The effect of enzyme treatment on untreated d-stage effluent: Short-term fish early life-stage toxicity test

Abstract

Short-term early-life-stage toxicity experiments were conducted using zebra fish (Brachydanio rerio) under semistatic conditions. The test parameters studied were percent hatching success, median time from fertilization to hatching, median survival of embryos and larvae, frequency of abnormal larvae, as well as larval growth. Test organisms were exposed to a sample of raw spent bleach liquor from the D-stage of a softwood bleached-kraft pulp mill and the sample after treatment with a peroxidase enzyme, which resulted in a 50% decrease in residual phenolic components (0.123 vs. 0.061mg/L). In the untreated D-stage sample, the 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-observed-effect concentration was 25ml/L. No dose response could be established for fish exposed to peroxidase-treated D-stage liquor; the treated effluent was only minimally toxic in this short-term test.