Heavy Metal Bioaccumulation in Periwinkle (Tympanostomus Spp) and Blue Crab (Callinectes amnicola) Harvested from a Perturbed Tropical Mangrove Forest in the Niger Delta, Nigeria

The last decade in Nigeria saw useful scientific contributions in biomonitoring different environmental matrices and understanding their health indices, however with scanty toxicological evidences, especially their oxidative stress response and oxygen affinity. The present study was designed to investigate the concentrations of heavy metals in edible food of periwinkle and crab harvested from a perturbed river in Niger Delta, Nigeria reported to constantly receive industrial effluent from two major oil and gas companies. Zn, Fe, Pb, Cu, Cr, Cd and Mn were assessed for two seasons from December 2009 to May 2010. Higher concentrations of heavy metals were obtained in the wet season than dry with crab bio-accumulating more metals than periwinkle. The bioavailability sequence of metals in periwinkle was Fe>Mn>Zn>Cu>Pb>Cr>Cd and crab, Fe>Mn>Pb>Zn>Cu>Cr>Cd. While Zn, Pb and Mn values in some of the stations in crab were above FAO/FEPA regulatory limits and Fe in Periwinkle above FAO/WHO during the wet season. The study has not only provided some useful information on metal accumulation in the icthyofauna of the river but call for more toxicological study and biomonitoring of anthropogenic sources to the river using crab and periwinkle.

Aims: The aim of the present study is to investigate the concentrations of heavy metals in periwinkle and crab by estimating their spatial and seasonal mean variation in the individual animals and compare.

Study Design: The design is comparative analytic study.

Place and Duration of Study: The study was conducted in Ekpan Creek, Warri, Delta State, Nigeria, from December 2009 to May, 2010.

Methodology: Five sampling stations were carefully selected for their proximity to anthropogenic activities from December 2009 to May 2010, to cover wet and dry seasons sampling. Samples of periwinkle and crab species were hand-picked monthly, between the hours of 7 am and 9:30 am on each sampling day, when human activities in the river were still very minimal along the sampling stations into a black polythene bag containing ice for storage in deep freezer. Samples were identified using appropriate keys and striking features, digested and analyzed for heavy metals.

Results: The study results showed the dominance of iron over other metals in both animals for both seasons, and have been observed in previous studies. Chromium and Cadmium levels were relatively stable temporally throughout the study, which is somewhat lower at station 5, expected to be higher, and was attributed to water velocity and other reported physiochemical parameters, such as increasing temperature. Crab bio-accumulated more metals than periwinkle with reports of higher concentrations.

Conclusion: Continues perturbation of the river from anthropogenic activities has remain a major concern to the water use, unregulated activities by Chevron, WRPC and other oil & gas related activities as well as human activities has placed the abundance and consumption of shell fishes (periwinkle and crab) as food delicious in the region at high risk, coupled with previous report of contamination of investigated periwinkle sold in market places, including the study area.