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).

Estimating potential risks to terrestrial invertebrates and plants exposed to bisphenol A in soil amended with activated sludge biosolids.

Bisphenol A (BPA) is a high production volume substance primarily used to produce polycarbonate plastic and epoxy resins. During manufacture and use, BPA may enter wastewater treatment plants. During treatment, BPA may become adsorbed to activated sludge biosolids, which may expose soil organisms to BPA if added to soil as an amendment. To evaluate potential risks to organisms that make up the base of the terrestrial food web (i.e., invertebrates and plants) in accordance with international regulatory practice, toxicity tests were conducted with potworms (Enchytraeids) and springtails (Collembolans) in artificial soil, and six plant types using natural soil. No-observed-effect concentrations (NOEC) for potworms and springtails were equal to or greater than 100 and equal to or greater than 500 mg/kg (dry wt), respectively. The lowest organic matter-normalized NOEC among all tests (dry shoot weight of tomatoes) was 37 mg/kg-dry weight. Dividing by an assessment factor of 10, a predicted-no-effect concentration in soil (PNEC(soil)) of 3.7 mg/kg-dry weight was calculated. Following international regulatory guidance, BPA concentrations in soil hypothetically amended with biosolids were calculated using published BPA concentrations in biosolids. The upper 95th percentile BPA biosolids concentration in North America is 14.2 mg/kg-dry weight, and in Europe is 95 mg/kg-dry weight. Based on recommended biosolids application rates, predicted BPA concentrations in soil (PEC(soil)) would be 0.021 mg/kg-dry weight for North America and 0.14 mg/kg-dry weight for Europe. Hazard quotients (ratio of PEC(soil) and PNEC(soil)) for BPA were all equal to or less than 0.04. This indicates that risks to representative invertebrates and plants at the base of the terrestrial food web are low if exposed to BPA in soil amended with activated sludge biosolids.

Refined aquatic risk assessment for aldicarb in the United States.

Aldicarb is a systemic insecticide applied directly to soil and to control mites, nematodes, and aphids on a variety of crops (e.g., cotton, potatoes, peanuts). It is highly soluble in water (6,000 mg/L) and mobile in soils (K(oc) = 100). As a result, aldicarb has the potential to be transported to aquatic systems close to treated fields. The US Environmental Protection Agency (USEPA) recently conducted an aquatic screening-level ERA for aldicarb as part of the re-registration review process. We conducted a refined risk assessment for aldicarb to characterize better the risks posed by aldicarb to fish and invertebrates inhabiting small freshwater ponds near agricultural areas. For the exposure assessment, tier II PRZM/EXAMS (Predicted Root Zone Model [PRZM] and Exposure Analysis Modelling System [EXAMS]) modelling was conducted to estimate 30-y distributions of peak concentrations of aldicarb and the carbamate metabolites (aldicarb sulfoxide, aldicarb sulfone) in surface waters of a standard pond arising from different uses of aldicarb. The effects assessment was performed using a species sensitivity distribution (SSD) approach. The resulting risk curves as well as available incident reports suggest that risks to freshwater fish and invertebrates from exposure to aldicarb are minor. The available monitoring data did not provide conclusive evidence about risks to aquatic biota.