Contamination, oral bioaccessibility and human health risk assessment of thallium and other metal(loid)s in farmland soils around a historic TlHg mining area.

In this study, tweenty-nine soil samples were collected from a historic TlHg mining area, located in southwest Guizhou, China. Total concentrations of metal(loid)s in soils and in vitro extracts were analysed by ICP-MS, and the bioaccessibility of metal(loid)s was conducted by two often used in vitro extraction methods, Simplified bioaccessibility Extraction Test (SBET) and Physiologically Based Extraction Test (PBET). The health risk assessment based on total concentrations of metal(loid)s, bioaccessibility of SBET and PBET through soil ingestion were investigated. Results indicated that the collected cultivated soils contained elevated concentrations of Tl (44.8 ± 67.7 mg kg-1), Hg (110 ± 193 mg kg-1), As (84.4 ± 89.2 mg kg-1) and Sb (14.8 ± 24.8 mg kg-1), exceeding the regional background values of Guizhou province, China and the Chinese farmland risk screening values. However, the bioaccessibility of Tl, Hg, As and Sb were relatively low, usually less than 30% for most samples and varied greatly among metal(loid)s and sampling sites. The average bioaccessibility values of Tl, Hg, As and Sb by SBET were lower than those by PBET. The non-carsinogenic risk (HQ and HI) and Carcinogenic Risk (CR) values were significantly reduced when incorporating the bioaccessibiltiy of metal(loid)s into health risk assessment. It is worth noting that the health risk to children exceeded adults. Moreover, Tl and As contributed the most to the risk, indicating that more attention should be paid on Tl and As during the daily environmental regulation and management of contaminated soils in Lanmuchang.

Energy and environmental impact assessment of a passive remediation bioreactor for antimony-rich mine drainage.

Industrial processes, such as smelting and mining, lead to antimony (Sb) contamination, which poses an environmental and human health risk. In this study, the energy consumption and environmental impacts of a passive biological treatment system were quantitatively evaluated using life cycle assessment (LCA), and the results were compared with that of an adsorption purification system. The results showed that the biosystem had a lower energy consumption compared with the adsorption system, with an energy savings of 27.39%. The environmental impacts of the bioreactor were also lower regarding acidification, ecotoxicity, carcinogens, climate change, resource depletion, and respiratory effects. The construction resulted in the most energy consumption (99%) for the passive bioreactor. Therefore, adopting environmentally friendly construction materials could make the biosystem a more energy-efficient option. Results demonstrated that the bioreactor in this research can have great potential for Sb mine drainage applications in terms of energy savings and environmental remediation without diminishing performance. The study findings can be useful for deciding the most energy effective process for mine drainage remediation. In addition, the identification of the energy and environmental impacts of the processes provide valuable information for the design of future systems that consume less materials and utilize new construction materials.

Pollution and health risk assessment of toxic metal(loid)s in soils under different land use in sulphide mineralized areas.

Toxic metal(loid) pollution in sulphide mineralized area has been increasingly concerned. In the present study, the pollution characteristics and the health risk of Hg, As, Tl and other metal(loid)s in soils under different land use, from a rural area impacted by Tl-Hg-rich sulphide mineralization, were assessed using statistical analysis, enrichment factor (EF), potential ecological risk index (RI) and health risk assessment model. The results showed that Tl, Hg and As were highly enriched in the mine area due to the historic sporadic mining activities, and Tl, Hg and Sb were enriched in the peripheral area. Hg and Tl pollution in soils of the mine area impacted by past mining activities posed high ecological risk. High contents and enrichment of Tl and Hg in forest/grass land had a greater impact on the ecological risk in the mine area; whereas Tl and Hg in the grain land and vegetable land dominated the soil ecological risk in the peripheral area. Human health risk assessment indicated that children are more sensitive and vulnerable to toxic metal(loid)s in soils than the adults. Hg, Tl and As have potential non-carcinogenic risk to local children and adults. The HQ levels for different exposure pathways of toxic metal(loid)s were in the order of ingestion > dermal contact > air inhalation for Tl and As, and dermal contract > ingestion > air inhalation for Hg. For carcinogenic risk, all the mean CR values of ingestion in the mine area were higher than 10-4, indicating seriously potential risk. The descending order of ILCR via different pathways was the same as the HQ, for which ingestion was predominant, followed by dermal and air inhalation. The findings may help provide basic knowledge and guidelines for toxic metal(loid) pollution remediation in similar sulphide mineralized areas.

Remediation of antimony-rich mine waters: Assessment of antimony removal and shifts in the microbial community of an onsite field-scale bioreactor.

An on-site field-scale bioreactor for passive treatment of antimony (Sb) contamination was installed downstream of an active Sb mine in Southwest China, and operated for one year (including a six month monitoring period). This bioreactor consisted of five treatment units, including one pre-aerobic cell, two aerobic cells, and two microaerobic cells. With the aerobic cells inoculated with indigenous mine water microflora, the bioreactor removed more than 90% of total soluble Sb and 80% of soluble antimonite (Sb(III)). An increase in pH and decrease of oxidation-reduction potential (Eh) was also observed along the flow direction. High-throughput sequencing of the small subunit ribosomal RNA (SSU rRNA) gene variable (V4) region revealed that taxonomically diverse microbial communities developed in the bioreactor. Metal (loid)-oxidizing bacteria including Ferrovum, Thiomonas, Gallionella, and Leptospirillum, were highly enriched in the bioreactor cells where the highest total Sb and Sb(III) removal occurred. Canonical correspondence analysis (CCA) indicated that a suite of in situ physicochemical parameters including pH and Eh were substantially correlated with the overall microbial communities. Based on an UPGMA (Unweighted Pair Group Method with Arithmetic Mean) tree and PCoA (Principal Coordinates Analysis), the microbial composition of each cell was distinct, indicating these in situ physicochemical parameters had an effect in shaping the indigenous microbial communities. Overall, this study was the first to employ a field-scale bioreactor to treat Sb-rich mine water onsite and, moreover, the findings suggest the feasibility of the bioreactor in removing elevated Sb from mine waters.