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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.

Recent years, soil pollution of heavy metal has affected human life seriously, especially in farmland. Heavy metal pollution in farmland is mainly caused by irrigation, fertilizing and atmospheric fallout. As the character of heavy metal input in farmland is chronic and low dosage, application of model would be more suitable than routine methods to illustrate the dynamic changes of heavy metals in soil. In this paper, we use the model of STEM-profile to analyze and predict Cd pollution in farmland in Tongzhou, Beijing, based on the data from field survey. The results showed that: the concentration of Cd in this land would exceed the national soil environment standard after 100 years under current situations, reaching 0.866 mg x kg(-1) in plow layer. Studies of the influence of the amount and the form of inputs and the amount of irrigation water on the distribution of Cd in soil showed that irrigated with reclaimed water or fertilized with organic manure could lead to accumulation of Cd in the soil, while groundwater irrigation with inorganic fertilization would not cause accumulation of Cd in soil. When Cd inputs changed from mineral to organic form, the concentration of Cd in plow layer would be 0.943 mg x kg(-1) after 100 year. When the amount of irrigation water increased from 0.8 ET to 1.5 ET and to 2.0 ET, the plow layer Cd content would be 0.952, 0.784 and 0.638 mg x kg(-1) respectively.

The diffusive gradients in thin films (DGT) technique with solid-state binding phases has been widely used for in situ collection and measurement of available heavy metals in waters, soils or sediments, whereas DGT with liquid binding phase is primarily used in the in situ analysis of heavy metals in waters. In this paper, rhizosphere soils of sugarcane were collected in Guangxi and the concentrations of cadmium (Cd) were determined by DGT with a solid-state binding phase of chelex100 (chelex100-DGT) and modified DGT with a liquid binding phase of sodium polyacrylate (CDM-PAAS-DGT). The result showed that the Cd contents in soils measured by DGT with both binding phases and Cd in the roots, leaves and unpolished stems of sugarcane had significant positive correlation. The extraction ability of the CDM-PAAAS-DGT was much higher than that of the chelex100-DGT. In addition, multivariate analyses were used to assess the impact of pH, cation exchange capacity (CEC), soil organic matter (OM) and texture. Two principal components were extracted and the linear regression models were established. The Cd bioavailability in soils could be accurately predicted by the CDM-PAAAS-DGT technique, which expanded its applicable area.

With rhizobox experiment, this paper studied the changes of Cd forms on wheat root-soil interface under the stress of combined cadmium (Cd) and chlorimuron-ethyl. The root-soil interface (0-5 mm) was separated into 6 parts every other 1 mm, and the sampling time was 14, 21, 28, 35 and 42 days after treatment. The correlativity between Cd forms and Cd absorption by wheat was made to assess the availability of each Cd form. The results showed that exchangeable Cd showed different spatial effect during various growth periods. The trend of carbonate-bound Cd and Fe-Mn oxide-bound Cd transforming to exchangeable Cd was weaken, but the trend of the two Cd forms transforming to residual Cd was strengthened from root-center zone to non-rhizosphere. The concentration of organic-bound Cd varied significantly in neighboring root zone. During the whole experiment period, the concentrations of carbonate-bound Cd, Fe-Mn oxide-bound Cd and organic-bound Cd decreased, while that of residual Cd increased. Correlation analysis suggested that exchangeable Cd and organic-bound Cd nearby the root were the main Cd forms that could be absorbed by wheat. It could be concluded that the transformation of carbonate-bound Cd and Fe-Mn oxide-bound Cd and the concentration of exchangeable Cd were affected by chlorimuron-ethyl significantly.

In this paper, the gradient (0, 10, 50, 100, 200 mg x kg(-1)) of soil Cd concentrations was established by mixing CdCl2 with soil and sand, and the growth responses of four northern broadleaved tree species Acer ginnala Pyrus ussuriensis, Acer mono and Malus baccata to soil Cd contamination were studied by growing their seedlings in pots in greenhouse. The results revealed that the seedling growth of all test species was enhanced under lower soil Cd concentrations (< or = 50 mg x kg(-1)), and Acer ginnala had the strongest response under 10 mg x kg(-1) treatment, with 135.8% and 146.0% increment of collar and height growth, respectively, in comparing with the control. But, the growth of aboveground part decreased with increasing soil Cd, and the collar and height growth of A. ginnala under the highest Cd concentration was only 24.1% and 28.0% of the control, respectively. Under lower Cd concentrations, an increase of foliage and new shoot growth was found in A. ginnala and P. ussuriensis, the biomass of new shoots increased but that of foliage decreased in M. baccata, and both foliage and new shoot decreased in A. mono. Under the highest Cd concentration, A. ginnala had the greatest decrease of foliage and new shoot biomass, being 4.6% and 7.3% of the control, respectively, while P. ussuriensis and M. baccata had a relatively less decrease. The biomass increase of new roots declined with increasing Cd concentration for all tree species except P. ussuriensis, and the least increase was A. ginnala, only 2.3% of the control. The new root biomass of P. ussuriensis was 125.5% and 117.1% of the control at 10 mg and 20 mg x kg(-1), respectively. The total biomass increment of A. ginnala and P. ussuriensis seedlings was greater than that of the control under lower Cd concentrations, while an obvious decrease was found for all tree species under higher Cd concentrations. Under the highest Cd concentration, the total biomass of A. ginnala, M. baccata, A. mono and P. ussuriensis was 13.7%, 27.2%, 36.4 and 40.1% of the control, respectively. Subordinate function analysis suggested that the tolerance of test tree species to soil Cd contamination was in order of M. baccata > A. ginnala > P. ussuriensis > A. mono. Analysis of Cd concentration in plant tissues demonstrated that P. ussuriensis had the highest Cd enrichment coefficient for its root, shoot and foliage, and M. baccata also had a higher Cd enrichment in its root and shoot.

The interaction between organic acids (citric and oxalic acids) and heavy metals was examined in this paper. Equilibrium dialysis showed that the extent organic acids bound metals depended on the metal involved, and their binding properties affected the adsorption of Pb and Cd by soil, which was increased in the presence of oxalic acid, and decreased in the presence of citric acid. The effect of citric acid on the behavior and toxicity of Pb and Cd to plants was also studied. The presence of citric acid could reduce the toxicity of Pb, and inhibit the uptake of Cd in shoots and roots. However, there was no significant effect on the apparent toxicity of Cd. The interaction between Pb and Cd was found to be complicated. The Pb content in rice was higher in the presence of Cd, while the content of Cd is lower in the presence of Pb.

Microplastics affect the sorption of heavy metals by soils and alter their migration and transformation in soils. In this paper, the changes in the soil adsorption performance of cadmium (Cd) in the presence of polyethylene microplastics (PE-MPs) with different particle sizes (13, 48, 150 μm) were investigated, to explore the related mechanisms with the help of scanning electron microscopy-X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The results showed that the effect of PE-MPs on soil adsorption of Cd2+ was manifested as inhibiting the adsorption of Cd2+ and promoting the desorption of Cd2+; this effect was more obvious when the dose of PE-MPs was higher or the particle size was larger. Regardless of the presence or absence of PE-MPs, the sorption process of Cd2+ by soil was more consistent with quasi-secondary kinetics and the Freundlich model, indicating that the processes were multilayer sorption controlled mainly by chemisorption. The adsorption mechanism of Cd2+ by soil is mainly surface complexation and precipitation. PE-MPs can cover the active sites on the soil surface and interfere with the interaction of Cd2+ with oxygen-containing functional groups in the soil, thus weakening the chemisorption of Cd2+ by soil. It can be seen that PE-MPs can enhance the mobility of Cd in soil and increase the risk of Cd pollution to the soil ecosystem. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Agro-Environment Science is the property of Journal of Agro-Environment Science Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Agro-Environment Science is the property of Journal of Agro-Environment Science Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to expound the present situation and the potential risk of soil cadmium (Cd) in Guangxi, the paper collected and analyzed literatures about soil Cd in Guangxi which were published in recent 20 years. Based on the uniform criteria, 60 references were selected involving more than 30 areas in Guangxi, 7 090 samples. The paper summarized the distribution of soil Cd content distribution and the situation of soil Cd content exceeding the standard in Guangxi, so as to provide reference for relevant research, environmental policy making and environmental management. Results show that the soil Cd content in Guanxi ranges 0.040-244.1 mg·kg-1, with arithmetic mean and geometric mean 12.23 and 1.884 mg·kg-1, respectively. There were great differences in soil Cd concentration distribution between different functional areas. The average background soil Cd content in the research area is 0.153 mg·kg-1. The geometric mean of Cd content in agricultural soils and urban soils of non-mining areas were 0.467 and 0.320 mg·kg-1, respectively. The geometric mean of Cd content in the soil of mining area and in agricultural soil of mining area were 7.147 and 6.643 mg·kg-1, which were 46.71 and 43.42 times of the background soil Cd content. The majority of farmland soils are maintained at moderate pollution levels. Soils in several counties such as Nandan, Huanjiang, Jinchengjiang and Daxin were greatly affected by the pollution in mining area. There are areas not involved in the collected literatures. We recommend that control measures should be taken in Nandan, Jinchengjiang, Big Huanjiang, Yangshuo and Diaojiang areas, major investigations should be made in Baise Debao, Pingguo, Tiandong and Tianyang aluminum ore producing areas, and monitors on agricultural soil surrounding the mining area should be done. [ABSTRACT FROM AUTHOR]

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)