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Knowledge gaps to aid appropriate MSMA regulation


Monosodium methyl arsenate (MSMA) is an arsenic-based herbicide commonly used in cotton and turfgrass systems. In recent years, concerns about potential adverse effects of MSMA-derived arsenic on human and environmental health have arisen. The USEPA enacted an MSMA phase-out in 2006; however, a subsequent MSMA review was initiated in 2009, and the final decision about future MSMA use is expected in 2019.

In a recent article published in Agricultural and Environmental Letters, researchers summarize current knowledge about MSMA-derived arsenic environmental fate and behavior, including factors controlling off-target movement of arsenic and transformation of arsenic from organic to more toxic inorganic species. The authors also discuss conflicting conclusions from previous research and highlight potential management considerations for areas where MSMA is repeatedly used.

Tractor spraying herbicide

Arsenic behavior can vary across different agricultural systems and environmental contexts, and discrepancies in MSMA-derived arsenic behavior may be due, in part, to use of unrealistically high MSMA loading rates in laboratory research compared with use of registered rates in field efforts. The authors suggest that regulatory and management efforts should encompass this knowledge about variability in arsenic fate and behavior to ensure that future MSMA use does not adversely impact human and environmental health.

Read the full open access paper in AEL.