Evaluating pollinator exposures to sulfoxaflor via bee-relevant matrices: a systems-level approach using...

Sulfoxaflor (SFX) is a newly registered IRAC Group 4C nAChR-receptor-agonist systemic insecticide that is used to control sap-sucking insects in a variety of crops. SFX has a short half-life (< 2 days) in agricultural soil and is only used as a foliar-applied product. Pollinators such as honey bees could be exposed directly to spray if application occurs shortly before or during blooming of flowers, or, as SFX is systemic, via oral exposures to nectar and pollen collected by bees. Guided by a Weight-of-Evidence rubric, this paper critically assessed studies on the fate of SFX in bee-relevant matrices submitted by the registrant in several jurisdictions as well as a few studies published in the open scientific literature. These studies provided data for residues in pollen and/or nectar from 16 crops grown in several countries in both hemispheres. SFX and transformation products were detected in nectar and pollen. Transformation products have low hazard to honeybees, so the focus was on the parent material, SFX, which was observed to dissipate rapidly from pollen and nectar after application. Dietary No-Observed-Adverse-Effect-Concentrations (NOAEC) derived from results of 10-day continuous feeding studies of adult (0.50 mg kg^-1 diet d^-1) and larval honeybees (1.69 mg kg^-1 diet d^-1) were used as precautionary toxicity benchmarks to characterize hazards. In this paper, we used a tiered process. The initial screening tier was based on the greatest concentration measured in the matrix. For scenarios that did not pass Tier-1, a second tier based on the 10-day time-weighted average (area under the curve, AUC) concentration in the matrix was used as a more realistic measure of exposure. Of the 90 scenarios of use that were characterized, 36 did not pass the initial screening benchmark based on ≥1concentration of SFX exceeding the 10-day NOAEC. When the 10-day AUC of exposure was estimated for these scenarios, 3 of 90 did not pass the more realistic toxicity benchmark. These three scenarios were for residues in pollen or anthers for alfalfa grown in California, strawberries grown in France, peaches grown in Michigan. The two-tier screening procedure for hazard assessment lessened the need for further assessment for 97% of the exposure scenarios and reduced the need for characterizing hazards in field-level whole-hive tests conducted under controlled conditions of exposure.