LAUSR

To date, the Xunyang mercury (Hg) mining district is the only ongoing large-scale Hg mining district in China. To understand the influence of Hg contamination mode from the Hg mining and smelting activities, 27 sampling sites in the Xunyang Hg mining district were chosen in this study. Total gaseous mercury (TGM) in ambient air was measured using a Lumex-RA915 automatic Hg analyzer in 2011. Rice samples and soil samples from rhizosphere were collected systematically and simultaneously. Total Hg (THg) and methylmercury (MeHg) concentrations in rice grain and soil samples and Hg speciation with modified sequential selective extractions were measured. The local environment was seriously polluted with Hg. The TGM (302 ± 376 ng·m−3, ranging from 24 to 2220 ng·m−3) in the local ambient air, THg (28 ± 30 mg·kg−1, ranging from 0.31 to 121 mg·kg−1) and MeHg (2.3 ± 1.9 μg·kg−1, ranging from 0.24 to 8.9 μg·kg−1) in soil samples were at the sample level with Hg contaminated area. The THg concentration (26 ± 16 μg·kg−1 ranging from 4.5 to 71 μg·kg−1) in most of the rice grain samples clearly exceeds the threshold level (20 μg·kg−1) in the Chinese national guidelines for cereals (NY 861-2004). The inorganic mercury (IHg) (9.1 ± 5.6 μg·kg−1, ranging from 1.2 to 24 μg·kg−1) and MeHg (14 ± 9.8 μg·kg−1, ranging from 2.1 to 59 μg·kg−1) concentration in rice grain samples were at the same level with Hg contaminated area. The main species of Hg in paddy soils reveal strong complex Hg and residue Hg. According to the correlation analysis, a Hg pollution mode from local Hg mining and smelting was hypothesized, including Hg emission, transportation, methylation, and uptake process.