Abstract: Mercury is one of the widespread trace elements in coal. The large amount of coal consumption makes it as a main source of
global mercury pollution. Seven kinds of stable isotopes, both mass-dependent fractionation (MDF) and mass-independent fractionation
(MIF), and significant variations in isotopic composition of the involved coal samples, make Hg isotope an ideal way to assess sources of
Hg pollution. Mercury isotope studies of coals have made significant progress over the past twenty years, which can be summarized as
follows. Firstly, δ202Hg value and its distribution of coals from 11 countries were preliminarily researched, which from the basis of
identifying coal Hg pollution source. Secondly, MIF was found in coals, which was beneficial to do tracing studies with δ202Hg. Thirdly, δ 202Hg and Δ199Hg values in different areas and geologic periods were preliminary determined in our country. Further work may focus on
the following areas: Mercury isotope database of coals from different areas and geologic periods in the world should be supplemented,
revised and perfect. Mercury isotopes changes associated with the interactions between gas-water environment and coal mining residues
such as coal gangue and residual coal should not be neglected. Mercury isotopes of coal combustion products such as atmospheric fine
particulate matter (PM2.5) should be studied. Migration and transformation of the coal fire surface mercury is complex because partial
mercury on the surface may become secondary mercury release. This fractionation process of mercury isotope will no doubt make it
difficult to trace the pollution source with mercury isotope studies. In a word, the study of mercury and mercury isotopes of coal is
burgeoning.

Key words: coal, mercury isotopes, mass-independent isotope fractionation, geochemical tracer