Zinc, copper, cadmium, and lead in minespoil, water, and plants from reclaimed mine land amended with sewage sludge

Abstract

Sewage sludge from the city of Philadelphia has been used as a fertilizer and soil conditioner for twelve years to reclaim surface-mined land. Over 1,000 ha have been reclaimed using an application rate of 138 to 145 Mg ha−1 (d.w.). Each of 49 sites was monitored for up to 2 yr following sludge application. Extractable Zn, Cu, Cd, and Pb in minespoil were determined before and after sludge was applied. Spoil percolate water, groundwater, and vegetation were also analyzed for metal concentrations. Data indicate that metals were retained mostly in the plow layer in which the sludge was incorporated, but there was evidence of smaller increases in metal concentrations at the 15 to 30 cm depth. Percolate water and groundwater quality appeared to be unaffected by sludge application. Foliar metal concentrations were within tolerance levels for agronomic crops and domestic animal diets. Other studies have shown that concentrations of metals in small mammals and rabbits consuming the sludge-grown vegetation were generally the same as those in animals living on areas not amended with sludge. Surface application of sludge containing low to median metal concentrations should pose no threat to soil, water, crop quality, or the food chain, even when applied in amounts higher than typical agricultural rates.