[Effects of Modified Distillers' Grains Biochar on Cadmium Forms in Purple Soil and Cadmium Uptake by Rice].

Biochar and modified biochar have been widely used as remediation materials in heavy metal-contaminated agricultural soils. In order to explore economical and effective materials for the remediation of cadmium (Cd)-contaminated acidic purple soil, distillers 'grains were converted into distillers' grains biochar (DGBC) and modified using nano-titanium dioxide (Nano-TiO2) to produce two types of modified DGBCs:TiO2/DGBC and Fe-TiO2/DGBC. A rice pot experiment was used to investigate the effects of different biochar types and application rates (1%, 3%, and 5%) on soil properties, nutrient content, Cd bioavailability, Cd forms, rice growth, and Cd accumulation. The results showed that:① DGBC application significantly increased soil pH, cation exchange capacity (CEC), and nutrient content, with TiO2/DGBC and Fe-TiO2/DGBC exhibiting better effects. ② DGBC and modified DGBCs transformed Cd from soluble to insoluble forms, increasing residual Cd by 1.22% to 18.46% compared to that in the control. Cd bioavailability in soil decreased significantly, with available cadmium being reduced by 11.81% to 23.67% for DGBC, 7.64% to 43.85% for TiO2/DGBC, and 19.75% to 55.82% for Fe-TiO2/DGBC. ③ DGBC and modified DGBCs increased rice grain yield, with the highest yields observed at a 3% application rate:30.60 g·pot-1 for DGBC, 37.85 g·pot-1 for TiO2/DGBC, and 39.10 g·pot-1 for Fe-TiO2/DGBC, representing 1.13, 1.40, and 1.44 times the control yield, respectively. Cd content in rice was significantly reduced, with grain Cd content ranging from 0.24 to 0.30 mg·kg-1 for DGBC, 0.16 to 0.26 mg·kg-1 for TiO2/DGBC, and 0.14 to 0.24 mg·kg-1 for Fe-TiO2/DGBC. Notably, Cd content in rice grains fell below the food safety limit of 0.2 mg·kg-1 (GB2762-2022) at 5% for TiO2/DGBC and 3% and 5% for Fe-TiO2/DGBC. In conclusion, Nano-TiO2 modified DGBC effectively reduced the bioavailability of soil Cd through its own adsorption and influence on soil Cd forms distribution, thus reducing the absorption of Cd by rice and simultaneously promoting rice growth and improving rice yield. It is a type of Cd-contaminated soil remediation material with a potential application prospect. The results can provide scientific basis for farmland restoration and agricultural safety production of Cd-contaminated acidic purple soil.

[Main Control Factors of Cadmium Content in Rice in Carbonate Rock Region of Guangxi Based on the DGT Technique].

In order to explore the main controlling factors of Cd enrichment in rice under a geological high background in the Guangxi carbonate rock area, this study was based on rice grain-root soil samples from the carbonate rock areas in the southwest and north of Guangxi. Combined with diffusive gradients in thin films technology (DGT), the relationship between soil pH, organic matter, cation exchange capacity (CEC), DGT-Cd, and ω(rice-Cd)-BCF value in rice grains was analyzed and discussed. The main factors were determined by principal component analysis, and a quantitative model was established. The results showed that the average value of ω(soil-Cd) was 0.975 mg·kg-1, and the over-standard rate was 33.33%; the average value of ω(rice-Cd) was 0.020 mg·kg-1, and the average BCF value was 0.038, and the over-standard rate of Cd content in rice grains was 4.2%. The content of Cd in paddy soil was high, but bioavailability was low in the study area. The BCF value of rice grains in the study area was significantly negatively correlated with soil pH and cation exchange capacity at the level of 0.01, positively correlated with DGT-CD at the level of 0.01, and negatively correlated with organic matter at the level of 0.05. The results of principal component analysis showed that the total amount of Cd in the soil, pH, and DGT-Cd were the main factors affecting the accumulation of Cd in rice in the Guangxi carbonate rock area. Taking the total amount of Cd in the soil, pH, and DGT-Cd as variables, the fitting equation of BCF value of rice grains in the Guangxi carbonate rock region was established, and the determination coefficient of the model was 0.717, which could better predict the content of Cd in rice grains in this region.

[Characteristics of Antimony Migration and Transformation and Pollution Evaluation in a Soil-Crop System Around a Tin Mine in Hunan Province].

This study used 193 sets of farmland soil and agricultural product samples collected from around a tin mine in Hunan Province, China, to explore the antimony (Sb) content characteristics and pollution status of soil and agricultural products and to provide a scientific basis for the prevention and control of soil antimony pollution in antimony mining areas and the safe use of farmland. We analyzed the amount of antimony in the soil, basic physical and chemical properties, and antimony content in agricultural products; studied the characteristics of antimony migration and transformation in the soil-agricultural product system; and conducted safety assessments on soil and agricultural products. The results showed that the soil ω(Sb) in the central area of the mine, the southern area of the mine, the central township area, the urban-rural transfer area, and the northern area of the mine reached (2348±2165), (1298±884.1), (311.8±526.5), (302.5±355.9), and (215.6±183.2) mg·kg-1, and the exceeding multiples reached 65.22, 36.06, 8.66, 8.40, and 5.99 times, respectively. The antimony enrichment coefficients of lettuce, scallion, cabbage, water spinach, garlic, and pea seedlings in agricultural products were 0.01-0.1, which indicated good antimony absorption capacity. The antimony enrichment coefficients of loofah, asparagus lettuce, pepper, carrot, bitter gourd, corn, eggplant, cowpea, and celery were less than 0.01, and the antimony absorption capacity was relatively poor. The safety assessment results showed that roots, allium, and garlic vegetables had a high risk of antimony pollution; leafy vegetables and legumes had a higher risk of antimony pollution; and solanaceous vegetables, melons, and fruit vegetables and corn (cereals) had a high risk of antimony pollution. Therefore, it is urgent to take soil antimony pollution control measures in the mining area. At the same time, in order to realize the safe use of agricultural land in the mining area, the farmland far away from the low antimony content of the soil in the central area of the mine should be selected as the planting area, and the agricultural products with weak antimony absorption capacity should be planted first.

[Accumulation Effects and Health Risks of Heavy Metals in Rice in Location-based Cadmium Anomaly Area in Liuzhou].

In order to explore the migration and transformation characteristics of soil heavy metals in rice in an area of ground source cadmium anomaly and to evaluate the safe planting of rice, a total of 91 pairs of soil and rice samples were collected from paddy fields in the typical area of Liuzhou city, Guangxi province, and the contents of heavy metals such as Cd, soil pH, and organic matter were tested. The results showed that:① Cd, Cu, Ni, and Zn in the paddy field exceeded the background values of 92.31%, 34.07%, 36.26%, and 90.11%, respectively. Compared with the screening values in the Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard, Cd and Zn exceeded 30.53% and 25.26%, respectively. Super standard points were mainly distributed in Fushi Town. ② Cd and Ni exceeded 35.16% and 3.30%, respectively, and Daliang town had the highest Cd enrichment coefficient and Cd exceeded rate. ③ Correlation analysis showed that soil pH was the main influencing factor of heavy metals in rice, and Cd and Ni had similar pollution sources in rice. ④ The results of rice health risk assessment showed that the THQ value of rice Cd in Daliang town was greater than 1.0, indicating the potential health risk of rice Cd in this area. The TTHQ values were all greater than 1.0, indicating that the risks to children were higher than those to adult women, which were higher than those of adult men, showing that reasonable dietary structure is crucial to prevent heavy metal intake in different ages and genders. Therefore, there are certain risks in rice planting in the Liuzhou area of ground source cadmium anomaly, which need to be controlled using different safety utilization measures.

[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).