MSMA: Knowledge Gaps to Aid Appropriate Regulation of an Efficacious Herbicide

Abstract

Core Ideas MSMA is an arsenic‐based herbicide currently registered in cotton and turfgrass. Will continued MSMA use threaten human and environmental health? Discrepancies about environmental fate exist among field and laboratory research. Factors that influence As species transformation should be further elucidated. Management plans should be devised where MSMA is used. Monosodium methyl arsenate (MSMA) is an efficacious postemergence herbicide commonly used in cotton (Gossypium hirsutum L.) and turfgrass systems. Concerns have arisen about potential adverse effects of MSMA‐derived arsenic on human and environmental health. The USEPA enacted a phase‐out of MSMA and other organic arsenical pesticides in 2006, although subsequent agreements allow for its continued use until a review is complete in 2019. Additional research is needed to further characterize MSMA environmental fate and species transformation kinetics in cotton and turfgrass systems of varying edaphic conditions, as there are current knowledge gaps and discrepancies in previous reports. Improved understanding of MSMA environmental fate under real‐case conditions will allow regulatory agencies to devise appropriate regulations and management plans to ensure environmental and human health are protected.

Natural Background and Anthropogenic Arsenic Enrichment in Florida Soils, Surface Water, and Groundwater: A Review with a Discussion on Public Health Risk

“…The remaining two crops on which MSMA is still used are cotton and golf course turf grass. Regulatory decisions on the use of MSMA are and will continue to be based on its rate of transformation to inorganic arsenic [ 81 ]. The agricultural exemption applied to the necessity for remediation based on labelled and permitted use of pesticides may not apply to golf course sites that contain soil concentrations of arsenic above regulatory action levels in the future.…”

Fate of 14C‐MSMA in a soil column study simulating herbicide use environments

“…In the context of MSMA environmental behavior, these conditions do not vary widely in managed agricultural fields that are typical MSMA use areas. Gannon and Polizzotto (2016) noted discrepancies between field and laboratory research on the environmental fate of MSMA, which appear to originate from a wide range of experimental conditions used by researchers, including excessive application of MSMA, set up of the studies, and varying solids used in the studies. Field studies conducted by North Carolina State University Matteson et al, 2014) show that when MSMA is used according to label directions, MMA residues remain in surface soils, and downward migration of arsenic was consistently limited to 8-15 cm or less, even after 1 year.…”

Reduction of Organoarsenical Herbicides and Antimicrobial Growth Promoters by the Legume Symbiont Sinorhizobium meliloti

“…In the United States, a massive amount of methylarsenicals, both MAs­(V) and DMAs­(V), have been utilized as herbicides since the early 1970s. Although the use of DMAs­(V) has been prohibited since the beginning of 2014 under the cancellation order issued by the U.S. Environmental Protection Agency, the monosodium salt of MAs­(V), or MSMA, is still allowed for use on cotton fields, golf courses, sod farms, and highway rights of way nationwide except in Florida, where the use is now banned in golf courses …”

“…Although the use of DMAs(V) has been prohibited since the beginning of 2014 under the cancellation order issued by the U.S. Environmental Protection Agency, the monosodium salt of MAs(V), or MSMA, is still allowed for use on cotton fields, golf courses, sod farms, and highway rights of way nationwide except in Florida, where the use is now banned in golf courses. 7 In addition to MSMA, synthetic pentavalent aromatic arsenicals, including Rox(V), nitarsone [4-nitrophenylarsenate; Nit(V)] and p-arsanilic acid [4-aminophenylarsenate; p-ASA(V)] have been widely used since the 1940s, especially in the poultry industry, as a feed additive to control protozoan parasitic diseases and promote growth. Approximately, 2 000 000 pounds of Rox(V) was released annually into the environment as manure from Rox(V)-fed animals, and the manure was applied as a fertilizer to farm crops.…”