PW09 Pesticide I
8:00 AM - Wednesday
(PW149) Survival and reproduction of Daphnia magna during episodic chlorpyrifos exposures.
Zahner, H1, Klaine, S1, 1 Clemson Institute of Environmental Toxicology, Clemson University, Pendleton, SC, 29670
ABSTRACT- Traditional aquatic toxicity bioassay methods stress continuous, constant exposure for a prescribed period of time. Unfortunately, these kinds of scenarios rarely occur in nature. Rather, aquatic organisms are exposed to stressors for varying durations and fluctuating concentrations. In many instances, stressor exposure ceases for some period of time followed by another exposure event. Organisms have the opportunity to recover from sublethal stress during these periods. Little quantitative information is available on the response of aquatic organisms to these episodic exposures. Still less information is available on the recovery of organisms between exposures. Our study characterized the response of Daphnia magna to varying combinations of short-term chlorpyrifos (CPF) exposure scenarios. The experimental design consisted of exposing <24-h D. magna to two pulses of varying CPF concentrations (0.187, 0.375, 0.75 
g/L), three exposure durations (3, 6, 24-h), and four recovery intervals (0, 24, 96 and 144-h). At the exposure termination, organisms were removed to CPF-free control water and the bioassay continued for 21 days. Organisms were monitored during and after the exposure for survival and reproduction. There was a significant effect (p<0.05) of pulse concentration and duration on D. magna survival. As the concentration and duration of the CPF exposure increased, the survival and reproduction decreased. The effects of pulse exposure frequency were dependent upon the exposure intensity and the interval of recovery allowed.
Key words: Chlorpyrifos, Episodic Exposure, Daphnia magna, Pulse Exposure