Determination of soil contamination sources in mining area using Zn/Cd ratios with mobile Cd.

Paddy fields near metalliferous mining area are sometimes contaminated by tailings or mine water. In the contaminated paddy fields around the abandoned Seoseong mine, South Korea, groundwater, surface water, and soil samples were assessed to infer sources (tailings and/or mine water) of soil contamination. Major contaminants in the soil included As and Pb which were not detected in the adit water. Moreover, δ34SSO4 values of groundwater at contaminated downstream paddy fields were higher than those of ground and surface water in the mining area, which indicated water-derived contamination is not evident. The Zn/Cd ratios of soil were assessed to verify the source (tailings) of soil contamination. Plots of the Zn/Cd ratio against Zn and As contents showed that soil samples contaminated from tailings had Zn/Cd ratios (108-247) which were similar with the Zn/Cd range of the tailings. In contrast, the ratios of the soil samples were different from the Zn/Cd range of contaminated water samples. The Zn/Cd ratios were determined using 0.1 M HCl-extractable Cd, and the fraction of 0.1 M HCl-extractable Cd in aqua regia-digestible Cd increased with increasing aqua regia-digestible Cd content. These observations suggest that Zn/Cd ratios in contaminated soil are primarily controlled by 0.1 M HCl-extractable Cd, possibly due to the greater exchangeability of 0.1 M HCl-extractable Cd than that of total Cd. This suggests that Zn/Cd ratios determined using 0.1 M HCl-extractable Cd can be especially sensitive and useful for determining sources of soil contamination in mining areas such as tailings or contaminated water.

Response of edible amaranth cultivar to salt stress led to Cd mobilization in rhizosphere soil: A metabolomic analysis.

The present study aimed to investigate the metabolic response of edible amaranth cultivars to salt stress and the induced rhizosphere effects on Cd mobilization in soil. Two edible amaranth cultivars (Amaranthus mangostanus L.), Quanhong (low-Cd accumulator; LC) and Liuye (high-Cd accumulator; HC), were subject to salinity treatment in both soil and hydroponic cultures. The total amount of mobilized Cd in rhizosphere soil under salinity treatment increased by 2.78-fold in LC cultivar and 4.36-fold in HC cultivar compared with controls, with 51.2% in LC cultivar and 80.5% in HC cultivar being attributed to biological mobilization of salinity. Multivariate statistical analysis generated from metabolite profiles in both rhizosphere soil and root revealed clear discrimination between control and salt treated samples. Tricarboxylic acid cycle in root was up-regulated to cope with salinity treatment, which promoted release of organic acids from root. The increased accumulation of organic acids in rhizosphere under salt stress obviously promoted soil Cd mobility. These results suggested that salinity promoted release of organic acids from root and enhanced soil Cd mobilization and accumulation in edible amaranth cultivar in soil culture.

Effects of exogenous sulfur on growth and Cd uptake in Chinese cabbage (Brassica campestris spp. pekinensis) in Cd-contaminated soil.

Soil pollution with heavy metals has many adverse effects on ecosystem health as well as food security. A pot experiment was performed to investigate the effects of different valence states of exogenous sulfur (S) on the uptake of cadmium (Cd) in Chinese cabbage in Cd-contaminated soil. The results showed that S significantly promoted plant growth in Chinese cabbage, with the following order of magnitude for the different S treatments: sodium sulfite (Na2SO3) > sodium sulfate (Na2SO4) > powdered sulfur (S0). Additionally, enzyme activity and the content of reductive substances in the leaves markedly increased, while malondialdehyde content significantly decreased; hence, S observably enhanced the ability of Chinese cabbage to tolerate Cd stress. S0 significantly reduced soil pH, thus increasing the mobility and bioavailability of Cd in the soil, while Na2SO3 increased soil pH, and Na2SO4 had no effect on soil pH. The acid-soluble and oxidizable fractions of Cd in soil increased with the S0 treatment. The applied Na2SO3 and Na2SO4 both increased the residual fraction of Cd in the soil, but they reduced the amount of the acid-extractable, reducible, and oxidizable Cd. The results showed that compared with S0, the Na2SO3 and Na2SO4 treatments decreased the acid-extractable Cd concentrations by 6.3 and 4%, respectively, in the most contaminated soil. In conclusion, the influence of S on the bioavailability and speciation of Cd varied not only with the soil Cd content but also with the application rate and S valence state.