Distribution and origin of mercury in soils of middle to south Kinki and Shikoku districts

Abstract

Concentration and stable isotope ratios of mercury were analyzed for the soils taken from Kii Peninsula to Shikoku. Mercury concentrations of more than 600 soil samples, including those of soils taken from surroundings of Osaka Plain, were mapped, and zonal distribution of highly concentrated mercury occurrence appeared in the south of Median Tectonic Line of Kii Peninsula and Shikoku (Median: 198 µg/kg; Average: 275 µg/kg). Mercury stable isotope ratios of 10 samples were within the same range of those of groundwaters taken near the faults in the surrounding Osaka Plain or smaller than those (delta²⁰²Hg: -2.5 - -0.4 pamil). Mass-independent fractionation was not observed for those isotope values. Thus, the geogenic mercury is presumed to emit in association with vapor-fluid fractionation to the surface.