Sulfur-Intercalated\nLayered Double Hydroxides Minimize\nMicrobial Mercury Methylation: Implications for <i>In Situ</i> Remediation of Mercury-Contaminated Sites

Conventional\napproaches for in situ remediation of mercury (Hg)-contaminated\nsoils and sediments rely mostly on precipitation or adsorption. However,\nthis can generate Hg-rich surfaces that facilitate microbial production\nof methylmercury (MeHg), a potent, bioaccumulative neurotoxin. Herein,\nwe prove the concept that the risk of mercury methylation can be effectively\nminimized by adding sulfur-intercalated layered double hydroxide (S-LDH)\nto Hg-contaminated soils. Hg bound to S-LDH has minimal methylation\npotential when incubated with model methylating bacteria Pseudodesulfovibrio mercurii ND132 and Geobacter sulfurreducens PCA. With a combination\nof spectroscopic and microscopic evidence, as well as theoretical\ncalculations, we confirm that dissolved Hg(II) tends to enter the\ninterlayers of S-LDH to bind to the sulfur groups intercalated within,\nleading to the formation of nanoscale metacinnabar (β-HgS).\nThis not only physically blocks the contact of methylating microorganisms\nbut also inhibits secondary release of bound mercury in the presence\nof strong binding ligands in porewater. This study highlights the\npromising concept of in situ risk reduction of heavy metal contamination\nby inducing precipitation within (nano)confined domains, achieving\na sustainable outcome of enhanced removal and reduced bioaccessibility\nfor pollutants that may otherwise be bioavailable in the form of nanoprecipitates.