Size-dependent characterisation of historical gold mine wastes to examine human pathways of exposure to arsenic and other potentially toxic elements

Legacy effects of historical gold mining on floodplains of an Australian river

The gold rush at the end of the nineteenth century in south-eastern Australia resulted in the mobilization and re-deposition of vast quantities of tailings that modified the geomorphology of the associated river valleys. Previous studies of contamination risk in these systems have either been performed directly on mine wastes (e.g., battery sand) or at locations close to historical mine sites but have largely ignored the extensive area of riverine alluvial deposits extending downstream from gold mining locations. Here we studied the distribution of contaminant metal(loids) in the Loddon River catchment, one of the most intensively mined areas of the historical gold-rush period in Australia (1851-1914). Floodplain alluvium along the Loddon River was sampled to capture differences in metal and metalloid concentrations between the anthropogenic floodplain deposits and the underlying original floodplain. Elevated levels of arsenic up to 300 mg-As/kg were identified within the anthropogenic alluvial sediment, well above sediment guidelines (ISQG-high trigger value of 70 ppm) and substantially higher than in the pre-mining alluvium. Maximum arsenic concentrations were found at depth within the anthropogenic alluvium (plume-like), close to the contact with the original floodplain. The results obtained here indicate that arsenic may pose a significantly higher risk within this river catchment than previously assessed through analysis of surface floodplain soils. The risks of this submerged arsenic plume will require further investigation of its chemical form (speciation) to determine its mobility and potential bioavailability. Our work shows the long-lasting impact of historical gold mining on riverine landscapes.

Arsenic, cadmium, lead, antimony bioaccessibility and relative bioavailability in legacy gold mining waste

Bioaccessibility and relative bioavailability of As, Cd, Pb and Sb was investigated in 30 legacy gold mining wastes (calcine sands, grey battery sands, tailings) from Victorian goldfields (Australia). Pseudo-total As concentration in 29 samples was 1.45-148-fold higher than the residential soil guidance value (100 mg/kg) while Cd and Pb concentrations in calcine sands were up to 2.4-fold and 30.1-fold higher than the corresponding guidance value (Cd: 20 mg/kg and Pb: 300 mg/kg). Five calcine sands exhibited elevated Sb (31.9-5983 mg/kg), although an Australian soil guidance value is currently unavailable. Arsenic bioaccessibility (n = 30) and relative bioavailability (RBA; n = 8) ranged from 6.10-77.6% and 10.3-52.9% respectively. Samples containing > 50% arsenopyrite/scorodite showed low As bioaccessibility (<20.0%) and RBA (<15.0%). Co-contaminant RBA was assessed in 4 calcine sands; Pb RBA ranged from 73.7-119% with high Pb RBA associated with organic and mineral sorbed Pb and, lower Pb RBA observed in samples containing plumbojarosite. In contrast, Cd RBA ranged from 55.0-67.0%, while Sb RBA was < 5%. This study highlights the importance of using multiple lines of evidence during exposure assessment and provides valuable baseline data for co-contaminants associated with legacy gold mining activities.

Uptake and Toxicity of Respirable Carbon-Rich Uranium-Bearing Particles: Insights into the Role of Particulates in Uranium Toxicity

Particulate matter (PM) presents an environmental health risk for communities residing close to uranium (U) mine sites. However, the role of the particulate form of U on its cellular toxicity is still poorly understood. Here, we investigated the cellular uptake and toxicity of C-rich U-bearing particles as a model organic particulate containing uranyl citrate over a range of environmentally relevant concentrations of U (0-445 μM). The cytotoxicity of C-rich U-bearing particles in human epithelial cells (A549) was U-dose-dependent. No cytotoxic effects were detected with soluble U doses. Carbon-rich U-bearing particles with a wide size distribution (<10 μm) presented 2.7 times higher U uptake into cells than the particles with a narrow size distribution (<1 μm) at 100 μM U concentration. TEM-EDS analysis identified the intracellular translocation of clusters of C-rich U-bearing particles. The accumulation of C-rich U-bearing particles induced DNA damage and cytotoxicity as indicated by the increased phosphorylation of the histone H2AX and cell death, respectively. These findings reveal the toxicity of the particulate form of U under environmentally relevant heterogeneous size distributions. Our study opens new avenues for future investigations on the health impacts resulting from environmental exposures to the particulate form of U near mine sites.

Bioaccessibility of potentially toxic elements in mine residue particles

Mining companies used to abandon tailing heaps in countryside regions of Mexico and other countries. Mine residues (MRs) contain a high concentration of potentially toxic elements (PTE). The wind can disperse dust particles (<100 μm) and once suspended in the atmosphere, can be ingested or inhaled; this is a common situation in arid climates. Nowadays, there is little information on the risk of exposure to PTEs from particulate matter dispersed by wind. The pseudo-total PTE in bulk and fractionated MR after aqua regia digestion, the inhalable bioaccessibility with Gamble solution (pH = 7.4), and the gastric bioaccessibility with 0.4 M glycine solution at pH 1.5 were determined. As and Pb chemical species were identified by X-ray absorption near-edge structure (XANES) spectroscopy. The highest rate of dispersion was observed with 74-100 μm particles (104 mg m-2 s-1); in contrast, particles <44 μm had the lowest rate (26 mg m-2 s-1). The highest pseudo-total As (35 961 mg kg-1), Pb (3326 mg kg-1), Cd (44 mg kg-1) and Zn (up to 4678 mg kg-1) concentration was in the <20 μm particles and As in the 50-74 μm (40 236 mg kg-1) particles. The highest concentration of inhaled bioaccessible As (343 mg kg-1) was observed in the <20 μm fraction and the gastric bioaccessible As was 744 mg kg-1, Pb was 1396 mg kg-1, Cd was 19.2 mg kg-1, and Zn was 2048 mg kg-1. The predominant chemical As species was arsenopyrite (92%), while 54% of Pb was in the adsorbed form. Erodible particle matter is a potential risk for humans in case of inhalation or ingestion.

Characterization of a mine legacy site: an approach for environmental management and metals recovery

The characterization of historical mine tailings provides important information for land-management decisions, in particular when considering potential reprocessing activities or the development of an environmental protection program. In addition, outcomes from such characterization may define the scope for a more detailed investigation. The present work describes the characterization of the waste material from the Cabeço do Pião tailings impoundment performed within the project ReMinE: Improve Resource Efficiency and Minimize Environmental Footprint. The purpose of the work was to investigate alternative mine waste management options such as the extraction of valuable resources from an environmental liability. The study involved the collection of 41 samples at different locations at two different depths, physical and chemical characterization of the wastes, natural leaching tests, and potential for acid generation. The results showed that, apart from the potential instability of the dyke (with an average slope of 35°), the drained solutions flowing by percolation contain very small particles with high arsenic contents that are being incorporated into the river sediments. In addition, these very fine-grained materials are available for the transport by the wind creating secondary sources of environmental contamination. This data is fundamental for economic and environmental assessment of the two main alternatives, reprocessing or removal.

The soil-plant transfer of risk elements within the area of an abandoned gold mine in Libčice, Czech Republic

Abandoned gold mines are often suggested as potential sources of environmental pollution. Thus, the soils within the area of a gold mine in Libčice, Czech Republic, were monitored. Elevated element contents were found of As, Cd, Cu, Hg, Pb, and Zn. The risk assessment codes (RACs) indicated high environmental risk from soil Cd, and moderate risk from Zn, whereas the risk of As, Cu, and Pb was low. It was supported by the analysis of 134 samples of aboveground biomass of plants, where the levels of As and Pb were below the detection limit. For Cd, the plant uptake reflected the high mobility of this element, where the bioaccumulation factors (BAFs) varied in range 0.032 (Fragaria vesca) and 1.97 (Circia arvensis). For 11% of samples the BAF values for Cd exceeded 1. For Hg, although the maximum BAF did not exceed 0.37 (Lotus corniculatus), the Hg contents in plants occasionally exceeded the threshold limits for Hg contents in raw feedstuffs. The investigated gold mine does not represent a direct environmental risk, but the fate of Cd and Hg in the soils and plants suggests the necessity of a deeper understanding of the penetration of these elements into the surrounding environment.

VegeSafe: a community science program generating a national residential garden soil metal(loid) database

VegeSafe is a national community science initiative aimed at characterising soils in Australian residential gardens and community gardens. The program has been operating for over 5 years and has generated soil metal(loid) data from over 8600 residential garden and community garden soil samples, submitted by almost 2000 community scientists. The VegeSafe program represents the largest archive of soil metal(loid) data and associated metadata for residential garden soils in Australia. Samples were collected across Australia, with 61% of samples collected from NSW (n = 5284), Victoria (VIC) 20% (n = 1688) of samples and Queensland (QLD) 7% (n = 592) of samples. Soil metal(loid) data obtained by analysis of bulk soil samples by portable X-ray florescence spectrometry (pXRF) for As, Cu, Cr Mn, Pb and Zn showed spatial patterns of greater soil metal(loid) concentrations around city areas, particularly in NSW and VIC. The Australian Health Investigation Levels for low-density residential land uses (HIL-A) were used in this study as guideline values for soil metal(loid) concentrations. Overall, there was a relatively small number of HIL-A exceedances in the dataset, with most metal(loid)s exceeding their HIL-A concentration in < 5% of incidences. The notable exception to this was for Pb, which had HIL-A (300 mg/kg) exceeded in 27% (n = 1427) of samples in NSW, 17% (n = 280) in VIC and 10% (n = 61) in QLD. Through the power of community engagement and community science, the VegeSafe program presents an unprecedented insight into soil metal(loid) concentrations in Australian residential gardens.

Mining and Planetary Health: A GeoHealth-Led Special Collection

Mining is a vital part of the global economy, but unmanaged releases of mine wastes can affect the health of humans, ecosystems, water, soil and Earth surface environments (e.g., rivers and estuaries). New technological developments and multidisciplinary collaborations are leading to new insights into the relationship between mining and the health of the Earth. In recognition of the importance of this topic, GeoHealth is leading in the creation of a special collection of papers on the theme of Mining and Planetary Health, to summarize the current state of knowledge, outline topics for urgent action and further research, and highlight positive efforts in environmental and health protection. Submissions are invited from researchers investigating the impacts of mining at the intersection of the Earth and environmental sciences and human, ecosystem, and planetary health.

In vitro assessment of arsenic mobility in historical mine waste dust using simulated lung fluid

Exposure studies have linked arsenic (As) ingestion with disease in mining-affected populations; however, inhalation of mine waste dust as a pathway for pulmonary toxicity and systemic absorption has received limited attention. A biologically relevant extractant was used to assess the 24-h lung bioaccessibility of As in dust isolated from four distinct types of historical gold mine wastes common to regional Victoria, Australia. Mine waste particles less than 20 µm in size (PM₂₀) were incubated in a simulated lung fluid containing a major surface-active component found in mammalian lungs, dipalmitoylphosphatidylcholine. The supernatants were extracted, and their As contents measured after 1, 2, 4, 8 and 24 h. The resultant As solubility profiles show rapid dissolution followed by a more modest increasing trend, with between 75 and 82% of the total 24-h bioaccessible As released within the first 8 h. These profiles are consistent with the solubility profile of scorodite, a secondary As-bearing phase detected by X-ray diffraction in one of the investigated waste materials. Compared with similar studies, the cumulative As concentrations released at the 24-h time point were extremely low (range 297 ± 6-3983 ± 396 µg L^-1), representing between 0.020 ± 0.002 and 0.036 ± 0.003% of the total As in the PM₂₀.

Evaluation of environmental and anthropogenic influences on ambient background metal and metalloid concentrations in soil

There has been a global shift in environmental risk assessment towards quantifying ambient background concentrations of metals/metalloids in soil. Whilst bedrock has been shown to be a key driver of metal/metalloid variability in soil, few researchers have assessed controls of ambient background concentrations in soils of similar bedrock. A soil survey was undertaken ofGreater Melbourne, Greater Geelong, Ballarat and Mitchell in Victoria, Australia for elements of potential environmental concern: As, Cd, Cr, Cu, Ni, Hg, Pb and Zn. Samples (n=622) were collected from surface (0 to 0.1m) and sub-surface (0.3 to 0.6m) soils, overlying Tertiary-Quaternary basalt, Tertiary sediments and Silurian siltstone and sandstone. In addition, background soil data from open-source environmental assessment reports (n=5512) were collated to support the understanding of natural enrichment, particularly at depths >0.6m. Factor analysis, supported by correlation analysis and auxiliary geo-spatial data, provided an improved understanding of where and how background metal/metalloid enrichment occurs in the environment. Weathering during paleoclimates was the predominant influence of background metal/metalloid variability in soils overlying similar bedrock. Other key influences of metal/metalloid variability in soil included hydraulic leaching of alkali elements, biological cycling, topography and alluvial transfer of silt and sand from mineralised regions. In addition, urbanisation positively correlated with Pb and Zn concentrations in surface soils suggesting that anthropogenic activities may have resulted in diffuse Pb and Zn contamination of urban soil.

Trace metal content in inhalable particulate matter (PM2.5-10 and PM2.5) collected from historical mine waste deposits using a laboratory-based approach

Mine wastes and tailings are considered hazardous to human health because of their potential to generate large quantities of highly toxic emissions of particulate matter (PM). Human exposure to As and other trace metals in PM may occur via inhalation of airborne particulates or through ingestion of contaminated dust. This study describes a laboratory-based method for extracting PM_2.5-10 (coarse) and PM_2.5 (fine) particles from As-rich mine waste samples collected from an historical gold mining region in regional, Victoria, Australia. We also report on the trace metal and metalloid content of the coarse and fine fraction, with an emphasis on As as an element of potential concern. Laser diffraction analysis showed that the proportions of coarse and fine particles in the bulk samples ranged between 3.4-26.6 and 0.6-7.6 %, respectively. Arsenic concentrations were greater in the fine fraction (1680-26,100 mg kg^-1) compared with the coarse fraction (1210-22,000 mg kg^-1), and Co, Fe, Mn, Ni, Sb and Zn were found to be present in the fine fraction at levels around twice those occurring in the coarse. These results are of particular concern given that fine particles can accumulate in the human respiratory system. Our study demonstrates that mine wastes may be an important source of metal-enriched PM for mining communities.