Complying with Effluent Toxicity Regulation in Canada

A questionnaire was sent to 75 mills in Canada requesting information on compliance in 1999 with respect to the toxicity regulation for liquid discharges. This regulation requires that at least 50% of rainbow trout and Daphnia magna survive in the discharge from the mill in toxicity tests. Of the 74 mills that responded, 81% and 74% reported no toxicity failures for process effluents in rainbow trout and Daphnia magna tests, respectively. For mills with infrequent or no toxicity episodes during the year (1 or 0 for trout; 1‐4 or 0 for Daphnia magna), 89% and 92% of the mills met this criterion for trout and Daphnia magna tests, respectively. In addition to process effluents, 28 mills had separate cooling water discharges and, of these, ten experienced at least one episode of cooling water toxicity. Ammonia and accidental spills were most frequently cited by the mills as likely causes of process effluent toxicity. The most frequent causes cited for cooling water toxicity were chlorine and accidental contamination from other sources.