Neonicotinoid insecticide residues in surface water and soil associated with commercial maize (corn) fields in southwestern Ontario

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.

Fig 1. Map of subject field locations in 2013 (modified from the original by Cartographic Office, Department of Geography, University of Guelph).

1–9: maize fields and bee yards; 10: fields for snow drift samples; 11: blank soil taken.

Fig 2. LC-ESI (+)-MS/MS MRM chromatograms of a soil sample spiked with 0.04 ng/g of clothianidin and thiamethoxam and 1 ng/g clothianidin-d3 and thiamethoxam-d3 internal standards.

Fig 3. Scatter distribution and notched boxplot of water samples collected from the puddles within/around commercial maize fields, ON, 2013.

(¹Total of clothianidin and thiamethoxam).

Fig 4. Temporal values of total neonicotinoid concentration (± SEM) for water collected within maize fields compared to samples collected from the puddles outside but in close proximity to these fields.

Different letters indicate significant differences in mean neonicotinoid concentration between sampling periods for water sampled within field. (SAS PROC mixed PDIFF, p = 0.05). (¹Total of clothianidin and thiamethoxam).

Fig 5. Concentration (± SEM) of neonicotinoid residues in soils, sampled from commercial maize fields, taken pre- and post-planting in ON, 2013.

Bars with different letters are significantly different (SAS PROC mixed PDIFF, p = 0.05). (¹Total of clothianidin and thiamethoxam).