Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
9454786 | Ecotoxicology and Environmental Safety | 2005 | 6 Pages |
Abstract
Hazard assessments based on two measures of toxicity were conducted for the water flea, Daphnia pulex (Leydig) exposed to the insecticide, fipronil. The measures of toxicity obtained were 48Â h acute lethal concentration estimates, and a direct measure of population growth rate, the 10-day instantaneous rate of increase (ri). Additionally, life tables were developed after exposure to several concentrations to tease out the apparent sublethal effects of this insecticide to D. pulex. The acute LC50 was estimated to be 0.0156 (0.0088-0.083)Â mg/L. In the 10-day population growth rate study, extinction of D. pulex populations occurred after exposure to 0.08Â mg/L of fipronil, which was equivalent to the 48Â h acute LC75. The NOEC and LOEC for population size after a 10-day exposure to fipronil were 0.03 and 0.05Â mg/L, respectively. An expected environmental concentration (EEC) in freshwater lakes/ponds based on an application rate of 250Â mg ai/ha (recommended rate for use in Tephritid fruit fly control programs) was estimated to be 0.00017Â mg/L. Hazard assessments were developed by dividing the EEC by the LC50 and NOEC for population size. The assessments based on the LC50 and NOEC for population size were 0.011 and 0.0057, respectively, indicating that fipronil does not pose a hazard to D. pulex when applied at the rates recommended for control of Tephritid fruit flies. Life tables were developed after exposure to two insecticide concentrations and a control. Exposure to 0.015Â mg/L, the approximate 48Â h acute LC50, resulted in only a slight decrease in the net reproductive rate (Ro), birth rate (b), and intrinsic rate of increase (rm) and an increase in generation time (T), death rate (d), and doubling time (DT) compared to the control. Exposure to 0.03Â mg/L, the approximate 48Â h acute LC60, and NOEC in the 10-day study, resulted in a 57% decline in the net reproductive rate, a 1.45-fold decrease in birth rate, a 1.5-fold decrease in the intrinsic rate of increase, a 6-day increase in generation time, a 4-fold increase in death rate, and a 1.5-fold increase in doubling time. The stable age distribution (after 60 days) of D. pulex changed after exposure to fipronil. Increasing concentrations of fipronil resulted in a decrease in the percentage of individuals in the first, second, third, and fourth juvenile stages, an increase in the adult stage, and no change in the adolescent stage. These results indicate that certain concentrations of fipronil approaching the LC50 can negatively affect population parameters of D. pulex, but that EECs, at least for fruit fly control, should be lower than the concentration necessary to cause damage.
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Authors
John D. Stark, Roger I. Vargas,