Reduction of Cd2+ and Pb2+ Bioavailability in Contaminated Soil Treated with Sisal Residues (Agave sisalana)

Biosorption is a technique that uses materials of biological origin to accumulate contaminants and represents an alternative for the treatment of soils contaminated by heavy metals. In our study, we analyzed the bioavailability of Cd2+ and Pb2+ in an Alfisol after the application of sisal residues (Agave sisalana) and related the adsorption of these ions with the characteristics of the residues. In a greenhouse experiment, we exposed the Sorghum bicolor plants to different types (mucilage (MUC), fibrils (FIB), and fiber dust (FD)) and levels of residues of sisal (0.0, 0.5, 1.0, 2.0, and 3.0% w/w) for 60 days. The application of FIB and MUC residues in the soil was able to reduce by up to 40% the available levels of Cd2+ and Pb2+ in the soil solution, regardless of the applied dose. In addition to the lower levels and accumulations of Cd in the roots and shoots, the application of residues increased dry mass of the plants. On the other hand, plants grown in soil contaminated by Pb2+ and which received application of the residues did not show symptoms of phytotoxicity; this is justified by the lower content and accumulation of Pb2+ in the plants that had a translocation factor < 1. Cd2+ was strongly correlated with all lignocellulosic parameters, while Pb2+ showed a lower correlation. Our results suggest that the application of residues decreases the availability of Cd2+ and Pb2+ in the soil solution, alleviates phytotoxicity, and maximizes the development of Sorghum bicolor.

Automated summary

Biosorption is a technique used to treat heavy metal-contaminated soils by using biological materials to accumulate contaminants. This study investigated the bioavailability of Cd2+ and Pb2+ in an Alfisol after applying sisal residues and correlated the adsorption of these ions with the characteristics of the residues. The application of sisal residues in the soil reduced the available levels of Cd2+ and Pb2+ by up to 40%, regardless of the dosage, and increased the dry mass of Sorghum bicolor plants. The residues also alleviated phytotoxicity caused by Pb2+ contamination. Cd2+ showed a strong correlation with lignocellulosic parameters, while Pb2+ showed a lower correlation.