Fractionation, distribution and transport of mercury in rivers and tributaries around Wanshan Hg mining district, Guizhou province, southwestern China: Part 1-Total mercury

The Wanshan Hg mining area in Guizhou, China, was one of the world’s largest Hg producing regions. Numerous mine-waste and calcines still remain, leaching Hg to local rivers and streams and potentially impacting the local population. Several studies have been published on local environmental impacts of these mining and retorting residues, but a comprehensive, regional survey on the distribution of Hg in the rivers in the region, as presented in this paper, has not previously been conducted. This study focuses on the regional distribution and temporal variation of aqueous Hg fractions in the five main watercourses draining the Wanshan Hg mining and retorting area, covering more than 700 km2. Three sampling campaigns were carried out in 2007 and 2008, covering high flow, normal flow and low flow periods. Total (THg), particulate (PHg), dissolved (DHg) and reactive (RHg) Hg fractions were determined. All rivers had the highest Hg concentrations at sample sites about 100–500 m downstream of the mine wastes. Total Hg concentrations ranged from extremely high (up to 12,000 ng L-1) at the sample site just 100 m below mine wastes, to quite low in tributary streams (1.9 ng L-1, about 14 km downstream of the mine wastes). Total Hg and PHg concentrations were usually highest during high flow periods in the Hg-contaminated areas (i.e. THgP50 ng L-1), while in the less-impacted downstream areas (with THg