Environmental fate of monosodium methanearsonate (MSMA)—Part 1: Conceptual model

• Published in: Integrated environmental assessment and management 2024-11, Vol.20 (6), p.1859-1875
• Main Authors: Eldan, Michal, Masue‐Slowey, Yoko
• Format: Article
• Language: English
• Subjects: Acidic soils; Aeration; Arsenic; Biological activity; Body temperature; Cotton; Dimethylarsinic acid; Environmental assessment; Environmental behavior; Environmental fate; Environmental Impact Assessment; Environmental management; Groundwater; Herbicides; Inorganic arsenic; Integrated environmental assessment; Leaching; Metabolites; Microbial activity; Microorganisms; MSMA; Nutrient availability; Nutrients; Organic arsenicals; Sequestration; Sodium; Sodium salts; Soil; Soil microorganisms; Soil temperature; Solid surfaces; Sorption; Toxicology; Turf; Weed control
• ISSN: 1551-3777; 1551-3793; 1551-3793
• DOI: 10.1002/ieam.4961

Monosodium methanearsonate (MSMA), the sodium salt of monomethylarsonic acid (MMA), is used as a selective, broad‐spectrum contact herbicide to control weeds in cotton and a variety of turf. In water, MSMA dissociates into ions of sodium (Na+) and of MMA−, which is the herbicide's active component. Certain soil microorganisms can methylate MMA to dimethylarsinic acid (DMA) other microorganisms can demethylate MMA to inorganic arsenic (iAs). To predict the groundwater concentration of iAs that may result from MSMA application, the processes affecting the environmental behavior of MSMA must be quantified and modeled. There is an extensive body of literature regarding the environmental behavior of MSMA. There is a consensus among scientists that the fate of MMA in soil is controlled by microbial activity and sorption to solid surfaces and that iAs sorption is even more extensive than that of MMA. The sorption and transformation of MMA and its metabolites are affected by several factors including aeration condition, temperature, pH, and the availability of nutrients. The precise nature and extent of each of these processes vary depending on site‐specific conditions; however, such variability is constrained in typical MSMA use areas that are highly managed. Monomethylarsonic acid is strongly sorbed on mineral surfaces and becomes sequestered into the soil matrix. Over time, a greater portion of MMA and iAs becomes immobile and unavailable to soil microorganisms and to leaching. This review synthesizes the results of studies that are relevant for the behavior of MSMA used as a herbicide to reliably predict the fate of MSMA in its use conditions. Integr Environ Assess Manag 2024;20:1859–1875. © 2024 The Author(s). Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC). Key Points The environmental fate of monosodium methanearsonate (MSMA) used as a herbicide should be evaluated based on studies conducted with experimental conditions and setup that are relevant to MSMA use. The environmental fate of MSMA in soil is controlled by sorption and sequestration to soil minerals and by microbial activity. The rate and extent of sorption and sequestration of MSMA vary depending on site‐specific conditions; however, such variability is constrained in typical MSMA use areas. With time, the majority of MSMA and its metabolites become immobile and unavailable to soil microorgan