Effects of low-molecular-weight organic acids and manganese-modified biochar application sequences on the environmental risk of soil cadmium and arsenic.
Source: PubMed, NCBI / U.S. National Library of Medicine
Although manganese-modified biochar (MBC) effectively immobilizes Cd and As, the effects of low-molecular-weight organic acids (LA) on the performance and efficiency of Cd and As remediation in agricultural soils when co-applied with MBC in different application sequences remain unclear. This study examined the effects of LA on the MBC-mediated remediation of Cd/As-contaminated soil via the immersion of MBC in LA and LA-MBC to facilitate co-applications on contaminated soil using different application sequences. Results revealed that after LA immersion, the pH of MBC decreased by 0.14-2.10 units, accompanied by increases in electrical conductivity and Mn concentration. LA treatment also induced surface alterations characterized by cracks, depressions, reduced Mn oxide particles, and weakened MnOdiffraction peaks. These changes promoted soil Cd/As mobilization, increasing the TCLP-Cd by 40.2-110.1% and available As by 22.0-70.0%, thereby reducing MBC immobilization efficiency. Application sequence markedly affected the remediation outcomes, in order of decreasing remediation effectiveness: LA pre-addition > MBC pre-addition > simultaneous application. Simultaneous LA-MBC application led to a 12.4-62.6% decrease in the relative abundance of soil Gemmatimonadota. In contrast, the relative abundance of Firmicutes and Myxococcota increased by 47.0-184.9% and 39.5-273.8%, respectively. This study systematically assessed the effects of LA and MBC applicat
Abstract
Although manganese-modified biochar (MBC) effectively immobilizes Cd and As, the effects of low-molecular-weight organic acids (LA) on the performance and efficiency of Cd and As remediation in agricultural soils when co-applied with MBC in different application sequences remain unclear. This study examined the effects of LA on the MBC-mediated remediation of Cd/As-contaminated soil via the immersion of MBC in LA and LA-MBC to facilitate co-applications on contaminated soil using different application sequences. Results revealed that after LA immersion, the pH of MBC decreased by 0.14-2.10 units, accompanied by increases in electrical conductivity and Mn concentration. LA treatment also induced surface alterations characterized by cracks, depressions, reduced Mn oxide particles, and weakened MnOdiffraction peaks. These changes promoted soil Cd/As mobilization, increasing the TCLP-Cd by 40.2-110.1% and available As by 22.0-70.0%, thereby reducing MBC immobilization efficiency. Application sequence markedly affected the remediation outcomes, in order of decreasing remediation effectiveness: LA pre-addition > MBC pre-addition > simultaneous application. Simultaneous LA-MBC application led to a 12.4-62.6% decrease in the relative abundance of soil Gemmatimonadota. In contrast, the relative abundance of Firmicutes and Myxococcota increased by 47.0-184.9% and 39.5-273.8%, respectively. This study systematically assessed the effects of LA and MBC application sequences at different time intervals on the bioavailability of Cd/As. A "LA-MBC-microorganism" interaction model is proposed, demonstrating that LA structurally reshapes MBC and alters microbial communities, which may modulate Cd/As speciation. Based on pollutant behavior and amendment dynamics, a spatiotemporally optimized strategy is proposed to improve in situ remediation and reduce environmental risks.