Predicting heavy metal accumulation in alfalfa (Medicago sativa) using soil properties of sewage sludge amendments.

Abstract

Sustainable management of sewage sludge (SS) produced from municipal wastewater treatment facilities has become one of the major challenges around the world. Despite its utilization as a soil amendment, the issue of heavy metal contamination persists as a major concern, given the potential for accumulation in the edible parts of crops. Therefore, the present study aimed to develop predictive models to evaluate the uptake of nine heavy metals (Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) by the shoots and roots of alfalfa plants (Medicago sativa L.) grown in soil mixed with varying contents of SS (0, 10, and 20 g/kg). The results of the present study showed that the mixing of SS enhanced soil nutrients but also elevated heavy metal contents. Alfalfa shoots accumulated significantly higher levels of Pb (26.03 mg/kg) and Zn (83.67 mg/kg) compared to roots, with Pb showing the highest bioaccumulation factor (7.1) and Mn exhibiting the strongest translocation factor (> 1.8). Predictive regression models indicated that soil pH, organic matter, electrical conductivity, and heavy metal contents were the most influential determinants of uptake. The best-fitting models achieved R² values up to 0.837, with efficiency indices and error parameters confirming their robustness. The findings of the current study showed that SS may improve soil fertility under alfalfa cultivation, while developed models can be used to mitigate risks of heavy metal contamination.