Are cover crops a potential threat for pollinators due to clothianidin residues in floral resources?

Gancedo Tarano, Inès;Boumal, Thomas;De Toffoli, Marc;Buron, Maxime;Agnan, Yannick;et.al.
(2025) Environmental Monitoring and Assessment : an international journal devoted to progress in the use of monitoring data in assessing environmental risks to man and the environment — Vol. 197, n° 1, p. 1260 (2025)

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Abstract
Cover crops are now mandatory in areas at risk of nitrogen leaching into groundwater. Many late-flowering entomophilous species used in these cover crops provide critical floral resources (pollen and nectar) for pollinators in early autumn. However, pesticide residues such as neonicotinoids can transfer to cover plants and their floral resources, posing a potential threat to pollinators. We investigated the transfer of clothianidin, a neonicotinoid insecticide, from soil to plants and floral resources in three common cover species (phacelia, white mustard, and faba bean). The study was conducted both in fields conditions (three years after clothianidin treatment on sugar beet) and under controlled growth chamber conditions (74 days post-treatment). We analysed clothianidin concentrations in soils, vegetative parts (stems and leaves), flowers, pollen, and fruits. Our results demonstrated that clothianidin persisted across the soil–plant–floral resource continuum in both field (soil concentration of 2.79 ng g−1) and growth chamber (soil concentrations of 34.4–106 ng g−1) experiments. Clothianidin residues accumulated in floral resources (ranging from 0.55 to 66.0 ng g−1 in pollen) posed a potential risk to pollinators through pollen consumption exposure (hazard quotient close to 1), and an even greater risk through soil contact exposure (hazard quotient > 1, reaching up to several hundred). These findings highlight that neonicotinoid residues in soil, and to a lesser extent in cover crop pollen, may threaten pollinator health.
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Gancedo Tarano, I., Boumal, T., De Toffoli, M., Buron, M., Kiljanek, T., Martel, A.-C., Jacquemart, A.-L., & Agnan, Y. (2025). Are cover crops a potential threat for pollinators due to clothianidin residues in floral resources? Environmental Monitoring and Assessment : an international journal devoted to progress in the use of monitoring data in assessing environmental risks to man and the environment, 197(1), 1260. https://doi.org/10.1007/s10661-025-14741-9 (Original work published 2025)