BIOGEOCHEMICAL CONTROLS ON THE FATE AND TRANSPORT OF ORGANOARSENICALS FROM POULTRY LITER

Organoarsenical feed additives are widespread in poultry farming for improving feed efficiency, pigmentation and weight gain, by controlling coccidial intestinal parasites. However, as the compounds are not taken up in tissue, they are excreted from the animals and can potentially leach from the litter into natural waters. Several 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 their environmental fate and transport within agricultural watersheds. This study examines the pathway of organoarsenical compounds released from poultry litter in a watershed within the Delmarva Peninsula, a region of intense poultry production. We hypothesize that the transport of roxarsone and its biotransformation products are controlled by geology and sorption processes and that biotransformation is controlled by a variety of microbial populations under different biogeochemical conditions. Twenty monitoring wells and four zero-tension lysimeters have been installed at the field site (which, prior to this study, had not been litter-applied for more than five years). The site is also instrumented with soil moisture sensors and a novel redox monitoring system (Hypnos) to monitor litter leachate through the vadose zone and to examine if the litter leachate affects redox conditions. Prior to litter application, detailed background sampling of soil and ground water was conducted, and sampling will continue post-application. Results will provide information on how organoarsenicals are cycled in agricultural watersheds.