贵州省典型矿区土壤重金属污染对蚯蚓的毒性效应评估

选取我国贵州省某矿区典型的重金属复合污染土壤开展28 d慢性毒性暴露试验,以蚯蚓体内2种抗氧化酶活性——过氧化氢酶(CAT)和超氧化物歧化酶(SOD)、8-羟基脱氧鸟苷(8-ODHG)和金属硫蛋白(MT)含量为生物指标,评估了以上生物指标与土壤重金属含量的相关性,探讨该研究方法用于矿区土壤重金属生态风险评估的可行性。结果表明,CAT和SOD在暴露周期内均出现先诱导后抑制的动态响应过程,表明蚯蚓通过提高CAT和SOD的活性来清除机体因污染胁迫而产生的自由基,以适应环境变化,在毒性缓解后,蚯蚓体内代谢产物的积累抑制了抗氧化氢酶活性,CAT和SOD活性下降并趋于稳定。暴露于重金属污染亚致死浓度时,蚯蚓体内的8-OHDG含量随着暴露时间的延长显著降低,随着暴露浓度的增加,损伤存在由低到高的转变。在28 d暴露周期内,蚯蚓体内MT在重金属胁迫下发挥了解毒作用,MT含量在蚯蚓暴露后第7天增加,随后逐渐降低。本文基于生物毒性试验综合评估了矿区典型重金属污染土壤的生态风险,研究结果对指导重金属复合污染土壤的修复与再利用具有重要意义。

Evaluation of Toxicity Effects of Heavy Metal Contaminated Soils on Earthworm (Eisenia foetida) in a Mining Area of Guizhou Province

Typical soils contaminated by multiple heavy metals were collected from a mining area in Guizhou province for 28d chronic toxicity assay. Activity of antioxidant enzymes, i.e. catalase (CAT) and superoxide dismutase (SOD), 8-hydroxy deoxyguanosine (8-OHDG) and metallothionein (MT) in the earthworm (Eisenia foetida) were determined to evaluate correlations between these indicators and soil heavy metal contents. Feasibility of using these indicators to assess ecological risk of heavy metal contaminated mining soils was investigated. Results showed that the activity of CAT and SOD in earthworms increased firstly, and was inhibited thereafter during the exposure duration. This might suggested that activity of CAT and SOD in earthworm was raised to remove free radicals caused by stress of heavy metal contamination so as to adapt to changes of the environment. The accumulation of metabolites in earthworms after alleviating of metal toxicity inhibited activity of antioxidant enzymes, which led to decrease in CAT and SOD activity. When exposed to sub-lethal heavy metal concentrations, content of 8-OHDG in earthworms showed significant decrease with exposure time. With increase in exposure concentrations, more serious damages on 8-OHDG were observed. Within the exposure duration of 28 days, MT in earthworm played a detoxification role under the stress of heavy metal contamination. MT contents increased after 7 days of exposure and decrease thereafter. This study performs a comprehensive evaluation on ecological risk of typical heavy metal contaminated soils of a mining area based on toxicity assay. Results of this study will be helpful to guide remediation of heavy metal contaminated soils as well as its reuse after treatment.