Ecotoxicological assessment of pollutants in Lake Victoria fishery, Kenya: Proof of fish consumption?

Abstract

This study set out to survey and document pollution in fishing grounds and thereby provide necessary information on environmental quality for purposes of management of the fishery in Lake Victoria, Kenya. The monitoring survey was conducted between June 2010 and June 2013 to identify changes or trends in water quality over time, collect information on biotic indicators of water quality as well as identify fish parasites in Lates niloticus. Physico-chemical parameters were monitored in situ using portable water quality meter while nutrients and trace metals were analyzed using standard methods. Dissolved oxygen concentrations ranged from 3.42 to 6.47 mg l -1 in Asembo Bay and Kowuor, respectively with a mean of 5.26 mg l -1 . The Gulf was more eutrophic than the open waters. Soluble reactive phosphorus showed significant positive correlations (r = 0.65; P < 0.01) with conductivity and a significant negative correlation (r = -0.53; P < 0.01) with transparency. Based on Effect Range Low (ERL) and Effect Range Mean (ERM) scheme, surface sediments had concentrations above ERL for Pb, Zn, Ni and Hg respectively and 1% for Ni was above ERM. The results showed that the effects of most metals of ecotoxicological importance in the sediments were of acceptable levels except for Pb, Zn, Ni and Hg with lead having the highest risk. The fish larval assemblage of Lake Victoria Kenyan waters was dominated by the R. argentea, with the highest numbers within Lwanda Gembe, attributed to the water clarity and reproductive strategy of the fish. The study recommends restoration of wetlands, especially those at the mouths of major rivers draining the lake to serve as buffers and filters.