The Liquid Pesticide Avian Risk Assessment Model (LiquidPARAM) was used to estimate risk for a wide variety of focal bird species and use patterns on the chlorpyrifos label. LiquidPARAM estimates the fate of each of 20 birds on each of 1000 treated fields. The model has a one hour time step, runs for 60 days, and estimates acute and chronic risk from single or up to three pesticide applications. The model included 29 bird species and accounted for their foraging behavior inside and outside treated fields as well as their specific diets. To estimate acute risk, the maximum hourly retained dose for each bird in each field was compared to the dose-response curve for those focal species with toxicity data and the fate of the bird calculated. For untested focal bird species, the dose was compared to each of three dose-response curves which represented species of high, median, and low sensitivity and were derived from a species sensitivity distribution (5th, 50th?, and 95th percentiles, respectively, combined with average slope for all tested species). For chronic risk, hourly doses were averaged over a duration selected to match the critical exposure period from chronic toxicity tests. The maximum running average was then compared to data on chronic effects. The results of modelling for chlorpyrifos across a broad range of use patterns indicate that sensitive bird species foraging extensively in fields treated at high application rates may experience some acute risk. The majority of bird species, however, are not at significant acute risk even for the use patterns with the high application rates. Chronic risk is not a significant concern for the flowable formulation of chlorpyrifos. The results from avian field studies conducted with flowable chlorpyrifos indicate that LiquidPARAM is likely over-predicting acute risk as little mortality was observed in those studies.

Refined avian risk assessment for agricultural uses of flowable chlorpyrifos in the United States

246th National Meeting (2013)

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