Accumulation of metals and histopathology in Oreochromis niloticus exposed to treated NNPC Kaduna (Nigeria) petroleum refinery effluent.

Accumulation of heavy metals and histopathology were observed in Oreochromis niloticus exposed to treated petroleum refinery effluent from the Nigerian National Petroleum Corporation, Kaduna. Analysis of fish metal burden showed that the fish concentrated trace metals a thousand times above the levels existing in the exposure medium. Some metals were preferentially accumulated more than others and the accumulation was, in decreasing order, Pb, Fe, Zn, Cu, Mn, Cr, Ni, and Cd. Whole fish metal burden was lower in fish from which the gill, liver, and kidney had been removed, suggesting that these organs accumulated the metals more than other tissues. Hemorrhaging of fins was observed in all treatment concentrations except that of the control, and fish exposed to 40 and 50% effluent were most affected. Erosion of the caudal fin was also observed in fish exposed to 40 and 50% effluent. Examination of the organs for histopathology revealed damages to the gills. Gills with edematous fused lamellae congested with blood were observed. No histopathological damage was observed in the liver and kidney. The extent of metal accumulation and histopathological damage were directly related to the effluent concentrations.