EFFECTS OF AZINPHOS-METHYL ON NORTHERN BOBWHITE - A COMPARISON OF LABORATORY AND FIELD RESULTS

The U.S. Environmental Protection Agency's (U.S. EPA's) ecological ris k assessment process uses laboratory toxicity data in quotient indices to characterize risks to wildlife, but with poor understanding of the relationship between these data and actual field effects. To explore this relationship. we compared toxicity results from a controlled fiel d study to those from a dietary toxicity (median lethal concentration) laboratory test. In the field test, northern bobwhite (Colinus virgin ianus) chicks were cross-fostered to bantam chicken (Gallus domesticus ) hens. Then, 12-d-old broods in enclosed alfalfa fields were exposed to sprayed azinphos-methyl (Guthion(R) 2S) at three application rates (0 [control], 0.77, and 3.11 kg active ingredient/ha). Chick survival was significantly lower at 3.11 kg/ha 0 to 5 d postspray and at both a pplication rates 6 to 10 d postspray compared to control (p < 0.05). C hick brain acetylcholinesterase (AChE) activity. growth, and weight of crop contents were significantly reduced in treatments compared to co ntrol (p < 0.05). In the laboratory test, 12-d-old bobwhite were expos ed to dietary concentrations of 0 !control), 150, 240, 380, and 600 pp m azinphos-methyl far 5 d. Survival was significantly lower at 600 ppm compared to control, and brain AChE activity and growth rates were si gnificantly reduced from control for all concentrations (p < 0.05. Chi ck survival, brain AChE activity, and growth in the field were signifi cantly different from equivalent exposures in the laboratory (p < 0.05 ), with equivalency determined by U.S. EPA's vegetation residue estima tes, and temporal patterns of effects differed between field and labor atory. We conclude that the effects observed in the field differed fro m that predicted by risk quotients because the quotient method does no t consider alternate routes of exposure. behavioral responses, influen ce of spatial and temporal environmental variability, or indirect effe cts.