Effectiveness of side-inlet vegetated filter strips at trapping pesticides from agricultural runoff.

Agriculture can be a contributor of pollutants, including pesticides and excess sediment, to aquatic environments. However, side-inlet vegetated filter strips (VFSs), which are planted around the upstream side of culverts draining agricultural fields, may provide reductions in pesticide and sediment losses from agricultural fields, and have the additional benefit of removing less land from production than traditional VFS. In this study, reductions of runoff, the soluble pesticide acetochlor, and total suspended solids were estimated using a paired watershed field study and coupled PRZM/VFSMOD modeling for two treatment watersheds with source to buffer area ratios (SBAR) of 80:1 (SI-A) and 481:1 (SI-B). Based on the paired watershed ANCOVA analysis, runoff and acetochlor load reductions were significant following the implementation of a VFS at SIA but not SI-B, indicating the potential for side-inlet VFS to reduce runoff and acetochlor load from a watershed with an area ratio of 80:1 but not a higher ratio of 481:1. VFSMOD simulations were consistent with the results of the paired watershed monitoring study, where simulated reductions of runoff, acetochlor loads, and TSS loads were substantially lower for SI-B than SI-A. VFSMOD simulations of SI-B with the SBAR ratio observed at SI-A (80:1) also show that VFSMOD can be used to capture variability in effectiveness of VFS based on multiple factors including SBAR. While this study focused on the effectiveness of side-inlet VFSs at the field scale, broader adoption of properly sized side-inlet VFSs could improve surface water quality at the watershed or larger scales. Additionally, modeling at the watershed scale could aid in locating, sizing, and assessing the impacts of side-inlet VFSs at this larger scale.

A field spray drift study to determine the downwind effects of isoxaflutole herbicide to nontarget plants.

Spray drift buffers are often required on herbicide labels to prevent potential drift effects to nontarget plants. Buffers are typically derived by determining the distance at which predicted exposure from spray drift equals the ecotoxicology threshold for sensitive plant species determined in greenhouse tests. Field studies performed under realistic conditions have demonstrated, however, that this approach is far more conservative than necessary. In 2016, the US Environmental Protection Agency estimated that isoxaflutole (IFT), a herbicide used to control grass and broadleaf weeds, could adversely affect downwind nontarget dicot plants at distances of ≥304 m from the edge of the treated field due to spray drift. This prediction implies that a buffer of at least 304 m is required to protect nontarget plants. To refine the predicted buffer distance for IFT, we conducted a field study in which sensitive nontarget plants (lettuce and navy bean, two to four leaf stage) were placed at various distances downwind from previously harvested soybean fields sprayed with Balance® Flexx Herbicide. The test plants were then transported to a greenhouse for grow out following the standard vegetative vigor test protocol. There were three trials. One had vegetation in the downwind deposition area (i.e., test plants placed in mowed grass; typical exposure scenario) and two had bare ground deposition areas (worst-case exposure scenario). For both plant species in bare ground deposition areas, effects on shoot height and weight were observed at 1.52 m but not at downwind distances of ≥9.14 m from the edge of the treated area. No effects were observed at any distance for plants placed in the vegetated deposition area. The field study demonstrated that a buffer of 9.14 m protects nontarget terrestrial plants exposed to IFT via spray drift even under worst-case conditions. Integr Environ Assess Manag 2022;18:757-769. © 2021 Bayer. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Evaluation of Watershed-Scale Simulations of In-Stream Pesticide Concentrations from Off-Target Spray Drift.

The estimation of pesticide concentrations in surface water bodies is a critical component of the environmental risk assessment process required by regulatory agencies in North America, the European Union, and elsewhere. Pesticide transport to surface waters via deposition from off-field spray drift can be an important route of potential contamination. The spatial orientation of treated fields relative to receiving water bodies make prediction of off-target pesticide spray drift deposition and resulting aquatic estimated environmental concentrations (EECs) challenging at the watershed scale. The variability in wind conditions further complicates the simulation of the environmental processes leading to pesticide spray drift contributions to surface water. This study investigates the use of the Soil Water Assessment Tool (SWAT) for predicting concentrations of malathion (O,O-deimethyl thiophosphate of diethyl mercaptosuccinate) in a flowing water body when exposure is a result of off-target spray drift, and assesses the model's performance using a parameterization typical of a screening-level regulatory assessment. Six SWAT parameterizations, each including incrementally more site-specific data, are then evaluated to quantify changes in model performance. Results indicate that the SWAT model is an appropriate tool for simulating watershed scale concentrations of pesticides resulting from off-target spray drift deposition. The model predictions are significantly more accurate when the inputs and assumptions accurately reflect application practices and environmental conditions. Inclusion of detailed wind data had the most significant impact on improving model-predicted EECs in comparison to observed concentrations.

A refined ecological risk assessment for California red-legged frog, Delta smelt, and California tiger salamander exposed to malathion.

The California red-legged frog (CRLF), Delta smelt (DS), and California tiger salamander (CTS) are 3 species listed under the United States Federal Endangered Species Act (ESA), all of which inhabit aquatic ecosystems in California. The US Environmental Protection Agency (USEPA) has conducted deterministic screening-level risk assessments for these species potentially exposed to malathion, an organophosphorus insecticide and acaricide. Results from our screening-level analyses identified potential risk of direct effects to DS as well as indirect effects to all 3 species via reduction in prey. Accordingly, for those species and scenarios in which risk was identified at the screening level, we conducted a refined probabilistic risk assessment for CRLF, DS, and CTS. The refined ecological risk assessment (ERA) was conducted using best available data and approaches, as recommended by the 2013 National Research Council (NRC) report "Assessing Risks to Endangered and Threatened Species from Pesticides." Refined aquatic exposure models including the Pesticide Root Zone Model (PRZM), the Vegetative Filter Strip Modeling System (VFSMOD), the Variable Volume Water Model (VVWM), the Exposure Analysis Modeling System (EXAMS), and the Soil and Water Assessment Tool (SWAT) were used to generate estimated exposure concentrations (EECs) for malathion based on worst-case scenarios in California. Refined effects analyses involved developing concentration-response curves for fish and species sensitivity distributions (SSDs) for fish and aquatic invertebrates. Quantitative risk curves, field and mesocosm studies, surface-water monitoring data, and incident reports were considered in a weight-of-evidence approach. Currently, labeled uses of malathion are not expected to result in direct effects to CRLF, DS or CTS, or indirect effects due to effects on fish and invertebrate prey. Integr Environ Assess Manag 2018;14:224-239. © 2017 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals, Inc. on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Runoff transport of pyrethroids from a residential lawn in central California.

An irrigation runoff study on a residential lawn was conducted in California, northeast of Sacramento, during the summer and fall of 2008 to investigate the contribution of turf uses of pyrethroids to residues in Californian urban creek sediments. This study examined how over irrigation (i.e., irrigation that produces runoff) in the summer season may transport recently applied pyrethroids. The study included liquid and granular applications of both bifenthrin [(2-methyl-3-phenyl-phenyl) methyl 3-(2-chloro-3,3,3-trifluoro-prop-1-enyl)-2,2-dimethyl-cyclopropane-1-carboxylate] and beta-cyfluthrin [Cyano(4-fluoro-3-phenoxyphenyl)methyl 3-(2,2-dichloroethenyl)-2,2-dimethyl-cyclopropanecarboxylate]. Generally, runoff did not occur at irrigation rates of 2.03 cm/h (0.8 in/h) but did occur when the irrigation rates were increased to about 3.81 cm/h (1.5 in/h), generating chemical losses in the first runoff event of up to 0.58 and 0.08% of applied for beta-cyfluthrin and bifenthrin, respectively. Chemical runoff losses dropped significantly between over-irrigation events with the third over-irrigation event chemical runoff losses representing 0.026 and 0.015% of applied for beta-cyfluthrin and bifenthrin, respectively. Runoff losses were generally less for liquid formulations than granular formulations but within a factor of three. Additionally, the study included a simulated winter rainstorm 8 wk after application. The low runoff losses from turf seen in this study suggest that other sources could be contributing to observed residues in urban streams. Other sources could include pyrethroids ending up on impervious surfaces, such as concrete driveways from off-target applications to turf, spills, and other poor handling practices, or pyrechroids applied directly to impervious surfaces for insect control.

The acetochlor registration partnership surface water monitoring program for four corn herbicides.

A surface drinking water monitoring program for four corn (Zea mays L.) herbicides was conducted during 1995-2001. Stratified random sampling was used to select 175 community water systems (CWSs) within a 12-state area, with an emphasis on the most vulnerable sites, based on corn intensity and watershed size. Finished drinking water was monitored at all sites, and raw water was monitored at many sites using activated carbon, which was shown capable of removing herbicides and their degradates from drinking water. Samples were collected biweekly from mid-March through the end of August, and twice during the off-season. The analytical method had a detection limit of 0.05 microg L(-1) for alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)-acetamide] and 0.03 microg L(-1) for acetochlor [2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)-acetamide], atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine], and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)-acetamide]. Of the 16528 drinking water samples analyzed, acetochlor, alachlor, atrazine, and metolachlor were detected in 19, 7, 87, and 53% of the samples, respectively. During 1999-2001, samples were also analyzed for the presence of six major degradates of the chloroacetanilide herbicides, which were detected more frequently than their parent compounds, despite having higher detection limits of 0.1 to 0.2 microg L(-1). Overall detection frequencies were correlated with product use and environmental fate characteristics. Reservoirs were particularly vulnerable to atrazine, which exceeded its 3 microg L(-1) maximum contaminant level at 25 such sites during 1995-1999. Acetochlor annualized mean concentrations (AMCs) did not exceed its mitigation trigger (2 microg L(-1)) at any site, and comparisons of observed levels with standard measures of human and ecological hazards indicate that it poses no significant risk to human health or the environment.