Organic amendments minimize the migration of potentially toxic elements in soil-plant system in degraded agricultural lands

The contamination of agricultural soil with potentially toxic elements (PTEs) such as cadmium (Cd), lead (Pb), chromium (Cr), zinc (Zn), nickel (Ni), and copper (Cu) persists and intensifies in food crops posing a risk to human health. When used as effective soil manures, biomass conversion to organic amendments can help to deal with this deteriorating problem and, at the same time, remediate PTEs within contaminated soil. The present study compared the potential of orange peel-derived biochar (OPDBC) and poultry manure (PM) toward reducing the bioavailability of PTEs when they are applied to degraded agricultural soil (DAS). It further evaluated PTEs bioaccumulation in okra (Abelmoschus esculentus L.) and the associated health risks. The DAS was amended with OPDBC and PM at 1%, 3%, and 5% application rates, and okra was grown in these modified soils in pots (2.5 kg soils each). Compared to control (contaminated soil), OPDBC treatments significantly reduced Cd availability, reduced Cd uptake to plants (21-37%), followed by Ni (18-27%), and increased okra plant biomass (15-39%) and fruits weight (40-93%). PM effectiveness was lower than OPDBC and reduced Cd uptake (8-33%) and increased vegetative biomass and fruit yield (3-22% and 13-33%, respectively). OPDBC 5% demonstrated the best results in terms of immobilization and reduction of Cd uptake by plants (37%) and fruits (41%). The contamination factor and pollution load index (PLI) of PTEs showed low pollution level (PLI <1) in terms of PTEs except Cd, in OPDBC treatments, as compared to PM and control. When compared to other PTEs, the Cd bioavailability in okra fruits decreased with 5% application rate of OPDBC. In the current study, OPDBC5 decreased the daily intake and health risk index (HRI(<)1) of Cd and other selected PTEs. The total hazard index (THI) values of selected PTEs were relatively lower for the adults than the children, thereby reduced by OPDBC and PM applications, while OPDBC5 reduced the incremental lifetime cancer risk (ILTCR) of Cd from (25-41%) via okra fruits consumption for both the adults and children when compared with 1%, 3%, and control treatments. The study results show that among amendments, orange peel waste conversion to biochar as OPDBC amendment and its addition to DAS should be a viable alternate method that could mitigate the health risk by remediating and immobilizing the PTEs like Cd and minimize its subsequent accumulation in vegetables.