New insights into the controversy of reactive mineral-controlled arsenopyrite dissolution and arsenic release.

Serious arsenic (As) contaminations could commonly result from the oxidative dissolution of As-containing sulfide minerals, such as arsenopyrite (FeAsS). Pyrite (Py) and calcite (Cal) are two typically co-existing reactive minerals and represent different geological scenarios. Previous studies have shown that a high proportion of Py can generate a stronger galvanic effect and acid dissolution, thereby significantly promoting the release of arsenic. However, this conclusion overlooks calcite's antagonistic effect on the release of As in the natural environment. That antagonistic effect could remodel the linear relationship of pyrite on the oxidative dissolution of arsenopyrite, thus altering the environmental risk of As. We examined As release from arsenopyrite along a gradient of Py to Cal molar ratios (Py:Cal). The results showed that the lowest As release from arsenopyrite was surprisingly found in co-existing Py and Cal systems than in the singular Cal system, let alone in the singular Py system. This phenomenon indicated an interesting possibility of Py assistance to Cal inhibition of As release, though Py has always been regarded as a booster, also evidenced in this research, for As release from arsenopyrite. In singular systems of Py and Cal, As continued to be released for 60 days. However, in co-existing Py and Cal systems, As was released non-linearly in three stages over time: initial release (0-1 Day), immobilization (1-15 Days), and subsequent re-release (>15 Days). This is a new short-term natural attenuation stage for As, but over time, this stage gradually collapses. During the re-release stage (> 15 Days), a higher molar ratio of Py:Cal (increasing from 1:9 to 9:1) results in a lower rate constant k (mg·L-1·h-1) of As release (range from 0.0011 to 0.0002), and a higher abundance of secondary minerals formed (up to 26 mg/g goethite and hematite at Py: Cal=9:1). This demonstrates that increasing the Py:Cal molar ratio results in the formation of more secondary minerals which compensate for the higher potential antagonistic mechanisms generated by pyrites, such as acid dissolution and galvanic effect. These results explain the mechanisms of the high-risk characteristics of As both in acidic mine drainage and karst aquifers and discover the lowest risk in pyrite and calcite co-existing regions. Moreover, we emphasize that reactive minerals are important variables that can't be ignored in predicting As pollution in the future.

Effects of copper oxide nanoparticles on Salix growth, soil enzyme activity and microbial community composition in a wetland mesocosm.

A model wetland with Salix was established to investigate the effects of CuO nanoparticles (NPs; the equivalent amount of Cu at 0, 100 and 500 mg/kg) on plant, soil enzyme activity and microbial community. Ionic Cu (100, 500 mg/kg) and bulk-sized CuO particles (BPs, 500 mg/kg) were included as controls. The results suggested the CuO NPs at 500 mg/kg and ionic Cu treatments inhibited the plant growth, while CuO NPs at 100 mg/kg and CuO BPs at 500 mg/kg played a facilitating role. CuO NPs significantly decreased the activities of peroxidase and polyphenol oxidase, while ionic Cu treatments increased peroxidase activity, BPs and ionic Cu (500 mg/kg) increased the polyphenol oxidase activity. Bacterial community richness and diversity were reduced in all Cu treatments; however, CuO NPs and BPs at 500 mg/kg significantly increased the richness and diversity of fungal community.Soil microbial community was significantly altered by Cu types and dose. In comparison with ionic Cu and CuO BPs, CuO NPs uniquely enriched the microbial community and the fungal families.Overall, it demonstrate that both particle size and dose regulate the impact of CuO on wetland ecology, which deepens our understanding on the ecological risks of CuO NPs in freshwater forested wetland.

Co-planting of Quercus nuttallii, Quercus pagoda with Solanum nigrum enhanced their phytoremediation potential to multi-metal contaminated soil.

To screen the efficient tree-herb co-planting patterns to remediate the heavy metal polluted soil, a greenhouse experiment was conducted for 150 days to examine the plant growth and metals accumulation across three co-planting patterns, including Solanum nigrum (S) co-planted with Quercus nuttallii (NS) or Quecrus pagoda (PS), and those three species are co-planted together (NPS). Results showed that the NPS pattern slightly decreased the tree biomass, while NS and PS treatments improved the plant growth (1.51-10.68%). It is worth noting that the NS treatment significantly (p < 0.05) increased photosynthetic pigment content (82.61-113.93%), net CO2 assimilation (21.44%), and the uptake of Cd (44.58%) in Q. nuttallii; the PS treatment significantly (p < 0.05) increased the net CO2 assimilation (8.61%) and the uptake of Cd (42.23%), Zn (31.18%) in Q. pagoda; and the uptake of Cd and Zn in the NPS co-planting treatment were only slightly increased. For S. nigrum, the photosynthetic pigment content was elevated and the metal accumulation in itself also maintained the relative stable in all the co-planting treatments. Thus, co-planting of Quercus with S. nigrum was a promising way to remediate heavily polluted soil by heavy metals. Novelty statement: Co-planting with multiple plant species, as a novel strategy, has great value for the remediation of heavy metal contaminated soil. The paper aimed to explore the suitable co-planting pattern of Quercus, arbor trees which showed phytoremediation potential, co-planted with Cd hyperaccumulator, Solanum nigrum. The result suggested the co-planting with S. nigrum enhanced the plant growth, photosynthesis, and metals extraction of Q. nuttallii and Q. pagoda. Co-planting also improved ecological adaptation of S. nigrum via elevating pigment content. Thus, co-planting of Quercus with S. nigrum was a promising way to remediate polluted soil.