Does Waterborne Exposure Explain Effects Caused by Neonicotinoid-Contaminated Plant Material in Aquatic Systems?

Abstract

Neonicotinoids are increasingly applied on trees as protection measure against insect pests. Consequently, neonicotinoids are inevitably transferred into aquatic environments either via spray drift or surface runoff or (due to neonicotinoids' systemic nature) via senescent leaves. There particularly leaf-shredding invertebrates may be exposed to neonicotinoids through both the water phase and the consumption of contaminated leaves. In 7 day bioassays (n = 30), we examined ecotoxicological differences between these two exposure scenarios for an amphipod and an insect nymph with their feeding rate as the response variable. Organisms either experienced waterborne neonicotinoid (i.e., imidacloprid, thiacloprid, and acetamiprid) exposure only or a combined exposure (waterborne and dietary) through both the consumption of contaminated leaves and neonicotinoids leaching from leaves into water. The amphipod (7 day ECs from 0.3 to 8.4 μg/L) was more sensitive than the insect nymph (7 day ECs from 7.0 to 19.4 μg/L). Moreover, for both species, concentration-response models derived from water concentrations indicated higher effects under the combined exposure. Together with the observed inability of shredders to avoid neonicotinoid-contaminated leaves, our results emphasize the relevance of dietary exposure (e.g., via leaves) for systemic insecticides. Thus, it would be prudent to consider dietary exposure during the registration of systemic insecticides to safeguard ecosystem integrity.

An update of the Worldwide Integrated Assessment (WIA) on systemic insecticides. Part 2: impacts on organisms and ecosystems

“…However, such differences tend to be species specific. For example, recent studies have shown that the amphipod Gammarus fossarum is more susceptible than the caddisfly Chaetopteryx villosa when exposed to three neonicotinoids (imidacloprid, thiacloprid, and acetamiprid), either alone or in mixtures (Englert et al 2017). Furthermore, the same study found that combined exposure of these shredder species to neonicotinoid residues in water and in food (tree leaves) had more negative impacts on their survival than direct exposure to contaminated water alone.…”

“…Eventually, soil residues move into the aquatic ecosystems, either by percolation and leaching through the soil profile (de Perre et al 2015;Wettstein et al 2016) or in surface runoff after rainfall and storms (Chrétien et al 2017). Foliar sprays and drenches applied to orchard trees also contribute to the contamination of waterways (Englert et al 2017;Kreutzweiser et al 2008b). There is sufficient evidence to date to state that water borne residues of neonicotinoids and fipronil are currently impacting on aquatic ecosystems, as shown in the recent review by Sánchez-Bayo et al (2016).…”

“…The main impacts include altering the invertebrate communities, mainly insects, that live in streams and ponds, which are responsible for the recycling of organic matter that falls into them (Englert et al 2017). The main taxa affected have been discussed above and include key species such as midges and other Diptera such as mayflies, stoneflies, and caddisflies as well as predatory dragonflies, damselflies, bugs, and beetles.…”

Acute Effects of Binary Mixtures of Imidacloprid and Tebuconazole on 4 Freshwater Invertebrates

“…Further, reduced fungal population on leaf litter has been shown to be associated with reduced amphipod growth, potentially attributable to reduced nutrition (Elskus et al ). These feeding effects could be exacerbated by coexposure to imidacloprid, which has also been shown to reduce macroinvertebrate feeding on leaf matter (Kreutzweiser et al ; Nyman et al ; Englert et al ). In this context of sublethal effects, it would be valuable to repeat the present study for the most sensitive species (e.g., N. triangulifer ) for a chronic exposure duration.…”

An update of the Worldwide Integrated Assessment (WIA) on systemic insecticides. Part 1: new molecules, metabolism, fate, and transport

“…Residue levels significantly depended on the dose and compound applied, as well as the physiological parameters of the trees. Englert et al (2017b) reviewed the literature on foliar residues of neonicotinoids and found that they ranged between 1000 and 6000 ppb for soil and trunk application in deciduous trees and 80 and 300 ppb for soil and trunk applications of evergreen trees.…”