Metal Concentrations in Tissues of Pseudolithus Senegalensis , (Croacker Fish) and Ethmalosa Fimbriata (Bonga Fish) Obtained from Carter Bridge River and Makoko River, Lagos State, Nigeria

his study assessed the concentrations of cadmium, lead, manganese, copper and iron in the tissues of commercially important Croacker fish (Pseudolithus senegalensis ) and Bonga fish ( Ethmalosa fimbriata ) obtained from Carter Bridge river and Makoko river,in Lagos State, Nigeria. These metals were determined using Perkin-Elmer Analyst 300-Atomic Absorption spectroscopy (AAS). Heavy metal content varied significantly (p<0.05) depending on fish species. This study revealed that the concentration of cadmium and lead in Pseudolithus senegalensis and Ethmalosa fimbriata tissues were above the maximum acceptable concentrations for human consumption, thus precaution need to be taken on order to prevent future contamination.


Heavy Metals
Heavy metals in aquatic environment are a major concern because of their to xicity and threat to plant and animal life disturbing the natural ecological balance. The specific problem associated with the heavy metals in the environ ment is their accu mulation through food chain and persistent in nature. Uptake of heavy metals such as copper, lead and cadmiu m through the food chain in hu man being may cause various physiological d isorders like hypertension, sporadic fever, nausea and renal damage [1].
Heavy metal po llut ion and its management has been a majo r g lobal concern fo r env iron mentalist due to their non-degradable and hazardous nature. Heavy metal pollution is the result of industrial waste, geochemical structure and min ing act iv it ies. Under so me env iron mental condit ions, heavy metals may accumu late to a to xic concentration and cause ecological damage [2]. Pollut ion enters fish through five main routes: via food or non-food particles, gills, oral consumption of water and the skin. The absorbed pollutants are then carried in the blood stream to either a storage point or to the liver for t ransformat ion and/or storage ( [3], [4]).
Heavy metals are present in the aquatic environ ment where they bioaccumulate along the food chain. For this reason, determination of chemical quality of aquatic organisms, particularly the contents of heavy metals is extremely important for hu man health. Therefore, the problem of food (including fish) contamination by to xic metals is receiving global attention [5]. Fish are often used as subjects to investigate toxic substances present in water, as studies have indicated that fish are able to accu mulate and retain heavy metals fro m their environment and that accumulat ion of metals in tissues of fish is dependent upon exposure, concentration and duration as well as other factors such as salinity, temperature, hardness and metabolis m of the animals [3].
The frequent presence of lead, cad miu m and copper in industrial wastes and its high toxicity along with considerable b ioaccumulat ion in fresh water fishes makes them to xicants that should be given due consideration in aquatic toxicology [6].
For the past several decades, the increasing usage of heavy metals in industry has led to serious environmental pollution through effluents and wastes. The enrich ment of heavy metals in Carter Bridge River and Makoko River has been reported in previous research paper [7] . In the present work, cadmiu m, lead, copper, iron and manganese levels in fish Fimbriata (Bonga Fish) Obtained from Carter Bridge River and M akoko River, Lagos State, Nigeria tissues of Ethmalosa fimbariata and Pseudolithussenegalen sis obtained from Carter Bridge river and Makoko river were determined to assess the public health risks associated with consuming fish harvested fro m these areas.

Sample and Sampling
The fish samples (Ethmalosa fimbriata and Pseudolithus senegalensis) were caught using local fishermen's net from Carter Bridge River and Makoko River. Samples of fishes were taken to the laboratory on the same day and later dissected to remove the intestine, liver and stomach of each species of fish.

Sample Preparation
The tissues of each fish samples were dried at 105℃ until they reached a constant weight. The ground fish tissues were transferred to porcelain basin and put to a Thermion P muffle furnace at a temperature of 550℃ or 4hrs. Samp les were digested with tri-acid mixtu re (HNO 2 : HCLO 4 : H 2 S0 4 = 10:4:1) at a rate of 5ml per 0.5g of sample and was placed on hot plate at 100℃ temperature. Digestion was continued until the liquor was clear [8]. All the digested liquors were filtered through Whatrmann 541 filter paper and d iluted to 25ml with distilled water.

Anal ysis of Heavy Metals
The concentrations of heavy metals in the fish samples were analy zed using Perkin-Elmer Analyst 300 Ato mic Absorption spectroscopy (AAS).

Discussion
Lead, cad miu m and copper accu mu lated in the tissue of Pseudolithus senegalensis (Croacker fish) and Ethmalosa fimbariata (Bonga fish). The results showed that lead, cadmiu m and copper levels in the tissues of this fishes were relatively higher when co mpared to European Regulation and WHO maximu m reco mmended limits of 0.5mg/ kg in fish food [9]. Metal accu mulat ions in fish bodies appear as site specific, corresponding with the metallic to xicity of three aquatic components via water, plankton and sediments [10]. Tilap ia fish obtained fro m Benya Lagoon and Saku mo Lagoon (Ghana) showed low concentrations of heavy metals below the permissible limits ( [11], [12]). Cad miu m levels in the Tilap ia fish was also low in comparison to the 0.576-1.257mg/kg recorded in fishes of Olo moro water bodies [13] and 0.270mg/kg reported fro m fishes of the River Niger [14].
The high levels of copper are due to the fact that freshwater fisher gills might be expected to be the primary route for the uptake of waterborne pollutants [15]. Copper can combine with other contaminants such as mercury and ammon ia to produce an additive toxic effect on fish. Lead accumulates significantly in the tissues of the two fish species. Similar findings showed that the highest concentration of lead was in gills in the rainbow trout [16]. Lead is high ly to xic to aquatic organis ms especially fish. The biological effects of sublethal concentrations of lead include delayed embryonic develop ment, suppressed reproduction, neurological problems and kidney dysfunction. [17]. Lead concentrations in the fish tissues exceed 0.5mg/g dry weight having the potential to harm fish reproduction.

Conclusions
Ethmalosa fimbariata and Pseudolithus Senegalensis fro m Makoko River and Carter Bridge River are fairly contaminated with lead, cad miu m and copper and may be toxic to other aquatic fauna and poisonous to human consumers through the trophic web.