EVALUATING MOBILIZATION AND TRANSPORT OF ORGANOARSENICALS AND OTHER LITTER-DERIVED SOLUTES RELEASED FROM POULTRY LITTER WITHIN AGRICULTURAL WATERSHEDS

Organoarsenical feed additives are used in poultry farming for improving feed efficiency. However, as the compounds have minimal uptake in tissue, they are excreted and potentially become environmental problems when applied as fertilizer. This study employed a field experiment within an area of intense poultry production to determine the transport and pathways of organoarsenicals and other litter-derived solutes released from poultry litter (PL). We applied PL to a site that had not received PL for more than five years. Prior to litter application, monitoring wells and zero-tension lysimeters were installed, followed by eight months of background sampling of soil and water. The site is also instrumented with soil moisture sensors and a redox monitoring system to continuously monitor litter leachate through the vadose zone. Results thus far have shown that applied PL contains 32 mg/kg of arsenic (As) which has high water solubility (63%). Results of adsorption experiments using litter extracts showed that only 8% of the mass of As adsorbed to shallow soil from the site, an indication that there is little retardation to As mobility and transport in the vadose zone. However, the maximum concentration of As in soil water was only 4.3 μg/L and As has not been detected in groundwater. Calculations using conservative and reactive species from the litter suggest that dilution, in addition to biogeochemical processes, control the concentration of As, as well as other litter-derived solutes (e.g., Cu, Zn, P, DOC) in soil and groundwater.