Leaching Mechanism and Health Risk Assessment of As and Sb in Tailings of Typical Antimony Mines: A Case Study in Yunnan and Guizhou Province, Southwest China

Review of Fe/Mn-based chemical stabilizers for remediating arsenic and antimony co-contaminated soil

Arsenic (As) and antimony (Sb) frequently co-occur in soil contaminated by mining, smelting and traffic emissions, creating an urgent need for effectively simultaneous remediation strategies. Although chemical stabilization has garnered significant attention for its high remediation efficiency, a systematic comparison of stabilization effects and mechanisms for As and Sb in co-contaminated soil remained unexplored. Iron-based materials are widely recognized as the most effective stabilizers for As and Sb in soil. Meanwhile, manganese-based materials, owing to their superior oxidizing capacity that maintains As and Sb in the less toxic pentavalent species, have also attracted considerable interest. Iron-manganese-based materials provide an efficient solution for stabilizing As and Sb in soil by synergistically combining the advantages of both iron and manganese components. This review therefore elaborated on the core stabilizers, including iron-, manganese-, and iron-manganese-based materials. The stabilization efficiencies and underlying mechanisms of As and Sb in soil were comprehensively examined, with key environmental factors also discussed in relation to their stabilization performance. As widely used soil amendments, raw biochar and clay materials demonstrate limited efficacy in stabilizing As and Sb in soil. However, they can be employed as functional modifiers to enhance the dispersion of iron or manganese particles, thereby improving stabilization performance. While current progress is systematically evaluated, the development of stabilizers enabling simultaneous immobilization of As and Sb remains a critical research priority for future research.

The metal release and transformation mechanisms of V-Ti magnetite tailings: Role of the alternate flooding and drying cycles and organic acids

V-Ti magnetite tailings (VTMTs) contain various heavy metals, such as Fe, Mn, V, Co, and Ni. The groundwater pollution caused by the tailing metal release has become a local environmental concern. Although studies have demonstrated the influence of alternate flooding and drying cycles (FDCs) on metal form and mobility in minerals, little was known about whether FDCs affect the metal release of VTMTs and the transformation of released metals. This study investigated the metal release kinetics of VTMTs and the metal transformation under FDCs in the absence and presence of acid rain (sulfuric and nitric acids) and bio-secreted organic acids (acetic, oxalic, and citric acids). The results showed that FDCs promoted metal release whether or not acids were present. The maximum released concentrations of V, Mn, Fe, Co, and Ni were as high as 78.63 mg L-1,1.47 mg L-1, 67.96 μg L-1, 1.34 mg L-1, and 0.80 mg L-1, respectively, under FDCs and citric acids. FDCs enhanced the tailing metal release by increasing the metal labile fraction proportion. However, the concentrations of released Fe, Mn, V, Co, and Ni all gradually decreased due to their (co-)precipitation. These precipitates conversely inhibited the subsequent mineral dissolution by covering the tailing surface. FDCs also enhanced the tailings' porosities by 2.94%-9.94%. The mineral dissolution, expansion and shrinkage, and changes in tension destroyed the tailing microstructure during FDCs. This study demonstrated the low metal pollution risk of VTMTs under FDCs, either in acid rain or bio-secreted organic acids. However, the increase in tailing porosity should be seriously considered as it would affect the tailing pond safety.

Environmental Toxicology and Human Health

Humans and animals may be exposed on a continuous daily basis to a mixture of environmental contaminants that may act on several organ systems through differing mechanisms [...].

Risk Assessment and Risk Reduction of Ptaquiloside in Bracken Fern

This study was conducted to determine the optimal boiling time to reduce ptaquiloside (PTA) and to carry out a risk assessment for PTA, a representative toxic substance found in bracken fern (BF; Pteridium aquilinum), which is frequently consumed as food in East Asian countries. High-performance liquid chromatography showed that the concentration of PTA in BF was reduced by up to 99% after boiling for 20 min. Risk assessment results showed that the cancer margin of exposure (MOE; ≥ 25,000 = safe) to PTA for an average daily exposure scenario after boiling BF for 20 min was considered safe. In addition, the non-cancer MOE (≥ 300 = safe) to PTA under an average daily exposure scenario after BF boiling for 20 min was considered safe. However, human exposure to PTA was considered unsafe under the non-boiled BF exposure and maximum daily exposure scenarios. Therefore, boiling BF for at least 20 min is recommended before consumption, to reduce exposure to PTA as much as possible.