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Methylmercury photodemethylation is inhibited in lakes with high dissolved organic matter.

Authors
  • Klapstein, Sara J1
  • Ziegler, Susan E2
  • O'Driscoll, Nelson J3
  • 1 Department of Earth Sciences, Memorial University of Newfoundland, St. John's, NL, Canada; Department of Earth and Environmental Science, Acadia University, Wolfville, NS, Canada. Electronic address: [email protected] , (Canada)
  • 2 Department of Earth Sciences, Memorial University of Newfoundland, St. John's, NL, Canada. Electronic address: [email protected] , (Canada)
  • 3 Department of Earth and Environmental Science, Acadia University, Wolfville, NS, Canada. Electronic address: [email protected] , (Canada)
Type
Published Article
Journal
Environmental pollution (Barking, Essex : 1987)
Publication Date
Jan 01, 2018
Volume
232
Pages
392–401
Identifiers
DOI: 10.1016/j.envpol.2017.09.049
PMID: 28993027
Source
Medline
Keywords
License
Unknown

Abstract

Photodemethylation can be one of the primary processes for loss of neurotoxic methylmercury (MeHg) in freshwater lakes. Few studies have quantified seasonal variations in photodemethylation rate constants as a function of dissolved organic matter (DOM). We conducted 1-week irradiation experiments in two seasons to test for spatial and temporal differences in photodemethylation potential in temperate lake waters. Six study lakes in Kejimkujik National Park, Nova Scotia were sampled in summer and fall to include a range of naturally occurring DOM concentrations (4.4-13.4 and 3.9-16.4 mg C L-1, respectively). A negative linear relationship (R2 = 0.76, p = 0.01) was found between DOM concentration and photodemethylation rate constant across seasons, indicating that DOM is a strong predictor of MeHg photodemethylation independent of seasonal effects. The two highest carbon lakes (BDW and PEB) had significantly higher energy-normalized photodemethylation rate constants in summer compared to fall corresponding with lower DOM concentrations in summer relative to fall. Additionally, there were negative linear relationships between MeHg photodemethylation and DOM photomineralization (R2s = 0.58-0.72) and DOM photobleaching (R2s = 0.83-0.90). This key finding suggests that competition for photons within DOM structures may reduce the potential for MeHg photodemethylation in high carbon waters and that this relationship persists across seasons.

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