of 0.01mg/l for drinking water. Mean levels in the corresponding sediment samples were 0.015mg/kg for arsenic, <0.001mg/kg for lead, 0.004mg/kg for mercury and cadmium 0.151mg/kg. Contamination factors computed were less than one (CF<1) for arsenic and lead in the sediments which imply low contamination and moderate contamination for cadmium (1 ≥ CF ≥ 3). Seepage of leachate from the landfill site into Densu must be monitored to ensure the quality of River Densu especially when it is being used as a drinking water source by downstream communities.

LIST OF TABLES

Table 4.1 Mean concentration, SD and range of arsenic in the River water

Table 4.2 Mean concentration, SD and range of lead in the River water

Table 4.3 Mean concentration, SD and range of mercury in the River water

Table 4.4 Mean concentration, SD and range of cadmium in the River water

Table 4.5 Mean concentration, SD and CF of arsenic levels in sediment

Table 4.6 Mean concentration, SD and CF of lead levels in sediment

Table 4.7 Mean concentration, SD and CF of mercury levels in sediment

Table 4.8 Mean concentration, SD and CF of cadmium levels in sediment

Table 4.9 Mean Physical parameters of the Densu River

Table 4.10 Drinking water quality standard/guidelines

LIST OF FIGURES

Fig 3.1 A Map of study area showing sampling sites

Fig.3.2 Map of study area showing sampling sites

Fig.5.1 Arsenic level in the Densu River

Fig. 5.2 Lead level in the Densu River

Fig. 5.3 Mercury level in the Densu River

DEDICATION

I dedicate this work to the Almighty God who made all things possible and to all men and women of God who have given my life a meaning.

LIST OF ABBREVIATIONS

Abbildung in dieser Leseprobe nicht enthalten

CHAPTER ONE

1.0 INTRODUCTION

Ghana aims at achieving an efficient and effective management system for the sustainable development of water resources and to ensure full socio-economic benefits for present and future generations by 2025. However, water management is still a major developmental challenge as human activities have resulted in the dwindling of freshwater resources, increased pollution load, health and transportation problems and reduced ecosystem resilience which pose significant threat to sustainable development (Roosbroeck et al., 2006).

Densu serves as a major fishing and drinking water resource for people living along the banks of the entire stretch of the river in Ghana. Rapid urbanization and industrialization in many developing countries have given rise to contamination of water resources. The fast expansion of urban, agricultural and industrial activities spurred by rapid population growth and the change in consumer habits have produced vast amounts of solid wastes. Unfortunately, managing this waste has been a challenge for many countries. In Ghana, technical, financial and institutional constraints have compounded this problem. Also, improperly designed solid waste disposal facilities and landfill sites have further contributed to contamination of surface and underground water resources. Akoteyon et al. (2011) investigated the heavy metal contamination of groundwater around a landfill site in Alimosho area of Lagos State, Nigeria and concluded that the leachates from the landfill have impacted on the groundwater resources of the sampled wells in the study area based on the direction of groundwater flow.

There are more than twenty heavy metals, but four are of particular concern to human health and the environment namely Lead (Pb), Cadmium (Cd), Mercury (Hg), and Arsenic (As), (ATSDR, 2011). They are toxic and can cause damaging effects even at very low concentrations. The Agency for Toxic Substances and Disease Registry (ATSDR) in Atlanta, Georgia, (a part of the U.S. Department of Health and Human Services) compiled a Priority List called the "Top 20 Hazardous Substances." The heavy metals arsenic (1), lead (2), mercury (3), and cadmium (7) appear on this list.

Heavy metals are produced from a variety of natural and anthropogenic activities like mining, disposal of effluents (Amman et al., 2002) from industries, and indiscriminate use of fertilizers and pesticides in agriculture. Sarpong et al., (2009) investigated the spatial distribution of levels of arsenic, lead and cadmium in River Subin, in Kumasi. High heavy metal concentrations were recorded in the river water samples and these levels were all above the World Health Organization acceptable limit for domestic water use in irrigation and therefore considered unsuitable for use in vegetable farming.

In an aquatic ecosystem, heavy metal pollution can result from atmospheric deposition, geological weathering or through the discharge of waste. Metals like Cu, Fe, Mn, Ni and Zn are essential as micronutrients for life processes in plants and microorganisms, while many other metals like Cd, Cr and Pb have no known physiological activity, but have been proved to be detrimental beyond certain limits (Marschner, 1995; Bruins et al., 2000).

An environmental concern is contamination of the River Densu by leachates from a decommissioned waste dump site. According to Christensen et al. (1998), municipal waste dump leachates are highly concentrated complex effluents which contain dissolved organic matters; inorganic compounds, and heavy metals. Watananugulkit et al. (2003) assessed the impact of leachate on the quality of surface water and ground water around the On-Nuch disposal site center in Bangkok. The impact of the leachate indicated that the surface water was more polluted than ground water. Drinking water containing high levels of these essential metals, or toxic metals such as arsenic, cadmium, chromium, lead, and mercury may be hazardous to health (Salem et al., 2000).

Despite the truism that every human on this planet needs drinking water to survive and that water can contain many harmful constituents, there are no universally recognized and accepted international standards for drinking water. Even where standards do exist, and are applied, the permitted concentration of individual constituents may vary by as much as ten times from one set of standards to another. Many developed countries in Europe and the USA have specific standards to be applied in their own country. Countries without a legislative or administrative framework for such standards, the World Health Organization published guidelines is often used. Where standards do exist most are expressed as guidelines or targets and very few have any legal basis or are subject to enforcement. The European Drinking Water Directive and the Safe Water Act in the USA are two exceptions where there is a requirement to legally comply with specific standards.

This project seek to monitor the surface water in Weija, Accra considering the spatial variations in heavy metal content and also to evaluate the status of the river water quality with respect to drinking purposes.

1.1 PROBLEM STATEMENT

Densu, a major river in southern Ghana, is the main source of water abstracted for treatment to persons living in west Accra and its environs. Rapid urbanization and industrialization in the nation’s capital have given rise to contamination of this water source. Landfill leachate rich in heavy metals discharges into the Densu River at Oblogo, Weija. Among the inorganic contaminants of the river water, heavy metals are of great concern because of their non-degradable nature and their potential to accumulate through trophic level causing a deleterious effect. Arsenic, lead, mercury and cadmium are among the ‘‘Top 20 Hazardous Substances’’ listed by the Agency for Toxic Substances and Disease Registry (ATSDR) which are of great concern to human health and the environment. Therefore, monitoring these metals is important for safety assessment of the environment and human health.

1.2 JUSTIFICATION OF THE STUDY

The rapid population growth along the Densu River has necessitated proper conservation and efficient utilization of freshwater bodies for sustainable development. This is necessary because there has been accelerated deterioration of water quality within Weija-Oblogo because of increased domestic, municipal and agricultural activities. Effluent discharge, urbanization and deforestation are the main causes of environmental degradation within the catchment (Karikari et al. 2006; Hagan et al, 2011). As a result of these anthropogenic influences on the River Densu (as source of drinking water), it becomes imperative that investigation of levels of pollution of the Densu River be carried out regularly.

1.3 OBJECTIVE OF THE STUDY

The objective of this project is to assess the level of Lead (Pb), Cadmium (Cd), Mercury (Hg), and Arsenic (As) in the Densu River to ascertain its water quality vis a vis leachate discharge from a decommissioned landfill.

The specific objectives are to investigate:

1. Levels of Arsenic (As), Lead (Pb), Mercury (Hg) and Cadmium (Cd) in the landfill leachate.
2. Levels of Arsenic (As), Lead (Pb), Mercury (Hg) and Cadmium (Cd) in the Densu River and sediment just at the point of leachate entry.
3. Levels of Arsenic (As), Lead (Pb), Mercury (Hg) and Cadmium (Cd) in River Densu and its sediments at a distance of a hundred and two hundred metres upstream from the leachate discharge point.
4. Levels of Arsenic (As), Lead (Pb), Mercury (Hg) and Cadmium (Cd) in River Densu and its sediments at a distance of a hundred and two hundred metres downstream from the leachate discharge point.

CHAPTER TWO

2.0 LITERATURE REVIEW

2.1 WATER QUALITY

Water quality refers to the chemical, physical and biological characteristics of water. It involves the process of evaluation of the physical, chemical and biological nature in relation to natural quality, human effects and intended uses, particularly uses which may affect human health and aquatic system. The most common standards used to assess water quality relate to health of ecosystems, safety of human contact and drinking water. Water quality depends on the local geology and ecosystem, as well as human uses such as use of water bodies as sink (Johnson et al., 1997).

The parameters for water quality are determined by the intended use. Water quality tends to be focused on water that is treated for human consumption, water for industrial use, or in the environment. Water contaminants that may be present in untreated water include microorganisms such as viruses and bacteria; inorganic contaminants such as salts and metals; organic chemical contaminants from industrial processes and petroleum use; pesticides and herbicides; and radioactive contaminants. Water Quality Standards have been established to regulate substances that potentially affect human health, environment and aesthetic qualities of water. The World Health Organization (WHO) guideline for Drinking Water Standards, United States Specification for Drinking Water and European Union Specification for Drinking Water are among the recognized water quality standards.

Dissolved minerals may affect suitability of water for a range of industrial and domestic purposes. The most familiar of these is the presence of ions of calcium and magnesium which interfere with the cleaning action of soap, and can form hard sulphate and soft carbonate deposits in water heaters or boilers. Hard water may be softened by removing these ions.

Environmental water quality, also called ambient water quality, relates to water bodies such as lakes, rivers, and oceans. Water quality standards for surface waters vary significantly due to different environmental conditions, ecosystems, and intended human uses. Toxic substances and high populations of certain microorganisms can present a health hazard for non-drinking purposes such as irrigation, swimming, fishing, rafting, boating and industrial uses. These conditions may also affect wildlife, which use the water for drinking or as a habitat. Modern water quality laws generally specify protection of fisheries especially endangered species and recreational use (Roosbroeck et al., 2006).

2.2 ANTHROPOGENIC IMPACTS ON WATER QUALITY

With the advent of industrialization and increasing populations, the range of requirements for water has increased together with greater demands for higher quality water. Water has been considered, the most suitable medium to clean, disperse, transport and dispose of wastes (domestic and industrial wastes, mine drainage waters, irrigation returns, etc.). These activities have undesirable, effects on the natural environment. Also, uncontrolled land use, urbanization, deforestation, accidental (or unauthorized) release of chemical substances and discharge of untreated wastes or leaching of noxious liquids from solid waste deposits have impacted negatively on the quality of water resources (UNESCO, 2003).

2.3. PHYSICAL INDICATORS OF WATER QUALITY

2.3.1. CONDUCTIVITY

Conductivity is a measure of the ability of water or solution to carry an electrical current. Conductivity in water is affected by the presence of inorganic dissolved solids. Organic compounds do not conduct electrical current very well and therefore have a low conductivity when in water. Conductivity is also affected by temperature, the warmer the water, the higher the conductivity. For this reason, conductivity is reported as conductivity at 25 degrees Celsius. Conductivity in streams and rivers is affected primarily by the geology of the area through which the water flows. Discharges to streams can change the conductivity depending on their make-up. Conductivity is measured in micro siemens per centimeter (ps/cm).

2.3.2. TOTAL DISSOLVED SOLIDS

Total Dissolved Solid represents the total concentration of dissolved substances in water. The degree to which these dissociate into ions, the amount of electrical charge on each ion, ion mobility and the temperature of the solution all have an influence on conductivity. Total dissolved solids (in mg/l) may be obtained by multiplying the conductance by a factor which is commonly between 0.55 and 0.75. This factor is determined for each water body, but remains approximately constant provided the ionic proportions of the water body remain stable. The multiplication factor is close to 0.67 for waters in which sodium and chloride dominate, and higher for waters containing high concentrations of sulphate (WHO, 1996).

2.3.3. TURBIDITY

Turbidity is the cloudiness or haziness of a fluid caused by individual particles (suspended solids). Turbidity in open water may be caused by growth of phytoplankton, human activities which lead to high sediment levels entering water bodies during rain storms (USEPA, 2005).

2.3.4. COLOR, ODOR AND TASTE

Physically, the color of water is affected by factors like the light source, absorption and scattering of light, as well as suspended materials in the water. Quality drinking water should be colorless (WHO, 2008) Color and turbidity determines the depth to which light penetrates in water systems. Odors and tastes in water are associated with the presence of variety of substances which include living microscopic organisms or decaying matter. Taste responses are often difficult to differentiate from odor responses because the senses of taste and smell are closely interrelated. Odors can be caused by volatile substances in concentrations too small to be detected by ordinary analytical techniques.

2.4. CHEMICAL INDICATORS OF WATER QUALITY 2.4.1 pH

The pH value of a water source is a measure of its acidity or alkalinity. It is a measurement of the activity of the hydrogen atom, because the hydrogen activity is a good representation of the acidity or alkalinity of water. For drinking water, the WHO guidelines set the pH in the range of 6.5-8.5 (WHO, 2008).

Human activities like industrial operations and toxic waste disposal have effect on the pH of water sources. A change in the pH of water can have consequences on aquatic life which are extremely sensitive to changes in water temperature and composition.

2.4.2. HARDNESS

Water hardness is determined by the concentration of multivalent cations in the water. Common cations found in hard water include Ca2+ and Mg2+. These ions enter water supply by leaching from minerals within an aquifer. Hardness is most commonly expressed as mg/l of CaCO3. The following equilibrium reaction describes the dissolving or formation of calcium carbonate scales:

Abbildung in dieser Leseprobe nicht enthalten

Calcium carbonate scales formed in water-heating systems are called lime scale (Weingärtner, 2006; Nitsch et al., 2005).

Temporary hardness of water is caused by the presence of dissolved bicarbonate minerals (calcium bicarbonate and magnesium bicarbonate). When dissolved, these minerals yield calcium and magnesium cations (Ca2+, Mg2+) and carbonate and bicarbonate anions (CO3 ", HCO3-). The presence of the metal cations makes the water hard. However, unlike the permanent hardness caused by sulphate and chloride compounds, this "temporary" hardness can be reduced either by boiling the water, or by the addition of lime (calcium hydroxide) through the process of lime softening. Boiling promotes the formation of carbonate from the bicarbonate and precipitates calcium carbonate out of solution, leaving water soft (Nitsch et al., 2005). Permanent hardness cannot be removed by boiling. Despite the name permanent, the hardness of the water can be easily removed using an ion exchange column.

2.4.3. SULPHATES

Sulphates occur naturally in drinking water. They have a detoxifying effect on the liver and stimulate the function of the gall bladder and thus aid the digestive function as well. In high doses, they have a laxative effect. Health concerns regarding sulphate in drinking water have been diarrhea which may be associated with the ingestion of water containing high sulphate levels. Sulphate in drinking water has a secondary maximum contaminant level of 250 milligrams per liter (mg/L), based on aesthetic effects (i.e., taste and odor). The presence of sulphate in drinking-water may also cause noticeable taste and may contribute to the corrosion of distribution systems. (WHO, 2008; USEPA, 2012).

2.4.4. NITRATES

Nitrates and nitrites are nitrogen-oxygen chemical units which combine with various organic and inorganic compounds. Nitrates (NO3) are essential source of nitrogen (N) for plants. The greatest use of nitrates is as a fertilizer; nitrates taken into the body are converted to nitrites. Nitrate levels in drinking water can also be an indicator of overall water quality. Elevated nitrate levels may suggest the possible presence of other contaminants such as disease-causing organisms from sewage, pesticides, or other inorganic and organic compounds that could cause health problems.

The US Environmental Protection Agency has set the Maximum Contaminant Level (MCL) of nitrate as nitrogen (NO3-N) at 10 mg/L (or 10 parts per million) for the safety of drinking water. Nitrate levels at or above this level have been known to cause a potentially fatal blood disorder in infants under six months of age called methemoglobinemia or "blue-baby" syndrome (USEPA, 2012).

2.4.5. PHOSPHATES

Phosphates are the naturally occurring form of the element phosphorus, found in many phosphate minerals. Natural waters have a phosphorus concentration of approximately 0.02 parts per million (ppm) which is a limiting factor for plant growth. The concentration of phosphates above 100 mg/liter may adversely affect the coagulation processes in drinking water treatment plants. The addition of large quantities of phosphates to waterways accelerates algae and plant growth in natural waters; enhancing eutrophication and depleting the water body of oxygen.

In biological systems, phosphorus is found as a free phosphate ion in solution and is called inorganic phosphate. An important occurrence of phosphates in biological systems is as the structural material of bone and teeth. These structures are made of crystalline calcium phosphate in the form of hydroxyapatite. Manmade sources of phosphate include human sewage, agricultural run-off from farms, sewage from animal feedlots, pulp and paper industry, vegetable and fruit processing, chemical and fertilizer manufacturing, and detergents (Hochanadel , 2010; Laws, 1993 ).

2.5. BIOLOGICAL INDICATORS

Coliform bacteria are commonly used bacterial indicator of sanitary quality of foods and water. They are defined as rod-shaped Gram-negative non-spore forming bacteria which can ferment lactose with the production of acid and gas when incubated at 35- 37°C (APHA, 1995). Coliforms can be found in the aquatic environment, in soil and on vegetation; they are universally present in large numbers in the feces of warm-blooded animals. Coliforms are themselves not normally causes of serious illness, they are easy to culture and their presence is used to indicate that other pathogenic organisms of fecal origin may be present. Fecal pathogens include bacteria, viruses, or protozoa and many multicellular parasites.

2.6. HEAVY METALS

Heavy metals are chemical elements with a specific gravity at least 5 times that of water. The specific gravity of water is 1 at 4°C. Specific gravity is a measure of density of a given amount of a solid substance when it is compared to an equal amount of water. Some well-known toxic metals with a specific gravity 5 or more times that of water are cadmium (8.65), iron (7.9), lead (11.34), and mercury (13.546) (Lide, 1992).

In small quantities, certain heavy metals are nutritionally essential for a healthy life. Some of these elements (eg, iron, copper, manganese, and zinc) or some forms of them are commonly found naturally in foodstuffs, fruits and vegetables, and in commercially available multivitamin products. Diagnostic medical applications include direct injection of gallium during radiological procedures, dosing with chromium in parenteral nutrition mixtures, and the use of lead as a radiation shield around x-ray equipment (Roberts, 1999). Heavy metals are also common in industrial applications.

Heavy metals become toxic when they are not metabolized by the body and accumulate in the soft tissues. They may enter the human body via food, water, air, or absorption through the skin in agriculture, manufacturing, pharmaceutical, industrial, or residential settings. Industrial exposure is common in adults and ingestion the most common route in children (Roberts, 1999). Children may develop toxic levels from normal hand-to- mouth activity (ie, coming in contact with contaminated soil or eating objects that are not food such as dirt or paint chips). Less common routes of exposure include a radiological procedure, inappropriate dosing or monitoring during intravenous (parenteral) nutrition, a broken thermometer or a suicide or homicide attempt (Lupton, 1985; Smith, 1997).

Heavy metals once released into the environment can remain in waterways for decades or even centuries, in concentrations that are high enough to pose a health risk. Several methods are used to clean up the environment from these kinds of contaminants, but most of them are costly and difficult to get optimum results. Currently, phytoremediation is an effective and affordable technological solution used to extract or remove inactive metals and metal pollutants from contaminated soil and water. This technology is environmental friendly and potentially cost effective (Bieby et al., 2011).

2.7 ARSENIC

Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. It has a specific gravity 5.73, melting point of 817°C (at 28 atmospheres). It boils at 613°C and a vapor pressure of 1 mmHg at 372°C. Arsenic is a semi metallic element, odorless and tasteless (Mohan et al, 2007.). Arsenic is number one on the ATSDR's toxic and hazardous substances ‘‘Top 20 List,” and is the most common cause of acute heavy metal poisoning in adults.

2.7.1 EXPOSURE ROUTES FOR ARSENIC TO THE ENVIRONMENT

Arsenic can be found naturally on earth in small concentrations. It occurs in soil and minerals and it may enter air, water and land through wind-blown dust and water run­off. Arsenic in the atmosphere comes from various sources, volcanoes release about 3000 tonnes per year and microorganisms release volatile methylarsines to the extent of 20,000 tonnes per year, but human activity is responsible for much more 80,000 tonnes of arsenic per year are released by the burning of fossil fuels. Arsenic occurs in various organic forms in the environment (Matschullat, 2000). Inorganic arsenic and its compounds, upon entering the food chain, are progressively metabolized to a less toxic form of arsenic through a process of methylation (Reimer et al, 2010).

Arsenic is a highly toxic element that exists in various species, despite its notoriety as a deadly poison, arsenic is an essential trace element for some animals, although the necessary intake may be as low as 0.01 mg/day. The toxicity of arsenic depends on its species, the pH, and redox conditions, surrounding mineral composition, and microbial activities affect the form (inorganic or organic) and the oxidation state of arsenic.

In general, inorganic compounds of arsenic are regarded as more highly toxic than most organic forms which are less toxic (Andrianisa et al., 2008).

Humans may be exposed to arsenic through food, water and air. Exposure may also occur through skin contact with soil or water that contains arsenic. The arsenic cycle has broadened as a consequence of human interference. Large amounts of arsenic end up in the environment and in living organisms.

Arsenic is released into the environment by the smelting process of copper, zinc, and lead, as well as the manufacturing of chemicals and glasses. Arsine gas is a common byproduct produced by the manufacturing of pesticides that contain arsenic. Arsenic may be also be found in water supplies worldwide, leading to exposure of shellfish, cod, and haddock. Other sources are paints, rat poisoning, fungicides, and wood preservatives. (Roberts, 1999; ATSDR, 2011). Arsenic cannot be destroyed once it enters the environment, and can therefore spread and cause health effects to humans and animals on many locations on earth.

2.7.2 HEALTH EFFECTS OF ARSENIC

Arsenic poisoning from naturally occurring arsenic compounds in drinking water remains a problem in many parts of the world. Residents who consumed water that had arsenic level greater than 5 μg/L for ten years or longer were more likely to report a diagnosis of skin cancer, adult onset diabetes, and cardiovascular disease than age- matched residents who drank water that contained no detectable arsenic (Knobeloch, 2002).

Arsenic from drinking water can cause severe skin diseases including skin cancer; lung, bladder, and kidney cancers, and perhaps other internal tumors; peripheral vascular disease; hypertension; and diabetes. It also seems to have a negative impact on reproductive processes (infant mortality and weight of newborn babies) (Hopenhayn, 2006). Arsenic is classified as an established human carcinogen by the International Agency for Research on Cancer. Epidemiologic studies have provided substantial evidence for the association of arsenic in drinking water with cancers of the skin (non­melanoma), lung and bladder. Limited epidemiologic evidence also suggests a possible association of arsenic in drinking water with cancers of the liver, kidney, and prostate (International Agency for Research on Cancer, 1987).

Plants absorb arsenic fairly easily, so that high-ranking concentrations may be present in food. Levels of arsenic in food are fairly high, however, levels of arsenic in fish and seafood may be higher, because fish absorb arsenic from the water they live in. The concentrations of the dangerous inorganic arsenics that are currently present in surface waters enhance the chances of alteration of genetic materials of fish. This is mainly caused by accumulation of arsenic in the bodies of plant-eating freshwater organisms. Birds eat the fish that already contain eminent amounts of arsenic and will die as a result of arsenic poisoning as the fish is decomposed in their bodies. Arsenic is not absorbed very well through the skin. Therefore, exposure from skin contact alone, such as bathing in arsenic-contaminated water, is unlikely to cause health problems (Fact sheet, 2003).

[...]