Cycling of Organoarsenicals Released from Poultry Litter: Results from a Field Experiment in an Agricultural Watershed
Virginia Tech and State University
The use of organoarsenicals in poultry feed has a wide variety of benefits which range from improved feed efficiency and pigmentation to weight gain. However, the compounds are not taken up in tissue and are instead excreted from the animals, resulting in elevated concentration (15-77 mg/kg) in poultry litter. When poultry litter is land applied as fertilizer, there is a potential for arsenic to leach from the litter into hydrologic systems. Laboratory studies on the biotransformation of roxarsone (3-nitro 4-hydroxybenzene arsonic acid), the dominant organoarsenic feed additive for poultry, have been conducted; but to date, there is little information on its environmental fate and transport within agricultural watersheds. This study examines the pathway of roxarsone released from poultry litter from the land surface to soil and groundwater and finally surface waters. The main objective is to determine how geologic (e.g. aquifer mineralogy, stratigraphy) and geochemical (e.g., redox) conditions impact arsenic mobility and to what extent arsenic is transported through hydrologic systems after poultry litter is land applied. To address the research objectives, we have installed monitoring wells, lysimeters and continuous monitoring equipment at a field site in the Delmarva Peninsula, a region of intense poultry production. Prior to this study, the site had not been litter-applied for more than five years. After collecting several sets of background samples, we conducted a poultry litter application (2 tons per acre) in October 2009. Results thus far show that water-soluble species from poultry litter are mobile, but so far, impact has been limited to soil water. Further sampling will continue to determine the arsenic form and species available in ground or surface waters at the site.