Ecotoxicological Assessment of Potentially Toxic Elements in Waterworks Sludge Amended Soils Using Bermudagrass Bioassay

Abstract

Waterworks sludge has the potential to be used as a soil amendment, but the ecotoxicological risk of potentially toxic elements should not be underestimated. In this regard, this study determined the contents of nine potentially toxic elements (Cr, Ni, Cd, Cu, Pb, Zn, As, Mn, and Al) of bermudagrass [Cynodon dactylon (L.) Pers.] grown in waterworks sludge amended soils. Treatments involved different loading rates of waterworks sludge, soil types, and fertilization options that represented different scenarios of greening applications. The recommended metal levels in plant tissues and maximum tolerable levels for feeding cattle are adopted as benchmarks for gauging the ecotoxicological risk to the first and second trophic levels of the ecosystem, respectively. No recommended levels for potentially toxic elements are exceeded when sludge loading rate is not higher than 50% (wt/wt). When various fertilization treatments are applied to 25% (wt/wt) sludge amended soils, the accumulation of aluminum and zinc deserves our attention because a few samples exceed the recommended levels. They are mainly samples of below-ground biomass. Overall, using waterworks sludge as a soil amendment does not cause an obvious ecotoxicological risk. The findings can provide a valuable reference to other cities for the sustainable management of waterworks sludge.