Concentration and movement of neonicotinoids as particulate matter downwind during agricultural practices using air samplers in southwestern Ontario, Canada.

Atmospheric emissions of neonicotinoid seed treatment insecticides as particulate matter in field crops occur mainly for two reasons: 1) due to abraded dust of treated seed generated during planting using vacuum planters, and 2) as a result of disturbances (tillage or wind events) in the surface of parental soils which release wind erodible soil-bound residues. In the present study, concentration and movement of neonicotinoids as particulate matter were quantified under real conditions using passive and active air samplers. Average neonicotinoid concentrations in Total Suspended Particulate (TSP) using passive samplers were 0.48 ng/cm2, trace, trace (LOD 0.80 and 0.04 ng/cm2 for clothianidin and thiamethoxam, respectively), and using active samplers 16.22, 1.91 and 0.61 ng/m3 during planting, tillage and wind events, respectively. There was a difference between events on total neonicotinoid concentration collected in particulate matter using either passive or active sampling. Distance of sampling from the source field during planting of treated seed had an effect on total neonicotinoid air concentration. However, during tillage distance did not present an effect on measured concentrations. Using hypothetical scenarios, values of contact exposure for a honey bee were estimated to be in the range from 1.1% to 36.4% of the reference contact LD50 value of clothianidin of 44 ng/bee.

Neonicotinoid insecticide residues in soil dust and associated parent soil in fields with a history of seed treatment use on crops in southwestern Ontario.

Using neonicotinoid insecticides as seed treatments is a common practice in field crop production. Exposure of nontarget organisms to neonicotinoids present in various environmental matrices is debated. In the present study, concentrations of neonicotinoid residues were measured in the top 5 cm of soil and overlying soil surface dust before planting in 25 commercial fields with a history of neonicotinoid seed treatment use in southwestern Ontario in 2013 and 2014 using liquid chromatography-electrospray ionization tandem mass spectrometry. The mean total concentrations were 3.05 ng/g and 47.84 ng/g in 2013 and 5.59 ng/g and 71.17 ng/g in 2014 for parent soil and soil surface dust, respectively. When surface and parent soil residues were compared the mean concentration in surface dust was 15.6-fold and 12.7-fold higher than that in parent soil in 2013 and 2014, respectively. Pooled over years, the surface dust to parent soil ratio was 13.7, with mean concentrations of 4.36 ng/g and 59.86 ng/g for parent soil and surface dust, respectively. The present study's results will contribute important knowledge about the role these residues may play in the overall risk assessment currently under way for the source, transport, and impact of neonicotinoid insecticide residues in a maize ecosystem.

Quantifying Neonicotinoid Insecticide Residues Escaping during Maize Planting with Vacuum Planters.

Neonicotinoid residues escaping in vacuum-planter exhaust during maize planting were measured in 25 fields in southwestern Ontario in 2013-2014 using filter bags to collect planter exhaust dust and horizontal and vertical sticky traps to collect planter operation-generated dust. Atrazine residues were used to differentiate between neonicotinoid residues originating from seed or from disturbed soil. Recovery rates of seed-applied neonicotinoids in exhaust were 0.014 and 0.365% in 2013 and 2014, respectively, calculated on the basis of neonicotinoid concentrations in preplant soil and seed application rates. Neonicotinoid exhaust emission rates were 0.0036 and 0.1104 g/ha for 2013 and 2014, respectively, with 99.9472 and 99.7820% originating from treated seed in 2013 and 2014, respectively, calculated on the basis of the atrazine marker. Rates of recovery of seed-applied neonicotinoid residues by exhaust filter bags were 0.015 and 0.437% for 2013 and 2014, respectively. Neonicotinoid residues captured on horizontal and vertical traps were 1.10 ng/cm2 (0.1104 g/ha) and 1.45 ng/cm2 (0.0029 g/ha), respectively, with 92.31 and 93.03% originating from treated seed, respectively, representing 0.3896% of the original active ingredient applied to the seed planted. Exposure to pollinators can be best reduced by strategies to keep active ingredient on the seed, below the soil surface, and in the field where applied.