Toxicity of cassava wastewater effluents to African catfish: Clarias gariepinus (Burchell, 1822)

Abstract

The relative lethal and sublethal toxicity of cassava wastewater effluents from a local food factory were investigated on Clarias gariepinus fingerlings using a renewable static bioassay. The physico-chemical characteristics of the cassava wastewater effluents showed a number of deviations from the standards of the Federal Environmental Protection Agency (FEPA) on the guidelines for effluent discharges. Considering the pollutants of the effluent, cyanide (CN) is suspected to be primarily responsible for the toxicity, although synergistic effect of other pollutants cannot be ruled out. At each exposure, in the two tests, the test-organisms showed signs of serious stress, swimming pattern changed and mortality increased over relatively small increase in concentration. The LC₅₀ for lethal and sublethal tests were 0.024 mg1^-1 and 0.0064 mg1^-1, respectively. The differences observed in the mortalities and bioconcentration of metals in fish muscles of varying concentrations were significant (p<0.05). It is suggested that deposition of cassava wastewaters into aquatic environments may impair the natural population size while the consumption of fish from such environment is deleterious.

Keywords: bioconcentration, Clarias gariepinus, effluent, toxicity, wastewater

SINET: Ethiopian Journal of Science Vol. 28(2) 2005: 189-194