ABSTRACT

Cassava mill effluent was collected from cassava mill plants which were used for acute toxicity test on the fingerlings of Clarias gariepinus. Four graded concentrations of cassava mill effluent 25ppm, 50ppm, 75ppm, 100ppm were prepared with replicates representing treatments 1, 2, 3, and 4 then a fifth treatment devoid of cassava concentration served as the control (0ppm). The mean temperature, pH, dissolved oxygen values of water used were 28.23C ± 0.09, 7.10 ± 0.08, and 6.91mg/l ± 0.03 respectively, These parameters fluctuated slightly except for the temperature which remained almost the sarne,r-throughout the experiments showing no significant difference at p > 0.05. Dissolved oxygen values decreased slightly with increase in concentration of the cassava mm effluent. Sixty percent mortality was recorded in treatments I and 2, while 70 and 80 percent mortality were recorded in treatments 3 and 4 respectively after the 96 hour. Opercular beats increased from 50 beats initially to 80 beats in the first 24hours and increased further to 82 beats in 48hours which then resulted to a lethal condition; pectoral fin beat increased in the first two days which 1ater reduced in the third and fourth day still leading to a lethal condition. Fingerlings of Clarias gariepimus used in this experiment I which had a mean weight and standard length of 8.6g ± 2.33g and 5. 75cm ± 0.86 respectively were exposed to different concentrations of cassava mill effluent for 96hrs . under laboratory conditions using static bioassay to determine its acute toxicity. The LC 50 of the exposed fish was found to be 38.02ppm with upper and lower limits being 53.57ppm and 26.98ppm respectively. The fish exhibited loss of balance, respiratory distress, vertical and erratic movement, accumulation of mucus on the body surface and gill filament and later, death. Also, effects of the different concentrations of the cassava mill effluent on haematological parameters like the Haemoglobin (HB), packed cell volume (PCV), White Blood Cell Counts (WBCC), Red Blood Cell Counts (RBCC), Mean Corpscular Volume (MCV), Mean Corpuscular Haemoglobin (MCH), and Mean Corpuscular Haemoglobin Concentration (MCHC) were studied. The lower concentrations of cassava mill effluent (25ppm and 50ppm) were not as toxic as those of the higher concentrations (75ppm and 100ppm). The changes observed in all the concentrations were significant (p <0.05). The HB, PCV, RBCC, MCV, MCH and MCHC decreased significantly (p <0.05) while WBCC increased significantly with increase in concentration. The median lethal concentration (96-hr LC 50) value was 22.39ppm, while the threshold value (safe level) was 15.85ppm. Also the mean values of cyanide concentration of cassava mill effluent was determined on monthly basis for a period of six months during which the volume of the cassava mill effluent discharged from cassava mills in the designated area was also determined for the time period of six months.