Effects of dissolved organic matter derived from cow manure on heavy metal (loid)s and bacterial community dynamics in mercury-thallium mining waste slag

Abstract

Abstract Organic amendments in aided phytostabilization of waste slag contain high levels of heavy metal (loid)s (HMs) is an important way to in situ control the release of HMs. However, the effects of dissolved organic matter (DOM) derived from organic amendments on HMs and microbial community dynamics in waste slag are still unclear. The results showed that the mercury (Hg)- thallium (Tl) mining waste slag without the addition of DOM continuously decreased pH and increased EC, Eh, SO42−, Hg, and Tl in the leachate with increasing incubation time. The addition of DOM significantly increased pH, EC, SO42−, and arsenic (As) but decreased Eh, Hg, and Tl. The addition of DOM significantly increased the diversity and richness of the bacterial community. The dominant bacterial phyla (Proteobacteria, Firmicutes, Acidobacteriota, Actinobacteriota, and Bacteroidota) and genera (Bacillus, Acinetobacter, Delftia, Sphingomonas, and Enterobacter) were changed in associated with increases in DOM content and incubation time. The DOM components in leachate were humic-like substances (C1 and C2), and the DOM content and maximum fluorescence intensity (FMax) values of components C1 and C2 in the leachate decreased and first increased and then decreased with increasing incubation time. The correlations between HMs and DOM and the bacterial community showed that the geochemical behaviours of HMs in Hg-Tl mining waste slag were directly influenced by DOM properties and indirectly influenced by DOM regulation of bacterial community changes. Overall, these results indicated that DOM properties associated with bacterial community changes increased As but decreased Hg and Tl mobilization from Hg-Tl mining waste slag.