Distribution Characteristics of Heavy Metals and Pb Isotope in Profile Soils from a Mining and Smelting Area in Northwestern China

The distribution characteristics of typical heavy metals (HMs) and Pb isotopic compositions in profile soils from different areas were investigated in Baiyin district, northwest China. The soil samples from the ore district and the sewage irrigation area showed an obvious enrichment of HMs in different depths, and the difference in the longitudinal migration depth of Pb, Cu, Zn, and Cd was insignificant, which might be due to the migration behavior of HMs mainly controlled by carbonate in alkaline soil. With the sewage irrigation activities, the content of soil organic matter was no longer the main controlling factor for the migration behavior of HMs. In ore district and sewage irrigation area, the HMs contents of nonresidual fractions in topsoil were much higher than that in the corresponding deep soil, which indicated that HMs activities in topsoil were significantly high. The Pb isotopic compositions of profile soils indicated that the long-term mining and smelting activities remained the main source of vertical enrichment of HMs in Baiyin district. Moreover, the Pb isotope ratios 206Pb/207Pb of nonresidual fractions (1.1359-1.1916) were all lower than that in the corresponding residual fractions (1.1641-1.2010), showing the characteristics that HMs input from anthropogenic source were in different degrees. The Pb isotopic compositions of residual fractions in the topsoil of ore district and sewage irrigation area (1.1641 and 1.1703) were between the two end-members composed of background soil and local mineral samples, which suggested that some anthropogenic HMs might enter into the residual components in the soil that was greatly affected by the input of HMs.

Source analysis of heavy metal pollution in agricultural soil irrigated with sewage in Wuqing, Tianjin

In this study, the contents of heavy metals and Cd and Pb isotope ratios of agricultural soil and potential source samples collected from farmland receiving sewage irrigation in Wuqing District, Tianjin, China were determined. Multiple methods were used for source analysis, including positive matrix factorization (PMF), correlation analysis, principal component analysis (PCA), and the Cd and Pb isotope ratio method. The results showed that agricultural soil was slightly contaminated by heavy metals in the research area, with relatively higher Cd and Pb accumulation levels compared to those of other heavy metals. Four types of pollution sources, including the soil parent material sources, industrial emission sources, agricultural practice sources, and mixed sources of sewage irrigation and transportation were apportioned and quantified by PMF, combined with the results of PCA and correlation analysis. The contribution rates quantified by the Cd and Pb isotope ratio method were similar, suggesting that no single source dominates Pb and Cd pollution. The contribution rates of Pb analyzed by the isotope ratio method were almost identical to those of the PMF model, indicating the rationality of the PMF result. Our results suggested that correlation analysis and PCA should be utilized to provide information for obtaining reasonable results and defining source categories for PMF, whereas the isotope ratio method should be applied to verify the accuracy of source contributions analyzed by PMF.

Mobility and Phytoavailability of Arsenic and Cadmium at the Soil-corn Interface in Sewage Irrigation Polluted Farmlands Northwest, China

The activity of heavy metals in farmland soil and the safety of food crops after long-term sewage irrigation are the premise of sustainable development of agriculture. The major pollutants of arsenic (As) and cadmium (Cd) in farmland-corn system affected by sewage irrigation for 40 years were studied. The results showed that although the content of total As in soil was high, the absorption and transport of total As by corn were relatively small, and As could not migrate down the soil profile. On the contrary, Cd mainly exists in the form of exchangeable and carbonate-bound which has strong fluidity. By optimizing the method of investigating the bioavailability of pollutants and systematically and comprehensively studying the migration law of pollutants in various parts of maize tissues, it is concluded that Cd still has high activity after stopping sewage irrigation, and the development process of maize roots has a significant relationship between the contact of heavy metals in the surface soil and the enrichment of heavy metals in the upper part of corn tissues (p < 0.01). Therefore, this study can increase the understanding of the migration law of pollutants in corn, and provide a basis for remediation of contaminated soil in local and other areas.