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ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Water Quality and Ecology Research » Research » Publications at this Location » Publication #368103

Research Project: Strategic Investigations to Improve Water Quality and Ecosystem Sustainability in Agricultural Landscapes

Location: Water Quality and Ecology Research

Title: Estimating sorption of monovalent acidic herbicides at different pH levels using a single sorption coefficient

item SPADATTO, CLAUDIO - Embrapa
item Locke, Martin
item Bingner, Ronald - Ron
item MINGOTI, RAFAEL - Embrapa

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/11/2020
Publication Date: 3/27/2020
Citation: Spadatto, C.A., Locke, M.A., Bingner, R.L., Mingoti, R. 2020. Estimating sorption of monovalent acidic herbicides at different pH levels using a single sorption coefficient. Pest Management Science. 76:2693-2698.

Interpretive Summary: Sorption of herbicide is an important process in soil that impacts the dissipation of organic compounds in the environment and efficacy in controlling weeds. Depending on chemical characteristics, herbicides may react differently as pH changes, i.e., ionizable acidic herbicide. Models describing the reactions of herbicides in soil need to account for these reactions. In this study, a method was described and tested to estimate the sorption of acidic herbicides with varying pH. This method was determined to be acceptable in the environmentally relevant pH range (4 - 9). This research will be important to modelers developing algorithms that account for herbicide fate and for users of those models.

Technical Abstract: Almost a third of the active ingredients of pesticides currently in use are ionizable compounds. These compounds exist in different proportions of neutral and ionic forms depending on pH. The ionized forms behave differently from the non-ionized molecules and agricultural efficacy and environmental behavior of these pesticides depend on extent of sorption. Databases and most literature report sorption data only at one pH in a given soil or sediment. Thus, a method to estimate sorption of ionizable pesticides at different pH levels using a single sorption coefficient was developed here. The described and tested procedure, named “high-pH boundary estimation method”, was practical, with good quality of fits especially in the environmentally relevant pH range. However, more combined calibration-testing research with different datasets is recommended. It should also be applied to pH-sorption datasets for other acidic pesticides to provide the respective ratios between the neutral and anionic forms theoretical maximum sorption coefficient, instead of using general fixed values or fixed ratios.