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

Science of the Total Environment
By: , and 

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Abstract

Monomethyl mercury (MMHg) and total mercury (THg) concentrations and Hg stable isotope ratios (δ202Hg and Δ199Hg) were measured in sediment and aquatic organisms from Cache Creek (California Coast Range) and Yolo Bypass (Sacramento Valley). Cache Creek sediment had a large range in THg (87 to 3870 ng/g) and δ202Hg (−1.69 to −0.20‰) reflecting the heterogeneity of Hg mining sources in sediment. The δ202Hg of Yolo Bypass wetland sediment suggests a mixture of high and low THg sediment sources. Relationships between %MMHg (the percent ratio of MMHg to THg) and Hg isotope values (δ202Hg and Δ199Hg) in fish and macroinvertebrates were used to identify and estimate the isotopic composition of MMHg. Deviation from linear relationships was found between %MMHg and Hg isotope values, which is indicative of the bioaccumulation of isotopically distinct pools of MMHg. The isotopic composition of pre-photodegraded MMHg (i.e., subtracting fractionation from photochemical reactions) was estimated and contrasting relationships were observed between the estimated δ202Hg of pre-photodegraded MMHg and sediment IHg. Cache Creek had mass dependent fractionation (MDF; δ202Hg) of at least −0.4‰ whereas Yolo Bypass had MDF of +0.2 to +0.5‰. This result supports the hypothesis that Hg isotope fractionation between IHg and MMHg observed in rivers (−MDF) is unique compared to +MDF observed in non-flowing water environments such as wetlands, lakes, and the coastal ocean.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Methylmercury degradation and exposure pathways in streams and wetlands impacted by historical mining
Series title Science of the Total Environment
DOI 10.1016/j.scitotenv.2016.04.139
Volume 568
Year Published 2016
Language English
Publisher Elsevier
Contributing office(s) National Research Program - Western Branch, Toxic Substances Hydrology Program
Description 12 p.
First page 1192
Last page 1203
Country United States
State California
Other Geospatial Cache Creek, Yolo Bypass
Online Only (Y/N) N
Additional Online Files (Y/N) N