U.S. Department of Energy Office of Biological and Environmental Research

BER Research Highlights

Clarifying Rates of Methylmercury Production
Published: January 27, 2018
Posted: March 07, 2018

New model provides more accurate rate constant estimates for mercury methylation and demethylation.

The Science
Using new experiments and re-analyses of previous experiments, a new two-site reversible sorption model was developed to describe the production of methylmercury over time. The new model takes into account competing processes and results in faster rates of production than previously estimated.

The Impact
Simulations of methylmercury production and transport demonstrate that methylmercury production is likely significantly larger than estimated by currently used models.

Mercury (Hg) is a toxic element that occurs naturally and as an anthropogenic pollutant in the environment. The neurotoxin monomethylmercury (MMHg) is a particular concern because it biomagnifies in aquatic environments and has adverse development effects on young children and developing embryos. MMHg is formed in the environment from inorganic Hg through the action of microorganisms in a process called Hg methylation. Because of its toxicity, there have been many attempts to measure Hg methylation and MMHg demethylation rates in various environmental settings with differing results. Even in laboratory experiments, rates for the methylation of Hg to MMHg often exhibit kinetics that are inconsistent with first-order kinetic models. In a new study, scientists from Oak Ridge National Laboratory used time-resolved measurements of filter-passing Hg and MMHg during methylation/demethylation assays, and they re-analyzed previous assays. Then they used a multi-site kinetic sorption model to show that competing kinetic sorption reactions can lead to apparent non-first-order kinetics in Hg methylation and MMHg demethylation. The new model can describe the range of behaviors for time-resolved methylation/demethylation data reported in the literature including those that exhibit non first-order kinetics. Additionally, the team showed that neglecting competing sorption processes can confound analyses of methylation/demethylation assays, resulting in rate constant estimates that are systematically biased low. Simulations of MMHg production and transport in a hypothetical periphyton biofilm bed illustrate the implications of the new model and demonstrate that methylmercury production may be significantly different than projected by single-rate first-order models.

Contacts (BER PM)
Paul Bayer
Paul.Bayer@science.doe.gov; 301-903-5324

(PI Contact)
Scott Brooks
brookssc@ornl.gov/ 865-574-6398

This work was funded by the U.S. Department of Energy, Office of Science, Biological and Environmental Research, Subsurface Biogeochemical Research Program and is a product of the Science Focus Area (SFA) at ORNL. The isotopes used in this research were supplied by the United States Department of Energy Office of Science by the Isotope Program in the Office of Nuclear Physics.

Publications Olsen, T.A., K. A. Muller, S. L. Painter, and S. C. Brooks. "Kinetics of Mercury Methylation Revisited" Environmental Science & Technology 52(4), 2063-2070 (2018). [DOI:10.1021/acs.est.7b05152]

Topic Areas:

  • Research Area: Earth and Environmental Systems Modeling

Division: SC-23.1 Climate and Environmental Sciences Division, BER


BER supports basic research and scientific user facilities to advance DOE missions in energy and environment. More about BER

Recent Highlights

May 10, 2019
Quantifying Decision Uncertainty in Water Management via a Coupled Agent-Based Model
Considering risk perception can improve the representation of human decision-making processes in age [more...]

May 09, 2019
Projecting Global Urban Area Growth Through 2100 Based on Historical Time Series Data and Future Scenarios
Study provides country-specific urban area growth models and the first dataset on country-level urba [more...]

May 05, 2019
Calibrating Building Energy Demand Models to Refine Long-Term Energy Planning
A new, flexible calibration approach improved model accuracy in capturing year-to-year changes in bu [more...]

May 03, 2019
Calibration and Uncertainty Analysis of Demeter for Better Downscaling of Global Land Use and Land Cover Projections
Researchers improved the Demeter model’s performance by calibrating key parameters and establi [more...]

Apr 22, 2019
Representation of U.S. Warm Temperature Extremes in Global Climate Model Ensembles
Representation of warm temperature events varies considerably among global climate models, which has [more...]

List all highlights (possible long download time)