ASSESSING THE PRESENCE AND FATE OF NEONICOTINOIDS IN GROUNDWATER RESOURCES IN ONTARIO

Neonicotinoids are a group of insecticides that are widely used in agriculture. Over the past 15 years, these insecticides have been applied as a seed coating to a significant majority of North American corn, soybeans and wheat seeds. Neonicotinoids have received international media attention over the past 5 years due to assertions that their use is linked to a decline in pollinator populations. This has led to bans and restrictions on the use of neonicotinoids by the European Union, the provincial Government of Ontario and, more recently, the Government of Canada. No agricultural neonicotinoid bans are in place in the United States.

This worldwide focus on neonicotinoid use has led to extensive studies on the persistence of neonicotinoids in soil, plants and surface water bodies. Studies looking at the presence of neonicotinoids in groundwater resources are sparse.

This research aims to spatially and temporally assess the presence and fate of neonicotinoids in two separate Ontario, Canada aquifers. One shallow, sandy aquifer resides in a region of intense agricultural activity where corn, canola, soybeans and tobacco are typically grown; the other fractured bedrock aquifer is situated in an area where cattle farming is more common, below a thin layer of overburden. Groundwater samples are taken once every season (4 rounds to date) from roughly 25 multilevel monitoring wells at each research site. The samples are then analyzed for concentrations of 6 types of neonicotinoids – Acetamiprid, Clothianidin, Dinotefuran, Imidacloprid, Thiacloprid, and Thiamethoxam. Groundwater sampling results have tested predominately negative to this point. However, the August 2016 sampling round found that 17.2% of the sandy aquifer wells had concentrations above the level of detection; this frequency reduced to 3.1% in the fractured bedrock region. The wells with positive concentrations vary greatly, from a minimum of 0.009 µg/L to a maximum of 2.09 µg/L.

These groundwater concentrations will be related to surface‑application rates of neonicotinoids using the numerical modelling software HydrogeoSphere. The results of this study will provide a greater understanding of the presence and fate of neonicotinoids in groundwater while enhancing the information available to inform policy development.