In this study, a starch-stabilized nanoscale zero-valent iron (S-nZVI) was produced using the liquid-phase reduction method and was used to remove chromium from wastewater, alongside a commercial nanoscale zero-valent iron (C-nZVI). Both nZVIs were characterized by Scanning Electron Microscope (SEM), X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). The characterization results showed that with a more uniform particle size distribution, the size of S-nZVI was smaller than that of C-nZVI. Both nZVIs showed a core-shell structure with the core of Fe⁰ prominently surrounded by less iron oxides of Fe²⁺ and Fe³⁺. The optimal application methods to remove Cr(VI) from wastewater were also explored. The results showed that both the removal efficiencies of total Cr and Cr(VI) increased with increases in the addition of nZVIs, while the removal efficiencies of total Cr and Cr(VI) by S-nZVI were apparently higher than that of C-nZVI, especially in a low pH range (pH = 1.0–6.0). This research indicated that starch stabilized nanoscale zero-valent iron is a valuable material to remove heavy metals from wastewater due to its stability and high reactivity.

Leather tanneries around the world, including China, introduce chromium (Cr) and other metals into the environment. In China, the population pressure compels the utilization of every piece of available land for food production. In this study, we investigated the content, leachability and possible storage sinks for Cr and other metals in soils around facilities of leather industry in southern China. It was found that Cr in soils impacted by tannery can be as high as 2484 mg Cr kg⁻¹ soil, and the mean contents of other metals such as Zn (214 mg Zn kg⁻¹ soil), Cd (5.4 mg Cd kg⁻¹ soil), As (17 mg As kg⁻¹ soil) exceeded the soil quality standards and guidelines in China and Canada. Simulated leaching studies (i.e., Synthetic Precipitation Leaching Procedure) indicated that these soils could release Cr and other metals in concentrations above the environmental quality guidelines and standards for water in China and Canada. As a result, the mobility of metals from these soils can potentially contaminate both groundwater and surface water. We also found differential leachability of metals with soil properties such as total metal and total carbon contents. Principal component analysis of the total contents of 32 elements showed that the possible major sinks for Cr are organic matter and oxides of Fe/Mn/Al, while sulfates and phosphates are potential storage of Cd, Zn, Cu and Pb. The information obtained from this study can be valuable for the restoration of ecosystem functions (i.e., food production) in the study area.

Forest leaf litter is an important source of soil nutrients, but how its decomposition products affect the availability of soil heavy metals is not totally clear. In order to understand the effects of leaf litter decomposition on soil heavy metal availability in a forest ecosystem, leaf litter samples were collected from Daluoshan in Wenzhou and the Wuyanling National Nature Reserve of Zhejiang and subjected to analysis. The leaf litter was produced by the forests’ dominant tree species, such as Myrica ruba, Bambusa cerosissima, Pinus sylvestris, Machilus thunbergia, Cunninghamia lanceolata, and Quercus acutissima. Decomposition of the leaf litter samples at room temperature and leaching decomposition of the samples were carried out to analyze the acid production characteristics of the litter samples and their impact on soil heavy metal availabilities. Oxalic acid, lactic acid, fumaric acid, succinic acid, malic acid, and citric acid were the dominant organic acids in the leaf litter decomposer, and the sum of these six organic acids accounted for more than 50% of the total organic acid. During a 30-day litter decomposition, the levels of organic acids basically increased, with significant increases appearing in the early stage. After leaching, the available contents of Cr, Mn, Ni, Cu, Zn, As, Cd, and Pb increased by a maximum of 11.95, 2.33, 12.00, 0.80, 0.83, 0.54, 51.50, and 0.28-fold, respectively, compared with those of the original soil sample. During leaching, the higher the content of low molecular weight organic acids in the leaf litter, the longer the leaching time required and the more obvious the influence on the level of available heavy metals. A stronger leaching effect was found for the soil samples taken from a depth of 0–20 and 20–40 cm accompanied by a more obvious increase in the available heavy metals in the soil. PLSPM results showed that there were significant differences between the soil acidity index and the available heavy metals in Daluoshan (p < 0.05) and that there were significant differences between the soil acidity index and the available heavy metals in Wuyanling (p < 0.01). The decomposition of litter produced low molecular weight organic acids, which caused a decrease in soil pH and an increase in exchangeable H⁺ and Al³⁺. Both changes had an impact on soil organic matter and further led to an increase in the activity of heavy metals in the soil. This will further lead to the increase of ecological and environmental risks to forest soil.