Fate of Arsenic after Msma Herbicide Treatment to Sod Farms in North Carolina.

Inorganic and organic arsenicals such as lead arsenate and monosodium monomethyl arsenate (MSMA) have been used for decades as pesticides. As of 2009, all arsenicals except for MSMA have been denied reregistration by the EPA due to their potential threat to human health by leaching of arsenic to groundwater and the conversion of organic arsenic species to the more mobile inorganic species. Currently, the registration of MSMA is under review until 2019 and limits the use of MSMA to only turf and cotton. Despite its lengthy history as a pesticide, the fate and accumulation of MSMA in turfgrass areas with widespread application (i.e. sod farms) is still lacking. Our aim was to chemically and spectroscopically assess any accumulation of arsenic (As) in environmentally susceptible sod farm fields and low-lying ponds in the Sandhills and Coastal Plains regions of North Carolina. Surface water, porewater, and sediment samples were collected for chemical analysis from 7 different sod farm ponds between 2013-2015. Surface water As concentrations were generally low and ranged from 0.37-8.18 µg/L, while a few porewater samples exceeded the EPA drinking water limit of 10 µg/L. Most solid-phase As concentrations were relatively low (< 2 mg/kg As in the soil), but the sites with porewater concentrations exceeding the EPA guideline showed an accumulation (up to 6 mg/kg) and active redox cycling of As. To determine whether the MSMA applied converted to inorganic species over time, As speciation was performed on collected porewater samples. As(V), As(III), dimethyl arsenate , and monomethyl arsenate were quantified in the ponds, with the inorganic species dominating most depths. This work suggests that MSMA gets converted to inorganic As species, but any accumulation of As in sod farm ponds is minimal, and does not pose much of a threat to groundwater contamination in the areas studied.