BIOTRANSFORMATION OF ROXARSONE, AN ORGANOARSENIC FEED ADDITIVE

The poultry industry is one of the largest and fastest growing livestock production systems in the world. Although the industry is economically successful, management of poultry waste is a challenging environmental problem. Roxarsone, an organoarsenic compound, is added to poultry feed to improve weight gain and feed efficiency. Recent work by Garbarino et al. (2003) shows that although roxarsone is stable in fresh poultry litter, it is converted to As(V) when the poultry litter is composted, suggestive of a microbial influence. However, there is little information on the rates of this biotransformation reaction, and the degree to which the transformation is affected by redox conditions and/or soil solution chemistry.

The main objective of our research is to evaluate the kinetics and extent of biotransformation of roxarsone using laboratory microcosms. Preliminary evidence from our experiments suggests rapid transformation of roxarsone to As(V) under aerobic conditions. Our experiments are also designed to evaluate if microorganisms in agricultural soils and/or poultry can reduce As(V) to As(III) under anaerobic conditions in the presence of excess organic carbon. Results from our multi-disciplinary research will provide new insight into the factors that control fate and transport of organoarsenic compounds in agricultural watersheds. This work will be applicable to other watersheds across the United States that are impacted by poultry-management practices.