The implication of neonicotinoids in bee declines led in 2013 to an EU moratorium on three neonicotinoids in bee-attractive crops. However, neonicotinoids are frequently detected in wild flowers or untreated crops suggesting that neonicotinoids applied to cereals can spread into the environment and harm bees. Therefore, we quantified neonicotinoid residues in nectar from winter-sown oilseed rape in western France collected within the five years under the EU moratorium. We detected all three restricted neonicotinoids. Imidacloprid was detected in all years with no clear declining trend but a strong inter- and intra-annual variation and maximum concentrations exceeding reported concentrations in treated crops. No relation to non-organic winter-sown cereals was identified even though these were the only crops treated with imidacloprid, but residue levels depended on soil type and increased with rainfall. Simulating acute and chronic mortality suggests a considerable risk for nectar foraging bees. We conclude that persistent imidacloprid soil residues diffuse on a large scale in the environment and substantially contaminate a major mass-flowering crop. Despite the limitations of case-studies and risk simulations, our findings provide additional support to the recent extension of the moratorium to a permanent ban in all outdoor crops.
Keywords: Environmental fate; Foraging bees; Imidacloprid; Neonicotinoid; Oilseed rape nectar; Risk assessment.
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