High‐Frequency Sampling of Small Streams in the Agroecosystems of Southwestern Ontario, Canada, to Characterize Pesticide Exposure and Associated Risk to Aquatic Life

Abstract

The temporal dynamics of pesticide concentrations in streams remains poorly characterized in southwestern Ontario, a region of the province where land use is dominated by agriculture. Understanding the magnitude and duration of pulsed exposures to pesticides in these small streams is critical when estimating the risk of pesticides to these aquatic ecosystems. The present study investigated the application of a high-frequency water sampling approach paired with the collection of flow data to characterize the pulsed exposure of pesticides to small streams in southwestern Ontario. Six sites along 2 different streams with different magnitudes of agricultural land use in their upstream catchments were sampled using half-day composite samples from July to October 2018 and from May to September 2019. A total of 1043 samples were collected over the 2 yr, of which 210 were analyzed. Samples for analysis were chosen based on flow, water level, and precipitation data. Liquid and gas chromatography coupled with tandem mass spectrometry was used to measure >500 pesticides in each water sample. A total of 35 different compounds were detected over the 6 sampling sites. For pesticides that were detected in >10% of water samples above the method quantification limit, a deterministic risk assessment using water quality guidelines and a probabilistic risk assessment using species sensitivity distributions were performed. The calculated hazard quotients showed that 2,4-D, atrazine, metolachlor, and metribuzin exceeded a level of concern of 1 at the highest concentrations detected. In all cases, hazard concentrations that would be protective of 95% of species from the species sensitivity distributions were greater than the 95th centile of the environmental exposure distributions, meaning that the risk from the pesticides was low.

Continuous high-frequency pesticide monitoring in a small tile-drained agricultural stream to reveal diel concentration fluctuations in dry periods

“…Plant protection products (PPPs) use promises to achieve global food security (Popp et al, 2012), but the consequent environmental contamination poses a global environmental hazard (Stehle and Schulz, 2015;Maggi et al, 2020). It is the common view that surface waters are predominantly exposed to high concentrations of PPPs during rain events (Schulz, 2001;Szocs et al, 2017) and to transformation products (TPs) in dry periods (Rasmussen et al, 2015;Spycher et al, 2018;Belles et al, 2019;Sanford and Prosser, 2020;Halbach et al, 2021;Le Cor et al, 2021). Given the large effort that goes with sampling and analyzing PPPs from streams, many studies increase sampling frequency in response to hydrological proxies, such as rainfalls or increments in discharge in accordance with the scientific evidence showing that the largest loads of PPPs in water bodies occur during rain events (Doppler et al, 2012;Halbach et al, 2021).…”

An Assessment of the Toxicity of Pesticide Mixtures in Periphyton from Agricultural Streams to the Mayfly Neocloeon triangulifer

“…The second objective of our study was to investigate whether dietary exposure to a mixture of pesticides that have partitioned into field-collected periphyton has an adverse effect on grazing aquatic organisms. For this second objective, the mayfly species Neocloeon triangulifer was selected as the test organism because it is widely distributed in North American streams and has a documented sensitivity to pesticide exposure (Raby, Nowierski, et al, 2018;Raby et al, 2018aRaby et al, , 2018bRaby et al, , 2019Sanford & Prosser, 2020). Periphyton is the natural diet for many mayfly species, including Neocloeon triangulifer (Sweeney & Vannote, 1984).…”

“…Southern Ontario is a region where the land use is dominated by agriculture. As a result, agricultural pesticides can move outside the intended area of application into surface waters where they can pose an ecotoxicological risk to aquatic life (Raby et al, 2022; Sanford & Prosser, 2020; Struger et al, 2017). Pesticides are transported from the surrounding agricultural fields into aquatic environments through surface runoff, soil erosion, and leaching (Chow et al, 2020; Holvoet et al, 2007).…”

“…For example, studies have demonstrated that periphyton communities can bioconcentrate glyphosate (Beecraft & Rooney, 2021), diuron (Chaumet et al, 2019), and carbofuran (Tien et al, 2017), among other compounds. Field conditions, however, often involve a diverse mixture of pesticides with highly dynamic concentration profiles (Chow et al, 2020; Raby et al, 2022; Sanford & Prosser, 2020); and therefore, periphyton are exposed to these mixtures.…”