Rice is an important source of Se for billions of people throughout the world. The Wanshan area can be
categorized as a seleniferous region due to its high soil Se content, but the Se content in the rice in
Wanshan is much lower than that from typical seleniferous regions with an equivalent soil Se level. To
investigate why the Se bioaccumulation in Wanshan is low, we measured the soil Se speciation using a
sequential partial dissolution technique. The results demonstrated that the bioavailable species only
accounted for a small proportion of the total Se in the soils from Wanshan, a much lower quantity than
that found in the seleniferous regions. The potential mechanisms may be associated with the existence of
Hg contamination, which is likely related to the formation of an inert HgeSe insoluble precipitate in soils
in Wanshan.