Concurrent photolytic degradation of aqueous methylmercury and dissolved organic matter

Fleck, Jacob A.; Gill, Gary A.; Bergamaschi, Brian A.; Kraus, Tamara E.C.; Downing, Bryan D.; Alpers, Charles N.

doi:10.1016/j.scitotenv.2013.03.107

Cited by 78 publications

(57 citation statements)

References 104 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…β : α values measured in this study ranged from 0.5 to 0.9, which are similar to the previously reported values of 0.8–0.9 by Fleck et al () for rice field drainage waters (Fig. d; Table ).…”

Section: Resultssupporting

confidence: 92%

Optical properties of dissolved organic matter (DOM): Effects of biological and photolytic degradation

Hansen

Kraus

Pellerin

et al. 2016

Limnology & Oceanography

Self Cite

739

462

View full text Add to dashboard Cite

Advances in spectroscopic techniques have led to an increase in the use of optical properties (absorbance and fluorescence) to assess dissolved organic matter (DOM) composition and infer sources and processing. However, little information is available to assess the impact of biological and photolytic processing on the optical properties of original DOM source materials. Over a 3.5 month laboratory study, we measured changes in commonly used optical properties and indices in DOM leached from peat soil, plants, and algae following biological and photochemical degradation to determine whether they provide unique signatures that can be linked to original DOM source. Changes in individual optical parameters varied by source material and process, with biodegradation and photodegradation often causing values to shift in opposite directions. Although values for different source materials frequently overlapped, multivariate statistical analyses showed that unique optical signatures could be linked to original DOM source material, with 17 optical properties determined by discriminant analysis to be significant (p < 0.05) in distinguishing between DOM source and environmental processing. These results demonstrate that inferring source material from optical properties is possible when parameters are evaluated in combination even after extensive biological and photochemical alteration.Dissolved organic matter (DOM) plays a central role in aquatic environments. Although quantifying DOM amount (commonly by measuring DOC concentration) is important, it is also important to characterize DOM composition because its chemical make-up determines how it reacts in the environment (Liang and Singer 2003;Minor et al. 2014). For example, a portion of the DOM pool is a source of bioavailable organic matter that supports aquatic food webs, attenuates light in the water column, and mobilizes and transports pollutants. In addition, a variety of studies have demonstrated that DOM composition can be used to infer the sources of DOM, which can help inform drinking water and watershed management (e.g., McKnight et al. 2001;Stedmon et al. 2003;Kraus et al. 2011).Both DOM amount and composition vary spatially and temporally due not only to its proximity to source material but also to its exposure to environmental processing (Hood et al. 2005;Coble 2007;Helms et al. 2008). Under some conditions sorption and the formation of colloids and even precipitation can transfer DOM into the particulate pool (POM), however the two main processes affecting DOM amount and composition in aquatic environments are biodegradation and photodegradation (Kieber et al. 1990;Miller and Moran 1997;Del Vecchio and Blough 2002). Both of these processes can lead to the conversion of DOM to inorganic compounds (i.e., CO 2 ) and its subsequent loss from the water column, and to the alteration of DOM chemical composition.Biodegradation-which can occur in both the photic and aphotic zone-typically leads to the rapid loss of labile, low molecular weight (LMW) aliphatic m...

show abstract

Section: Resultssupporting

confidence: 92%

Optical properties of dissolved organic matter (DOM): Effects of biological and photolytic degradation

Hansen

Kraus

Pellerin

et al. 2016

Limnology & Oceanography

Self Cite

739

462

View full text Add to dashboard Cite

show abstract

“…Burns et al 13 reported enhanced reactivity of mirex with solvated electrons when associated with dissolved chromophoric humic substances. Enhanced photochemical reactivity was also observed for hydrophobic 1 O 2 probe molecules, 28,29 methyl mercury, 30,31 and silver ions as a result of association with CDOM. 32 The enhanced phototransformation rates of positively charged radical probes over neutral or negatively charged probes in CDOM containing solutions were ascribed to enhanced sorption of the positively charged probes to CDOM through attractive electrostatic interactions.…”

Section: ■ Introductionmentioning

confidence: 87%

Enhanced Indirect Photochemical Transformation of Histidine and Histamine through Association with Chromophoric Dissolved Organic Matter

Chu

Lundeen

Remucal

et al. 2015

Environ. Sci. Technol.

View full text Add to dashboard Cite

Photochemical transformations greatly affect the stability and fate of amino acids (AAs) in sunlit aquatic ecosystems. Whereas the direct phototransformation of dissolved AAs is well investigated, their indirect photolysis in the presence of chromophoric dissolved organic matter (CDOM) is poorly understood. In aquatic systems, CDOM may act both as sorbent for AAs and as photosensitizer, creating microenvironments with high concentrations of photochemically produced reactive intermediates, such as singlet oxygen (1O2). This study provides a systematic investigation of the indirect photochemical transformation of histidine (His) and histamine by 1O2 in solutions containing CDOM as a function of solution pH. Both His and histamine showed pH-dependent enhanced phototransformation in the CDOM systems as compared to systems in which model, low-molecular-weight 1O2 sensitizers were used. Enhanced reactivity resulted from sorption of His and histamine to CDOM and thus exposure to elevated 1O2 concentrations in the CDOM microenvironment. The extent of reactivity enhancement depended on solution pH via its effects on the protonation state of His, histamine, and CDOM. Sorption-enhanced reactivity was independently supported by depressed rate enhancements in the presence of a cosorbate that competitively displaced His and histamine from CDOM. Incorporating sorption and photochemical transformation processes into a reaction rate prediction model improved the description of the abiotic photochemical transformation rates of His in the presence of CDOM.

show abstract

“…High concentrations of pore water dissolved organic C are generated from tissue leaching and decay, which promotes partitioning of MeHg into the dissolved phase, enhancing its bioavailability for uptake in biota and rice plants (Fleck et al, in press). Rice plant density also influences net MeHg yields in surface water and pore water.…”

Section: The Influence Of Rice Cultivation Practices On Hg Cyclingmentioning

confidence: 99%

“…For example, photodegradation of MeHg is important in lakes, abiotically reducing MeHg concentrations (Hammerschmidt and Fitzgerald, 2006; Sellers et al, 1996). However, dense leaf canopies in rice fields (Leaf Area Index: up to 7 (unitless); from Hatala et al, 2012) limit the amount of incident radiation on the water surface, thus lowering photodemethylation of MeHg in the shallow surface waters of rice fields (Fleck et al, in press; Windham-Myers et al, 2010). In rice fields, photodemethylation reduced surface water MeHg loads by only ~6% over the growing season, while surface water MeHg concentrations increased 3–5 fold from inlet to outlet due to evapotranspiration (Alpers et al, in press).…”

Section: The Influence Of Rice Cultivation Practices On Hg Cyclingmentioning

confidence: 99%

Rice methylmercury exposure and mitigation: A comprehensive review

Rothenberg

Windham‐Myers

Creswell

2014

Environmental Research

169

151

View full text Add to dashboard Cite

Rice cultivation practices from field preparation to post-harvest transform rice paddies into hot spots for microbial mercury methylation, converting less-toxic inorganic mercury to more-toxic methylmercury, which is likely translocated to rice grain. This review includes 51 studies reporting rice total mercury and/or methylmercury concentrations, based on rice cultivated or purchased in 15 countries. Not surprisingly, both rice total mercury and methylmercury levels were significantly higher in polluted sites compared to non-polluted sites (Wilcoxon rank sum, p<0.001). However, rice percent methylmercury (of total mercury) did not differ statistically between polluted and non-polluted sites (Wilcoxon rank sum, p=0.35), suggesting comparable mercury methylation rates in paddy soil across these sites and/or similar accumulation of mercury species for these rice cultivars. Studies characterizing the effect of rice cultivation under more aerobic conditions were reviewed to determine the mitigation potential of this practice. Rice management practices utilizing alternating wetting and drying (instead of continuous flooding) caused soil methylmercury levels to spike, resulting in a strong methylmercury pulse after fields were dried and reflooded; however, it is uncertain whether this led to increased translocation of methylmercury from paddy soil to rice grain. Due to the potential health risks, it is advisable to investigate this issue further, and to develop separate water management strategies for mercury polluted and non-polluted sites, which minimize methylmercury exposure through rice ingestion.

show abstract

Concurrent photolytic degradation of aqueous methylmercury and dissolved organic matter

Cited by 78 publications

References 104 publications

Optical properties of dissolved organic matter (DOM): Effects of biological and photolytic degradation

Optical properties of dissolved organic matter (DOM): Effects of biological and photolytic degradation

Enhanced Indirect Photochemical Transformation of Histidine and Histamine through Association with Chromophoric Dissolved Organic Matter

Rice methylmercury exposure and mitigation: A comprehensive review

Contact Info

Product

Resources

About