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Sublethal toxicity tests successfully measured the improved quality of pulp mill effluents from the first cycle of environmental effects monitoring (1992–1996) to the second cycle (1997–2000). Test endpoints showed notable shifts to higher concentrations (less toxic). During the second cycle of monitoring, significantly more tests showed no effect in full-strength effluent. Five case studies were considered as part of this exercise. Most of the improvement came with installation of secondary treatment. Twelve Ontario mills with secondary treatment showed reduced toxicity, compared to results with primary treatment. All 29 sets of sublethal data showed higher IC25s during the second cycle, and 23 of these differences were statistically significant. Any other changes between the two cycles of study caused only marginal overall improvement in toxicity, judging by 12 freshwater mills in British Columbia which had secondary treatment during both cycles. Sublethal tests successfully predicted the zone of potential effect in receiving water, agreeing with effects observed in biological surveys. Overlapping zones from multiple discharges could also be demonstrated. In a situation near Niagara Falls, sublethal tests estimated the proportions of toxic loading that four mills contributed to one water body. The prediction was realistic; the actual toxicity found for a mixed effluent was 57% of that predicted from separate toxicities. The conservative prediction agrees with the usual less-than-additive sublethal action of combined toxicants.

This book is relatively short and easy to assimilate. It is an explanation of water pollution problems, how they affect fish and other aquatic organisms, approaches that lead to improvements and those that are not so successful. The chapters indicate the comprehensive coverage, and include: defining pollution; how to test for lethal and sublethal toxicity; toxic action of common pollutants; effects of mixtures; water quality standards; regulatory methods; and economic value of fisheries. The book grew from lectures which Richard Lloyd delivered as Buckman Professor under the auspices of the Buckman Foundation which devotes itself to economic fish culture.

Four-day LC50s for Venezuelan Tia Juana crude oil were 0.86 mg/liter for first-stage larvae of the American lobster (Homarus americanus) and 4.9 mg/liter for third- and fourth-stage larvae. The 30-day LC50 was 0.14 mg/liter for larvae starting the test in their first stage. The threshold for retardation of larval development was about the same as the 30-day LC50. Decreased food consumption was demonstrated at 0.19 mg/liter. More "intermediate" larvae developed in oil exposures but no threshold was estimated. The ratio of "safe" to acutely lethal concentrations was about 0.03.Oil concentrations decreased during exposures; stated values could be multiplied by 0.59 to arrive at conventional average exposures. Stirring and ultrasonic vibration for 30 min dispersed averages of 7.4 and 18% of added oil. This and other techniques apparently dispersed similar components since toxicities were the same when based on measured concentrations. Aged dispersions were also equally toxic on a measured basis. Particles larger than 1.2 μm made up 84–96% of the dispersed oil and were about one-third as toxic as smaller particles and dissolved oil. For the reference toxicant DSS, the 4-day LC50 was 0.72 mg/liter for first-stage larvae indicating that lobster larvae are sensitive. Post-larval lobsters dug significantly more burrows when the substrate contained oil but did not avoid oiled substrate nor was growth or survival affected for substrates containing up to 1740 mg/liter of oil.

Three groups of Atlantic salmon (Salmo salar) parr were acclimated to water temperatures of 3, 11, and 19 C. When exposed at their acclimation temperature to lethal concentrations of zinc, cold-acclimated salmon survived longer than warm-acclimated salmon. However, the threshold lethal concentration (LC50) of zinc was highest for salmon at 19 C, i.e. there was less toxicity at the high temperature. At test temperatures lower than prior acclimation temperatures, survival times in zinc were longer but the threshold LC50 was lower, i.e. fish were less tolerant of zinc. The opposite results were seen at temperatures above prior acclimation temperatures.The threshold LC50 may be predicted by the equation LC50 = 1.9611 − 0.1873 Ta + 0.8699 Te − 0.0414 Te2 + 0.00004 Ta Te3, where Ta = temperature of acclimation and Te = temperature of exposure.In polluted rivers, zinc concentrations may be most damaging to fish populations during the winter months. Measured concentrations of zinc and copper in the Miramichi River, New Brunswick were highest in winter when estimated toxicity of metal was also greatest.

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