土壤外源Sb(Ⅲ)的老化对其形态和跳虫(Folsomia candida)毒性的影响

Effects of Aging on the Speciation of Trivalent Antimony in Soil and Its Toxicity to Folsomia candida

老化是影响土壤重金属生物可利用性和毒性的重要因素。为了解老化对土壤Sb形态和毒性的影响,结合化学分析和生物测试,以模式生物跳虫(Folsomia candida)为受试生物,研究了北京潮土中外源Sb(Ⅲ)分别老化7 d、60 d后价态、水溶态和急性/慢性毒性的变化。结果表明,老化仅7 d后,土壤较低浓度的Sb主要以Sb(Ⅴ)存在,而浓度较高(1 600、2 400、4 800 mg·kg-1)时Sb(Ⅴ)分别仅占47.4%、27.5%和2.2%,但老化长达60 d后,浓度最高(4 800 mg·kg-1)的土壤中Sb(Ⅴ)的比重上升到38.1%,其他浓度处理的土壤中,均以Sb(Ⅴ)为主。随着老化时间的延长,土壤中水溶态Sb含量占总Sb的比例显著降低。与土壤老化过程中毒性较大的Sb(Ⅲ)向毒性较小的Sb(Ⅴ)转化与水溶态Sb含量下降相一致,Sb对跳虫的毒性随老化时间的延长明显减弱:7 d老化后土壤Sb对跳虫急性存活的半数致死浓度(LC50)为2 105 mg·kg-1,对跳虫慢性存活的LC50为683 mg·kg-1,对跳虫繁殖的半数效应浓度(EC50)为307 mg·kg-1;老化60 d后土壤Sb对跳虫急性存活、慢性存活的LC50均大于设置的最高浓度,对跳虫繁殖的EC50为1 419 mg·kg-1。因此,对于Sb这种变价金属而言,当进行土壤Sb生态毒性评价时,为避免高估其生态风险,考虑老化作用显得尤为重要。

Metal aging in soils has been regarded as an important factor influencing its availability and toxicity to organisms. To understand the effect of aging on the speciation and toxicity of antimony （Sb） in soil, combining with chemical analysis and bioassay, we reported the changes of the oxidative state, water soluble fraction of exogenous Sb（Ⅲ） and its acute/chronic toxicity to Folsomia candida after 7 d and 60 d aging in moisture soil of Beijing. The results indicated that Sb（Ⅴ） was predominant in soil with low Sb concentrations when just being aged for 7 d, whereas only 47.4%, 27.5% and 2.2% of Sb（Ⅲ） were transformed into Sb（Ⅴ） when concentrations reached 1 600, 2 400, 4 800 mg·kg^-1, but the percentage of Sb（Ⅴ） increased to 38.1% in soil with the highest concentration of 4 800 mg·kg^-1 and the Sb（Ⅴ） predominated in the other treatments when being aged for 60 d. The water soluble Sb in soil decreased significantly during the aging. Consistent with the changes of water soluble Sb and oxidation of high toxic Sb（Ⅲ） to low toxic Sb（Ⅴ）, the toxicity of Sb to Folsomia candida reduced greatly as aging time prolonged. When the soil being aged for 7 d, the LC50 value of acute survival was 2 105 mg·kg^-1, the LC50 of chronic survival was 683 mg·kg^-1, and the EC50 values of reproduction was 307 mg·kg^-1; when the soil being aged for 60 d, the mortality did not reach 50% in acute and chronic survival test, and the EC50 of reproduction was 1 419 mg·kg^-1.Therefore, in order to avoid overestimating the ecological risk of Sb with varying oxidative state, it is especially important to consider the effect of aging.