Methylmercury formation in boreal wetlands in relation to chemical speciation of mercury(II) and concentration of low molecular mass thiols

Methylmercury (MeHg) is a neurotoxin formed from inorganic divalent mercury (HgII) via microbial methylation, and boreal wetlands have been identified as major sources of MeHg. There however lack studies investigating the relationship between chemical speciation HgII MeHg formation in such environments, particular regarding to role thiol compounds. We determined methylation potentials, kmeth, wetland soils using two isotope tracers: 198Hg(OH)2(aq) bonded groups natural organic matter, 200HgII–NOM(ads), representing with high low availability for methylation. The tracer was consistently methylated 5-fold higher extent than independent environmental conditions. This suggests that concentration porewater decisive factor A comprehensive thermodynamic model (including complexes sulfide (H2S), polysulfides (H2Sn), thiols associated matter (NOM–RSH) specific molecular mass (LMM–RSH) provided new insights on porewaters, but did not demonstrate any clear kmeth calculated speciation. In contrast, significant positive relationships were observed sum LMM compounds biological origin. suggest possible mechanisms underlying these correlations: 1) kinetically control size composition pool available uptake, and/or 2) are produced by microbes correlation reflects relation activity formation.