Bioaccumulation of Heavy Metals in <i>Tilapia zilli</i> Exposed to Industrial Effluents Under Laboratory Conditions

Abstract

Characterization of the effluents from Agbara Industrial Estate treatment plant showed that the effluents were complex and varied in composition. Though the treatment methods used by the treatment plant (aeration and use of chemicals) made the discharged effluents conform to the effluent discharge requirement in Nigeria. As far as the temperature, PH, level of Pb, Zn, Mn, and Cd were concerned. The color (443.00±12.08Hz, BOD (240.50±10.26mgl -1 ), Fe (9.20±1.28mgl -1 ) were however above the permissible level of discharge while dissolved oxygen (2.30±0.38mgl -1 ) was below the permissible level. Tilapia zilli was found to accumulate heavy metals in the effluent above the what was in the media of exposure. After about eight weeks of exposure, the level of heavy metals in the fish were about 10 times in the exposure media. This is a testimony of the amazing power of T. zilli to concentrate heavy metals in its body. In this study, T. zilli was found to accumulate 275.42mgl -1 of lead in 40% effluent compared with 88.06 in 10% effluent. After eight weeks of exposure, the heavy metals were 10 times in the fish than the effluent. The amount of heavy metals accumulated were also found to be concentration of effluents and period of fish exposure dependent. In general, the metals were preferably accumulated by T. zilli in the order of Pb>Fe>Cu>Mn>Cd. In the tissues, the heavy metals were accumulated in the order of whole fish>gill>gut>liver>muscles. It is thus not safe to fertilize fish ponds with industrial effluents as this could increase the level of metals in consumers knowing that heavy metals are toxic when above the level recommended in foods.