Arsenic Accumulation in Pond Water and Sediments Near Sod Farms and Golf Courses in North Carolina.

Inorganic and organic arsenical herbicides have been applied to crops and fields for over a century. All arsenical herbicides except monosodium monomethyl arsenate (MSMA) have been denied reregistration by the US EPA in recent years. Little is known about the fate of MSMA in the environment, but recent evidence has indicated that continual application of organic arsenical herbicides can threaten human health by leaching to groundwater, and accordingly, the EPA is currently reviewing the registration of MSMA. Our aim was to chemically and spectroscopically assess the accumulation of arsenic (As) previously applied to sod farms and golf courses in the Sandhills region of North Carolina.

Sediments, porewater, and surface water samples were collected in 2013 and 2014 from golf course and sod farm ponds. Golf course ponds had lower porewater and surface water As levels compared to sod farm ponds, which occasionally exceeded the EPA drinking water limit of 10 µg/L. In those ponds with As concentrations exceeding the EPA limit, As concentrations of sediment and porewater were elevated compared to a nearby pond with no herbicide contact.  Solid-phase concentration profiles of As in pond sediments suggest accumulation and active redox cycling of As in the subsurface. To discern whether the increased levels were from inorganic or organic species, As speciation was analyzed on collected porewater samples; all 4 As species (As(V), As(III), dimethyl arsenate (DMA), MMA) were detected, with As(V) and As(III) dominating at most sites. Micro-X-ray adsorption near edge structure (µ-XANES) spectra of sediments from micro-X-ray fluorescence (µ-XRF) maps indicated that both inorganic species (As(V) and As(III)) were present within sod farm pond sediments. This work suggests that land applied arsenicals likely converted to inorganic species, but As has slowly leached into pond sediments over time.