Risk assessment of antimony-arsenic contaminated soil remediated using zero-valent iron at different pH values combined with freeze-thaw cycles.

Soil in mining wastelands is seriously polluted with heavy metals. Zero-valent iron (ZVI) is widely used for remediation of heavy metal-polluted soil because of its excellent adsorption properties; however, the remediation process is affected by complex environmental conditions, such as acid rain and freeze-thaw cycles. In this study, the effects of different pH values and freeze-thaw cycles on remediation of antimony (Sb)- and arsenic (As)-contaminated soil by ZVI were investigated in laboratory simulation experiments. The stability and potential human health risks associated with the remediated soil were evaluated. The results showed that ZVI has a significant stabilizing effect on Sb and As in both acidic and alkaline soils contaminated with dual levels of Sb and As, and the freeze-thaw process in different pH value solution systems further enhances the ability of ZVI to stabilize Sb and As, especially in acidic soils. However, it should be noted that apart from the pH=1.0 solution environment, ZVI's ability to stabilize As is attenuated under other circumstances, potentially leading to leaching of its unstable form and thereby increasing contamination risks. This indicates that the F1 (2% ZVI+pH=1 solution+freeze-thaw cycle) processing exhibits superior effectiveness. After F1 treatment, the bioavailability of Sb and As in both soils also significantly decreased during the gastric and intestinal stages (about 60.00%), the non-carcinogenic and carcinogenic risks of Sb and As in alkaline soils are eliminated for children and adults, with a decrease ranging from 60.00% to 70.00%, while in acidic soil, the non-carcinogenic and carcinogenic risks of As to adults and children is acceptable, but Sb still poses non-carcinogenic risks to children, despite reductions of about 65.00%. These findings demonstrate that soil pH is a crucial factor influencing the efficacy of ZVI in stabilizing Sb and As contaminants during freeze-thaw cycles. This provides a solid theoretical foundation for utilizing ZVI in the remediation of Sb- and As-contaminated soils, emphasizing the significance of considering both pH levels and freeze-thaw conditions to ensure effective and safe treatment.

Bioaccessibility of antimony and arsenic in highly polluted soils of the mine area and health risk assessment associated with oral ingestion exposure.

In this study, the bioaccessibility and the human health risks of Sb and As in soils from Xikuangshan (XKS) Sb mine, Hunan, China were investigated using two commonly used in vitro extraction methods, Simplified Bioaccessibility Extraction Test (SBET) and Physiologically Based Extraction Test (PBET). Soils in the XKS Sb mine area were mainly co-contaminated by Sb (74.2-16,389; mean: 3061mgkg(-1)) and As (7.40-596; mean: 216mgkg(-1)). The bioaccessibility values of Sb and As in most cases were less than 30%, and the average bioaccessibility values of Sb and As were 5.89±6.44% and 2.13±2.55% for the SBET extraction; 7.83±9.82% and 6.62±6.37% for the PBET (Gastric) extraction; and 3.03±3.53% and 2.40±2.01% for the PBET (Intestinal) extraction, respectively. The bioaccessible Sb and As were significantly positively correlated with the total concentrations, but negatively correlated with the Fe, Al, Mn and organic matter (OM) contents in soils. Risk assessment results based on total concentrations might overestimate the risk existing in the studied area. After considering the bioaccessibility, the Hazard Quotient (HQ) values of Sb for most of the sampling sites and of As for all of the sampling sites became lower than 1. The Carcinogenic Risk (CR) values of As were also significantly reduced, 8.77E-06 and 1.74E-05 on average for the SBET and PBET methods, respectively. Considering the bioaccessibility can provide more applicable guidelines for risk assessments and more rational suggestions in the management of the soils contaminated with Sb and As.

Source identification and health risk assessment of metals in urban soils around the Tanggu chemical industrial district, Tianjin, China.

We conducted an investigation to identify the sources of metals in urban surface soils, and to assess the associated human health risks, around the Tanggu chemical industrial district, Tianjin, China. The metal concentrations and spatial distributions in 70 soil samples from the study area were determined. Pollution sources were identified using multivariate statistical analysis. They mainly attributed Cu, Pb, and Zn pollution to vehicular traffic and industrial discharges, Cd pollution to industrial activities and anthropogenic waste including industrial discharges, sewage sludge, and municipal solid waste, As and Hg pollution to coal combustion and point source emissions from the chemical industry, and Cr and Ni pollution to the soil parent material. Soil properties, particularly the organic matter content, were found to be important factors in the distribution and composition of metals. A health risk assessment showed that samples from the northwestern and southeastern parts of the study area may pose significant health risks to the population.