Mercury pathways in the carson river—lahontan reservoir system, nevada, usa

Abstract

Concentrations of mercury (Hg) were determined in surface waters and associated river bank sediment samples in a river—reservoir system contaminated by mine wastes. The distribution of total and methyl Hg in surface waters along the Carson River was similar to that measured in river bank sediments and influenced by flow regimes. High levels of Hg (up to 7,585 and 7.2 ng Hg/L for total and methyl Hg, respectively) determined on surface water samples were in large part discharged from Hg‐contaminated tailings, distributed in the river bank sediments. Once introduced into the river during the spring snowmelt runoff, Hg was transported downstream and accumulated in the lacustrine part of the system. Elemental Hg (Hg0) increased from 0.02 ng/L in the noncontaminated region to about 2 ng/L in the reservoir. The vertical distribution of total methylmercury (MeHgT) in water of the reservoir differs from that observed elsewhere, in both Hg‐contaminated and noncontaminated lakes. The highest levels of MeHgT (<1 ng/L as Hg) and acid‐reactive Hg (4 ng/L) were observed in the alkaline and oxic surface waters. The decrease of pH with depth and the absence of oxygen in depth >10 m did not enhance MeHg production. In the anoxic hypolimnion of the reservoir, the recycling of MeHgT was more influenced by the redox cycling of Mn. The addition of group VI anions (SeO2−4, MoO2−4, and WO2−4) in the range of concentrations of oxyanion‐forming elements found in the Carson River system to anoxic sediment slurry spiked with SO2−4 resulted in the reduction of rates of MeHg production. Their negative effect on MeHg production was enhanced by increasing pH. Group VI anions, analogous to SO2−4 are inhibitory to sulfate‐reducing bacteria, which are known to play a key role in MeHg production in anoxic sediments. Accordingly, the particular water geochemistry of the Carson River system could partly explain the observed low levels of MeHg where one would expect higher concentrations.

Is Clear Lake Methylmercury Distribution Decoupled From Bulk Mercury Loading

“…For example, the MeHg:TotHg ratios for most parameters typically resemble more pristine or non-contaminated sites. Contaminated sites (dashed boxes): 6, eutrophic lake influenced by urban sources in Saskatchewan, Canada (urban wastes; Jackson 1986); 7, reservoir and pond in Wanshan, China (Hg mining; Horvat et al 2003); 8, Lahontan Reservoir, Nevada, USA (gold/silver mining; Bonzongo et al 1996); 9, Onondaga Lake, New York (chloralkali plant; Henry et al 1995, Jacobs et al 1995; 9A, maximum for epilimnion; 9B, maximum for hypolimnion); 10, Clay Lake, Ontario (chloralkali plant; Parks et al 1989; 10A, maximum for epilimnion; 10B, maximum for hypolimnion). 8), remote lakes appear to produce as much MeHg as Clear Lake, but from approximately one to two orders of magnitude lower TotHg.…”

Inhibition of mercury methylation in anoxic freshwater sediment by group VI anions

“…Surface sediment samples (0–5 cm) were collected upstream of “Table Mountain,” a sampling site in the Carson River‐Lahontan Reservoir system, located about 44 km downstream of Carson City. The area under study and the sampling location have been described in detail elsewhere [9–11]. Samples were collected using clean polyethylene shovels and put in new Whirl‐pack® bags (Fisher Scientific, Fairlawn, NJ, USA).…”

“…Recovery of MeHg from spiked sediment samples averaged 93 ± 3% ( n = 5). Hg T in sediment samples was determined as described by Bonzongo et al [10]. Sediment water‐extractable sulfate was determined by ion chromatography.…”

“…For example, values as high as 0.1 mM and 0.7 mM for Mo and W, respectively, have been found in terminal lakes of these aquatic systems. Our previous investigations of concentrations and fate of Hg in the Carson River‐Lahontan Reservoir system showed that, although the level of total‐Hg (Hg T ) is high, concentrations of MeHg in both water and sediment are relatively low, particularly in the artificial terminal basin (Lahontan Reservoir) where large values would be expected [9–11].…”

Reviews of Environmental Contamination and Toxicology

“…Mercury contamination was still severe in this region in 1993 (see Table 2). Nevada authorities have issued health advisories against fish consumption from the Carson River; an 80-km stretch of the river has been declared a Superfund site (Da Rosa and Lyon 1997 ), both of which are inhibitory to sulfate-reducing bacteria known to play a key role in methylmercury production in anoxic sediments (Bonzongo et al 1996a). Methylmercury concentrations ranged from 0.1 to 0.7 ng/L in this ecosystem and were positively associated with total suspended solids (Bonzongo et al 1996b).…”