Bioaccessibility and human health risks of arsenic from geological origin in lateritic red soil on construction land.

Current human health risk assessments of soil arsenic (As) contamination rarely consider bioaccessibility (IVBA), which may overestimate the health risks of soil As. The IVBA of As (As-IVBA) may differ among various soil types. This investigation of As-IVBA focused As from geological origin in a typical subtropical soil, lateritic red soil, and its risk control values. The study used the SBRC gastric phase in vitro digestion method and As speciation sequential extraction based upon phosphorus speciation extraction method. Two construction land sites (CH and HD sites) in the Pearl River Delta region were surveyed. The results revealed a high content of residual As (including scorodite, mansfieldite, orpiment, realgar, and aluminum arsenite) in the lateritic red soils at both sites (CH: 84.9%, HD: 91.7%). The content of adsorbed aluminum arsenate (CH: 3.24%, HD: 0.228%), adsorbed ferrum arsenate (CH: 8.55%, HD: 5.01%), and calcium arsenate (CH: 7.33%, HD: 3.01%) were found to be low. The bioaccessible As content was significantly positively correlated with the As content in adsorbed aluminum arsenate, adsorbed ferrum arsenate, and calcium arsenate. A small portion of these sequential extractable As speciation could be absorbed by the human body (CH: 14.9%, HD: 3.16%), posing a certain health risk. Adsorbed aluminum arsenate had the highest IVBA, followed by calcium arsenate, and adsorbed ferrum arsenate had the lowest IVBA. The aforementioned speciation characteristics of As from geological origin in lateritic red soil contributed to its lower IVBA compared to other soils. The oxidation state of As did not significantly affect As-IVBA. Based on As-IVBA, the carcinogenic and non-carcinogenic risks of soil As in the CH and HD sites decreased greatly in human health risk assessment. The results suggest that As-IVBA in lateritic red soil should be considered when assessing human health risks on construction land.

[Hg Content Characteristics and Safe Planting Zoning of Paddy Soil and Rice in Guizhou Province].

Guizhou Province ranks first in terms of Hg reserves and production in the country, and rice is its largest grain crop. In order to study the characteristics and pollution causes of soil-rice Hg content at the provincial level in Guizhou and to carry out safe planting zoning, 1 564 pairs of soil-rice samples, 470 natural soil samples, and 203 individual paddy soil samples were collected to test their Hg content and basic physical and chemical properties of the soil. The results showed that:① Paddy soil was mainly neutral and acidic, the paddy soil ω (Hg) range was 0.005-93.06 mg·kg-1, and the geometric mean was 0.864 mg·kg-1. The Hg content of paddy soil in Guizhou Province was significantly higher than that in natural soil (0.16 mg·kg-1,P < 0.05). Compared with the filtered value and control value, the soil samples exceeded the standard by 63.25% and 14.71%, respectively. Among them, the soil Hg pollution in Danzhai County of Qiandongnan Prefecture, Wuchuan County of Zunyi City, Zhenfeng County of Qianxinan Prefecture, and Wanshan District of Tongren City was more prominent. ② Rice ω(Hg) ranged from 0.000 5 to 0.52 mg·kg-1, and the geometric mean was 0.010 mg·kg-1, the percentage of rice Hg content exceeding the standard was 25.87%, and the exceeding points were mainly distributed in Suiyang County of Zunyi City, Zhenfeng County of Qianxinan Prefecture, Xixiu District of Anshun City, Bijiang District of Tongren City, and other industrial and mining activity-intensive areas. ③ The majority of the study area was in the priority protection category (74.75%); the safe use category accounted for (24.62%); and the strictly controlled category (0.93%) was scattered in Danzhai County at the border between Qiannan Prefecture and Qiandongnan Prefecture, Zhenfeng County in Qianxinan Prefecture, and Wanshan District in Tongren. It is not recommended to plant rice, which can be used as feed for reproduction.

Microbial mechanisms in nitrogen fertilization: Modulating the re-mobilization of clay mineral-bound cadmium in agricultural soils.

Soil cadmium (Cd) can affect crop growth and food safety, and through the enrichment in the food chain, it ultimately poses a risk to human health. Reducing the re-mobilization of Cd caused by the release of protons and acids by crops and microorganisms after stabilization is one of the significant technical challenges in agricultural activities. This study aimed to investigate the re-mobilization of stabilized Cd within the clay mineral-bound fraction of soil and its subsequent accumulation in crops utilizing nitrogen ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3--N), at 60 and 120 mg kg-1. Furthermore, the study harvested root exudates at various growth stages to assess their direct influence on the re-mobilization of stabilized Cd and to evaluate the indirect effects mediated by soil microorganisms. The results revealed that, in contrast to the NO3--N treatment, the NH4+-N treatment significantly enhanced the conversion of clay mineral-bound Cd in the soil to NH4NO3-extractable Cd. It also amplified the accumulation of Cd in edible amaranth, with concentrations in roots and shoots rising from 1.7-6.0 mg kg-1 to 4.3-9.8 mg kg-1. The introduction of NH4+-N caused a decrease in the pH value of the rhizosphere soil and stimulated the production and secretion organic and amino acids, such as oxalic acid, lactic acid, stearic acid, succinic acid, and l-serine, from the crop roots. Furthermore, compared to NO3--N, the combined interaction of root exudates with NH4+-N has a more pronounced impact on the abundance of microbial genes associated with glycolysis pathway and tricarboxylic acid cycle, such as pkfA, pfkB, sucB, sucC, and sucD. The effects of NH4+-N on crops and microorganisms ultimately result in a significant increase in the re-mobilization of stabilized Cd. However, the simulated experiments showed that microorganisms only contribute to 3.8-6.6 % of the re-mobilization of clay mineral-bound Cd in soil. Therefore, the fundamental strategy to inhibit the re-mobilization of stabilized Cd in vegetable cultivation involves the regulation of proton and organic acid secretion by crops.

[Provincial-scale Soil As Migration and Transformation and Rice Safe Planting Zoning: A Case Study of Guizhou Province].

To explore the distribution characteristics of paddy soil and rice AS content, as well as the health risks of rice consumption, and to evaluate the safe planting ability of rice, 209 paddy soil samples and 1 567 groups of paddy soil-rice samples were collected, their As content and basic soil physical and chemical properties were determined, and the single-factor pollution index method was used to evaluate the pollution degree of the samples. The results showed that:① the soil of paddy fields in Guizhou Province was mainly neutral, and its fertilizer retention capacity and organic matter content were above the medium level, and the soil was relatively fertile. The range of ω(As) in paddy soil was 0.042-91.75 mg·kg-1, the geometric mean was 10.03 mg·kg-1, and the cumulative effect of paddy soil As was lower than that of natural soil As (P<0.05) by independent sample T. Compared with the screening value (0.2 mg·kg-1) of the Soil Pollution Risk Management and Control Standard for Agricultural Land (GB 15618-2018), the excess rate of soil samples was 15.37%. ② The ω (As) range of rice grain samples was 0.001-0.937 mg·kg-1, the geometric average value was 0.108 mg·kg-1, 10.21% of the rice grain samples exceeded the limit value of "Limit of Contaminants in Food (trial)" (GB 2762-2022), and the locations where the exceedances are mainly found are in the central and northern parts of Qiannan Prefecture, as well as around industrial and mining activity zones in the southern counties and districts of Zunyi. ③ As ingested through rice posed non-carcinogenic risk and carcinogenic risk for adults and children, and the impact on children was greater than that of adults. There is no strict control area for safe rice planting in Guizhou Province, and rice can be safely planted.

Urea reduces the sustainability of soil Cd immobilization by upregulating the expression of AmSTOP1 and AmMATE genes in edible amaranth roots.

After cadmium (Cd) immobilization remediation in contaminated farmland soil, which forms of nitrogen fertilizer should be implemented to keep its sustainability? Urea and nitrate were used to compare for their effects on the remobilization of stabilized Cd in the rhizosphere soil of edible amaranth at nitrogen concentrations of 60, 95, and 130 mg kg-1. The results showed that compared to nitrate nitrogen, the Cd content in shoots increased by 76.2%, 65.6%, and 148% after applying three different concentrations of urea, and the total remobilization amount of Cd also increased by 16.0%, 24.9%, and 14.0% respectively. Urea application promotes root secretion of citric acid, malic acid, pyruvate, and γ-aminobutyric acid, crucial in remobilizing stable Cd. The application of urea promoted the expression of genes involved in sucrose transport, glycolysis, the TCA cycle, amino acid secretion, citric acid efflux, and proton efflux. Arabidopsis heterologous expression and yeast one-hybrid assays identify critical roles of AmMATE42 and AmMATE43 in citric acid and fumaric acid efflux, with AmSTOP1 activating their transcription. Inhibition of SIZ1 expression in urea treatment reduce AmSTOP1 SUMOylation, leading to increased expression of AmMATE42 and AmMATE43 and enhanced organic acids efflux. Using edible amaranth as a model vegetable, we discovered that urea is not beneficial to preserving the sustainability of stabilized Cd during the reuse of remediated farmlands contaminated with Cd.

Inoculation of Escherichia coli enriched the key functional bacteria that intensified cadmium accumulation by halophyte Suaeda salsa in saline soils.

The enhancement of cadmium (Cd) extraction by plants from contaminated soils associated with phosphate-solubilizing bacteria (PSB) has been widely reported, but the underlying mechanism remains scarcely, especially in Cd-contaminated saline soils. In this study, a green fluorescent protein-labeled PSB, the strain E. coli-10527, was observed to be abundantly colonized in the rhizosphere soils and roots of halophyte Suaeda salsa after inoculation in saline soil pot tests. Cd extraction by plants was significantly promoted. The enhanced Cd phytoextraction by E. coli-10527 was not solely dependent on bacterial efficient colonization, but more significantly, relied on the remodeling of rhizosphere microbiota, as confirmed by soil sterilization test. Taxonomic distribution and co-occurrence network analyses suggested that E. coli-10527 strengthened the interactive effects of keystone taxa in the rhizosphere soils, and enriched the key functional bacteria that involved in plant growth promotion and soil Cd mobilization. Seven enriched rhizospheric taxa (Phyllobacterium, Bacillus, Streptomyces mirabilis, Pseudomonas mirabilis, Rhodospirillale, Clostridium, and Agrobacterium) were obtained from 213 isolated strains, and were verified to produce phytohormone and promote soil Cd mobilization. E. coli-10527 and those enriched taxa could assemble as a simplified synthetic community to strengthen Cd phytoextraction through their synergistic interactions. Therefore, the specific microbiota in rhizosphere soils enriched by the inoculated PSB were also the key to intensifying Cd phytoextraction.

[Mercury Pollution in Dryland Soil and Evaluation of Maize Safety Production in Guizhou Province].

Guizhou Province is the province with the largest Hg production and reserves in China, and maize is the second largest grain crop in Guizhou Province. It is necessary to identify the status of soil Hg content in Guizhou Province and evaluate the safety of maize production. A total of 990 soil-maize samples and 270 single soil samples were collected in the main maize-producing areas to determine soil pH, cation exchange capacity (CEC), and organic matter content (SOM), as well as Hg content in soil and maize. The results showed that the pH of dryland soil in Guizhou Province ranged from 3.93 to 9.82, the geometric mean of ω(SOM) was 27.5 g·kg-1, and the geometric mean of CEC was 11.7 cmol·kg-1. Soil ω(Hg) ranged from 0.005 to 686 mg·kg-1, the geometric mean was 0.632 mg·kg-1, and the over-standard rate was 7.22%. Among them, the soil Hg pollution in Tongren was the most prominent, with the exceedance rate of 21.3%. At the county level, Danzhai County, Qiandongnan Miao and Dong Autonomous Prefecture, and Tongren City Wanshan District and Bijiang District had high exceedance rates of Hg. According to the Limit of Pollutants in Food according to National Standards for Food Safety (GB 2762-2017), the exceedance rate of Hg content in maize grains was 1.11%, and the exceedance points were mainly distributed around industrial and mining activity areas such as Wanshan District in Tongren City and Xixiu District in Anshun City. According to the results, there was serious soil Hg pollution in Guizhou Province. On the whole, maize can be safely planted, but it is necessary to pay close attention to the Hg content in grains and the Hg exposure risk of residents around industrial and mining areas.

Estimation of the fraction of soil-borne particulates in indoor air by PMF and its impact on health risk assessment of soil contamination in Guangzhou, China.

The fraction of soil-borne particulates in indoor air (fspi), a principal exposure factor in health risk assessment of soil, is used to calculate the inhaled dose of contaminants in air particulates (PM10) from soil. To investigate the fspi, consecutive 24-h PM10 samples (n = 180) of indoor ambient were collected from September 2019 to January 2020 in Guangzhou main urban areas, China. The concentrations of twenty-six metal elements, five anions, organic carbon (OC) and elemental carbon (EC) in samples were measured. The sources of indoor ambient PM10 and the value of fspi were identified by the method of Positive Matrix Factor analysis (PMF). Results showed that the main sources contributing to indoor PM10 content were combustion sources (50.53%) and vehicular sources (28.17%). The soil sources (the local fspi) were 19.96%. The soil contents of indoor PM10 in Guangzhou main urban areas were in accordance with those in similar monsoon climate regions, such as Malaysia. The health risks of the inhalation route were dropped by about 62% for some common brownfield contaminants (Cr (VI), Ni, Be and Cd) with the investigated local fspi in Guangzhou main urban areas, compared with using the fspi (0.8) recommended by the C-RAG model in China. The results supplied a new effective methodology for estimation of the local fspi value in health risk assessment of soil contamination in urban areas.

Improving cadmium accumulation by Solanum nigrum L. via regulating rhizobacterial community and metabolic function with phosphate-solubilizing bacteria colonization.

Soil cadmium (Cd) mobilized with phosphate-solubilizing bacteria (PSB), especially for strains effectively colonized in rhizosphere, is an important pathway for promoting its accumulation by Cd-hyperaccumulators. In this study, screened PSB strains, Acinetobacter pittii (AP) and Escherichia coli (EC), were used to evaluate their effects on Cd mobilization in rhizosphere, Cd accumulation by Solanum nigrum L., and rhizobacterial community and metabolic function under different colonization condition. Results indicated that AP or EC inoculated in soils significantly promoted plant growth, and simultaneously motivated Cd accumulation in S. nigrum L. by 119% and 88%, respectively, when compared with that of uninoculated treatment. Higher efficiency colonization of AP contributed to more organic acids (malic, l-proline, l-alanine, and γ-aminobutanoic) production in the rhizosphere soil and Cd accumulation by S. nigrum L., when compared with that of EC treatment. Taxonomic distribution and co-occurrence network analyses demonstrated that inoculation of AP or EC enriched dominant microbial taxa with plant growth promotion function and keystone taxa related to Cd mobilization in the rhizosphere soil, respectively. Inoculated strains up-regulated the expression of genes related to bacterial mobility, amino acid metabolism, and carbon metabolism among rhizobacterial community. Overall, this study provided a feasible method for soil Cd phytoremediation by promoting Cd mobilization with the enhancement of keystone taxa and organic acid secretion based on the high-efficiency colonization of PSB.

Biomineralization of Cd2+ and inhibition on rhizobacterial Cd mobilization function by Bacillus Cereus to improve safety of maize grains.

Reducing cadmium (Cd) bioavailability and rhizobacterial Cd mobilization functions in the rhizosphere via the inoculation of screened microbial inoculum is an environmental-friendly strategy to improve safety of crop grains. In this study, Bacillus Cereus, a model Cd resistant strain, was selected to explore its effects on Cd bioavailability and uptake, bacterial metabolic functions related to Cd mobilization. Results indicated that inoculation of Bacillus Cereus in maize roots of sand pot with water-soluble Cd (0.06-0.15 mg/kg) and soil pot with high Cd-contaminated soil (total Cd: 2.33 mg/kg; Cd extracted by NH4NO3: 38.6 µg/kg) could decrease water-soluble Cd ion concentration by 7.7-30.1% and Cd extracted with NH4NO3 solution by 7.8-22.5%, inducing Cd concentrations in maize grains reduced by 10.6-39.9% and 17.4-38.6%, respectively. Even for a single inoculation in soil, Cd concentration in maize grains still satisfy food safety requirements (Cd content: 0.1 mg/kg dry weight) due to its successful colonization on root surface of maize. Bacillus Cereus could enrich more plant growth promotion bacteria (PGPB) and down-regulate the expression of genes related to bacterial motility, membrane transports, carbon and nitrogen metabolism in the rhizosphere soil, decreasing Cd bioavailability in soil. Approximately 80% Cd2+ in media was transferred into intracellular, meanwhile Cd salts (sulfide and/or phosphate) were produced in Bacillus Cereus through biomineralization process. Overall, this study could provide a feasible method for improving safety of maize grains via the inoculation of Bacillus Cereus under Cd pollution.

Nitrogen fertilizer affects rhizosphere Cd re-mobilization by mediating gene AmALM2 and AmALMT7 expression in edible amaranth roots.

In-situ stabilization of Cd-contaminated farmland is a commonly used remediation technology. Yet, rhizosphere metabolites (e.g., organic acids) during crop cultivation may cause Cd re-mobilization and over-accumulation. Here, we identified four pivotal cytomembrane-localized genes underlying Cd accumulation difference between two contrasting edible amaranth cultivars based on root gene expression profile, studied their subcellular localization and functional characteristics, and then investigated effects of nitrogen fertilizer on their expression and rhizosphere Cd re-mobilization. Results showed that more Cd accumulated by edible amaranth was due to rhizosphere Cd mobilization by mediating high expression of AmALMT2 and AmALMT7 genes, not Cd transporters in roots. This was confirmed by heterologous expression of AmALMT2 and AmALMT7 genes in Arabidopsis thaliana, since they mediated malic, fumaric, succinic, and aspartic acids efflux. Furthermore, nitrogen influencing rhizosphere acidification might be closely associated with organic acids efflux genes. Compared with N-NO3- application, N-NH4+ was massively assimilated into glutamates and oxaloacetates through up-regulating glutamine synthetase and alanine-aspartate-glutamate metabolic pathways, thereby enhancing TCA cycle and organic acids efflux dominated by binary carboxylic acids via up-regulating AmALMT2 and AmALMT7 genes, which finally caused Cd re-mobilization. Therefore, N-NO3--dominated nitrogen retarded rhizosphere Cd re-mobilization via inhibiting organic acids efflux function of AmALMT2 and AmALMT7 proteins.

Nitrogen fertilizer management affects remobilization of the immobilized cadmium in soil and its accumulation in crop tissues.

Immobilization of soil cadmium (Cd) has been the strategy mostly used in remediation of Cd-contaminated arable soil. However, Cd might be remobilized after the immobilization process through the acid-soluble and complexation effects. Development of agronomic management technologies to prevent soil Cd remobilization after the immobilization process was an important pathway to control the food safety of agricultural products in soils with the immobilized Cd. In this study, the ammonia (NH4+-N) and nitrate (NO3--N) forms with concentrations of 60, 90, and 150 mg-N kg-1 soil were performed for evaluating their effects on Cd remobilization with planted or unplanted treatments and Cd accumulation in tissues of edible amaranth (Liuye). With an initial soil palygorskite-bound fraction Cd concentration of 0.6 mg kg-1, bioavailable Cd in rhizosphere soils and Cd in crop shoots respectively increased from 11.4 to 20.6 µg kg-1 (dry soil weight) and 6.92 to 14.92 mg kg-1 (dry plant weight) in planted NH4+-N treatments, while significantly lower concentrations of bioavailable Cd in rhizosphere soils and Cd in crop tissues were observed with planted NO3--N treatments. Compared with that of planted NO3--N treatments, decreasing pH value (i.e., 7.64 to 7.18) induced by root proton efflux during the absorption of NH4+-N, enhancive organic/amino acid (oxalic acid, lactic acid, L-proline, and so on) secretion from roots, and increasing abundance of bacteria distributed in phyla Proteobacteria, Cyanobacteria, and Bacteroidetes with Cd mobilization ability in rhizosphere soils were the main reasons found in this study for the higher Cd remobilization in soils and Cd accumulation in crop under NH4+-N treatments. Moreover, the direct effect of NH4+-N on remobilization of immobilized Cd by upregulating the expression abundances of genes associated with pyruvate metabolism and amino acids metabolism was more significant than that of NO3--N. In summary, the use of NO3--N as preferred N fertilizer was more efficient to ensure the food safety of agricultural products than that of NH4+-N in Cd-contaminated arable soil after immobilization process.

[Safety Assessment of Rice Planting in Soil Cadmium Geological Anomaly Areas in Southwest Guangxi].

To evaluate the safety of rice planting in cadmium geological anomaly areas, 41 natural soil, 479 paddy soil, and 432 rice samples were collected in southwestern Guangxi. The contents of Cd, Cu, Ni, and Zn and soil physical and chemical properties were measured. The single factor pollution index method (Pi) was used to evaluate the degree of contamination of the sample, and correlation analysis were used to explore the main factors affecting the heavy metal content in rice. The results showed that ① soil pH of the paddy field was 6.8; the organic matter content was 39.00 g·kg-1; the risk screening value was based on the soil environmental quality standards for soil pollution risk control and control of agricultural land (GB 15618-2018), the exceeding standard rates of Cd, Cu, Ni, and Zn in soil were 60.75%, 2.09%, 0.83%, and 1.88%. ② The over-standard rates of Cd and Ni in rice were 9.03% and 4.39%, respectively. Considering straw as raw material for feed and organic fertilizer, the corresponding over-standard rates of Cd were 6.94% and 1.16%. ③ Correlation analysis showed that soil pH, organic matter, total heavy metal, and available content were the main factors affecting the content of heavy metals in rice. Cd and Ni in the study area all exhibited certain over-standard phenomena, and the low-accumulation rice varieties could be planted to reduce heavy metal content in rice.

[Spatial Distribution Characteristics and Pollution Assessment of Heavy Metals on Farmland of Geochemical Anomaly Area in Southwest Guangxi].

To understand spatial distribution characteristics and pollution status of Cd, Cu, Ni, Pb, and Zn in soils within geochemical anomaly areas in southwestern Guangxi, 256 natural and farmland soils were collected, and heavy metal contents in soils were analyzed. The results show the following:① The background values of Cd, Cu, Ni, Pb, and Zn in natural soils were 0.890, 32.58, 51.50, 55.57, and 168.1 mg·kg-1, respectively. The pH value of farmland soil (n=193) ranged from 4.8 to 7.9. The geometric mean values of Cd, Cu, Ni, Pb, and Zn were 0.637, 30.76, 27.04, 39.59, and 123.9 mg·kg-1, respectively. ② Kriging interpolation results showed that the spatial distribution characteristics of Cd, Ni, Pb, and Zn in farmland soils were similar, and high-content areas were mainly concentrated in Chongzuo-Longzhou area. The highest content of Cu was found in Tianlin County, Lingyun County, Baise City, and Tianyang County. ③ Taking the "Standard for Risk Control of Soil Pollution in Agricultural Land of Soil Environmental Quality" (GB 15618-2018) and soil baseline values as evaluation criteria, the above-standard rates of Cd, Cu, Ni, Pb, and Zn in farmland were 57.5%, 6.2%, 0.5%, 3.6%, 10.9%, and 4.1%, 14.0%, 0.5%, 2.1%, and 2.1%, respectively. The comprehensive pollution index shows that Tiandeng County, Longan County, Daxin County, Longzhou County, and Chongzuo City have severe combined pollution characteristics. The most important reason behind the high background value (particularly the Cd element) in the geochemical anomaly area of southwestern Guangxi is that the topography of the study area is complex, and the types of heavy metal deposits are numerous, which means that the parent material (rock) itself has a high content of heavy metals, which is weathered into soil. This soil inherits heavy metals from the parent material (rock).

[Cd Content Characteristics and Ecological Risk Assessment of Paddy Soil in High Cadmium Anomaly Area of Guangxi].

To investigate the levels of heavy metal Cd in paddy soils in high cadmium anomaly areas in Guangxi, and to assess their potential ecological risks to the environment. Through preliminary screening and detailed investigation, 912 pieces of soil samples from high-cadmium abnormal area were collected in multiple batches to determine the soil Cd content. The single-factor pollution index method and potential risk index method were used to control the Cd pollution degree of paddy soil. Potential risks were evaluated. The results showed that:① The average Cd values of natural soil, paddy soil, and dryland soil in the initial screening were 0.915, 0.591, and 0.593 mg·kg-1, respectively. ② In the detailed investigation, the soil pH is 4.6-8.7, which is between acidic and weakly alkaline. If the Soil Environmental Quality Standard (GB 15618-2018) is used as the evaluation standard, the Cd of the soil sample in Pingguo County, Tiandong County, Long'an County, and Liucheng County is seriously exceeded, and the soil sample in the paddy field of Rongshui Country is not polluted. Based on the soil baseline value, the Cd in the soil samples of Tiandong County, Liucheng County, and Rongshui County were non-polluting. In the paddy soils of Tianyang County, Pingguo County, Tianxian County, Daxin County, Long'an County, and Rong'an County, the proportion of Cd in mild to moderate pollution was 4.2%, 3.7%, 14.9%, 2.6%, 7.1%, and 1.4%, respectively. ③ Cd in paddy soils of nine counties and cities presents different levels of potential ecological risks. The soil Cd of some paddy fields in Tiandeng County, Daxin County, and Long'an County was at a high ecological risk ratio of 4.3%, 2.6%, and 2.4%. The soil Cd of Tianyang County, Pingguo County, Rong'an County, and Liucheng County was medium-Middle and high potential risks. Tiandong County and Rongshui County are at low potential ecological risks. In conclusion, the overall Cd in the paddy soil of the study area is high, which may affect the safe planting of rice in the long-term. It will eventually pose a health threat to local residents and should be taken care of. It is recommended to carry out research on soil cadmium bioavailability and rice cadmium accumulation in the study area in order to assess its ecological risk and health risk more scientifically and reasonably.

[Accumulation of Cd and Its Risks in the Soils of the Xijiang River Drainage Basin in Guangxi].

To understand the distribution and risk of soil cadmium (Cd) in the Xijiang River drainage basin in Guangxi, a total of 2512 soil samples were collected nonferrous metal mining area, farmland (paddy soils and dryland soils) and the background soils, in the Xijiang River drainage basin in Guangxi.The results showed that Cd concentration was 0.514 mg·kg-1 in background soils significantly higher than previously resulted(0.148 mg·kg-1)and that in Guangxi background soil(0.267 mg·kg-1). The geometric average concentration of Cd in dryland soils, paddysoils and mining soils was 0.559, 0.787, 5.71 mg·kg-1, respectively, which were significantly higher than background soils. The Cd concentration exceeded the background soils and baseline by 51.2% and 35.2% in dryland soil, 66.7% and 39.6% in paddy soil, 77.8% and 71.4% in mining soil, high Cd concentration occurred in the Nandan County, Dahua County, Duan County, Huanjiang County and Yizhou City, as well as Liujiang County, These regions have developed severe and even extremely serious pollution, medium-high pollution accumulation and higher-extremely high potential ecological risks. The Cd-pollution in soils in agricultural and mining soils in upstream of Xijiang River in Guangxi is serious, due to mining activities and high Cd geological background. People in the mining area and surrounding areas who live on local crops, vegetables, may expose to the Cd-pollution. It is recommended to further develop a Cd risk assessment through a soil-plant-human system, taking appropriate measures to control risk.