USGS Science⌕ Search
Home/Archive/USGS

USGS · 70265839

Sulfate reduction drives elevated methylmercury formation in water column of eutrophic freshwater lake

Benjamin D. Peterson·Sarah E. Janssen·Brett A. Poulin·Jacob M. Ogorek·Amber White·Elizabeth A. McDaniel·Robert A. Marick·Grace Jane Armstrong·Nicholas D. Scheel·Michael T. Tate·David P. Krabbenhoft·Katherine D. McMahon
View original source ↗Export metadata ↓

Abstract

Mercury (Hg) contamination of aquatic food webs is controlled in part by the formation and accumulation of toxic and bioaccumulative methylmercury (MeHg). MeHg production is mediated by metabolically diverse microorganisms carrying the hgcAB gene pair, while the demethylation reaction is mediated by several biotic and abiotic processes. However, the relative importance of these two processes on MeHg accumulation and the environmental factors that influence them are poorly characterized, especially in eutrophic environments. In this study, both Hg methylation and MeHg demethylation in a eutrophic freshwater lake were linked to ambient MeHg concentrations and hgcA abundance and expression. High methylation rate potentials indicated in situ MeHg formation was a key source of MeHg to the water column, driven by high hgcA abundance and transcription. Molybdate treatment decreased methylation rate potentials, highlighting the importance of sulfate reduction in driving MeHg formation. Sulfate-reducing bacteria accounted for over 50% of the hgcA gene transcription, despite representing less than 10% of the hgcA -carrying microbial community. An arsR -like transcriptional regulator preceded many hgcA sequences; these were transcriptionally active and linked to lower hgcA expression. Overall, this study elucidates the microbial and biogeochemical processes that influence the in situ formation of MeHg in understudied eutrophic freshwater environments.

Explore related subjects

Environmental Science and TechnologyArticle
90° N90° S · 180° W ← longitude → 180° E
Source-reported bounding extent: 43.07718992939806° to 43.1556562534559° latitude; -89.48563662246688° to -89.36268622801506° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Benjamin D. Peterson, Sarah E. Janssen, Brett A. Poulin, Jacob M. Ogorek, Amber White, Elizabeth A. McDaniel, Robert A. Marick, Grace Jane Armstrong, Nicholas D. Scheel, Michael T. Tate, David P. Krabbenhoft, Katherine D. McMahon. 2025-03-28. Sulfate reduction drives elevated methylmercury formation in water column of eutrophic freshwater lake. https://doi.org/10.1021/acs.est.4c12759

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2026

Anthropogenic and geogenic factors affecting groundwater arsenic and potential drinking water exposure in the San Luis Valley, Colorado

Groundwater arsenic is a serious health threat in many regions with limited surface water drinking supplies. In the San Luis Valley, Colorado, USA, where most residents rely on groundwater for drinking water, elevated groundwater arsenic concentrations (≥5 μg/L) were observed in 19.8% of private wells. Many recent studies have leveraged data science methods to estimate the spatial variability of arsenic at local, regional, and global scales. These studies typically predict depth-independent arsenic concentrations due to limited well depth information. However, arsenic concentrations may vary greatly with depth due to heterogeneous aquifer geochemistry, including redox potential, pH, and biogeochemical conditions. In this study, we apply random forest modeling to predict elevated groundwater arsenic concentrations (≥5 μg/L) over space and depth continuously across the San Luis Valley using a community-driven data set of 435 groundwater measurements of major ions and trace metals. Our model reveals the influence of several known or hypothesized drivers or proxy drivers of arsenic in groundwater, including surface elevation, fraction of fine-grained aquifer sediments, well depth, soil pH, long-term subsidence, and geothermal influences. Elevation, percentage of fine-grained sediments, and elemental indicators of geothermal fluid influence are some of the most important predictors of arsenic, while long-term subsidence is found to have a weak but positive relationship with arsenic. The model has a specificity of 0.82 and a sensitivity of 0.81 on held-out test data sets. In addition to improving understanding of drivers of arsenic in the region, this model produces pseudo-3D estimates of groundwater arsenic. The model can also be used to assess the time-dependent exposure to arsenic as the depth of domestic wells changes over time.

Colorado↗
USGS2026

Transdisciplinary approach to private well research

More than 60 million people in the United States and Canada rely on private drinking water systems (mostly private wells), which fall outside of national regulations for water quality and management. This decentralized infrastructure creates unique challenges. First, fragmented policy oversight leads to inconsistent data availability. Second, population heterogeneity in well users requires accounting for the social determinants of health and behavioral differences. Additionally, the individualized nature of well management creates persistent gaps between knowledge generation and the protective action. A broad goal of private well research is to (1) understand, predict, and prevent potential health problems related to well water consumption and (2) enable individual and collective action to reduce exposures to contaminants in well water. Here, we propose a conceptual model to advance private well research through a transdisciplinary approach that links water sources to health and prioritizes engagement among researchers, communities, and decision makers. We also identify challenges and opportunities aimed at improving data systems, refining hazard and risk assessments, linking interdisciplinary research and practical knowledge, and sustaining long-term partnerships. While our geographic focus is on North America, the principles and strategies outlined are globally relevant to addressing health risks associated with unregulated private drinking water sources.

Environmental Science and Technology↗
USGS2026

Digging into soil: Effects of soil texture on RT-QuIC performance for environmental prion surveillance.

Chronic wasting disease (CWD) is a fatal neurodegenerative disease caused by infectious prions affecting wild and captive cervids. Transmission occurs directly between hosts or indirectly through contact with prion-contaminated environments. Soils, particularly those rich in clay, are hypothesized to enhance prion stability, retention, and bioavailability. Accurate detection of prions is therefore important for understanding environmental transmission risks. Real-time quaking-induced conversion (RT-QuIC) is a sensitive assay used to detect PrP CWD in tissue, excreta, and environmental materials. However, RT-QuIC performance across soil textures has not been evaluated. This study assessed RT-QuIC sensitivity and specificity using laboratory-prepared soils spiked with CWD-positive brain homogenate or water controls under a standardized extraction method. Conditional on the extraction method used, results suggest that RT-QuIC performance depends on soil texture, and thus, an optimal time-to-threshold (TTT) cutoff required to balance sensitivity and specificity will also vary with soil texture. RT-QuIC exhibited higher sensitivity and moderate specificity in soils with low clay (<20%) and moderate to high silt content, whereas high-clay soils (>20%) with low to moderate silt content (2%–60%) reduced both sensitivity and specificity, and required shorter TTT cutoffs. These findings highlight the importance of accounting for soil texture in environmental CWD surveillance.

Environmental Science and Technology↗