土壤中Cr(Ⅵ)和Cr(Ⅲ)生态毒性的差异性研究

Study on ecotoxicity differences of Cr(Ⅵ)and Cr(Ⅲ)in soils

土壤铬(Cr)的毒性与其价态密切相关,为了比较不同价态Cr对多种生物指标和生态系统的毒性差异,并为Cr污染土壤的生态风险评价提供依据。本文通过文献搜集的基于中国土壤的Cr(Ⅵ)和Cr(Ⅲ)生态毒理学数据,分别建立了Cr(Ⅵ)和Cr(Ⅲ)对各生物指标的半数有效浓度(EC_(50))和10%有效浓度(EC_(10))与土壤性质关系的预测模型,在模型种间外推和归一化处理后,利用BurrⅢ构建了中性土壤情景下Cr(Ⅵ)和Cr(Ⅲ)的物种敏感性分布(SSD)曲线,并根据潜在影响比例(PAF)的公式反推出在不同PAF下Cr(Ⅵ)与Cr(Ⅲ)在生态系统水平上的毒性差异。结果表明:小白菜根伸长和土壤脱氢酶活性分别是对土壤Cr(Ⅵ)和Cr(Ⅲ)污染最敏感的生物指标;在物种水平上,两种价态Cr的毒性差异因生物指标的变化而不同;在生态系统水平上,两种价态Cr的毒性差异随PAF而发生变化,在较大的PAF范围内(基于EC_(50)和EC_(10)数据的PAF分别在84.4%和87.3%以下)和通常的保护水平(PAF为5%)下,Cr(Ⅵ)的生态毒性显著高于Cr(Ⅲ)。本研究表明Cr(Ⅵ)和Cr(Ⅲ)的生态毒性存在着显著差异,根据Cr的价态组成从生态系统毒性水平上进行研究,能够综合反映土壤Cr污染的生态风险并为土壤修复管理等提供参考。

The toxicity of soil chromiunl （Cr） is related to its valence states. The present study aims to compare the toxicity differences of various valence states of soil Cr to diverse biological indicators and ecological system, and provide a basis for ecological risk assessment of the Cr-contaminated soils. Based on the collected ecotoxicological data of Cr （ Ⅵ） and Cr（ Ⅲ ） in Chinese soils, the prediction models refleeting the quantitative relationship between median effective concentration （EC20） or 10% effective concentration （EC10） of Cr （ Ⅵ ） or Cr （Ⅲ ） and soil properties were developed, respectively. After interspecific extrapolation and normalization were processed using the prediction models, the species sensitivity distribution（SSD） curves of Cr（ Ⅵ ） and Cr（ Ⅲ ） for various biological indicators in neutral soil seenarios were fitted with Burr Ⅲ. According to the formula of potential affected fraction （PAF）, the differences between the toxicities of Cr（ Ⅵ ） and Cr（ Ⅲ ） to soil ecosystem were further evaluated in the condition of various PAFs. The results showed that root elongation of pakchoi and soil dehydrogenase activity were the most sensitive indicators for soil Cr（Ⅵ ） and Cr（ Ⅲ） contamination, respectively.The toxicity difference of the two valence states of Cr varied with distinct biological indicators at the species level and changed depending on PAF at the ecosystem level. Cr（ Ⅵ ） has the higher toxicity to soil ecosystem than Cr（ Ⅲ） in a large range of PAF（i.e. PAFs derived from EC50 and EC10 data were less than 84.4% and 87.3%, respectively） and under the common protection level（i.e.PAF was equal to 5%）.These findings indicated that the ecotoxicities of soil Cr （ Ⅵ ） and Cr （Ⅲ ） were obviously different, and the ecological risk of soil Cr contamination could be comprehensively reflected based on the valence states of Cr and their toxicities to ecosystem, which would help the restoration management of the soils contaminated with Cr.