Net methylmercury production in 2 contrasting stream sediments and associated accumulation and toxicity to periphyton

Klaus, J.; Hammerschmidt, Chad R.; Costello, David M.; Burton, G.A.

doi:10.1002/etc.3324

Cited by 12 publications

(5 citation statements)

References 49 publications

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“…The transient, often reversible, effects of contaminants, including metals such as Ag, Cd, Cu, Pb, and Zn on photosynthesis, pigment composition, enzymatic activities, nucleic acid incorporation are most often used to characterize metabolic and physiological perturbations over short‐term exposure and to determine biomarkers for early effects . Nonetheless, no effect on metabolism has been observed in biofilms exposed to sediments enriched with Hg concentrations up to 59 μg g −1 dry weight sediment . Based on experiments with isolated microorganisms, it can be anticipated that exposure to high Hg concentrations will negatively affect photosynthesis, increase reactive oxygen species, induce phytochelatin synthesis, and affect nutrient metabolism .…”

Section: Hg Toxicity To Freshwater Biofilmsmentioning

confidence: 99%

Mercury bioavailability, transformations, and effects on freshwater biofilms

Dranguet

Faucheur

2017

Enviro Toxic and Chemistry

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Mercury (Hg) compounds represent an important risk to aquatic ecosystems because of their persistence, bioaccumulation, and biomagnification potential. In the present review, we critically examine state-of-the-art studies on the interactions of Hg compounds with freshwater biofilms, with an emphasis on Hg accumulation, transformations, and effects. Freshwater biofilms contain both primary producers (e.g., algae) and decomposers (e.g., bacteria and fungi), which contribute to both aquatic food webs and the microbial loop. Hence they play a central role in shallow water and streams, and also contribute to Hg trophic transfer through their consumption. Both inorganic and methylated mercury compounds accumulate in biofilms, which could transform them mainly by methylation, demethylation, and reduction. Accumulated Hg compounds could induce diverse metabolic and physiological perturbations in the microorganisms embedded in the biofilm matrix and affect their community composition. The bioavailability of Hg compounds, their transformations, and their effects depend on their concentrations and speciation, ambient water characteristics, biofilm matrix composition, and microorganism-specific characteristics. The basic processes governing the interactions of Hg compounds with biofilm constituents are understudied. The development of novel conceptual and methodological approaches allowing an understanding of the chemo-and biodynamic aspects is necessary to improve the knowledge on Hg cycling in shallow water as well as to enable improved use of freshwater biofilms as potential indicators of water quality and to support better informed risk assessment. Environ Toxicol Chem 2017;36:3194-3205. # 2017 SETAC

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Section: Hg Toxicity To Freshwater Biofilmsmentioning

confidence: 99%

Mercury bioavailability, transformations, and effects on freshwater biofilms

Dranguet

Faucheur

2017

Enviro Toxic and Chemistry

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“…Anoxic sediments have long been considered the primary location of MMHg production ( 4 ), but their central role in MMHg production has been recently challenged by studies on Hg transformations in littoral biofilms (i.e., periphyton) ( 5 , 6 ), which consist of heterogeneous communities of photosynthetic and heterotrophic microorganisms attached to a submerged substrate ( 7 ). Periphyton was previously shown to be an important site of Hg accumulation ( 8 – 10 ) and a source of Hg for entry into benthic trophic webs ( 11 , 12 ). However, knowledge gaps remain on the contribution of periphyton to Hg cycling in boreal aquatic environments, specifically on the capacity of periphyton to produce MMHg.…”

Section: Introductionmentioning

confidence: 99%

Microbial Diversity and Mercury Methylation Activity in Periphytic Biofilms at a Run-of-River Hydroelectric Dam and Constructed Wetlands

Leclerc

Harrison

Storck

et al. 2021

mSphere

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Periphytic biofilms have the potential to greatly influence the microbial production of the neurotoxicant monomethylmercury in freshwaters although few studies have simultaneously assessed periphyton mercury methylation and demethylation rates and the microbial communities associated with these transformations. We performed a field study on periphyton from a river affected by run-of-river power plants and artificial wetlands in a boreal landscape (Québec, Canada). In situ incubations were performed on three sites using environmental concentrations of isotopically enriched monomethylmercury (MM198Hg) and inorganic mercury (200Hg) for demethylation and methylation rate measurements. Periphytic microbial communities were investigated through 16S rRNA gene analyses and metagenomic screenings for the hgcA gene, involved in mercury methylation. Positive mercury methylation rates ([5.9 ± 3.4] × 10−3 day−1) were observed only in the wetlands, and demethylation rates averaged 1.78 ± 0.21 day−1 for the three studied sites. The 16S rRNA gene analyses revealed Proteobacteria as the most abundant phylum across all sites (36.3% ± 1.4%), from which families associated with mercury methylation were mostly found in the wetland site. Metagenome screening for HgcA identified 24 different hgcA sequences in the constructed wetland site only, associated with 8 known families, where the iron-reducing Geobacteraceae were the most abundant. This work brings new information on mercury methylation in periphyton from habitats of impacted rivers, associating it mostly with putative iron-reducing bacteria. IMPORTANCE Monomethylmercury (MMHg) is a biomagnifiable neurotoxin of global concern with risks to human health mostly associated with fish consumption. Hydroelectric reservoirs are known to be sources of MMHg many years after their impoundment. Little is known, however, on run-of-river dams flooding smaller terrestrial areas, although their numbers are expected to increase considerably worldwide in decades to come. Production of MMHg is associated mostly with anaerobic processes, but Hg methylation has been shown to occur in periphytic biofilms located in oxic zones of the water column. Therefore, in this study, we investigated in situ production of MMHg by periphytic communities in habitats impacted by the construction of a run-of-river dam by combining transformation rate measurements with genomic approaches targeting hgcAB genes, responsible for mercury methylation. These results provide extended knowledge on mercury methylators in river ecosystems impacted by run-of-river dams in temperate habitats.

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“…Moreover, periphyton has been identified as the principal entry point for methylmercury in an Amazonian region (Roulet et al, 2000). Indeed, several studies have shown that periphyton supports high Hg methylation rates due to microbial activity in tropical ecosystems (Guimarães et al, 1998;Acha et al, 2005, Klaus et al 2016.…”

Section: Samplingmentioning

confidence: 99%

Hg concentrations and stable isotope variations in tropical fish species of a gold-mining-impacted watershed in French Guiana

Laffont

Menges

Goix

et al. 2021

Environ Sci Pollut Res

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The aim of the study was to determine if gold mining activities could impact the mercury (Hg) concentrations and isotopic signatures in freshwater fish consumed by riparian people in French Guiana. Total Hg, MeHg concentrations and Hg stable isotopes ratios were analyzed in fish muscles from different species belonging to three feeding patterns (herbivorous, periphytophagous and piscivorous). We compared tributaries impacted by gold-mining activities (Camopi, CR) with a pristine area upstream (Trois-Sauts, TS), along the Oyapock River. We measured  15 N and  13 C to examine whether Hg patterns are due to differences in trophic level. Differences in  15 N and  13 C values between both studied sites were only observed for periphytophagous fish, due to difference of CN baselines, with enriched values at TS. Total Hg concentrations and Hg stable isotopes fractionations showed that Hg accumulated in fish from both areas have undergone different biogeochemical processes. Δ 199 Hg variation in fish (-0.5 to 0.2‰) was higher than the ecosystem baseline defined by a Δ 199 Hg of -0.66‰ in sediments, and suggested limited aqueous photochemical MeHg degradation. Photochemistry-corrected  202 Hg in fish were 0.7‰ higher than the baseline, consistent with biophysical and chemical isotope fractionations in aquatic environment. While THg concentrations in periphytophagous fish were higher in the gold-mining area than in TS, the ensemble of Hg isotope shifts in fish is affected by the difference of biotic (methylation/demethylation) and abiotic (photochemistry) processes between both areas and did therefore not allow to resolve the contribution of gold-mining related liquid Hg(0) in fish tissues. Mercury isotopes of MeHg in fish and lower trophic level organisms can be complementary to light stable isotope tracers.

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Net methylmercury production in 2 contrasting stream sediments and associated accumulation and toxicity to periphyton

Cited by 12 publications

References 49 publications

Mercury bioavailability, transformations, and effects on freshwater biofilms

Mercury bioavailability, transformations, and effects on freshwater biofilms

Microbial Diversity and Mercury Methylation Activity in Periphytic Biofilms at a Run-of-River Hydroelectric Dam and Constructed Wetlands

Hg concentrations and stable isotope variations in tropical fish species of a gold-mining-impacted watershed in French Guiana

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