The organophosphorus insecticide chlorpyrifos (CPY) is widely used in North America on a number of crops on which pollinators can forage. Bees, the most important pollinators of agricultural crops, were the focus of this risk assessment. The conceptual model identified a number of potential exposure pathways for pollinators, some more significant than others. CPY is toxic to honey bees by direct contact, but label precautions minimize the risk of CPY to pollinators through this pathway. The primary potential exposure for honey bees is dietary and contact exposure from flowers sprayed with CPY. Potential secondary exposure is mainly through pollen and nectar brought to the hive by forager bees. Tier-1 estimates suggested that CPY poses a risk to honey bees through consumption of pollen and nectar. However, a Tier-2 assessment of concentrations reported in pollen and honey from monitoring work in North America indicated there is little risk of acute toxicity from CPY through consumption of these food sources. Models used to estimate CPY exposure through consumption of water from puddles or dew suggested that the risk is below the LOC for this pathway. Semi-field and field tests with honey bees, bumble bees, and alfalfa leafcutting bees indicate that exposure to foliage, pollen and/or nectar is hazardous to bees for up to 3 days after application of CPY within a crop. Pollinators exposed to foliage, pollen, or nectar after this period should be minimally affected. Reported bee kill incidents involving CPY are rare. Although there is a lack of exposure and toxicological data on non-Apis pollinators, we conclude that provided label directions and good agricultural practices are followed, the use of CPY in agriculture in North America does not present an unacceptable risk to honeybees.

Risks of chlorpyrifos to pollinators: Risk assessment

246th National Meeting (2013)

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