Incorporating oral, inhalation and dermal bioaccessibility into human health risk characterization following exposure to Chromated Copper Arsenate (CCA)-contaminated soils.

Exposure to potentially toxic metal(loid)s (PTMs) in soil may happen via ingestion, inhalation, and dermal pathway. A more accurate risk characterization should consider PTM bioavailability. Using ten soil samples collected in the Montreal area (Canada) near CCA-treated utility poles, this study aims to characterize non-carcinogenic and carcinogenic human health risks associated with As, Cr, Cu, Pb, and Zn through a multi-pathway exposure approach. This innovative study incorporates, for the first time, the bioaccessible fraction of the metal(loid)s for three exposure routes and two different scenarios. For the residential and industrial scenarios, the oral and dermal pathways yielded a hazard index (HI) much higher than 1 with and without bioaccessibility considerations (range 1.7 - 349 without bioaccessibility and 0.8-134 with bioaccessibility), whereas the inhalation pathway caused a lower hazard (HI < 1). For the dermal pathway, the hazard quotient was higher when bioaccessibility of field-collected samples was considered due to inherent assumptions from the US EPA soil approach to calculate the dermal dose. For carcinogenic risk, As and Pb were the most significant contributors to risk for the oral pathway, followed by the same elements for the dermal pathway. The overall carcinogenic risk was higher than the acceptable risk ( > 10-4) with and without bioaccessibility considerations (range 1.9E-4 - 9.6E-3 without bioaccessibility and 6.8E-5 - 3.8E-3 with bioaccessibility). Bioaccessibility tests provide a more accurate assessment of exposure to PTMs compared to total concentrations in soils.

Response of soil microbial activities and ammonia oxidation potential to environmental factors in a typical antimony mining area.

Mining, smelting and tailing deposition activities can cause metal(loid) contamination in surrounding soils, threatening ecosystems and human health. Microbial indicators are sensitive to environmental factors and have a crucial role in soil ecological risk assessment. Xikuangshan, the largest active antimony (Sb) mine in the world, was taken as the research area. The soil properties, metal(loid) contents and microbial characteristics were investigated and their internal response relationships were explored by multivariate statistical analysis. The assessment of the single pollution index and Nemerow synthetic pollution index (PN) showed that the soils were mainly polluted by Sb, followed by Cd and As, in which sampling site S1 had a slight metal(loid) pollution and the other sampling sites suffered from severe synthetic metal(loid) pollution. The microbial characteristics were dissimilar among sampling points at different locations from the mining area according to hierarchical cluster analysis. The correlation analysis indicated that fluorescein diacetate hydrolase, acid phosphatase, soil basal respiration and microbial biomass carbon were negatively correlated with PN, indicating their sensitivity to combined metal(loid) contamination; that dehydrogenase was positively correlated with pH; and that urease, potential ammonia oxidation and abundance of ammonia-oxidizing bacteria and archaea were correlated with N (nitrogen) contents. However, ß-glucosidase activity had no significant correlations with physicochemical properties and metal(loid) contents. Principal components analysis suggested bioavailable Sb and pH were the dominant factors of soil environment in Xikuangshan Sb mining area. Our results can provide a theoretical basis for ecological risk assessment of contaminated soil.

Biological roles of soil microbial consortium on promoting safe crop production in heavy metal(loid) contaminated soil: A systematic review.

Heavy metal(loid) (HM) pollution of agricultural soils is a growing global environmental concern that affects planetary health. Numerous studies have shown that soil microbial consortia can inhibit the accumulation of HMs in crops. However, our current understanding of the effects and mechanisms of inhibition is fragmented. In this review, we summarise extant studies and knowledge to provide a comprehensive view of HM toxicity on crop growth and development at the biological, cellular and the molecular levels. In a meta-analysis, we find that microbial consortia can improve crop resistance and reduce HM uptake, which in turn promotes healthy crop growth, demonstrating that microbial consortia are more effective than single microorganisms. We then review three main mechanisms by which microbial consortia reduce the toxicity of HMs to crops and inhibit HMs accumulation in crops: 1) reducing the bioavailability of HMs in soil (e.g. biosorption, bioaccumulation and biotransformation); 2) improving crop resistance to HMs (e.g. facilitating the absorption of nutrients); and 3) synergistic effects between microorganisms. Finally, we discuss the prospects of microbial consortium applications in simultaneous crop safety production and soil remediation, indicating that they play a key role in sustainable agricultural development, and conclude by identifying research challenges and future directions for the microbial consortium to promote safe crop production.

Using Mediterranean Native Plants for the Phytoremediation of Mining Sites: An Overview of the Past and Present, and Perspectives for the Future.

Mining exploitation in the Mediterranean Basin has left evident scars on the environment, and poses serious risks for human health and biodiversity, especially when mine wastes are left abandoned. This review analysed the main issues of metal(loid)s pollution related to mine exploitation in the Mediterranean Basin. Here, a list of Mediterranean native plant species studied for phytoremediation is given and, considering their biological forms, vegetational types, and ecology, we categorised them into halotolerant and hydro/hygrophilous vegetation, annual and perennial meadows, garrigues and maquis, and high maquis and woods. The main conclusions of the review are as follows: (1) plant communities established on mine environments are often rich in endemic taxa which ensure a high biodiversity and landscape value, and can help in the psychophysical health of local inhabitants; (2) political and land management should take greater account of the use of native plants for the remediation of contaminated soils; (3) a multidisciplinary approach that includes, among others, studies on biochemical response to metal(loid)s as well as the application of innovative soil amendments gives better results; (4) phytoextraction applications require a detailed recovery plan that takes into consideration several issues, including the negative influence on biodiversity due to extensive use of monotypic plantations, disposal of harvested hazardous plants, and the risk of phytoextracts entering the food chain; and (5) more studies are necessary to increase knowledge and to detect suitable species-especially halophytic ones-for phytoremediation purposes.

Preliminary Screening of Soils Natural Radioactivity and Metal(loid) Content in a Decommissioned Rare Earth Elements Processing Plant, Guangdong, China.

Radiological aspects such as natural radioactivity of 238U, 232Th, 226Ra, 40K combined with potentially toxic metal(loid) (PTM) distribution features were seldom simultaneously investigated in rare earth element (REE) processing activities. This work was designed to investigate the distribution levels of natural radioactivity, air-absorbed dose rate of γ radiation as well as PTMs at a typical REE plant in Guangdong, China. Ambient soils around REE processing facilities were sampled, measured and assessed. The natural radioactivity of radionuclides of the samples was determined using a high-purity germanium γ-energy spectrometer while the air-absorbed dose rate of γ radiation was measured at a height of 1 m above the ground using a portable radiometric detector. The PTM content was measured by inductively coupled plasma mass spectrometry (ICP-MS). The results showed that the specific activities of the radionuclides ranged from 80.8 to 1990.2, 68.2 to 6935.0, 78.4 to 14,372.4, and 625.4 to 2698.4 Bq·kg-1 for 238U, 226Ra, 232Th, and 40K, respectively, representing overwhelmingly higher activity concentrations than worldwide soil average natural radioactivity. The radium equivalent activity and external hazard index of most samples exceeded the limits of 370 Bq·kg-1 and 1, respectively. The measured air-absorbed dose rate of γ radiation was in a range of 113~4004 nGy·h-1, with most sites displaying comparatively higher values than that from some other REE-associated industrial sites referenced. The content levels of PTMs of Cu, Ni, Zn, Mn, Pb, Cd, Cr, and As were 0.7~37.2, 1.8~16.9, 20.4~2070.5, 39.4~431.3, 2.3~1411.5, 0.1~0.7, 6.7~526.1, and 59.5~263.8 mg·kg-1, respectively. It is important to note that the PTM contents in the studied soil samples were 2.1~5.4 times higher for Zn-As and 1.4 times higher for Pb than the third level of the China soil standard while 2.5~13 times higher for Zn-As and 1.2 times higher for Pb than Canadian industry standard. The findings call for subsequent site remediation to secure the ecological environment and human health after the REE processing plant was decommissioned.

Trace metal(loid) mobility in waste deposits and soils around Chadak mining area, Uzbekistan.

The assessment of potential trace metal(loid) contamination in tailing dumps and soils was characterized in the Chadak mining area (Uzbekistan). Concentrations of trace elements (V, Cr, Co, Ni, Cu, Zn, As, Cd, Sb, Pb) were determined by X-ray fluorescence analysis and compared with background and intervention values (IV). The concentrations of As, Zn, Sb, and Pb were higher in the abandoned than in the active tailing dump, ranging from 42-1689mg/kg for As, 73-332mg/kg for Zn, 14-1507mg/kg for Sb, and 27-386mg/kg for Pb. Selective extractions were applied in order to assess the mobility and availability of trace metal(loid)s in samples. Oxyanion-forming elements such as As and Sb were immobilized by Fe oxides, although to some extent also extractable with acetic acid and soluble-in-water forms were detected, indicating potential bioavailability that can impose a potential toxicity risk for the environment. Selective extractions data also showed that Zn and Pb were relatively immobile, although in higher contamination sites significant amounts of these elements were also extractable with acetic acid. In tailing materials Zn and Pb mobility were negatively correlated by the cation-exchange capacity (CEC) and clay content, indicating the importance of these factors in the reduction of the potential toxicity for these elements. Total concentration of As, Sb, and Pb were also negatively correlated with soil pH, indicating that the oxidation process of sulphide tailings and thus the generation of acidic conditions may lead to release of contaminants over time. However, due to the calcium carbonate content, the acid neutralization capacity of the tailings is not yet exhausted and contaminant concentrations in soil-pore water are still relatively low. The results of our investigation suggest that environmental risk associated with these wastes in semi-arid climate is therefore not a short-term problem but rather requires constant monitoring and additional ecotoxicological studies.