Abstract

We report experimentally determined first-order rate constants of MeHg photolysis in three waters along a Boreal lake-wetland gradient covering a range of pH (3.8-6.6), concentrations of total organic carbon (TOC 17.5-81 mg L-1), total Fe (0.8-2.1 mg L-1), specific UV254 nm absorption (3.3-4.2 L mg(-1) m(-1)) and TOC/TON ratios (24-67 g g(-1)). Rate constants determined as a function of incident sunlight (measured as cumulative photon flux of photosynthetically active radiation, PAR) decreased in the order dystrophic lake > dystrophic lake/wetland > riparian wetland. After correction for light attenuation by dissolved natural organic matter (DOM), wavelength-specific (PAR: 400-700 nm, UVA: 320-400 nm and UVB: 280-320 nm) first-order photodegradation rate constants (k(pd)) determined at the three sites were indistinguishable, with average values (+/- SE) of 0.0023 +/- 0.0002, 0.10 +/- 0.024 and 7.2 +/- 1.3 m(2) E-1 for k(pdPAR), k(pdUVA), and k(pdUVB), respectively. The relative ratio of k(pdPAR), k(pdUVA), and k(pdUVB) was 1:43:3100. Experiments conducted at varying MeHg/TOC ratios confirm previous suggestions that complex formation with organic thiol groups enhances the rate of MeHg photodegradation, as compared to when O and N functional groups are involved in the speciation of MeHg. We suggest that if the photon fluxes of PAR, UVA, and UVB radiation are separately determined and the wavelength-specific light attenuation is corrected for, the first-order rate constants k(pdPAR), k(pdUVA), and k(pdUVB) will be universal to waters in which DOM (possibly in concert with Fe) controls the formation of ROS, and the chemical speciation of MeHg is controlled by the complexation with DOM associated thiols.

Published in

Environmental Science and Technology
2013, Volume: 47, number: 12, pages: 6279-6287
Publisher: AMER CHEMICAL SOC

SLU Authors

• Drott, Andreas

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

• Skyllberg, Ulf

  • Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
    

Sustainable Development Goals

SDG6 Ensure availability and sustainable management of water and sanitation for all
SDG3 Ensure healthy lives and promote well-being for all at all ages


UKÄ Subject classification

Forest Science
Environmental Sciences


Publication identifier

DOI: https://doi.org/10.1021/es400373s

Permanent link to this page (URI)

https://res.slu.se/id/publ/50308