Refined avian risk assessment for chlorpyrifos in the United States

Refined risk assessments for birds exposed to flowable and granular formulations ofCPY were conducted for a range of current use patterns in the United States. Overall,the collective evidence from the modeling and field study lines of evidence indicate that flowable and granular CPY do not pose significant risks to the bird communities foraging in agro-ecosystems in the United States. The available information indicates that avian incidents resulting from the legal, registered uses of CPY have been very infrequent since 2002 (see SI Appendix 3). The small number of recent incidents suggests that the current labels for CPY are generally protective of birds.However, incident data are uncertain because of the difficulties associated with finding dead birds in the field and linking any mortality observed to CPY.Plowable CPY is registered for a variety of crops in the United States including alfalfa, brassica vegetables, citrus, corn, cotton, grape, mint, onion, peanut, pome and stone fruits, soybean, sugar beet, sunflower, sweet potato, tree nuts, and wheat under the trade name Lorsban Advanced. The major routes of exposure for birds to flowable CPY were consumption of treated dietary items and drinking water. The Liquid Pesticide Avian Risk Assessment Model (Liquid PARAM) was used to simulate avian ingestion of CPY by these routes of exposure. For acute exposure,Liquid PARAM estimated the maximum retained dose in each of 20 birds on each of1,000 fields that were treated with CPY over the 60-d period following initial application.The model used a 1-h time step. For species lacking acceptable acute oral toxicity data (all focal species except northern bobwhite (C. virginianus) and redwinged blackbird (A. phoeniceus)), a species sensitivity distribution (SSD) approach was used to generate hypothetical dose-response curves assuming high, median and low sensitivity to CPY. For acute risk, risk curves were generated for each use pattern and exposure scenario. The risk curves show the relationship between exceedence probability and percent mortality. The results of the Liquid PARAM modeling exercise indicate that flow able CPY poses an acute risk to some bird species, particularly those species that are highly sensitive and that forage extensively in crops with high maximum application rates (e.g., grapefruit, orange). Overall, most bird species would not experience significant mortality as a result of exposure to flowable CPY.The results of a number of field studies conducted at application rates comparable to those on the Lorsban Advanced label indicate that flowable CPY rarely causes avian mortality. The results of the field studies suggest that Liquid PARAM is likely over-estimating acute risk to birds for flowable CPY.For chronic exposure, Liquid PARAM estimated the maximum total daily intake (TDI) over a user-specified exposure duration (28-d in the case of CPY).The maximum average TDI was compared to the chronic NOEL and LOEL from the most sensitive species tested for CPY, the mallard. This comparison was done for each of the 20 birds in each of the 1000 fields simulated in Liquid PARAM.The outpu· ~ are estimates of the probabilities of exceeding the NOEL and LOEL.Liquid PAkAM did not predict significant adverse effects resulting from chronic exposure to flowable CPY. The small number of incidents (2) involving CPY reported since 2002 suggests that the current labels for CPY are generally protective of birds.Granular CPY is registered for a wide variety of crops including brassica vegetables, corn, onion, peanut, sugar beet, sunflower, and tobacco under the trade name Lorsban 15G. Consumption of grit is required by many birds to aid in digestion of hard dietary items such as seeds and insects. Because CPY granules are in the same size range as natural grit particles consumed by birds, there is a potential for birds to mistakenly ingest granular CPY instead of natural grit. We developed the Granular Pesticide Avian Risk Model (GranPARAM) to simulate grit ingestion behavior by birds. The model accounts for proportion of time that birds forage for grit in treated fields, relative proportions of natural grit versus pesticide granules onthe surface of treated fields, rates of ingestion of grit, attractiveness of pesticide granules relative to natural grit and so on. For CPY, each model simulation included20 birds on each of 1,000 fields to capture variability in rates of ingestion of grit and for aging behavior between birds within a focal species, and variability in soil composition between fields for the selected use pattern. The estimated dose for each birdwas compared with randomly chosen doses from relevant dose-response curves forCPY. Our analysis for a wide variety of use patterns on the Lorsban 15G label found that granular CPY poses little risk of causing mortality to bird species that frequent treated fields immediately after application. The predictions of the model have been confirmed in several avian field studies conducted with Lorsban 15G at application rates similar to or exceeding maximum application rates on the Lorsban 15G label.