Do Neonicotinoid Pesticide Seed Coatings Pose a Hazard to Seed-eating Birds?

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Treating or “dressing” of seeds with pesticides is a commonly used method to enhance crop yield in agriculture.  Regrettably, such treated seeds can be ingested by wildlife, and depending on the extent of exposure, can cause adverse effects.

The Challenge: Neonicotinoids are now the most widely applied class of insecticides in the United States, and are predominantly used in the form of seed treatments. Compared to invertebrates, neonicotinoids are less toxic to wildlife, although genotoxic, cytotoxic, immunological, behavioral and reproductive effects have been reported in studies with birds. At present, little is known about the pharmacokinetics (absorption, distribution, metabolism and excretion) of these pesticides in birds, which can dictate and affect the timecourse of their toxicity. Such information will greatly assist in evaluating the hazard and risk of neonicotinoid seed coatings to wild birds.

The Science: Research in Japanese quail, as a model species, indicate that the neonicotinoid imidacloprid is rapidly absorbed into blood, distributed to tissues, and cleared to below detection limits within 24 hours.  Metabolism to 5-hydroxy and olefin metabolites is extensive and rapid.  Application of these toxicokinetic data was used to predict residue levels in liver with reasonable results for some field exposure and avian mortality events.  It appears that affected species either must consume larger quantities of seeds or exhibit substantial differences in sensitivity than predicted by read-across from these data.

The Future: The data generated will be used to identify potential biomarkers of exposure and effects, develop an adverse outcome pathway, and better characterize the hazard and risk of imidacloprid to seed-eating birds.