THE MOBILITY OF ARSENIC ADSORBED TO PARTICULATES WITHIN AGRICULTURAL WATERSHEDS

Arsenic contamination of water in agricultural watersheds is a recent concern, as poultry litter applied to croplands can release arsenic to the environment. Roxarsone, an organoarsenic poultry feed additive, is used to improve weight gain, feed efficiency, and pigmentation of chickens. The roxarsone is not retained in the tissues of the animals, but is instead excreted into the nutrient-rich litter. In agricultural regions, this litter is used as a fertilizer, and the roxarsone quickly biotransforms into inorganic arsenic after its application to agricultural fields.

Our preliminary data, collected from a poultry dominated watershed in Rockingham Co., Virginia, suggest that arsenic released from litter application can adsorb to mobile particulates in the subsurface. These particulates can then be transported from the litter-applied fields through soil water and subsequently into groundwater and stream water.

We are conducting a small-scale field application of poultry litter, and will combine water sampling from this application site with field filtration and laboratory ultrafiltration to determine if the arsenic seen in these waters is primarily dissolved or adsorbed to particulates. We will also attempt to identify the composition of the mobile particulates using microscopic techniques. In addition, we are performing laboratory experiments to determine if phosphate and organic acids will compete with arsenic for sorption sites on these mobile particulates. Our results should shed insight into the mobility of litter-derived arsenic in agricultural watersheds.