Bioaccumulation and biotransfer of lead in a food chain involving earthworm, Eudrilus eugeniae and mud catfish, Clarias gariepinus.

Abstract

The bioaccumulative properties of heavy metals increase their chances of being incorporated into the food chain. In this study, the bioaccumulation and biotransfer of lead (Pb) was studied in an experimental food chain involving the earthworm, Eudrilus eugeniae and the catfish, Clarias gariepinus. Earthworms were exposed to soils contaminated with Pb at different concentrations for 14 and 28 days: Control (Group 1), 3000 (Group 2), 4500 (Group 3) and 5000 ppm (Group 4). Earthworms from the 14 days exposure were subsequently fed to four corresponding groups of C. gariepinus for 28 days and the fish organs were analysed for Pb content. The highest earthworm Pb load was observed in group 4 at 1774 ppm on day 14 and 1898 ppm on day 28. In fish, Pb concentration was in the order of gut > bone > muscle. Highest Pb load was observed in the group 4 fish gut (1.40 ppm) while group 4 fish bone had 1.17 ppm. All results showed significant differences (p< 0.05) from the control group. Bioaccumulation and biotransfer of Pb from earthworm to fish was observed to be concentration and time dependent. The Pb load in muscles of exposed fish exceeds the FAO (1983) permissible limit for Pb in fish. Heavy metals, however, need not bioaccumulate in large amounts to exert their toxic effects on living organisms, hence, bioaccumulation at low concentrations should not be ignored.