|Abstract or Summary
- The effects of sublethal concentrations of cyanide, pentachlorophenol and zinc individually and in combination on the growth and production of juvenile chinook salmon, Oncorhynchus tshawytscha (Walbaum), and aquatic invertebrates in model stream communities were studied in three experiments during 1971 and 1972 at the Oak Creek Fisheries Research Laboratory, Oregon State University. The individual toxicants were tested at concentrations of 0.1 toxic units (96 hour TLm) in experiments I and II, while the tests with mixtures were carried out at values of 0.1 (low treatment) and 0.3 (high treatment) toxic units. All treatment concentrations were doubled in experiment III, which resulted in individual concentrations equivalent to 0.2 toxic units for cyanide, pentachlorophenol and zinc. The three toxicants were tested in combination at concentrations equivalent to 0.2 toxic units (low treatment) and to 0.6 toxic units (high treatment). The juvenile salmon were weighed biweekly during the course of each experiment. Benthic invertebrate samples were taken monthly and drift samples were generally taken every three weeks. The individual toxicant concentrations of 0.1 toxic units of cyanide, pentachlorophenol and zinc did not result in any marked reductions of juvenile salmon growth or benthic densities during experiments I and II. Individual toxicant concentrations of 0.2 toxic units of cyanide, pentachlorophenol and zinc during experiment III adversely affected salmon growth and production as well as benthic densities. Zinc appeared to be the most deleterious of the individual treatments while cyanide was the least harmful of the three toxicants to salmon growth. Cyanide appeared to enhance salmon production at 0.1 toxic units (10 ppb), In both experiments I and III, reductions in salmon biomass were always greater in streams receiving mixtures
of toxicants and reductions were always greater in the high treatments than in the low treatments. Decreases in salmon production and biomass in the high and low combination treatments were not predictable based on the responses of salmon exposed to the individual toxicants, but were always greater than the decreases observed in any one individual treatment. The results, of experiments I and III indicated that levels
of individual toxicants apparently safe for juvenile salmon were deleterious to salmon growth and production when combined at levels
equivalent to those of the individual toxicants. The results, especially those of experiment I, indicate that mixtures of the three toxicants equivalent to 0.1 toxic units impair salmonid growth, and suggest that even lower concentrations may be harmful to juvenile salmon.