The Dynamics of Tungsten in Soil: An Overview

Chemical imaging reveals environmental risk of minor tungsten and lead shotgun pellet constituents during weathering in soil

Tungsten (W)-based shots are considered more environmentally safe than lead (Pb)-based shots, but knowledge about the W-shot fate in the soil environment is still limited, especially in terms of minor constituents such as iron, copper, and nickel (Ni). Contaminant behaviour in soil strongly depends on pH; in turn, the corrosion of metal composites may affect the pH locally. The aim of this study was to compare Pb- and W-shot weathering dynamics in soil (silt loam, pH 6.3) and reveal the interplay of shot weathering-induced pH-changes on the mobility of elements using in situ chemical imaging (Diffusive gradients in thin films for labile elements, planar optodes for soil pH) and batch incubation experiments over time (16 months). Despite our expectation to find acidification due to W oxidation, we observed a pH increase by 0.2 units in extracted soil solutions and by 0.6 units in the soil around W-shots as Ni dissolved from the binder phase of the shot. After 10 weeks, release of labile Ni was 3-times higher compared to W despite the low Ni content in the shot (7 %, m/m). Pb-shot oxidation increased soil solution pH by 0.5 units which likely supported mobility of Pb-shot-derived antimony (Sb). Steep gradients of labile W and Pb and soil solution concentrations <0.8 μmol L^-1 indicated that transfer from shot to soil was low. Contrastingly, labile Ni and Sb were found up to ~4 mm from the shot surface and in higher soil solution concentrations as suggested by the shot constitution, indicating higher mobility of minor as compared to major shot constituents. After 16 months, 36 % of total Ni were dissolved in the soil solution highlighting the environmental relevance of minor shot constituents in Pb-shot alternatives after short term weathering in soil.

Toxicological effects of WS2 nanomaterials on rice plants and associated soil microbes

As an important member of transition-metal dichalcogenides family, tungsten disulfides nanomaterials (WS₂ NMs) have a wide range of applications. To date, their environmental risks remain largely unknown. In this study, rice plants were grown in soil amended with different concentrations (0, 10, and 100 mg/kg) of WS₂ NMs for 4 weeks. WS₂ NMs at 100 mg/kg significantly increased MDA (malondialdehyde) content and decreased total antioxidant capacities of leaves, indicating the oxidative response induced by WS₂ NMs. Meanwhile, WS₂ NMs at 100 mg/kg significantly decreased root biomass compared to control, indicating the negative impacts of WS₂ NMs on plant growth. While exposure to 100 mg/kg WS₂ NMs significantly increased soil bioavailable Cu, Fe, Zn, and Olsen-P, and increased the content of Cu, Fe, Zn, and P in rice leaves. Inductively coupled plasma-optical emission spectroscopy (ICP-OES) analysis showed that W was taken up by rice roots and translocated into leaves. The impact of WS₂ on soil microbial communities was evaluated by 16S rRNA gene sequencing. WS₂ NMs at 100 mg/kg significantly decreased soil microbial diversity, as indicated by decreased Shannon index. In addition, 100 mg/kg WS₂ shifted the soil microbial profile, the relative abundance of the phylum Acidobacteriota decreased, and Actinobacteriota increased. Taken together, the soil microbial community's diversity and composition have been altered upon exposure to 100 mg/kg WS₂ NMs. The results of this study provide some basic information regarding the environmental behavior and phytotoxicity of WS₂ NMs, which is valuable for safe use of WS₂ NMs.

Soil Pollution Assessment and Sustainable Remediation Strategies

When the presence of a chemical in soil affects humans or other living organisms, producing undesired effects, that soil is considered polluted [...]