Assessment of organochlorine pesticides and polychlorinated biphenyls in water from cage aquaculture farms in the Volta Lake in Southern Ghana

Abstract

The Volta Lake system in southern Ghana has witnessed much agricultural activity in its catchment for over 50 years. There is documented evidence of an increased release of agrochemicals into the aquatic ecosystem. In recent years, cage aquaculture activities have also increased, raising the concern of further release of contaminants and issues of ecological risks in the lake environment. Therefore, this research documents the preliminary investigation into the possible release of contaminants by cage aquaculture activities into the aquatic medium. Sixty (60) water samples were taken from four (4) cage farms along the basin to examine the levels of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs). Water samples in hexane solvent system were sonicated on an ultrasonic bath, electronically rocked, cleaned by liquid-phase extraction, and GC/ECD and GC/MS analyses for OCPs and PCBs, respectively. The water from the farms contained eleven (11) OCPs: δ-HCH, γ-HCH, heptachlor, α-endosulfan, β-endosulfan, endrin, o,p'-DDE, p,p'-DDE, o,p'DDD, p,p'-DDT, and methoxychlor, as well as five (5) PCBs: PCB-18, PCB-52, PCB-101, PCB-138, and PCB180. The OCPs concentration ranged 0.026± 0.018 µg/l (ww) for p,p'-DDE in fish farm B to 1.541± 0.031 µg/l (ww) for methoxychlor in fish farm A . Methoxychlor (1.541±0.031µg/l), δ-HCH (0.520±0.001 µg/l), endrin (1.173±0.161 µg/l), δ-HCH (0.280±0.057 µg/l) and δ-HCH (0.037±0.009 µg/l) recorded the highest levels with detection frequencies of 90%, 10%, 30%, 20% and 30% in fish farms A, B, C, D and controls respectively. PCBs concentrations varied from 0.070±0.011 ng/l for PCB 138 in farm D to 0.815±0.211 ng/l for PCB 101 in the fish farm C. PCB-18 and PCB-180 were predominant and accounted for 100% PCB in the water samples. The levels of heptachlor in farms A, B, and D and endrin in farm C exceeded the WHO MRL for drinking water. The pesticides found in the water samples were largely due to polluted aquaculture activities and most probable from fish feeds used in the farms.