Project Abstract

<p> Ten representative soil samples were collected along major gutters within Nkpor<br>metropolis. The soil samples were digested using mixtures of HF and aqua regia<br>in ratio11. The heavy metals contents of the digested soil samples were<br>determined via Flame Atomic Absorption Spectrophotometer FAAS. Sample A<br>had the highest concentration of heavy metal and the trend was Ni &gt; Cr &gt; Hg &gt;<br>Zn &gt; As ~ Cd, it was followed by sample B with Ni &gt; Cr &gt; Zn &gt; Zn &gt; Cd &gt;g &gt;<br>As, sample C had Ni&gt;Cr &gt;Zn&gt;Hg&gt;Cd&gt;As, sample E had Ni &gt; Zn &gt; Cd &gt; Cr &gt;<br>Hg &gt; As. While sample D had Cr &gt; Ni &gt; Zn &gt; Cd &gt; Hg &gt; As. Also the results of<br>the sequential extraction of each soil sample indicated that Ni had the highest<br>percentage bioavailability (49.61%), Hg (47. 72%), Cr (42. 19%), Zn (39.66%),<br>Cd (35.10%), As (0.00%). The high concentration of Hg, Cr and Cd in most areas<br>of the metropolis indicated gross contamination, which could have resulted from<br>human activities, hence the need to adequately monitor the release of these toxic<br>metals to the environment. <br></p>

Project Overview

<p> </p><p>INTRODUCTION<br>1.0 GENERAL INTRODUCTION<br>Minerals, metals and metalloids, toxic or essential, are present in soils or sediments in<br>various forms with varying bioavailability, toxicities and mobilities. Heavy metals are<br>natural components of the earth’s crust and the ecosystem with variations in<br>concentration. They cannot be degraded or destroyed and they enter our bodies via<br>food, drinking water and air [1].<br>Unlike organic contaminants, most metals do not undergo microbial or chemical<br>degradation and the total concentration of these metals in soils persist for a long time<br>after their introduction [2].<br>These metals are a cause of environmental pollution (heavy-metal pollution) from a<br>number of sources. For example lead in petrol, industrial effluents and leaching of<br>metal ions from the soil into lakes and rivers by acid rain [3].<br>Living organisms require varying amounts of “heavy metals”. Iron, cobalt, copper,<br>manganese, molybdenum and zinc are required by humans. Excessive levels can be<br>damaging to the organisms. Other heavy metals such as mercury, plutonium and lead<br>are toxic metals that have no beneficial effect on organisms and can cause serious<br>illnesses (3).<br>Therefore, with greater public awareness of the implications of contaminated soils on<br>humans and animal health, there has been increasing interest among scientific<br>communities in the development of technologies to determine the total concentrations<br>of these elements of interest in the soil as well as their chemical forms.</p><p>2<br>2</p><p>The use of sequential extraction techniques to fractionate metals in soils and evaluate<br>their potential effects has become very useful and well recognized (4)<br>1.1 SCOPE OF STUDY<br>This research covers the analysis of six heavy metals in each of the five selected<br>drainage pathways or gutters in Nkpor. The heavy metals are mercury (Hg)<br>Nickel; (Ni), Zinc (Zn), Arsenic (As), Cadmium (Cd), Mercury (Hg)<br>Soil samples were collected from each of the drainage systems as follows:<br>Five soil samples each along Nkpor/Enugu Old Road, Nkpor/Obosi Road (site for<br>Geolis Cables Industry), Limca Road Nkpor, New Market Road Nkpor and<br>Nkpor/Enugu Express Road.<br>The samples will be collected at a distance of 10 meters each to avoid bias. A total of<br>25 soil samples will be analysed to determine the total concentration of each metal in<br>each sample.</p><p>3<br>3<br>1.2 AIMS AND OBJECTIVES OF STUDY<br>Heavy metal content of soil sample in some selected drainage systems in Nkpor<br>will be investigated. As earlier on stated, heavy metals are dangerous because<br>they tend to bioaccumulate i.e increase in their concentration over time. Also<br>heavy metals can enter water supply by industrial and consumer waste or even<br>from acidic rain and release heavy metal into streams, lakes, rivers and ground<br>water.<br>Hence, the study will help in assessing the potential environmental impacts of<br>these metals by determination of their concentrations in soils as well as the<br>chemical form of these metals in the soil.<br>OBJECTIVES OF THIS STUDY<br>The objectives of this study are:<br>(a) To determine the total concentration of some selected heavy metals in gutter.<br>(b) To use sequential extraction technique to fractionate metals in soil samples.</p><p>4<br>4<br>1.3 LITERATURE REVIEW<br>A heavy metal is a member of an ill defined subset of elements that exhibit metallic<br>properties, which would mainly include the transition metals, some metallic<br>lanthanides and actinides. Many different definitions have been proposed – some<br>based on density, some on atomic number or atomic weight and some on chemical<br>properties or toxicity [5]<br>Pollution is the release of substances which alter the environment and make it<br>unfavourable to man, animals and plants [6]. Water, air and soil stand the risk of being<br>polluted.<br>1.3:1 SOIL POLLUTION<br>Soil pollution is the introduction of undesirable materials such as solids, liquids or<br>even gases into the soil, which interfere with its sustenance of plant or animal life [7].<br>Soil particles may hold chemicals and nutrients making them available for plant roots<br>and keeping them from moving into lakes or streams or entering the ground water [8].<br>Metals from soils come from various sources. They may have been present in the<br>geologic rock, or they may occur as atmospheric additions of copper, mercury, lead<br>and zinc [9]. Metals also may have been deposited by past industrial activities, such<br>as; battery productions, brass and steel manufacturing industries, mining and many<br>different processes involving Nickel, Cadmium, Copper and Lead. Lead is especially<br>evident in the soil near roadways because of automobile emissions. [10]. Again as<br>lead paints and some soldered pipes used in houses wear and deteriorate they add lead<br>to nearby soils [11]. Other on-going sources of metals and organic waste materials in<br>the soil are landfills [12] and dump sites that are poorly maintained or unregulated</p><p>5<br>5<br>[13]. Land fill materials eventually decompose and form a highly variable type of<br>unseen soil. Heavy metals remain in topsoil layer which is a result of chemical<br>reaction between heavy metals and organic matter [14].<br>1.3.2 SOIL POLLUTION AND PLANT GROWTH<br>Metal contamination on a site maybe evidenced by plant growth [15], animal<br>behaviour [16] or paint flasks containing lead from older building [17]. Many plants<br>simply cannot grow well where the level of certain metals is high. Other plants grow<br>well in contaminated soil but fail to set seed or do not grow as well as expected [15].<br>Absence of plant growth in a locality is a warning sign that a site may be severely<br>contaminated. Metals may be present at a site but with no risk for gardening or<br>recreation, depending on the soil properties, drainage and vegetation at the site.<br>1.3:3 SOIL ORGANISMS AND BIOCHEMISTRY<br>Soil is made up of mineral particles and organic matter [12] as well as the<br>decomposed remains of living things [18]. Bacterial fungi and other micro organisms<br>are largely responsible for breaking down dead plants and animals in the soil. Small<br>organisms (microbes) have negatively charged sites where soil nutrients and metals<br>can bond to form soil aggregates and compounds [19]. Earthworms and larger animals<br>eat and digest organic materials and minerals; transform them into soil aggregates and<br>deposit them as waste.<br>1.3:4 SOIL ACIDITY<br>An acid is a substance that has positive charge and usually yields hydrogen ions when<br>dissolved in water. The pH scale (1-14) is a common measure of soil reaction [12].<br>The lower the number, the greater the acidity. The midpoint of the pH scale is neutral</p><p>6<br>6<br>(7.0) which is a good level for the growth of most plants. Changes in soil reaction, as<br>measured by pH, have significant effects on metals in soils. Metal toxicity to plants<br>and animals increases in strongly acid soils with low pH (3.5) [20]. Metals in these<br>soils are released from negative sites back into soil solution. At a higher pH (8.5), the<br>metals often are sequestered in the soil [21]. The term ‘sequestered’ indicates that the<br>positively charged metal ions are bound tightly to negatively charged sites in the soil<br>[22]. These sites may be on clays, mineral compounds, or organic matter, including<br>the surfaces of some microorganisms.<br>1.3:5 HEAVY METAL POLLUTION<br>These metals are a cause of environmental pollution from a number of sources<br>including lead in petrol, industrial effluents and leaching of metal ions from the soil<br>into lakes and rivers by acid rain [3].<br>Heavy metals occur naturally in the ecosystem with large variations in concentration.<br>Today, anthropogenic sources of heavy metals ie pollution, have been introduced into<br>the ecosystem. Wastes derived fuels are especially prone to contain heavy metals so<br>there should be a central concern in a consideration of their use.<br>Heavy metal pollution can arise from many sources but most commonly arises from<br>the purification of metals e.g. the smelting of copper and the preparation of nuclear<br>fuels. Electroplating is the primary source of chromium and cadmium. Through<br>precipitation of their compounds or by ion exchange into soils and mud.<br>1.3:6 HEAVY METAL RELATIONSHIP TO LIVING ORGANISMS<br>Some metals are necessary for humans in minute amounts (cobalt, copper, chromium,<br>Nickel etc). Some of them are dangerous to health or to the environment even at low</p><p>7<br>7<br>concentration (mercury, cadmium, arsenic, lead, chromium etc). Some are harmful in<br>other ways e.g. Arsenic may pollute catalysts, whilst others are carcinogenic or toxic<br>thereby affecting, among others, the central nervous system (mercury, lead, Arsenic),<br>the kidneys or liver (Mercury, lead cadmium, copper) or skin, bones or teeth ( Nickel,<br>cadmium, copper, chromium) [23]. Certain elements are normally toxic to some<br>organisms while others may be beneficial e.g. Vanadium, tungsten and cadmium [24].<br>In medical circle, heavy metals are loosely defined [24] and include all toxic metals<br>irrespective of their atomic weights. Heavy metal poisoning can occur when excessive<br>amounts of Iron, Manganese, Aluminum or Beryllium (the fourth lightest element) or<br>such as semi metal as Arsenic are present in the environment. Early farmers in the<br>New Zealand suffered from bush sickness which was later discovered to be a<br>deficiency in cobalt [ 24 ]<br>1.3:7 REPORTED CASES OF ENVIRONMENTAL POLLUTION<br>In 1932, sewage containing mercury was released by Chisso’s Chemical works into<br>Minamata Bay in Japan. The mercury accumulated in sea creatures, leading<br>eventually to mercury poisoning in the population.<br>Again, Denis L. Feron and others used a secret discharge pipe to deliberately pump<br>hundreds of tons of heavy metal wastes into the Mississippi River from 1986 to 1996.<br>Feron is now an international fugitive and one of the Environmental Protection<br>Agency’s most wanted man because of the environmental hazards caused by his<br>pollution of the River.</p><p>8<br>8<br>In addition to that, the first incidents of mercury poisoning appeared in the population<br>of Minimata bay in Japan, in 1952. This was caused by consumption of fish polluted<br>with mercury which brought about over 500 fatalities. [25].<br>In 1986, in Sandoz, water used to extinguish a major fire carried C. 3ot fungicide<br>containing mercury into the upper Rhine. Fishes were killed over a stretch of 100km.<br>The shock drove many Federal Environmental Agency (FEA) projects forward.<br>Also, toxic chemicals in water from a burst dam belonging to a mine contaminated the<br>Coto De Danana nature reserve in Southern Spain, C.5 in Southern Spain, C.5 million<br>M-of mind containing sulphur, lead, copper, zinc and cadmim flowed down the Rio<br>Guardimar. Experts estimated that Europe’s largest bird sanctuary as well as Spain’s<br>Agriculture and fisheries suffered permanent damage from this pollution.[25]<br>1.2.8 EFFECTS OF CADMIUM ON THE ENVIRONMENT.<br>Cadmium derives its toxicological properties from its chemical similarity to zinc an<br>essential micro element for plants, animals and humans (25).<br>In humans, long-term exposure is associated with renal disfunction. High exposure<br>can lead to lung disease and has been linked to lung cancer. The average daily intake<br>for humans is estimated as 0.15 mg from air and 1 µg from water. Smoking of 1<br>packet of 20 cigarettes can lead to the inhalation of around 2.4 µg of cadmium. [25]<br>1.3:9 EFFECT OF ANTIMONY ON THE ENVIRONMENT.<br>Antimony is a metal used in the compound antimony trioxide, a flame retardant.<br>Exposure to high levels of antimony for short period of time causes nausea, vomiting<br>and diarrhea. There is little information on the effects of long-term exposure, but it is</p><p>9<br>9<br>a suspected human carcinogen. Most antimony compounds do not bioaccumulate in<br>aquatic life. [25].<br>1.3:10 EFFECTS OF COPPER ON THE ENVIRONMENT<br>Copper is an essential substance to human life, but in high doses it can cause anaemia,<br>liver and kidney damage. It can also lead to stomach and intestinal irritation. People<br>with Wilson’s disease are at greater risk from over exposure to copper. Copper<br>normally occurs in drinking water from copper pipes and also from additives designed<br>to control alga growth.<br>1.3.11 EFFECTS OF CHROMIUM ON THE ENVIRONMENT<br>Chromium is used in metal alloys and pigments for paints, cement, paper and rubber.<br>Low-level exposure can irritate the skin and cause ulceration. Long-term exposure can<br>cause kidney and liver damage and damage to circulatory and nerve tissues. It often<br>accumulates in aquatic environments thereby adding to the danger of eating fish that<br>may have been exposed to high levels of chromium.<br>1.3.12 EFFECTS OF LEAD ON THE ENVIRONMENT<br>Lead is a trace metal that is present naturally in soils and water in trace amounts (26).<br>In humans, exposure to lead can result in a wide range of biological effects depending<br>on the level and duration of exposure. Various effects occur over a broad range of<br>doses, with the developing foetus and infant being more sensitive than adult. High<br>levels of exposure may result in toxic biochemical effects on humans, which in turn<br>cause problems in the synthesis of hemoglobin, effects on the kidneys, gastro<br>intestinal tract, joints and reproductive system and acute or chronic damage to the<br>nervous system. [25].</p><p>10<br>10<br>Average daily lead intake for adult in UK is estimated at 1.6 µg from air, 20 µg from<br>drinking water and 28µg from food. Although most people receive the bulk of their<br>lead intake from food, in specific populations, other sources may be more important,<br>such as water in areas with lead piping and air near point of source emissions, soil,<br>dust, paint flakes in old houses of contaminated land. [25]<br>1.3.13 EFFECTS OF MERCURY ON THE ENVIRONMENT<br>Mercury is a toxic substance which has no known function in human biochemistry and<br>physiology and does not occur naturally in living organisms. Inorganic mercury<br>poisoning is associated with tumor and/or minor psychological changes together with<br>spontaneous abortion and congenital malformation.<br>Monomethyl mercury causes damage to the brain and the central nervous system, it<br>also gives rise to abortion, congenital malformation and development changes in<br>young children. [25]<br>1.3.14 EFFECTS OF NICKEL ON THE ENVIRONMENT<br>Small amounts of nickel are needed by the human body to produce red blood cells. In<br>great amounts, it can become mildly toxic. Long term exposure can cause decreased<br>body weight, heart and liver damage but short-term over exposure to Nickel is not<br>known to cause any problems. nickel can accumulate in aquatic life, but its presence is<br>not magnified along food chain. [25]<br>1.4 SOLUBILITY OF HEAVY METALS IN SOIL.<br>Solubility of heavy metals is directly related to sorption capacity of residuals and soil.<br>Soil pH and iron oxides are very important factors controlling metal solubility in these<br>systems. Sorption is an important chemical process that regulates partitioning of</p><p>11<br>11<br>heavy metals between solution and solid phases in soils. Recent studies on this have<br>shown that heavy metal solubility and availability in land applied residuals is<br>governed by fundamental chemical reactions between metal constituents and soil and<br>residual components [27].<br>Iron, aluminum and manganese oxide soil minerals are important sinks for heavy<br>metals in soil and residual amended soils. Heavy metal cations sorb to soil organic<br>matter (som) and other forms of humified natural organic matter (NOM). The type of<br>sorption by NOM affects the environmental fate of heavy metals. Heavy metal cations<br>form sparingly soluble phosphates, carbonates, sulphides and hydroxides. Sorption<br>and many metal precipitation processes are highly pH dependent. The pH of the soil<br>residual system is often the most important chemical property governing sorption and<br>precipitation of heavy metals. [27]<br>1.5 PHYTO AVAILABILITY OF HEAVY METALS IN RESIDUAL –<br>TREATED SOILS.<br>Application of residuals to soil affects phytoavailability by introducing heavy metal<br>into the soil and / or redistributing heavy metal into different chemical pools that vary<br>in phytoavailability (28). Application of biosolids increases heavy metal solubility and<br>availability in soil. Increases in availability are a function of metal type and metal<br>loading. Transmission of heavy metal through the food chain is affected by the soil<br>plant barrier (29). The barrier limits transmission of metal through the food chain<br>either by soil chemical processes that limit solubility (e.g soil barrier) or by plant<br>senescence (showing sign of old age) from phytotoxicity (e.g. plant barrier). The soil<br>plant barrier limits transmission of many heavy metals through the soil-crop-animal</p><p>12<br>12<br>food chain, except aluminum, zinc, molybdenum, and selenium. Cadmium, which has<br>lower affinity for metal-sobbing phases (e.g. oxides, NOM), has the greatest potential<br>for transmission through the food chain in levels that present risk to consumers (30).<br>1.6 LONG TERM ENVIRONMENTAL FATE AND BIOAVAILABILITY OF<br>HEAVY METALS IN RESIDUAL TREATED SOILS.<br>Heavy metals do not degrade in soil and many are considered persistent<br>bioacumulative toxins (PBTs). The risk to human and ecosystem health from land<br>application of PBTs in residuals depends on solubility and bioavailabilty of these<br>contaminants in the residual – treated soil. Uncertainties exist in the effect of<br>decomposition of soil organic matter complexes that bind metal and uncertainties of<br>the effect of slower long term reactions between metals adsorbed to inorganic oxide<br>surfaces in soils on metal solubility and bioavailability. Recent research findings show<br>that heavy metal is adsorbed to oxide phases of Biosolids (31). Heavy metals<br>sequestered to oxide surfaces will likely remain sequestered longer than metal<br>complexed by biosolids NOM. However, the stability of metal sequestered by oxide<br>depends on the metal and the mineral oxide surface. Long term mineral crystallization<br>reactions may “eject” metals from the solid phase into solution. The long-term<br>stability of sequestered metal bounded to metal oxide surfaces remains uncertain.<br>1.7 SOLUTE INTERACTIONS IN SOILS IN RELATION TO<br>BIOAVAILABILITY AND REMEDIATION OF THE ENVIRONMENT.<br>For diffuse distribution of metals (e.g). Fertilizer-derived cadmium input in pasture<br>soils), remediation options generally include amelioration of soils to minimize the<br>metal bioavailability.</p><p>13<br>13<br>The bioavailability of a chemical in the soil environment has been defined as the<br>fraction of the total contaminant in the interstitial pore water (i.e., soil solution) and<br>soil particle that is available to the receptor organism [32]. Bioavailability can be<br>minimized through chemical and biological immobilization of metals using a range of<br>inorganic compounds such as lime and phosphate (p) compounds (e.g. apatite rocks),<br>and organic compound such as “exceptional quality” biosolids [33]. Reducing metal<br>availability and maximizing plant growth through inactivation may also prove to be an<br>effective method of in situ soil remediation on industrial, urban, smelting and mining<br>sites.<br>The more localized metal contamination found in urban environments (e. g chromium<br>contamination in timber treatment plants) is remedied by metal mobilization process<br>that include bioremediation (including phyto remediation) and chemical washing.<br>Bioavailability of metals in soils can be examined using chemical extraction and<br>bioassay tests. Chemical extraction test includes single extraction and sequential<br>fractionation [34]. Bioassay involves plants, animals and microorganism [35].<br>A number of amendments are used either to mobilize or immobilize heavy metals into<br>soil solution, which is subsequently removed using higher plants. In contrast, in case<br>of the immobilization technique, the metal concerned is removed from soil solution<br>either through adsorption, complexation and precipitation reactions, thereby rendering<br>the metals unavailable for plant uptake and leading to groundwater.<br>Since one of the primary objectives of remediating contaminated sites is to reduce the<br>bioavailability of metals, in-situ immobilization using soil amendments that are low in<br>heavy metal content may offer a promising option. However, a major inherent</p><p>14<br>14<br>problem associated with immobilization technique is that although the heavy metals<br>become less bioavailable, their total concentrations in soils remain unchanged. The<br>immobilized heavy metal may become bioavailable with time through natural<br>weathering process or through breakdown of high molecular weight organic metal<br>complexes.<br>1.8 A CRITICAL REVIEW OF THE BIOAVAILABILITY AND IMPACTS<br>OF HEAVY METALS IN MUNICIPAL SOIL WASTE COMPOSTS.<br>The concentration, behaviour and significance of heavy metals in composted waste<br>materials is important from two potentially conflicting aspects of environmental<br>legislation in terms of: (a) defining end-of-water criteria and increasing recycling of<br>composted residuals on land and (b) protecting soil quality by preventing<br>contamination. All types of municipal soil waste (m s w) compost contain more heavy<br>metals than the background concentrations present in soil and will increase their<br>contents in amended soil. [36] Total concentrations of heavy metals in such segregated<br>and green waste compost are typically below UK PAS100 limits and mechanical<br>segregated material can also comply with the metal limits in UK PAS100 , although<br>this is likely to be more challenging [36]. Zinc and lead are the elements presents in<br>the largest amounts in MSW-compost. Lead is the most limiting element to use of<br>mechanical segregated compost in domestic gardens, but concentrations are typically<br>below risk based thresholds that protect human health.<br>There is general consensus in the scientific literature that aerobic composting<br>processes increase the complexation of heavy metals in organic waste residuals, and<br>that metals are strongly bound to the compost matrix and organic matter, limiting their</p><p>15<br>15<br>solubility and potential bioavailability in soil. Lead is the most strongly bound<br>element and nickel the weakest, with zinc, copper and Cadmium showing intermediate<br>sorption characteristics. The strong metal sorption properties of compost produced<br>from m s w or sewage sludge have important benefits for the remediation of metals<br>contaminated industrial and urban soils.<br>The availability of metals in soil depends on the nature of the chemical association<br>between a metal with the organic residual and soil matrix, the pH value of the soil, the<br>concentration of the element in the compost and the soil, and the ability of the plant to<br>regulate the uptake of a particular element.<br>However, there is good experimental evidence demonstrating the reduced<br>bioavailability and crop uptake of metal from composted biosolids compared to other<br>types of sewage sludge. [36] The total metal concentration in compost is important in<br>controlling crop uptake of labile elements, like zinc and copper, which increases with<br>increasing total content of these elements in the compost.<br>1.9.1 HEAVY METALS TRANSPORT IN THE SOIL PROFILES UNDER<br>THE APPLICATION OF SLUDGE AND WASTEWATER.<br>The results of packed-column studies may be overly optimistic in predicting soil<br>immobilization of metals, by pass flow via preferential flow paths in field soils may<br>allow significant metal transport to ground water (37). The lack of significant metal<br>deposition in subsoil may not be reliable evidence for immobility of sludge application<br>metals (38).<br>Alloway and Jackson (1991) cited several studies reporting some downward metal<br>translocation in soil, noting a potential correlation with climate (39). Soluble and</p><p>16<br>16<br>colloidal organics have been shown experimentally to moblize metals (40). Land<br>application of sludge or compost can have both beneficial and harmful aspects. Its<br>organic matter content, which constitutes approximately 50% of the solid fraction,<br>may improve soil physical properties. Nitrogen and phosphorous, ranging from 2 to<br>8% and 1 to 4% respectively, in sewage sludge and sludge compost are nutrients<br>essential for growth of crops. Municipal sludge, however, often contain undesirable<br>chemicals which may be toxic to plants and/or eventually toxic to animals and human<br>that consume edible parts of such plants (41).<br>It was concluded that the use of wastewater and sludge application in agricultural<br>lands, enriched soils with heavy metals to concentrations that may pose, potential<br>environmental and health risks in the long term.</p> <br><p></p>