Effects of sewage sludge on the immune defenses of mallards

Sewage sludge contains numerous chemicals that, if ingested, could affect the immunological status of wild birds and, in particular, their resistance to infectious disease. Mallard ducks were fed a diet containing 0, 5, or 20% dried sewage sludge from either Milwaukee or Madison, Wisconsin, for 28 and 57 days, respectively. When subsequently challenged with Pasteurella multocida, the mortality in the sludge-treated groups was no greater than that in the untreated control groups. There was, however, significantly more cadmium (two- to three-fold higher concentration) retained in the livers of birds receiving 20% of either sludge in their feed, as compared to controls.