Quantitative evaluation of ecological toxicity effect of real heavy metal combined pollution in site soil

Quantitative evaluation of ecological effect of combined pollution of heavy metals in real site soil is considered as a great issue in ecological risk assessment of contaminated sites. In this work, a quantitative ecological assessment approach for combined contaminated soil in field by heavy metals was developed based on “top-down” and “bottom-up” knowledge, which was made up of three steps, namely, “screening of effective biomarkers-identification of dominant pollutants-evaluation of joint effect of different exposure types/contaminants”. Finally, taking an abandoned electronic planting site in Jiangsu Province as a case, the developed approach was verified using soil microcosm of earthworm. Results of the experiment by taking the biomarkers including malondialdehyde (MDA), metallothionein (MT), catalase (CAT), superoxide dismutase (SOD), reduced glutathione (GSH)as effect endpoints, suggested that the bioaccumulation of main heavy metal contaminants including Cd, Cu, Zn, Ni, Pb and Cr by earthworms ranged in an order: Cd>Cu>Zn>Ni>Pb>Cr. Principal component analysis (PCA)revealed that GSH, CAT and MDA were screened as effective biomarkers, and heavy metals Cd and Zn were dominant contaminants. It was found that there was a significant multivariate linear relationship between the change of GSH and concentrations of total Cd and DTPA-Zn in soil. And the change of MDA could be predicted by DTPA-Cd in soil. The change of CAT activity was predictive by the total Zn in soil and the bioaccumulated Zn in earthworm. Evaluation of half effect dose (EC50) based on the site-specific soil properties and heavy metal contamination characteristics revealed that the sensitivity of the 3 screened effective biomarkers ranged in an order: GSH>CAT>MDA. Interactions will occur in between different heavy metals and exposure types (e.g., between soil total Cd and DTPA-Zn corresponding to GSH change), and (or) in between different exposure types of the same heavy metal (e.g., between soil total Zn and bioaccumulated Zn corresponding to the change of CAT activity)