Availability of sludge‐borne silver to agricultural crops

Abstract

AbstractThree green house studies were conducted to evaluate the availability of sludge‐borne silver to a variety of agricultural crops. Two studies utilized anaerobically digested domestic sewage sludge that had been amended with silver sulfide in the laboratory prior to mixing the sludge with a screened topsoil. A third study utilized an aerobically digested, laboratory‐prepared sludge synthesized by feeding sludge microorganisms a representative solution from a standard photoprocessing operation. The synthetic sludge was also mixed with screened topsoil. There were no differences in the mean number of days to emergence or percent emergence of seedlings grown in sludge‐amended soils containing silver sulfide or seedlings grown in soils amended with silver‐laden, waste‐activated sludge. The growth and yields of corn, oat, and turnip plants were not affected by the presence of silver sulfide in sludge‐amended soils at concentrations as high as 106 mg Ag/kg soil. The dry weights of Chinese cabbage plants grown in the sludge‐amended soils containing silver sulfide at concentrations of ≥14 mg Ag/kg were significantly less than the controls. The presence of silver sulfide in the sludge‐amended soils did not remove the beneficial effects of adding sludge to the soil as plant growth was greater in sludge‐amended soils than in soil alone. The yields of lettuce, oat, turnip, and soybean plants grown in soils amended with the laboratory‐prepared, silver‐laden, waste‐activated sludge were significantly greater than those of the controls. At maturity, selected tissues of each species were analyzed for silver. With the exception of lettuce, there were no significant differences in the silver concentrations of the edible tissues of the crops grown in soils containing silver sulfide when compared with controls. The results of these studies indicate that sludge‐amended soils containing silver sulfide are not likely to affect adversely the growth of crops, and accumulation of low levels of silver may occur in the leaves of lettuce plants grown in soils containing silver.