Arsenic Retention In Foliage and Soil Following MSMA Application To Turfgrass.

Arsenic (As), a known toxin and carcinogen, is a particular element of concern in turfgrass systems. Although inorganic arsenical pesticides are no longer produced, certain organic arsenicals, such as monosodium methyl arsonate (MSMA), are still used as herbicides for cotton and turfgrass today.  Due to concern that As might leach into the subsurface and threaten the health of those who use groundwater as a drinking source, in 2009, the Environmental Protection Agency proposed a phaseout of organic arsenical pesticides to turfgrass and cotton to begin in 2013, but this was temporarily overturned. However, to date, little research has evaluated the mobility of MSMA in natural systems, and accordingly, the fate of As in turfgrass environments is not completely understood. We have engaged in systematic field and laboratory studies to evaluate loading limits, retention capacities, and potential for As leaching to groundwater over time following normal MSMA application to bermudagrass golf course fairways and bareground soils. Through 334 days after treatment, dissolved arsenic concentrations from 76.2-cm-depth porewater in the MSMA-treated soils were indistinguishable from background concentrations and consistently less than 2 µg/L, suggesting that As was rather immobile in the unsaturated sandy soil at our field area. Within MSMA-treated plots, the highest concentrations of solid-phase As (up to ~10 mg/kg) were found in the above-ground vegetation and surface soils through 364 days post application. From As measured by adsorption isotherm experiments, MSMA retention by the sandy soil from our field site was markedly less than retention by a washed sand and a clay loam. Collectively, our results demonstrate strong retention of As by soil and foliage, with slight to moderate downward leaching of As at our field area. Future work will investigate As species conversion, As cycling into and out of foliage, and the fate of As in turfgrass clippings.