Mercury is an important global pollutant, with the characteristics of persistence, bioaccumulation and long-distance transport. In the terrestrial, lakes and marine environment, natural organic matter (NOM) is important binding ligand for divalent inorganic mercury and methylmercury, which plays important roles in the biogeochemical cycling of mercury, including migration, distribution, bioaccumulation and toxicity. In addition, NOM plays crucial roles in the dispersion of HgS and molecular transformation of mercury and methylmercury, including reduction, oxidation, methylation of inorganic mercury and de-methylation of methylmercury. The research progress on the binding of mercury with NOM and its roles in the transformation of mercury is reviewed and future prospects in this field are discussed.

Contents
1 Introduction
2 Natural organic matter
3 Binding of Hg²⁺ and MeHg with natural organic matter
4 Molecular transformation of Hg mediated by natural organic matter
4.1 Reduction of Hg²⁺ mediated by natural organic matter
4.2 Oxidation of Hg⁰ mediated by natural organic matter
4.3 Methylation of inorganic Hg mediated by natural organic matter
4.4 Photo-demethylation of MeHg mediated by natural organic matter
5 Dispersion of HgS by natural organic matter
6 Conclusions and outlook