Input and leaching potential of copper, zinc, and selenium in agricultural soil from swine slurry.

Trace elements, such as copper, zinc, and selenium, used as feed additives were determined in samples of both fresh (N = 14) and anaerobically digested (N = 6) swine slurry collected on medium- to large-size farms in northeast Spain. Considering both fresh and anaerobically digested samples, mean concentrations of zinc (1,500 mg kg(-1) dry mass [dm]) were greater than those of copper (mean 239 mg kg(-1 )dm), and the selenium concentrations detected were even lower (mean 139 μg kg(-1) dm). Zinc concentrations were significantly greater in anaerobically digested samples, whereas no significant differences were found for copper or selenium.