Acute toxicity data and hazard assessments were developed for three cladoceran species, Ceriodaphnia dubia, Daphnia pulex, and Daphnia magna, and juvenile Coho salmon, Oncorhynchus kisutch after exposure to the insecticide, spinosad and adjuvant R-11. The effect of a mixture of these compounds was also determined with C. dubia and O. kisutch. Spinosad was virtually non-toxic to O. kisutch. Hazard assessments indicated that R-11 posed no hazard to any of the species tested while spinosad only posed a hazard to C. dubia. Mixture studies indicated that spinosad and R-11 may interact synergistically in C. dubia.
The effects of the natural insecticide, spinosad, and the agricultural adjuvant, R-11, were evaluated on populations of the water flea, Ceriodaphnia dubia after chronic 8-day exposures. The number of individuals used to start the chronic exposure studies (founders) and the number of offspring/surviving female were significantly reduced after exposure to spinosad concentrations ≥ 2.5 μg/L. The final number of individuals was significantly reduced after exposure to spinosad concentrations ≥ 1.0 μg/L. Population growth rate was significantly reduced after exposure to spinosad concentrations ≥ 1 μg/L. Extinction occurred (defined as negative population growth rate) after exposure to spinosad concentrations of 10 μg/L. Therefore, negative effects were observed in C. dubia after exposure to spinosad at a concentration near the chronic expected environmental concentration (EEC) of 2.3 μg/L. R-11 was much less toxic to C. dubia than spinosad. The number of founders was not significantly reduced until C. dubia were exposed to 12,000 μg/L. The number of offspring/surviving female, final number of individuals, and population growth rate were significantly reduced after exposure to R-11 concentrations ≥ 5,000 μg/L. Extinction occurred after exposure to R-11 concentrations of 12,000 μg/L which was above the EEC of 790 μg/L. These results indicate that spinosad and R-11 both have lethal and sublethal effects on C. dubia. However, spinosad appears to affect C. dubia at or near the EEC while R-11 does not negatively affect this species until concentrations are much higher than the EEC.
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