Title: Ecosystem Controls on Methylmercury Production by Periphyton Biofilms in a Contaminated Stream: Implications for Predictive Modeling

Abstract

Periphyton biofilms produce a substantial fraction of the overall monomethylmercury (MMHg) flux in East Fork Poplar Creek, an industrially contaminated, freshwater creek in Oak Ridge, Tennessee. We examined periphyton MMHg production across seasons, locations, and light conditions using mercury stable isotopes. Methylation and demethylation rate potentials ($$k_{m, trans av}$$ and $$k_{d, trans av}$$, respectively) were calculated using a transient availability kinetic model. Light exposure and season were significant predictors of $$k_{m, trans av}$$, with greater values in full light exposure and in the summer. Season, light exposure, and location were significant predictors of $$k_{d, trans av}$$, which was highest in dark conditions, in the spring, and at the upstream location. Light exposure was the controlling factor for net MMHg production, with positive production for periphyton grown under full light exposure and net demethylation for periphyton grown in the dark. Ambient MMHg and km, trans av were significantly correlated. Transient availability rate potentials were 15 times higher for km and 9 times higher for kd compared to full availability rate potentials ($$k_{m, full av}$$ and $$k_{d, full av}$$) calculated at 1 d. No significant model for the prediction of $$k_{m, full av}$$ and $$k_{d, full av}$$ could be constructed using light, season, and location. In addition, there were no significant differences among treatments for the full availability $$k_{m, full av}$$ and $$k_{d, full av}$$, or net MMHg calculated using the full availability rate potentials. km, full av was not correlated with ambient MMHg concentrations. The present results underscore the importance of applying transient availability kinetics to MMHg production data when estimating MMHg production potential and flux.

Authors:

Schwartz, Grace E. ^[1]; Olsen, Todd A. ^[1]; Muller, Katherine A. ^[1]; Brooks, Scott C. ^[1]

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+ Show Author Affiliations

1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Environmental Sciences Division

Publication Date:

2019-07-31

Research Org.:

Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1605912

Report Number(s):

PNNL-SA-147041
Journal ID: ISSN 0730-7268

Grant/Contract Number:  

AC05-76RL01830

Resource Type:

Accepted Manuscript

Journal Name:

Environmental Toxicology and Chemistry

Additional Journal Information:

Journal Volume: 38; Journal Issue: 11; Journal ID: ISSN 0730-7268

Publisher:

SETAC

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES; Periphyton; Methylmercury; Kinetics