The Occurrence of Heavy Metals in Gills, Muscle, and Liver of Chrysichthys Nigrodigitatus From Oguta Lake
Chapter One
Aim and objectives
The purpose of this research project is to:
- Find out if fish in this river contain concentrations of heavy metals in their tissues that could render them dangerous for human consumption.
- To analyze the level of heavy metals contamination in gills, muscle and liver of Chrysichthys nigrodigitatus.
CHAPTER TWO
LITERATURE REVIEW
Heavy Metals
A heavy metal refers to any metallic chemical element that has a relatively high density and is toxic or poisonous at low concentrations. These metallic chemical elements have a relatively high density and are toxic at low concentrations, (Irwandi and Farida, 2009) and generally do not break down further into less harmful constituents and they accumulate where they are released, (Akan et al, 2009).Examples of heavy metals include mercury (Hg), cadmium( Cd), arsenic (As), chromium (Cr), thallium( TI) and lead (Pb) which can be of serious threat to animals and human beings because of their high toxicity and tendency to bioaccumulate in the food chain even at low concentrations, (Suantak et al. 2011).
Environmental pollution with toxic heavy metals is mainly due to anthropogenic activities and this has become a global issue,( Gosh and Singh, 2005; Tandy et al. 2006).Rapid industrialization has resulted to discharge of potentially toxic trace metals such as mercury, cadmium, copper, chromium and nickel into the marine environment, (Yasar et al. 2007).
Heavy metals are regarded as environmental pollutants due to their toxicity, persistency and bioaccumulation problem and their effects on health, (Tam and Wong, 2000).
After entering into aquatic environment they accumulate in tissues and organs of aquatic organisms. Absorption and assimilation depends on ecological, physical, chemical, biological condition, the kind of element and physiology of organisms. The quantification of heavy metals is therefore important for the environment and public health especially in cases of edible products. (Jaffa et al., 1998: Temara et al., 1996; Warnau et al., 1997).
The contamination of food with heavy metals constitutes a serious health hazard depending on their relative levels. Some of these metals, such as cadmium and mercury, affect the kidney and cause symptoms of chronic toxicity, including impaired kidney function, poor reproductive capacity, hypertension, tumors and hepatic dysfunction. (Luckey and Venugopal, 1977). Moreover, lead causes renal failure and liver damage (Luckey and Venugopal, 1977). Some other metals (e.g., chromium, zinc and copper) cause nephritis, anuria and extensive lesions in the kidney, (Luckey and Venugopal, 1977).
Cadmium is a nonessential heavy metal but it has accumulative polluting effect, and causes toxicity to aquatic organisms even in minute concentrations. Therefore, it is regarded as one of the most toxic elements in the environment. The occurrence of cadmium in considerably toxic amounts was reported by earlier workers in various aquatic ecosystems, (Arno et al. 2002; Audrys et al. 2004; Chrastny et al. 2006). It can act as an endocrine disrupter, interfering with biological functions such as reproduction, growth, development, osmoregulation and the ability to cope up with stress in fish. It causes significant metabolic alterations and injuries of biological system at different levels after entering into the organs of freshwater fishes through the gills, (Pratap and Bonga 1990; Brown et al. 1984). Cadmium is reported to cause anemia in a variety of fish species at low as well as high concentrations after entering into the organism of freshwater fishes through the gills, (Larson et al. 1976).
Absorption of cadmium compounds is dependent on the solubility of the compounds and accumulates primarily in the kidneys and has a long biological half-life in humans of 10–35 years. There is evidence that cadmium is carcinogenic by the inhalation route. However, there is no evidence of carcinogenicity by the oral route. Cadmium metal is used in the steel industry and in plastics. Its compounds are widely used in batteries and is released to the environment in wastewater, and diffuse pollution is caused by contamination from fertilizers and local air pollution. Contamination in drinking-water may also be caused by cadmium impurities in the zinc of galvanized pipes and solders and some metal fittings. Food is the main source of daily exposure to cadmium, (WHO, 2003).
Lead is another non- essential heavy metal that serves no biological purpose but present in all organisms. It is one of the oldest occupation and environmental diseases in the world. Extensive research indicates that lead may have adverse effects. Lead poisoning is associated with cognitive impairment and also affects the renal, hematologic and neurologic systems, (Needleman et al. 1990). It is hazardous as it accumulates in the body and affects the central nervous system. Exposure to lead is a differential diagnosis of microcytic anemia as lead inhibits heme synthesis and increases the rate of erythrocyte destruction, (Schuhmacher et al., 1997).Common sources of lead exposure in the environment include lead paint, airborne lead from combustion of petroleum products containing tetraethyl lead, soil or dust near highways or lead painted homes, plumbing leachates from pipes or solder and lead from leaded chips, and batteries, (Committee of Environmental Health , 2005)
Accumulation of heavy metals in fish
Heavy metals can be accumulated by marine organisms through a variety of pathways, including respiration, adsorption and ingestion of water or contaminated food. Some of the common toxic heavy metals that are found in fish include mercury, lead and cadmium. Other heavy metals like calcium, iron, copper, zinc and manganese are essential metals and play important roles in biological system in human and fish,( Irwandi and Farida, 2009). The most non-essential heavy metals of particular concern to fish and surface water are cadmium (Cd), Lead (Pb) and mercury (Hg) which enter into fish mainly via gills,( Ahmed and Hussein 2004).The progressive and irreversible accumulation of these metals in various organs of marine creatures ultimately leads to metal related diseases in the long run because of their toxicity, thereby endangering the aquatic biota and other organisms including humans, (Melville and Burchett, 2002).
CHAPTER THREE
MATERIALS AND METHODS
Climate of the Lake
The Uguta Lake is exposed to two distinct seasons namely the wet and the dry. Rainy season lasts from May to October and dry season lasts from November to April. Although, the month of August falls into wet season, usually a sharp drop in rainfall (downpour) is experienced (August break). The rainfall of Uguta is largely influenced by the southwest trade winds from the Atlantic Ocean and the dust-laden northeast trade (dry) winds from the Sahara desert become dominant during the dry months producing hazy weather conditions.
Water and Fish Sampling
The sampling strategies adopted for this study was stratified random sampling in which the lake was divided into three zones based on geographic locations and logistical characteristic: The upper, middle and lower zones (ISO, 2006). In each of the zones, three stations were randomly selected and chosen based on the major community settlement along the Uguta Lake, thus giving a total of nine stations within the lake (Figure 1). The sampling was conducted between November 2011 and September 2013 covering 2 Dry and 2 Wet seasons. Water samples were taken bi-monthly throughout this period at the designated stations for analysis.
CHAPTER FOUR
RESULTS
Levels of Metals in Water
Iron varied from below the detection limit (BDL) to 5.87mg/l, with a grand mean of 1.87 ± 0.52mg/l (Table 2). The highest (2.10 ± 1.13mg/l) and lowest (1.35 ± 1.15mg/l) mean Fe concentration were obtained at middle zone and lower zone, respectively (Table 1). Wet season average iron value of 2.10 ± 1.35mg/l was higher than 1.62 ± 0.44 mg/l for dry season (Table 3). Results of ANOVA analysis showed significant differences in Fe values between seasons (p < 0.05). Copper ranged between below the detection limit (BDL) and 0.83mg/l, with the grand mean of 0.25 ± 0.04mg/l (Table 2). Mean Cu concentration varies slightly among zones, and was least (0.21 ± 0.18mg/l) at the lower zone and highest (0.25 ± 0.19mgL-1) at the middle zone (Table 1). Seasonal trend (Table 3) revealed dry season had higher copper mean (0.28 ± 0.25mg/l) than wet season (0.18 ± 0.12mg/l). Statistical analysis on the results revealed that Cu values between seasons differed significantly (p < 0.05).
CHAPTER FIVE
DISCUSSION AND CONCLUSION
The relatively higher metals concentration in fish tissues as compared to water in this study was in agreement with opinion of Chale, (2002) that concentrations of trace metals in fish tissues were always higher than that of water. Generally, heavy metals exist in low levels in water and attained considerable concentration in sediments and biota (Naminga and Wilhm, 1976).
The mean concentrations of metals (Fe, Cu, Zn, Cr and Cd) in water and finfish from Uguta Lake in this study though slightly lower, compared favourably with previous studies (Okoye, 1989; Oyewo 1998; Don-Pedro et al., 2004 and Adeniyi and Yusuf, 2007) in the Imo lagoon complex and adjoining water bodies. However, Pb concentrations in water and finfish in the present study were higher than the Nigeria coastal waters background levels and permissible limits. The high Pb concentration in water and finfish observed in this study may be attributed to increasing automobile traffic emissions from lead tetraethyl in gasoline and emissions from heavy duty electric generators used in the industry to the environment. Pb is a great threat to life if present in substantial quantity because it is toxic even at low concentrations and has no known function in biochemical processes (Burden et al., 1998). The probable sources of Cd in surface water as recorded in this study may be attributed to leaching from Ni – Cd batteries, run off from agricultural soils where phosphate fertilizers are used and other wastes (Pate et al., 2001).
The relatively lower wet season Cu, Pb, Cr and Cd in water could be attributed to a dilution effect of rainfall. Although, presently the mean concentrations of all the heavy metals except Pb in this study were moderate and within the permissible standard limit of FEPA, (1991), the elevation of metal concentrations in the lake is inevitable under the prevailing conditions of increasing urbanization in Uguta and environs. In comparison among metals studied in this lake water, Cr concentrations were highest in the water samples. Similar finding was reported in Awassa and Koka Rift Valley Lakes, Ethiopia (Dsikowitzky et al., 2012).
Fish attracted a lot of attention as bio indicators for monitoring aquatic pollution, due to their relatively large body size, long life cycle, position in the aquatic food chain and their use for human consumption (Zhou et al. 2008). The fish investigated for heavy metals in the present study Cat Fish (Chrysichthys nigrodigitatus) is a commercially exploited species and occur frequently in Nigeria coastal waters. Accordingly, a couple of studies about heavy metal levels in different tissues of this fish species were published (Oyewo, 1998; Asuquo et al., 2004; Ladigbolu et al., 2011 and Opaluwa et al., 2012).
The high value of Fe observed in C. nigrodigitatus in this study compared to other metals may be due to increase in total dissolved iron in the lake. The values of Fe in the fish organs were in the order: Gill > Liver > Kidney > Muscle. High concentration of Fe had been reported in fish organs (El-Naggar et al., 2009) and was reported as the most abundant in C. nigrodigitatus compared to other fishes evaluated (Asuquo et al., 2004). However, the concentrations obtained for Fe in this study were higher compared to values reported for this fish in Ibeshe, Imo lagoon (Ladigbolu et al., 2011).
All the metals investigated in the fish species except Cu (highest concentration in the liver) had highest concentrations in the gills part. This observation may be attributed to the fact that the gills helps in respiration and filtration of water. Kebede and Wondimu (2004) reported higher Pb concentrations in the gills compared with the muscles in O. niloticus from Lake Awassa and Lake Ziway. In fish, gills are considered to be the dominant site for contaminant uptake because of their anatomical and/or physiological properties that maximize absorption efficiency from water. In the present study, Cr contents were generally higher in the gills and livers than in the muscles. This observation agrees with those of Amundsen et al., (1997) freshwater fish species from the border region between Norway and Russia.
Conclusion
This study has established the current levels of some metals in water and Cat fish (Chrysichthys nigrodigitatus) in Uguta Lake ecosystem. Based on information gathered, all investigated metals except Pb were within the permissible standard limit for aquatic life. The implication is that Pb is posing an environmental risk in this water body and calls for in-depth monitoring.
The levels of Pb and Cd in this study was generally high in the analyzed organ samples from Uguta Lake compared to the other lakes .However, there was no significantdifference in the tissues analyzed for the concentration of Pb in the two state since pr/t/>0.05.
Cadmium concentration in the gonad was significantly different between Uguta Lake and other water bodies since pr/t/=0.05.The brain, liver and muscle did not show any significant difference in the concentration of Cadmium between the two state since pr/t/ >0.05 .
The higher levels of lead and cadmium detected in organ samples from Uguta Lake may be attributed to the high agricultural activities carried out in the Imo state.
Lead levels in the liver and the brain were above the international permissible limits while cadmium levels were above the permissible limits in all tissue studied. It is however important to note that lead and cadmium residues were detected in only 40% of all samples analyzed. The residues were below the detection limit in 60% of the samples analyzed. More work needs to be done in this area to identify the actual source of these contaminants. Rearing fish in uncontaminated water, controlling industrial and agriculture effluents into surface water and proper sitting of ponds could minimize the risk of heavy metal contamination of farmed fish for improved human health.
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