Species distribution and potential bioavailability of exogenous Hg (II) in vegetable-growing soil investigated with a modified Tessier scheme coupled with isotopic labeling technique

The species distribution of exogenous Hg (II) simulated to contaminate vegetable-growing soil has been investigated by a modified Tessier scheme of sequential extraction procedures (SEPs) detected with a quantitative analytical method and an isotopic labeling method, respectively. The results showed that the summed value of Hg concentrations in all eight species extracted with the SEPs protocol was lower than the total Hg concentration directly measured in soil. The exogenous Hg (II) was found to rarely distribute in the residual species (the maximum fraction in soil with more than 70% of intrinsic Hg), which indicated that Hg species in residual fraction might be inert for plants. However, the exogenous Hg (II) was found to largely distribute in humus substances, in which humic acid could effectively immobilize and weaken the bioactivity of Hg in soil, while fulvic acid bound Hg might be readily assimilated by plants. The exogenous Hg (II) was also found to readily distribute in water-soluble fractions and exchangeable fractions of soil which would result in serious impacts on plants. Little exogenous Hg (II) was observed to distribute in the fractions of carbonate, Fe/Mn oxides and organically bound species, which meant that the toxicity and bioavailability of these Hg species might be slight for plants. The results suggest that the isotopic labeling technique coupled with the modified Tessier scheme provides a novel method which can distinctly indicate the distribution, mobility and potential bioavailability of exogenous Hg (II) in contaminated soil.