Surface runoff and subsurface tile drain losses of neonicotinoids and companion herbicides at edge-of-field
Citation
Chrétien, F., Giroux, I., Thériault, G., Gagnon, P., Corriveau, J. (2017). Surface runoff and subsurface tile drain losses of neonicotinoids and companion herbicides at edge-of-field. Environmental Pollution, [online] 224 255-264. http://dx.doi.org/10.1016/j.envpol.2017.02.002
Plain language summary
Neonicotinoids are a class of insecticides that have received increasing attention in the recent years due to their potential impacts on non-target organisms such as pollinators, predatory insects, earthworms and aquatic species. The use of these insecticides increased dramatically during the last 10 years with their application as seed coatings. In Quebec (Canada), it is estimated that almost 100% of corn and 50% of soybeans seeds planted are coated with neonicotinoids which correspond to about 500,000 ha. These high usage rates coupled with their chemical properties have led to frequent detection of neonicotinoids in aquatic environments. Aquatic ecosystems may be contaminated by insecticides through various routes but monitoring data for neonicotinoids transport mechanisms are very limited. The intent of this study was to document surface runoff and tile drain losses of two commonly used neonicotinoids and companion herbicides. This study showed that surface runoff and tile drain discharge were key transport mechanisms with respective contributions of 53% and 47% of neonicotinoids losses. Detection frequencies close to 100% in water samples were observed over two years. Even if the studied neonicotinoids were applied at relatively low rates and had low exportation values, the relative toxicity was one to two orders of magnitude higher than those of the other companion herbicides applied. In light of these observations, it is recommended that neonicotinoids should not be used systematically when no infestation by insect pests has been observed and their application for agricultural purposes should be justified by an agronomist.
Abstract
With their application as seed coatings, the use of neonicotinoid insecticides increased dramatically during the last decade. They are now frequently detected in aquatic ecosystems at concentrations susceptible to harm aquatic invertebrates at individual and population levels. This study intent was to document surface runoff and subsurface tile drain losses of two common neonicotinoids (thiamethoxam and clothianidin) compared to those of companion herbicides (atrazine, glyphosate, S-metolachlor and mesotrione) at the edge of a 22.5-ha field under a corn-soybean rotation. A total of 14 surface runoff and tile drain discharge events were sampled over two years. Events and annual unit mass losses were computed using flow-weighted concentrations and total surface runoff and tile drain flow volumes. Detection frequencies close to 100% in edge-of-field surface runoff and tile drain water samples were observed for thiamethoxam and clothianidin even though only thiamethoxam had been applied in the first year. In 2014, thiamethoxam median concentrations in surface runoff and tile drain samples were respectively 0.46 and 0.16 μg/L, while respective maximum concentrations of 2.20 and 0.44 μg/L were measured in surface runoff and tile drain samples during the first post-seeding storm event. For clothianidin, median concentrations in surface runoff and tile drain samples were 0.02 and 0.01, μg/L, and respective maximum concentrations were 0.07 μg/L and 0.05 μg/L. Surface runoff and tile drain discharge were key transport mechanisms with similar contributions of 53 and 47% of measured mass losses, respectively. Even if thiamethoxam was applied at a relatively low rate and had a low mass exportation value (0.3%), the relative toxicity was one to two orders of magnitude higher than those of the other chemicals applied in 2014 and 2015. Companion herbicides, except glyphosate in tile drains, exceeded their water quality guideline during one sampling campaign after application but rapidly resumed below these limits.