Aquatic-terrestrial transfer of neonicotinoid insecticides in riparian food webs

Current-use pesticides are ubiquitous in freshwaters globally, often at very low concentrations. Emerging aquatic insects can accumulate pesticides during their aquatic development, which can be retained through their metamorphosis into terrestrial adults. Emerging insects thus provide a potential, yet largely understudied linkage for exposure of terrestrial insectivores to waterborne pesticides. We measured 82 low to moderately lipophilic organic pesticides (logKow:-2.87 to 6.9) in the aquatic environment, emerging insects and web-building riparian spiders from stream sites impacted by agricultural land use. Insecticides, mainly neuro-active neonicotinoids were ubiquitous and had the highest concentrations in emerging insects and spiders ( n-ary sumation insecticides: 0.1-33 and 1-240 ng/g, respectively), although their concentrations in water were low, even when compared to global levels. Furthermore, neonicotinoids, although not considered to be bioaccumulative, were biomagnified in ri-parian spiders. In contrast, concentrations of fungicides and most herbicides decreased from the aquatic envi-ronment to the spiders. Our results provide evidence for the transfer and accumulation of neonicotinoids across the aquatic-terrestrial ecosystem boundary. This could threaten food webs in ecologically sensitive riparian areas worldwide.

Automated summary

Current-use pesticides are found in freshwaters globally, with emerging aquatic insects serving as a potential link for exposure of terrestrial insectivores to waterborne pesticides. In this study, we measured the presence of 82 organic pesticides in the aquatic environment, emerging insects, and riparian spiders impacted by agriculture. The results showed that neuro-active neonicotinoids were widespread and had the highest concentrations in emerging insects and spiders, suggesting the transfer and accumulation of these pesticides from water to land.