Geological Survey of Jiangsu Province, Nanjing, 210018, China.
Department of Geosciences, Faculty of Land Resource Engineering, Kunming University of Science and Technology, Kunming, 650093, China.
Environ Geochem Health. 2022 Feb;44(2):301-318. doi: 10.1007/s10653-021-00876-4. Epub 2021 Mar 24.
This study developed a method to build relationships between chemical fractionations of heavy metals in soils and their accumulations in rice and estimate the respective contribution of each geochemical speciation in the soils from the Yangtze River Delta, China. In contaminated areas, residue and humic acid-bound fractions in soils were the main phases for most heavy metals. The mobility of heavy metals was in this following order: Cd > Pb ≈ Zn > Ni > As ≈ Cr > Hg. Transfer factors calculated by the ratios of specific fractionations of heavy metals in the soil-rice system were used to assess the capability of different metal speciation transfer from soil to rice. The carbonate and Fe/Mn oxyhydroxides bound phase had significant positive correlations with total metal concentrations in rice. Hg uptake by rice might be related to the exchangeable and carbonate-bound fractions of soil Hg. Results of PCA analysis of transfer factors estimated that the labile fractions (i.e. water soluble, exchangeable and carbonate bound) contributed more than 40% of the heavy metal accumulations in rice. Effect of organic matter and residue fraction on metals transfer was estimated to be ~ 25 to ~ 30% while contribution of humic acid and Fe/Mn oxyhydroxides-bound fractions was estimated to be ~ 20 to ~ 30%. Modified risk assessment code (mRAC) and ecological contamination index (ECI) confirmed that the soil samples were polluted by heavy metals. Soil Cd contributed more than 80% of mRAC. Contrarily, the main contributors to ECI were identified as As, Hg, Pb and Zn. The average values of total target hazard quotient (TTHQ) and Risk were above 1 and 10 respectively, implying people living in the study area were exposed to both non-carcinogenic and carcinogenic risk. As and Pb were the main contributor to high TTHQ value while As, Cd and Cr in rice contributed mostly to Risk value. Spatial changes of ecological risk indexes and human health risk indexes showed that the samples with high TTHQ values distributed in the area with high values of mRAC. Likewise, the area with high ECI values and with high carcinogenic risk overlapped.
本研究开发了一种方法，用于建立土壤中重金属的化学形态与其在水稻中的积累之间的关系，并估计来自中国长江三角洲土壤中各地球化学形态的各自贡献。在污染地区，土壤中残渣和胡敏酸结合态是大多数重金属的主要形态。重金属的迁移性按以下顺序排列：Cd> Pb≈Zn>Ni>As≈Cr>Hg。通过土壤-水稻系统中重金属特定形态比计算得出的转移因子来评估不同金属形态从土壤向水稻转移的能力。水稻中重金属的碳酸盐和铁/锰氢氧化物结合相与重金属总量呈显著正相关。水稻对汞的吸收可能与土壤汞的可交换态和碳酸盐结合态有关。基于转移因子的 PCA 分析结果表明，不稳定态（即水溶性、可交换态和碳酸盐结合态）贡献了水稻重金属积累的 40%以上。有机质和残渣态对金属转移的影响估计在 25%至 30%之间，而胡敏酸和铁/锰氢氧化物结合态的贡献估计在 20%至 30%之间。改良风险评估码（mRAC）和生态污染指数（ECI）证实土壤样品受到重金属污染。土壤 Cd 对 mRAC 的贡献超过 80%。相反，ECI 的主要贡献者被确定为 As、Hg、Pb 和 Zn。总目标危害系数（TTHQ）和风险的平均值分别高于 1 和 10，这表明研究区域的居民面临着非致癌和致癌风险。As 和 Pb 是 TTHQ 值高的主要原因，而水稻中的 As、Cd 和 Cr 则主要导致 Risk 值高。生态风险指数和人类健康风险指数的空间变化表明，高 TTHQ 值的样品分布在 mRAC 值高的区域。同样，高 ECI 值和高致癌风险区域也存在重叠。
