Distribution and wet deposition fluxes of total and methyl mercury in Wujiang River Basin, Guizhou, China

Guizhou is one of the most seriously contaminated regions with mercury in China, but mercury deposition fluxes in this region have not been well studied. Concentrations and wet deposition fluxes of total mercury (THg) and methyl mercury (MeHg) were measured from January to December 2006 at 5 sites in Wujiang River Basin, Guizhou, China. Monthly-integrated samples were collected using bulk precipitation samplers. Samples were treated rigorously according to our trace metal protocol, and THg was analyzed by cold vapor atomic fluorescence spectrometry (CVAFS) and MeHg by aqueous phase ethylation, GC separation, and CVAFS detection. The annual volume-weighted mean concentration and wet deposition fluxes of THg and MeHg for 5 sites were 36.0 ng L−1 and 34.7 μg m−2 yr−1, and 0.19 ng L−1 and 0.18 μg m−2 yr−1 in 2006, respectively. The proportion of MeHg to THg ranged from 0.2% to 2.3%, with the mean value of 0.7%. The results also showed that each site had a similar seasonal trend for mercury concentration and wet deposition flux. The largest wet deposition fluxes of THg and MeHg occurred during the rainy season (May–October) when the rainfall was greater, whereas the highest concentrations of THg and MeHg appeared during winter months (December–February). The monthly concentrations of THg and MeHg negatively correlated well with the monthly precipitation depth (r2 = 0.17 and 0.12), suggesting that scavenging of particle-bound mercury from the atmospheric is an important mechanism contribution to mercury in rain.