Abstract
Neonicotinoid insecticides have come under scrutiny for their potential unintended effects on non-target organisms, particularly pollinators in agro-ecosystems. As part of a larger study of neonicotinoid residues associated with maize (corn) production, 76 water samples within or around the perimeter of 18 commercial maize fields and neighbouring apiaries were collected in 5 maize-producing counties of southwestern Ontario. Residues of clothianidin (mean = 2.28, max. = 43.60 ng/mL) and thiamethoxam (mean = 1.12, max. = 16.50 ng/mL) were detected in 100 and 98.7% of the water samples tested, respectively. The concentration of total neonicotinoid residues in water within maize fields increased six-fold during the first five weeks after planting, and returned to pre-plant levels seven weeks after planting. However, concentrations in water sampled from outside the fields were similar throughout the sampling period. Soil samples from the top 5 cm of the soil profile were also collected in these fields before and immediately following planting. The mean total neonicotinoid residue was 4.02 (range 0.07 to 20.30) ng/g, for samples taken before planting, and 9.94 (range 0.53 to 38.98) ng/g, for those taken immediately after planting. Two soil samples collected from within an conservation area contained detectable (0.03 and 0.11 ng/g) concentrations of clothianidin. Of three drifted snow samples taken, the drift stratum containing the most wind-scoured soil had 0.16 and 0.20 ng/mL mainly clothianidin in the melted snow. The concentration was at the limit of detection (0.02 ng/mL) taken across the entire vertical profile. With the exception of one sample, water samples tested had concentrations below those reported to have acute, chronic or sublethal effects to honey bees. Our results suggest that neonicotinoids may move off-target by wind erosion of contaminated soil. These results are informative to risk assessment models for other non-target species in maize agro-ecosytems.
Highlights
Neonicotinoids are a class of systemic insecticides, which are absorbed and translocated throughout the plant and provide in-plant protection from pests for a period during plant establishment [1]
Because clothianidin and thiamethoxam are the neonicotinoids used most commonly in southwestern Ontario, and clothianidin is a metabolite of thiamethoxam, we report the total quantity of clothianidin and thiamethoxam to represent the neonicotinoid residue, except when noted
Clothianidin was detected above the limits of detection (LOD) in 100% of the 76 samples collected during the 9week sampling period and thiamethoxam was detected in 98.7% (75 out of 76) of the samples
Summary
Neonicotinoids are a class of systemic insecticides, which are absorbed and translocated throughout the plant and provide in-plant protection from pests for a period during plant establishment [1]. The variety of methods for their application, along with their systemic properties and low toxicity to mammalian vertebrates has resulted in wide-spread adoption for crop protection [2,3]. Their convenience as seed treatments has resulted in a shift from their prescriptive use in response to pest scouting, to prophylactic use as insurance against pest damage [3]. Three of these, clothianidin, thiamethoxam and imidacloprid are registered for use on almost all major field crops in Canada. Clothianidin and thiamethoxam are the neonicotinoids most commonly used in southwestern Ontario. This group of insecticides dominates the seed treatment market in Ontario—with over 99% of maize (corn), 60–80% of soybean, 95% of dry bean, 25% of winter wheat and 100% of canola crop areas planted with a neonicotinoid seed treatment in 2013 [5]
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