Bird response to grit and pesticide granule characteristics: Implications for risk assessment and risk reduction

Granular pesticides (insecticides and nematicides) pose a hazard for birds because of the potential for birds to ingest the granules. Avian risk from granular pesticides is currently assessed by using a U.S. Environmental Pro tection Agency risk index based on the acute toxicity of the pesticide, the pesticide concentration on the granules, and the number of granules availa ble on the soil surface after application (LD50/ft(2)). Recent evaluations have demonstrated that avian response to pesticide granules as a source of grit also can influence exposure to pesticide granules; such information sh ould be included in the risk assessment process. Herein we review the limit ations of the current risk assessment process and summarize the extant info rmation regarding bird response to grit and granule characteristics (i.e., granule carrier type, color, size, shape, and surface texture) and pesticid e load per granule. Suggestions are made for assessing and reducing avian r isk from granular pesticides by testing granular formulations against stand ards for various granule characteristics and by using frequency distributio ns of avian responses to granules. Granule characteristics selected as stan dards should be similar to grit used by free-ranging birds (e.g., silica pa rticles, earth-tone hues). Comparisons of granular formulations against the standards would demonstrate the potential for birds to consume pesticide g ranules as grit, relative to naturally occurring particles. Frequency distr ibutions constructed for grit sizes used by birds and gizzard grit counts c an be used to estimate the effect of granule size and pesticide load per gr anule, respectively, on avian risk. Because bird response to pesticide gran ules is highly variable, we recommend using probabilistic approaches when a ssessing avian risk from pesticide granules to account for the ranges of re sponse.