WATER-QUALITY OF THE RIVER NILE .3. TOXICITY ASSESSMENT OF 6 INDUSTRIAL EFFLUENTS POLLUTING THE RIVER NILE

Six different industrial effluents were chemically and physically char acterized. Their toxicity was evaluated using biotests with Selanastru m capricornutum strain NIVA-CHL1. The growth of the test alga showed e ither inhibition or stimulation. Two of the effluents were highly inhi bitory with EC50 values ranging between 1 and 10% (v/v) effluent conce ntrations. Others showed low growth inhibitory effects (50% < EC50 < 1 00%). EC50 values derived from the growth parameters, algal dry weight , cell count, growth rate, and area under the growth curve were almost similar for those two effluents exhibiting highly inhibitory effects. The toxicity values, calculated from algal dry weight and cell count showed, a strong positive linear relationship (r = 0.97 at p < 0.0001) . The potential toxicity of some effluents was partly related to their high content of heavy metals. Changes in mean cell volume of the test alga may be used as an indicator for the potential effects of toxic e ffluents on the overall cellular activities. The results emphasized th e indispensable role of algal bioassays among the basis of relevant an d quantitative information about the biological impacts of the investi gated effluents on the receiving waters. (C) 1993 John Wiley & Sons, I nc.