ZnO nanoparticles in composted sewage sludge enhance soil fertility and rice nutrition but elevate As and Pb accumulation

Abstract

The widespread use of metal-based nanoparticles (NPs) in a variety of industries results in their release into sewage systems. This presents a risk when composted sewage sludge (CSS) is used as fertilizer. This study examined the effects of ZnO NPs in CSS on rice-soil systems and assessed the health risks associated with consuming rice grown under these circumstances. ZnO NPs were added to CSS at concentrations lower than the regulatory safety limit of 2800 mg Zn kg⁻¹. The results show that higher levels of ZnO NPs in CSS improved the mineral composition of rice grains and increased soil fertility, as evidenced by significant increases in N (1.6–2.3-fold) and K levels. The levels of tyrosine-like fraction, C4, and the biological index (BIX) in soil dissolved organic matter increased upon the introduction of ZnO NPs into CSS, indicating that microbial activity and nutrient cycling have been enhanced. However, the concentrations of As and Pb in rice grains were significantly increased by the elevated levels of ZnO NPs in CSS, reaching up to 1.5 and 2.3 times the control levels, respectively. This increased hazard quotients and pushed hazard indexes beyond acceptable levels, suggesting that rice consumers are at significant health risk. This study underscores the critical need for more stringent and comprehensive regulatory frameworks to ensure the safety of CSS application in crop production and to manage the intricacies of NP use in agriculture.