THE EFFECT OF ENZYME TREATMENT ON UNTREATED D-STAGE EFFLUENT - SHORT-TERM FISH EARLY LIFE-STAGE TOXICITY TEST

Short-term early-life-stage toxicity experiments were conducted using zebra fish (Brachydanio rerio) under semistatic conditions. The test p arameters studied were percent hatching success, median time from fert ilization to hatching, median survival of embryos and larvae, frequenc y of abnormal larvae, as well as larval growth. Test organisms were ex posed to a sample of raw spent bleach liquor from the D-stage of a sof twood bleached-kraft pulp mill and the sample after treatment with a p eroxidase enzyme, which resulted in a 50% decrease in residual phenoli c components (0.123 vs. 0.061mg/L). In the untreated D-stage sample, t he median survival of embryos and larvae was calculated to be 151 ml/L ; the lowest-observed-effect concentration was 50 ml/L, and the no-obs erved-effect concentration was 25ml/L. No dose response could be estab lished for fish exposed to peroxidase-treated D-stage liquor; the trea ted effluent was only minimally toxic in this short-term test.