Inclusion of Pesticide Transformation Products Is Key to Estimating Pesticide Exposures and Effects in Small U.S. Streams

Abstract

Improved analytical methods can quantify hundreds of pesticide transformation products (TPs), but understanding of TP occurrence and potential toxicity in aquatic ecosystems remains limited. We quantified 108 parent pesticides and 116 TPs in more than 3 700 samples from 442 small streams in mostly urban basins across five major regions of the United States. TPs were detected nearly as frequently as parents (90 and 95% of streams, respectively); 102 TPs were detected at least once and 28 were detected in >20% samples in at least one regionTPs of 9 herbicides, 2 fungicides (chlorothalonil and thiophanate-methyl), and 1 insecticide (fipronil) were the most frequently detected. TPs occurred commonly during baseflow conditions, indicating chronic environmental TP exposures to aquatic organisms and the likely importance of groundwater as a TP source. Hazard quotients based on acute aquatic-life benchmarks for invertebrates and nonvascular plants and vertebrate-centric molecular endpoints (sublethal effects) quantify the range of the potential contribution of TPs to environmental risk and highlight several TP exposure–response data gaps. A precautionary approach using equimolar substitution of parent benchmarks or endpoints for missing TP benchmarks indicates that potential aquatic effects of pesticide TPs could be underestimated by an order of magnitude or more.

Food, Beverage, and Feedstock Processing Facility Wastewater: a Unique and Underappreciated Source of Contaminants to U.S. Streams

“…This detection of methomyl oxime did not have a corresponding methomyl parent compound detection, demonstrating why evaluation of TPs is crucial in environmental research. Methomyl is used for chemical control of flies in poultry facilities and is not commonly found in streams and rivers . Methomyl can degrade in the presence of Cl – , but the most effective degradation is by microbial digestion, − both of which are used by MEAT-2 (Table ).…”

“…Therefore, this poultry processing facility could have received large concentrations of methomyl from the poultry facilities that was degraded into TP during food processing and/or treatment. While toxicity data are lacking for the TP methomyl oxime, methomyl is moderately to highly toxic to fish and very highly toxic to aquatic invertebrates at concentrations as low as 8.8 μg L –1 …”

Continuous high-frequency pesticide monitoring to observe the unexpected and the overlooked

“…This is of practical importance because concerns about compounds may rise at later stages, after samples were discarded. For example, we could include key TPs as soon as their corresponding AQS become available to enhance the robustness of risk calculations ( Mahler et al., 2021 ). Despite a broad spectrum of analytes currently implemented in MS 2 Field , we could not measure pyrethroids, thus leading to a probable underestimation of the acute risk to non-target organisms including invertebrates ( Rosch et al., 2019 ; Schulz et al., 2021 ).…”

Comparative Toxicity of Herbicide Active Ingredients, Safener Additives, and Commercial Formulations to the Nontarget Alga Raphidocelis Subcapitata

“…Based on 2012 herbicide usage data, in the United States, SMET was ranked third, and ACE was ranked seventh (Atwood & Paisley‐Jones, 2017). Because of their heavy usage, both SMET and ACE as well as their transformation products have been found in streams across the United States (Mahler et al, 2020). Although the popularity of SMET and ACE stems from their effectiveness in controlling grasses and broadleaf weeds for more than 20 crops worldwide, they are mostly used for maize crops (corn) and soybeans (O'Connell et al, 1998).…”