Isotopic Composition of Inorganic Mercury and Methylmercury Downstream of a Historical Gold Mining Region

Abstract

3We measured total mercury (THg) and monomethyl mercury (MMHg) concentrations and 4 mercury (Hg) isotopic compositions in sediment and aquatic organisms from the Yuba River 5

Methylmercury degradation and exposure pathways in streams and wetlands impacted by historical mining

“…43,50 Studies in the relatively less-contaminated Eel River (CA Coast Range), and in the gold mining contaminated Yuba River, have allowed comparison of the estimated isotopic composition of MMHg in food webs with IHg in sediment and other environmental reservoirs to infer MDF between these Hg pools. 42,44 This study, combined with the results of our previous work in the Yuba River, 42 42 This result contrasted with lower δ 202 Hg in IHg compared to MMHg (+MDF from IHg to MMHg) that was previously observed in lakes, estuaries and the coastal ocean. [51][52][53][54] In Cache Creek and Yolo Bypass, sediment is thought to be an important source of IHg that can be methylated, leading to MMHg bioaccumulation in local food webs.…”

“…in sediment and biota was measured at the USGS (Menlo Park, CA) simultaneously with samples from a previous study in the Yuba River. 42 Therefore QA/QC of MMHg analyses, reported here for the entire dataset, can also be found elsewhere. 42 Briefly, sediment was sub-sampled (20-30 mg) and extracted for MMHg using 25% KOH in methanol (25 g of KOH in 100 mL methanol) at 60°C for four hours.…”

“…42 Therefore QA/QC of MMHg analyses, reported here for the entire dataset, can also be found elsewhere. 42 Briefly, sediment was sub-sampled (20-30 mg) and extracted for MMHg using 25% KOH in methanol (25 g of KOH in 100 mL methanol) at 60°C for four hours. 55 Biota was sub-sampled (3-7 mg) and extracted for MMHg using 30% HNO3 at 60°C (overnight, 12-16 hrs), as adapted from ( 56 ).…”

“…59 In this study, we use Δ 199 Hg and Procedural blanks and two CRMs (NRC Tort-2 and NIST 1944) were processed and analyzed in an identical manner alongside samples from this study and samples from a previous study in the Yuba River. 42 Therefore, CRM and process blank measurements are reported for the entire dataset here and can also be found elsewhere (see Donovan et al 42 ).…”

“…[42][43][44] Fish feeding studies show essentially no isotopic fractionation of MMHg during trophic transfer, [45][46][47][48][49] and therefore the estimated isotopic composition of MMHg provides insight into MMHg biogeochemical transformations in the environment prior to bioaccumulation. For example, changes in Δ 199 Hg values of MMHg have been used to identify spatial changes in the extent of MMHg photodegradation between different environments (streams, forests, etc.).…”