Effects of insecticide and adjuvant mixtures on cladocerans and Coho salmon

Angela Diane Deardorff

Acute lethal concentration estimates and instantaneous rates of increase (ri) were determined on the cladocerans, Ceriodaphnia dubia Richard, Daphnia pulex (Leydig), Daphnia magna Straus, and Coho salmon, Oncorhynchus kisutch (Walbaum) exposed to the agricultural adjuvant, R-11, and the insecticide, spinosad. Mixtures of R-11 and spinosad were also evaluated on C. dubia and O. kisutch in acute studies. Using acute data and life tables, the accuracy of using one species to predict effects on other species was determined using three species of Daphnia. Acute mortality estimates for R-11 indicated that all LC50 estimates were higher than the Expected Environmental Concentration (EEC) of 0.79 mg/l, for all species tested. The LC50 estimate for spinosad was much lower than EEC (0.068 mg/l) for C. dubia and D. magna. Spinosad was not hazardous to D. pulex and O. kisutch at EEC. The hazard assessments for C. dubia and D. magna indicated that at EEC, spinosad poses a significant threat. When C. dubia was exposed to a binary mixture of spinosad and R-11 LC25s, it indicated that synergism may have occurred. The mixture of R-11 and spinosad resulted in bottom gilling and erratic swimming behavior in O. kisutch, although mortality did not differ from the controls. The chronic 8-day studies of R-11 and spinosad and C. dubia were found to cause extinction at concentrations slightly higher than the acute LC75 and LC70, respectively, indicating that C. dubia cannot withstand high levels of mortality without population decline (ri < 0). Although the three daphnid species had similar life history traits, modeling indicated that exposure to EEC resulted in population recovery times of 1, 5, and 12 weeks for D. pulex, D. magna, and C. dubia populations, respectively. Recovery times were equivalent to 0.31, 1.28, and 3.48 generation times for D. pulex, D. magna, and C. dubia populations, respectively. Recoveries > 1 generation time are indicative of damage at the population level. Even though these species had similar life history traits, exposure to the same pesticide concentration resulted in very different recovery times. Therefore, the use of surrogate species to make predictions about even closely related species may not be prudent.

Effects of insecticide and adjuvant mixtures on cladocerans and Coho salmon

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