Dynamics of Copper and Lead Originating from Biosolids in Arid Calcareous Soils: Effect of Nanomaterials Produced from Byproducts of Water Treatment Industry

This study investigates the dynamics of copper (Cu) and lead (Pb) in biosolids-amended calcareous soils under arid conditions and evaluates the potential of nano-sized water treatment residuals (nWTRs), derived from drinking water treatment byproducts, as a sustainable remediation agent. A field lysimetric experiment was conducted using calcareous soil amended with 3% biosolids and varying rates of nWTRs (0.1%, 0.2%, 0.3%). The effects on Cu and Pb uptake by maize (Zea mays L.), their speciation in soil solution, and geochemical fractionation were assessed over two growing seasons. Characterization of nWTRs revealed high specific surface area (129 m²/g), amorphous morphology, and reactive Al/Fe-oxide surfaces conducive to heavy metal sorption. Application of biosolids alone significantly increased both Cu and Pb bioavailability, plant uptake, and soluble concentrations in soil solution. In contrast, the incorporation of nWTRs reduced soluble and plant-available Cu and Pb, particularly at the 0.3% rate. Sequential extraction results confirmed a shift in Cu and Pb from labile (exchangeable, carbonate-bound, and oxide-bound) fractions toward the residual, stable form, rising from 22% to 81% for Cu and from 51% to 79% for Pb. Chemical speciation modeling using MINEQL+ showed a dramatic reduction in free Cu²⁺ and Pb²⁺ ions, with increased formation of less mobile hydroxide and carbonate species in nWTR-amended soils. These findings demonstrate that nWTRs effectively immobilize Cu and Pb in biosolids-amended soils by altering their speciation and distribution, thus reducing environmental risk and enhancing the sustainability of biosolid reuse in agriculture.