Effect of Thioligands on Plant-Hg Accumulation and Volatilisation from Mercury-contaminated Mine Tailings

This study investigated the effect of thioligands on mercury (Hg) volatilisation and plant accumulation for Brassica junceaplants grown in mine tailings collected from artisanal gold mines in Brazil (the Serra Pelada mine) and China (the Gold Mountain mine). Plants were treated with either (NH4)2S2O3or NH4SCN and enclosed in gas-tight volatilisation chambers. Elemental Hg released from substrates was captured in a two-trap system containing 5 KMnO4dissolved in 2N H2SO4. Mercury accumulation was enhanced in the presence of (NH4)2S2O3 for plants grown in GM tailings. There was no significant increase in the plant-Hg accumulation after application of NH4SCN to the SP tailings. Volatilisation from planted substrates was not affected by the application of thioligands to either GM or SP mine tailings. Mercury volatilisation from planted substrates was significantly higher than from control substrates. Abiotic (photoreduction) and biotic (microbial interactions) factors might be linked to the enhanced plant effect on Hg volatilisation. There was no significant correlation for the Hg mass released from substrates and the amount of Hg uptake by roots and translocated to shoots. Our results indicate that volatilisation and plant-Hg accumulation are two independent processes. Thiosulphate-induced plant-Hg accumulation may be a potential tool for the phytoextraction of Hg contaminated soils but there are risks of groundwater contamination by Hg-containing leachates.