Yang Yu

In this study, soil and rice samples from 85 sites in six cities in Hunan Province were analyzed for Cu, Zn, Pb, Cd, Hg, Mn, and Co (total and bioavailable concentrations for soil) in July 2014. The results indicated that the total concentrations of Cu, Zn, Pb, Cd, and Hg in soil had increased significantly compared with the 1980s, and were correlated with their bioavailable concentrations in soil positively. The total concentrations of Cd and Co in soil were correlated with those in rice. Bioavailable concentrations of Cd, Mn, Co, Pb, and Cu represented 64.4%, 33.2%, 12.0%, 11.6%, and 6.1% of the total soil concentrations, respectively. The bioavailable concentrations of Cd and Co in soil had a extremely significant (p < 0.01) positive correlation with those in rice, suggesting that bioavailable concentrations was a better indicator for soil potentially toxic elements contamination. The pH values had a significant influence on the bioavailability of Cd and Cu and the amounts taken up by rice. The Cd contamination in 27.0% rice samples exceeded World Health Organization recommended thresholds. The results added basic pollution distribution data, further revealing the relationships of metals in soil and crops and would offer great help to the metallic pollution control in these areas.

The concentrations, chemical availability, distribution, and sources of potentially toxic elements (PTEs) in the soil of Xiangjiang Basin in Hunan Province, China were investigated at 85 sites. The highest mean concentrations of Cd, Cu, Zn, As, and Pb were observed in Hengyang, whereas those for Mn, Co, and Hg were observed in Changde. The pollution index values followed the order: Cd > Hg > Cu > Zn > As > Pb; the mean geo-accumulation index values were in the order: Cd > Hg > Pb > Cu > Zn > As > Co > Mn. Cd was associated with moderate contaminated level, Hg and Pb were associated with moderate contaminated to uncontaminated level, and Cu, Zn, As, Co, and Mn were associated with uncontaminated level of pollution. Furthermore, 64.5% of Cd was water-soluble and exhibited exchangeable fractions; its chemical availability posed a risk to the ecosystem. Spatial analysis, principal component analysis, and a positive matrix factorization model were used to assess the PTE sources. Four principal components contributed to 88.8% of the 8 PTEs concentrations. Mining, smelting, industrial, and agricultural activities, alongside sewage irrigation, the use of agrochemicals, and vehicular emissions are the possible anthropogenic sources that pollute agricultural products and threaten human health in the Xiangjiang Basin.

Environmental problems caused by the exploitation of mineral resources are worsening, especially the heavy metal pollution in soil. Food safety caused by heavy metal pollution in soil has become the focus of increasing attention.Sampling points were selected in Hunan Province. By sampling the soil and rice point by point, the total concentration and the concontration in rice were monitored. The results showed that the mean concentration of Cd, Cu, Hg, Pb and Zn were 1.31 mg/kg, 45.3 mg/kg, 0.61 mg/kg, 49.15 mg/kg and 133.3 mg/kg. The soils were contaminated in some parts of the 85 investigated sites in Hunan Province.Also, the analysis results showed that the average of PI (pollution index) descended in the order of Cd (2.58) > Hg (1.05) > Cu (0.52)> Zn (0.51)> Pb (0.41).The NIPI values of the research area were 28.59, belong to the high-level pollution, which mainly caused by Cd. The pollution ratio of soil samples were 100.0% in Zhuzhou-Xiangtan and Changning, 94.1%, 90.9% and 88.2% in Changde, Yiyang and Yongzhou. According to the potential ecological risk evaluation result, there was a medium level risk in the investigation area of Hunan and the potential ecological risk mainly caused by Cd.

The issue of food safety being compromised by heavy-metal contamination in soil has become the focus of increasing attention. Sampling points with a low, middle, and high Cd content in the soil were selected in Hunan Province. By sampling the soil and rice point by point, the total and the available Cd content and the content in rice were monitored. The 85 samples were subdivided into three groups according to the total Cd concentration: for the 25 low-risk samples, the content was 0.19–0.80 mg/kg; in the 51 moderate-risk samples, the content was 0.31–3.62 mg/kg; and in the nine high-risk samples, the content was 1.52–24.25 mg/kg. The results showed that: (1) the mean Cd concentration of the soil in the three groups was 0.45, 0.92 and 5.94 mg/kg, respectively; the available concentration was 0.30, 0.57 and 3.71 mg/kg; and the concentrations in rice were 0.09, 0.19, and 0.64 mg/kg. The total Cd content in the soil, the available content and the content in rice increase from low risk group to high risk group. (2) The Cd contents in rice show a significant positive correlation with the total amount in both the soil (the correlation coefficient (r) = 0.343) and the available contents (r = 0.377).(3) The total Cd content in the low-risk group is small, with three of the 25 rice samples exceeding the standard; the effective rate (available content/total content) of Cd was 50.7–97.5%. This showed that rice could still exceed the standard even when the total Cd content of the soil was low but the available content of Cd was relatively high. (4)Among the nine samples in the high-risk group, three did not exceed the standard; the effective rate of Cd was 32.7–62.5%, obviously lower than that in the rice samples that exceeded the standard (51.2–99.4%). This showed that even the total content was high and the available content was low, the Cd content in rice might not exceed the standard. (5) According to the total Cd content in the soil and the amount of Cd exceeding the standard in rice, the risk level was adjusted. After adjustment, the low-risk group contained 61 samples, the rate at which the standard was exceeded was 0%; the moderate-risk group had 12 samples, the excess rate was 75%; and 12 samples formed the high-risk group, where the excess rate was 100%. The adjusted classification is more consistent with what is expected from the standard grouping. The modification of the standard proposed here should improve the accuracy and thereby the usefulness of the standard, and may be useful for the improvement of similar laws and regulations in other countries.