Trace metal retention in the incorporation zone of land-applied sludge

Recycling nutrients in wastewater sludge (biosolids) via land application i s a desirable goal. However, potential movement of sludge-applied trace met als is of concern and an area of ongoing research. In this paper, we examin e the first-order model used by the United States Environmental Protection Agency (U.S. EPA) for predicting losses from the zone of incorporation as p art of the risk assessment that undergirded the development of Part 503 reg ulations (1, 2). We found that when empirical adsorption partition coeffici ents from the site are used as model inputs, the U.S. EPA model for the inc orporation zone is similar to that derived from preferential flow theory an d simulates well the loss of metal from the surface soil layer at an orchar d site where sludge was applied 15 years earlier.