[Accumulation of Heavy Metals in Agricultural Soils and Crops from an Area with a High Geochemical Background of Cadmium, Southwestern China].

In order to investigate the accumulation and transfer of heavy metals in agricultural soils and crops in an area with a high geochemical background of cadmium, soil and crop samples from a black shale outcropped area in Chongqing were collected and analyzed, and the results were then compared with those from other representative black shale outcropped areas. The results showed that some soil samples had a very low pH, and the metals Cd, Cr, Ni, and Zn were enriched. Cadmium concentrations in soil samples exceeded the safety limit, followed by Cr and Ni. Overall, 91.3% of soil samples were heavily to extremely polluted by Cd. The residual fractions accounted for more than 80% of the total metals, except for Cd and Pb. The weak acid soluble fraction of Cd accounted for 27.0%±6.4% of the total Cd, followed by Zn and Ni. The results demonstrate that weathering of black shales can result in elevated heavy metals in soils, and Cd is the primary contaminant in local soils. The high bioavailability of Cd and the high acidity of soils induced the enrichment of Cd in local crops. Cadmium has a higher transfer factor than other metals, and the crops were seriously polluted by Cd, particularly the leaf vegetables, which presented a high concentration of 11.5 mg·kg-1 based on dry weight, and thus, these vegetables are not suitable for cultivating as food stuff. In addition, the risks from Cr should be of concern as well. Therefore, it is recommended that countermeasures be carried out to address the pollution situation, for example, by classifying the pollution levels of agricultural soils and adjusting the planting structures accordingly to reduce the health risks to local inhabitants.

[Spatial Distribution, Sources and Bioavailability of Heavy Metals in the Surface Sediments of Longjiang River, Southern China].

In order to evaluate the pollution status, possible sources, and bioavailability of heavy metals (As, Cd, Pb, Sb, Zn, and Tl), 33 surface sediments were collected from Longjiang River, Southern China. The total concentrations and potential bioavailable concentrations of the heavy metals were analyzed using ICP-MS. Enrichment factors (EFs), Pearson correlation analysis, and principal component analysis (PCA) were used to further assess their pollution degree and potential sources. Results showed that the surface sediments of Longjiang River have been suffering heavy metal (As, Cd, Pb, Sb, and Zn) pollution to different degrees. The maximum concentrations of As, Cd, Pb, Sb, and Zn were 67.0, 7.42, 227, 229, and 807 mg·kg-1, respectively, while the Tl concentration were very low, with little variation. Moreover, the polluted sites were mostly located in the mid-lower of the main stem and in tributaries (Dongxioajiang and downstream of Dahuanjiang), and the pollution degree of the heavy metals, in a descending order, were Cd > Sb > Zn > Pb > As > Tl. Pearson correlation analysis and PCA indicated that As, Cd, Pb, Sb, and Zn predominantly originated from anthropogenic inputs, including nonferrous metal mining and smelting, municipal sewage, and agricultural activities, and Tl mostly derived from natural rock weathering. The bioavailability of heavy metals in the sediments tended to be controlled by their sources. The percentages of bioavailable heavy metals (As, Cd, Pb, Sb, and Zn) in the highly anthropogenic impacted areas (the mid-lower of the main stem and downstream of Dongxiaojiang tributary) were also high, with the average percentages of bioavailable As, Cd, Pb, Sb, and Zn of 26%, 51%, 49%, 38%, and 47%, respectively. High EF values and high bioavailable percentages of heavy metals easily and greatly cause high ecological risk of Longjiang River.

[Spatial Distribution Characteristics and Potential Ecological Risk of Antimony and Selected Heavy Metals in Sediments of Duliujiang River].

In order to investigate the spatial distribution characteristics of Sb and selected heavy metals, and to discriminate their sources and potential ecological risks in surface sediments of the Duliujiang river,a total of 62 surface sediment samples were collected in this study. Total contents of Sb, As, Cd, Co, Cr, Cu, Mo, Ni, Pb, Tl, Zn and Fe in these samples were measured by inductively coupled plasma mass spectrometry(ICP-MS) and the inductive plasma optical emission spectrometry(ICP-OES). Principal component analysis(PCA) and Pearson correlation analysis were used to deduce the potential sources of these elements. Geo-accumulation index(Igeo), enrichment factor(EF) and Hakanson's potential ecological risk index(Eri and RI) were calculated to evaluate the pollution degree of heavy metals in sediments. The results indicated that the contents of heavy metals in sediments were impacted by human activities to different extents, and the Duliujiang River was significantly contaminated by Sb. The contents of Sb in sediments reached up to 7080 mg·kg-1, and gradually decreased from upstream to downstream, while the contents of As, Cd, Co, Cr, Cu, Mo, Ni, Pb, Tl and Zn varied indistinctively. The PCA results showed that the cumulative proportion of the first two components accounted for 77.67% of the total variables, suggesting that two major sources of Sb and other heavy metals were mining/smelting industry and natural sources. The calculated Igeo and EFs also showed that the surface sediments of the Duliujiang River were majorly polluted by Sb, followed by As and Co, lightly contaminated with Co, Cu, Mo, Ni, Pb and Tl, and uncontaminated with Cr. The ecological hazards(Eri) for each metals in a descending order were Sb > Cd > As > Co > Ni > Pb > Cu > Zn > Cr. The comprehensive index of potential ecological risks(RI) for heavy metals indicated that 58.1% of the 62 sediments samples had more than moderate ecological risks, and the sites with high RIs were generally located around Sb mining area and the downstream of the Baluo River. In addition, the Eri of Sb was a predominant component of RI, indicating that the Duliujiang River is an area with extremely high potential ecological risk of Sb.

[Cadmium and selected heavy metals in soils of Jianping area in Wushan County, the Three Gorges region: distribution and source recognition].

Abnormally high cadmium (Cd) concentrations were existed in soils of Jianping area in the Three Gorges region, but little information is available about the geochemical distribution of Cd and source identification. In the present paper, total contents of Cd and other selected heavy metal elements, the characteristics of soil, the contents of Cd in typical soil profiles, and chemical forms of Cd in selected soils were studied. The correlation analysis, the principal component analysis, and the comparison between different soil types were conducted. The concentration distribution of Cd and selected elements in local soils was investigated and their sources were identified. The results showed that Cd in local rocks, coal and coal wastes ranged from 0.22-101 mg x kg(-1), 0.42-42 mg x kg(-1) in the arable topsoil, and 0. 12-8.5 mg x kg(-1) in natural soils. The soils were also rich in other elements such as V, Cr, Ni and Zn. The weak acid fraction of Cd accounted for 17%-35% of total contents. This study demonstrated that soils from the Jianping area of Wushan County had a serious Cd pollution, and both local rocks and soils display a significant geochemical interrelation. Cd particularly accumulates in the topsoil, and it is mainly derived from the geogenic source. Human such as the historical coal mining may overload Cd in the soils. The local soils had a high portion of bioavailable Cd, through which Cd may easily transfer to and accumulate in the local crops growing in the Cd-rich soils and cause potential health risk to local residents.

[Geochemical distribution and environmental quality of cadmium in river sediment around the Jinding Pb-Zn mine area in Yunnan].

A long-term mining activity of Jinding Pb-Zn mine area in Yunnan has caused the serious cadmium pollution to the river sediments of the ambient area. The Cd contents of Beidagou river sediments (mean value <10 mg x kg(-1)) are lower than those of Nandagou river sediments (mean value = 266 mg x kg(-1)). The Cd contents of river sediments in different section of Bijiang river occur distinct difference. The Cd contents are rather lower in upstream sediments of Bijiang river, and increase substantially along downstream contaminated section of Bijiang river. The Cd pollution coefficient is higher (R = 21.9-45.2) than Zn (R = 4.9-9.7) and Pb (R = 2.7-4.6). The degree of pollution is estimated by the geoaccumulation index, which indicates the following rank of pollution elements: Cd > Zn > Pb. The river sediments are extremely contaminated in Nandagou river and downstream section of Bijiang river from Nandagou, strongly contaminated in most part of Beidagou river, moderately to strongly contaminated in few river section of Nandagou river, uncontaminated or moderately contaminated in upstream of Bijiang river from Jinding. The heavy metals pollution of river sediments presents increasing trend from Nandagou outlet to Wenzhuang section of Bijiang river.