外源有机酸对蚯蚓Zn积累的影响及毒性研究

Study on the Effect of Exogenous Organic Acid on Zn Uptake in Earthworm(Eisenia fetida) and Ecological Toxicity

为研究外源有机酸是否会增加土壤动物蚯蚓对重金属的吸收,从而加剧重金属对土壤生态系统的危害,采用溶液法,以锌为目标污染物,研究添加有机酸(乙酸、草酸、柠檬酸和EDTA)后,重金属对蚯蚓的毒害效应。结果表明,有机酸能有效缓解Zn对蚯蚓的毒性,缓解强弱顺序为EDTA>柠檬酸>草酸>乙酸,主要表现为蚯蚓死亡率降低。暴露在Zn浓度为5,10,15 mg/L的溶液中时,死亡率分别为20%,55%,83.75%,随着有机酸浓度增加,蚯蚓死亡率下降越显著;抗氧化酶(SOD、CAT)和丙二醛(MDA)含量下降,不同的有机酸对蚯蚓SOD、CAT活性的影响不一,MDA含量则有明显的下降趋势,甚至接近于对照水平。这主要是由于有机酸抑制了蚯蚓对Zn的富集,有机酸的络合作用改变了Zn的亚细胞分布,E(胞残渣)组分的比例下降,而H(热稳定组分)组分上升,从而降低了重金属所引起的毒害。因此,有机酸在控制重金属的生物可利用性方面具有重要作用。

In order to study whether exogenous organic acid can enhance the uptake of heavy metals by earthworms and aggravate the harm to the soil ecosystem,this paper adopted simulated soil solution test and selected Zn as target pollutant,to investigate the effects of organic acids（acetic acid,oxalic acid,citric acid and EDTA）on Eisenia fetida exposed to different concentrations of Zn.The results showed that,organic acids had obvious detoxification effect to Zn toxicity of Eisenia fetida,with the detoxification effect increasing in the order of acetic acid〈oxalic acid〈citric acid〈EDTA,which took the form of the decreasing mortality of earthworms.When the earthworms were exposed to the Zn solution of the concentrations of 5mg/L,10mg/L and 15mg/L,the mortalities of earthworms were 20%,55%and 83.75%,respectively,and with the increase of organic acids concentration,the earthworm mortality reduced.The contents of antioxidant enzymes（SOD and CAT）and malondialdehyde（MDA）reduced with the increase of organic acid concentration,and different organic acids had different effects on SOD and CAT,but the content of MDA decreased obviously,even close to the control level.The detoxification mechanisms of organic acids for Zn should be related with their inhibition capacity of Zn enrichment in earthworms and complexation effect,which changed the subcellular distribution of Zn,decreasing the ratio of E component and increasing the ratio of H component.Thus,the organic acids reduced the toxicity of the heavy metal.Therefore,organic acids play an important role in the control of biological availability of heavy metals.