RESUMO
In order to study the characteristics and factors influencing Cd accumulation in surface soils and crops in karst areas, and to provide a theoretical basis for safe land use, 360 surface soil samples, 7 deep soil samples, and 85 rice samples were collected from central Qianjiang District, Chongqing. The samples and 73 corn samples (corresponding to root-zone soil samples), were analysed to determine the content of Cd, TFe2 O3, Mn, organic matter (Corg), Se, and pH. Based on geostatistical analyses, the spatial distribution and Cd enrichment of the surface soils were determined and a safety evaluation for the soil and crops was carried out. The results showed that the spatial distribution of Cd in the surface soil was uneven, with the surface layer showing significant enrichment. This pattern was controlled by the soil parent material and human activities. The enrichment of surface layer was mainly affected by iron manganese oxides and organic matter (Corg). Soil Cd was mainly found at 'non-polluted' and 'lightly polluted' levels, although some areas present strong ecological risks. The main contaminated area occurs in association with Permian strata, demonstrating a geological control on soil Cd pollution. Slight-to-severe Cd pollution was identified in bulk crops; the recommended daily consumption limit for rice is 0.87 kg·d-1 and corn is 1.53 kg·d-1. The bioavailability of Cd is affected by soil pH and Se content. Under acidic conditions, Cd bioavailability is high, and crops in areas with high soil Se are safer. It is recommended that crops with low Cd accumulation are planted in the Permian outcrop area of Shuitian Township, or alternatively, soil pH should be adjusted to control the risk of Cd pollution and ensure safe land use. In addition, planting crops in areas with high soil Se content is preferable.
RESUMO
In order to determine the distribution characteristics of Se in soil-crop systems, we carried out a study on the Se-rich soil threshold by collecting 8789 surface soils and 155 deep soils in the Qianjiang District of Chongqing City, China, and 141 corn seeds and 159 rice seeds (simultaneously collecting 141 and 159 corresponding root soil samples, respectively). We then analyzed the Se content, organic matter, S, Mn, TFe2O3, Al2O3, and K2O in soils and crops, and soil pH. We also analyzed the surface layer using geostatistical methods and the distribution characteristics of Se in deep soils using multiple regression analysis to study the factors influencing the bioavailability of Se. Based on the contents of each component of root soil and the Se contents of crops, the Se rich threshold was examined. The results showed that the high-Se soils in the study area account for 32.72% of the total area; the distribution of Se contents in the surface and deep soils is mainly controlled by the parent material, the source of soil Se is stable, and the surface enrichment is obvious. The Se-rich rates of corn and rice were 75.35% and 46.81%, respectively, and soil organic matter and S content will limit the bioavailability of Se. If the planted crop is corn, it is recommended to use 0.3 mg·kg-1 as the Se-rich soil threshold; if the planted crop is rice, when the soil pH is ≤ 7.5, it is recommended to use 0.3 mg·kg-1 as the Se-rich soil threshold, while at a soil pH>7.5, it is recommended to use 0.4 mg·kg-1 as the threshold. Similarly, if other large crops are planted in the study area, this method can also be used to carry out a study on the proposed Se-rich soil threshold.
RESUMO
To investigate the impact of mining activities and geological background on the soil environment, 156 soil samples were collected from an agricultural land in southern Youyang County, Chongqing. The content and pH of heavy metals in the soil were analyzed, and the Nemerow index method was used to evaluate the pollution status of soil heavy metals. The source of soil heavy metals was discussed using the principal component analysis/absolute principal component score (PCA/APCS) receptor model. The results showed that the soil Cd pollution was distributed in a planar shape, while soil Hg mainly appeared as point pollution. The medium-severe soil pollution was mainly distributed at the junction of Tushi Town, Mawang Town, and Longtan Town, where the soil was predominantly acidic and there was a higher risk of crop contamination; the indicator Kriging evaluation results showed that there was a higher probability of soil contamination at the junction of the three towns and the northern part of Tushi Township. The results of the PCA/APCS receptor model analysis showed that the sources of soil As, Cd, Cr, and Ni were mainly controlled by geological background; soil Hg, Pb, and Zn were mainly controlled by mining activities; further, soil Cu was affected by both geological background and mining activities. In addition, the agricultural activities were also one of the sources of soil As, Cd, Pb, Cu, and Zn. The medium-heavy pollution of the soil in the study area was mainly caused by mining activities, while the heavy metal pollution of the soil caused by geological background was mainly light pollution. This study can provide a theoretical basis for the safe use of land and the prevention and control of soil pollution in typical regions.
