摘要：Abstract
Environmental contamination from legacy mine waste deposits is a persistent problem due to the long history of hard‐rock mining. Sulfide ore deposits can contain elevated levels of toxic metal(loid)s that, when mobilized by weathering upon O2 and H2O infusion, can result in groundwater contamination. Dry climate and lack of vegetative cover result in near‐surface pedogenic processes that produce fine‐particulate secondary minerals that can be translocated as geodusts leading to ingestion or inhalation exposure in nearby communities. In this study, in vitro bioassays were combined with synchrotron‐based X‐ray spectroscopy and diffraction to determine the potential risk for toxic element release from dust (PM10) samples into biofluid simulants. PM10 were isolated from across the oxidative reaction front in the top meter of tailings subjected to 50 years of weathering under semiarid climate and introduced to synthetic gastric and alveolar fluids. Aqueous concentrations were measured as a function of reaction time to determine release kinetics. X‐ray diffraction and absorption spectroscopy analyses were performed to assess associated changes in mineralogy and elemental speciation. In vitro bioaccessibility of arsenic and lead was highest in less‐weathered tailings samples (80–110 cm) and lowest in samples from the suboxic transition zone (40–52 cm). Conversely, zinc release to biofluids was greatest in the highly weathered near‐surface tailings. Results indicate that bioaccessibility of As and Pb was controlled by (i) the solubility of Fe2+‐bearing solids, (ii) the prevalence of soluble SO42−, and (iii) the presence of poorly crystalline Fe(III) oxide sorbents, whereas Zn bioaccessibility was controlled by the pH‐dependent solubility of the stable solid phase.
Plain Language Summary
Legacy sulfide‐ore‐derived mine tailings often contain elevated concentrations of toxic metal(loid)s, such as arsenic, lead and zinc. Through natural weathering processes, such tailings material generates fine particulate matter (PM10) that may be transported off site as “geo‐dust”, thereby representing a significant health risk to proximal communities. This study examined the impacts of oxidative weathering of sulfide‐ore derived tailings on the biological availability of arsenic, lead, and zinc when tailings PM10 were introduced into synthetic lung and gastric fluids. We found that the natural oxidative process of weathering that occurs in the decades following tailings deposition decreased the bioaccessibility of the arsenic and lead present in the PM10, whereas zinc bioaccessibility increased with increased weathering under semi‐arid environment, and we identified the molecular processes controlling these observations.
Key Points
Sulfide ore tailings undergo oxidative weathering that alters the speciation and lability of toxic metal(loid)s
Oxidative weathering of tailings decreases bioaccessibility in synthetic gastric fluid
The decrease in bioaccessibility with weathering can be attributed to an increase poorly crystalline ferric solids that are high‐affinity sorbents
