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我国土壤镉的点位超标率为7.0%,在诸多无机污染物中居首[1]。镉可通过多种途径进入人体,对多个组织器官存在毒害作用[2-3]。对于建设用地的场景以及长期户外劳作、卫生意识较差的特定人群,污染土壤的口部暴露已成为其机体镉摄入的最大贡献者。然而,即便是我国最新的土壤污染风险管控标准[4]和相应的评估技术导则[5],仍沿用传统的基于重金属总量的评估手段,这将高估土壤重金属对人体的健康风险,以镉等污染物的生物可给性(Bioaccessibility)为科学依据的in vitro试验方法学已得到国际学界的广泛认可,而PBET(Physiologically Based Extraction Test)[6]及IVG(In Vitro Gastrointestinal)[7]是其中最被广泛接受和应用的两个主流模型[8-10]。In vitro试验有一个重要的应用研究方向是探索哪些因素乃影响土壤镉生物可给性的关键,而前人的研究大致从两个方面开展。首先,土壤基本理化特性方面,与pH相关的研究最为丰富,如Tang等[11]的研究表明,土壤镉在模拟人体胃肠消化过程中的生物可给性与土壤pH无相关性;而崔岩山和陈晓晨[12]研究发现,模拟胃液中镉的生物可给性与土壤pH呈显著负相关。Mendoza等[13]发现土壤质地与土壤镉的生物可给性显著相关,然而Xia 等[14]却得出了与之相悖的结论。此外,阳离子交换量[11]、氧化铁铝含量[14] 、土壤有机质含量[15]也被视为可能影响土壤镉生物可给性的因素。其次,在镉的赋存形态方面,单步/Tessier连续提取法[16]是解析土壤镉赋存形态的经典方法。苏彬彬[17]的研究表明,氯化钙提取态镉含量与人体胃阶段镉的生物可给性呈显著正相关;Tang等[11]研究表明,几种供试土壤中镉的生物可给性均与可交换态镉含量存在显著正相关,与残渣态镉含量存在显著负相关。尽管前人在探究土壤镉的生物可给性的影响因素方面做了大量的工作,但得到的结果却不尽相同甚至相反,这意味着土壤镉的生物可给性是受包括土壤类型在内的多种因素共同影响的。前述研究所涉及的土壤类型及影响因素都相对单一而片面,急需具有全面性和综合性的研究来弥补。
本研究针对红壤、棕壤、褐土和黑土这四种中国典型土壤,制备人工镉污染土,基于in vitro试验方法分析土壤镉在人体胃及小肠阶段的生物可给性并评估其健康风险,之后结合对土壤基本理化特性和镉赋存形态的全面测定,综合阐释镉的生物可给性的影响因素,以期为今后大规模污染土壤风险评估工作的精准化提供有价值的参考。
中国典型土壤中镉的生物可给性影响因素研究及其健康风险评估
Influencing factors of Cd bioaccessibility in China’s representative soils and the human health risk assessment
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摘要: 采集我国红壤、棕壤、褐土和黑土等4种典型土壤,制备成镉含量为180 mg·kg−1的人工污染土,基于in vitro试验方法分析土壤镉在人体消化道不同阶段的生物可给性并评估健康风险,之后结合对土壤基本理化特性和镉赋存形态的全面测定,阐释镉的生物可给性的影响因素以及土壤间差异的原因。结果表明,镉在胃阶段的生物可给性(94.36%—96.54%)显著高于小肠阶段(50.46%—80.07%);各土壤镉经口部摄入的致癌风险均超过可接受限值2个数量级,而非致癌风险未超限。此外,土壤镉的生物可给性与氯化钙提取态镉含量、迁移系数以及土壤有机质含量存在相关性,而影响土壤镉在胃阶段生物可给性的主导因子为迁移系数,小肠阶段则为土壤有机质含量。本研究体现了in vitro试验方法的优越性,其成果将为大规模污染土壤风险评估工作的精准化做出积极贡献。Abstract: In this study, four typical Chinese soils (i.e., red soil, brown soil, cinnamon soil and black soil) were artificially contaminated with a Cd concentration of 180 mg·kg−1. The bioaccessibility of soil Cd was then studied using in vitro test, and the relevant health risk was assessed. Besides, the influencing factors on Cd bioaccessibility, together with the causes for differences between soils, were investigated from the aspects of physicochemical properties and Cd fractionation of the soils. Results showed that the bioaccessibility of Cd in the gastric phase (94.36%—96.54%) was significantly higher than that in the small intestinal phase (50.46%—80.07%). The carcinogenic risk of Cd in all soils was two orders of magnitude higher than the acceptable limit, while the non-carcinogenic risk did not exceed it. In addition, the bioaccessibility of soil Cd was found closely correlated with the content of CaCl2 extractable-Cd, the mobility factor and the content of soil organic matter. The latter two were determined to be the dominant factors of soil Cd bioaccessibility in the gastric phase and the small intestinal phase, respectively. The superiority of in vitro test was showed in this study, and the results make contributions to the accurate health risk assessment of contaminated soils in large scale.
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Key words:
- soil /
- Cd /
- in vitro test /
- bioaccessibility /
- health risk /
- soil property
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表 1 土壤镉对人体的健康风险
Table 1. Human health risks of soil Cd
土壤类型
Soil type胃阶段Gastric phase 小肠阶段Small intestinal phase 致癌风险
Carcinogenic risk非致癌风险
Non-carcinogenic risk致癌风险
Carcinogenic risk非致癌风险
Non-carcinogenic risk红壤
Red soil3.86×10−4±5.59×10−6 a 3.85×10−1±5.58×10−3 a 3.21×10−4±1.22×10−5 a 3.19×10−1±1.21×10−2 a 棕壤
Brown soil3.80×10−4±2.28×10−6 a 3.79×10−1±2.27×10−3 a 3.10×10−4±8.69×10−6 ab 3.09×10−1±8.66×10−3 ab 褐土
Cinnamon soil3.78×10−4±4.05×10−6 a 3.76×10−1±4.04×10−3 a 2.96×10−4±8.06×10−6 b 2.95×10−1±8.03×10−3 b 黑土
Black soil3.79×10−4±3.77×10−6 a 3.78×10−1±3.75×10−3 a 2.02×10−4±7.52×10−6 c 2.01×10−1±7.50×10−3 c 注:同一列不同英文字母表示土壤间存在显著的差异(P<0.05).
Note: Different letters in the same column indicate significance of difference between soils (P<0.05).表 2 土壤基本理化特性
Table 2. Basic physicochemical properties of the soils
土壤类型
Soil typepH 有机质/(g·kg−1)
Organic matter黏粒含量/(g·kg−1)
Clay阳离子交换量/(cmol·kg−1)
CEC游离氧化铁/(mg·kg−1)
Free Fe oxide游离氧化铝/(mg·kg−1)
Free Al oxide红壤
Red soil5.23 3.6 300 2.08 11210 1909.5 棕壤
Brown soil7.37 6.3 160 10.72 9215 1163.5 褐土
Cinnamon soil7.07 9.3 280 11.20 14350 1779.0 黑土
Black soil6.37 99.2 200 16.36 11335 1860.5 表 3 土壤基本理化特性与土壤镉生物可给性之间的相关性
Table 3. Correlations between soil physiochemical properties and bioaccessibility of soil Cd
项目
ItempH 有机质
Organic matter黏粒含量
Clay阳离子交换量
CEC游离氧化铁
Free Fe oxide游离氧化铝
Free Al oxide镉的生物可给性(胃)
Cd bioaccessibility in gastric phase−0.833 −0.337 0.406 −0.859 −0.387 0.229 镉的生物可给性(小肠)
Cd bioaccessibility in
small intestinal phase−0.410 −0.991** 0.358 −0.806 −0.061 −0.328 *和**分别表示显著相关(P<0.05)和极显著相关(P<0.01).
* and ** indicate significant correlation (P<0.05) and extremely significant correlation (P<0.01), respectively.表 4 氯化钙和DTPA提取态镉含量
Table 4. Concentrations of CaCl2- and DTPA-extractable Cd
土壤类型
Soil type氯化钙提取态镉/(mg·kg−1)
CaCl2-extractable CdDTPA提取态镉/(mg·kg−1)
DTPA-extractable Cd红壤
Red soil116.26 92.60 棕壤
Brown soil7.41 86.59 褐土
Cinnamon soil5.67 69.06 黑土
Black soil4.13 127.05 表 5 土壤镉的赋存形态与镉的生物可给性之间的相关性
Table 5. Correlations between soil Cd fractions and Cd bioaccessibility
项目
Item镉的生物可给性(胃)
Cd bioaccessibility in gastric phase镉的生物可给性(小肠)
Cd bioaccessibility in small intestinal phase氯化钙提取态镉CaCl2-extractable Cd 0.959* 0.491 DTPA提取态镉DTPA-extractable Cd 0.082 −0.822 迁移系数Mobility factor 0.960* 0.685 *表示显著相关(P<0.05).
*Indicates significant correlation (P<0.05).表 6 土壤镉的生物可给性与影响因素的多元回归
Table 6. Multivariate regression analysis between bioaccessibility of soil Cd and the influencing factors
因变量(Y)
Dependent variable (Y)回归方程
Regression equation决定系数(R2)
Determination coefficient (R2)显著性(P)
Significance (P)镉的生物可给性(胃)
Cd bioaccessibility in gastric phaseY=87.031+10.716MF 0.921 P<0.05 镉的生物可给性(小肠)
Cd bioaccessibility in small intestinal phaseY=79.038−0.289OM 0.982 P<0.01 注:MF为迁移系数;OM为有机质含量.
Note: MF stands for mobility factor; OM stands for organic matter. -
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