The use of the mangrove oyster (Crossostrea gasar) as a bio-indicator for chemical element contamination in the Niger Delta

Abstract

The study evaluated the concentrations of some chemical elements namely Copper (Cu), Manganese (Mn), Zinc (Zn), Chromium (Cr), Nickel (Ni) and Lead (Pb) in the mangrove oyster (Crossostrea gasar) and water from Golubo creek in the Niger Delta region of Nigeria, to ascertain the impact of these metals on the investigated ecosystem. The evaluation was carried out using Atomic Absorption spectroscopy technique. The mean  concentrations of the aforementioned elements in C.gasar were 1.06 mg/kg, 0.38 mg/kg, 50.13 mg/kg, 0.14 mg/kg, 0.39 mg/kg and 1.55 mg/kg, respectively while the mean concentrations of the elements in water were 0.65 mg/l, 0.04 mg/l, 16.47 mg/l, 0.86 mg/l, 0.85 mg/l and 1.50 mg/l, respectively. Copper, Manganese, Zinc and Lead were  bioaccumulated by C.gasar while the estimated daily intake of these elements ranged from 0.0056 mg/person/day for Chromium to 2.01 mg/person/day for Zinc. The Maximum Acceptable Risk values for Copper, Manganese, Zinc, Chromium, Nickel and Lead in C. gasar were 0.79, 0.05, 24.67, 0.94, 1.08 and 1.94, respectively. The Toxicity Quotient values for the chemical elements in C.gasar ranged from 0.66 for Zinc to 0.93 for Chromium while in the case of water, the range was from 0.65 for Copper to 1.5 for Lead. With regard to health risk to man, the mean concentrations of the chemical elements in the oysters, did not exceed the Federal Environmental Protection Agency (FEPA) maximum allowable limit for chemical elements in food. The mean concentrations of these metals in the bivalve were, therefore, within health limits and therefore do not present an immediate health threat to consumers. It was observed that the mean concentrations of the chemical elements in water were generally below the FEPA maximum allowable limits for chemical elements in drinking water with the exception of Lead. The study, thus, revealed that there is a potential health risk to man as a result of consuming Pb-contaminated water. Based on the findings from this study, it is advocated that the creek be closely monitored for toxic metals in order to avert the occurrence of episodic ecological accidents.

Key words: Chemical elements, Oyster, Niger Delta