| 1. |
- Cabrol, Léa, et al.
(författare)
-
Redox gradient shapes the abundance and diversity of mercury-methylating microorganisms along the water column of the Black Sea
- 2023
-
Ingår i: mSystems. - : American Society for Microbiology. - 2379-5077. ; 8:4
-
Tidskriftsartikel (refereegranskat)abstract
- In the global context of seawater deoxygenation triggered by climate change and anthropogenic activities, changes in redox gradients impacting biogeochemical transformations of pollutants, such as mercury, become more likely. Being the largest anoxic basin worldwide, with high concentrations of the potent neurotoxic methylmercury (MeHg), the Black Sea is an ideal natural laboratory to provide new insights about the link between dissolved oxygen concentration and hgcAB gene-carrying (hgc+) microorganisms involved in the formation of MeHg. We combined geochemical and microbial approaches to assess the effect of vertical redox gradients on abundance, diversity, and metabolic potential of hgc+ microorganisms in the Black Sea water column. The abundance of hgcA genes [congruently estimated by quantitative PCR (qPCR) and metagenomics] correlated with MeHg concentration, both maximal in the upper part of the anoxic water. Besides the predominant Desulfobacterales, hgc+ microorganisms belonged to a unique assemblage of diverse—previously underappreciated—anaerobic fermenters from Anaerolineales, Phycisphaerae (characteristic of the anoxic and sulfidic zone), Kiritimatiellales, and Bacteroidales (characteristic of the suboxic zone). The metabolic versatility of Desulfobacterota differed from strict sulfate reduction in the anoxic water to reduction of various electron acceptors in the suboxic water. Linking microbial activity and contaminant concentration in environmental studies is rare due to the complexity of biological pathways. In this study, we disentangle the role of oxygen in shaping the distribution of Hg-methylating microorganisms consistently with MeHg concentration, and we highlight their taxonomic and metabolic niche partitioning across redox gradients, improving the prediction of the response of marine communities to the expansion of oxygen-deficient zones. IMPORTANCE Methylmercury (MeHg) is a neurotoxin detected at high concentrations in certain marine ecosystems, posing a threat to human health. MeHg production is mainly mediated by hgcAB gene-carrying (hgc+) microorganisms. Oxygen is one of the main factors controlling Hg methylation; however, its effect on the diversity and ecology of hgc+ microorganisms remains unknown. Under the current context of seawater deoxygenation, mercury cycling is expected to be disturbed. Here, we show the strong effect of oxygen gradients on the distribution of potential Hg methylators. In addition, we show for the first time the significant contribution of a unique assemblage of potential fermenters from Anaerolineales, Phycisphaerae, and Kiritimatiellales to Hg methylation, stratified in different redox niches along the Black Sea gradient. Our results considerably expand the known taxonomic diversity and ecological niches prone to the formation of MeHg and contribute to better apprehend the consequences of oxygen depletion in seawater.
|
|
| 2. |
- Dastoor, Ashu, et al.
(författare)
-
Arctic mercury cycling
- 2022
-
Ingår i: Nature Reviews Earth & Environment. - : Springer Nature. - 2662-138X. ; 3:4, s. 270-286
-
Forskningsöversikt (refereegranskat)abstract
- Anthropogenic mercury (Hg) emissions have driven marked increases in Arctic Hg levels,which are now being impacted by regional warming, with uncertain ecological consequences. This Review presents a comprehensive assessment of the present-day total Hg mass balance in the Arctic. Over 98% of atmospheric Hg is emitted outside the region and is transported to the Arctic via long-range air and ocean transport. Around two thirds of this Hg is deposited in terrestrial ecosystems, where it predominantly accumulates in soils via vegetation uptake. Rivers and coastal erosion transfer about 80 Mg year−1 of terrestrial Hg to the Arctic Ocean, in approximate balance with modelled net terrestrial Hg deposition in the region. The revised Arctic Ocean Hg mass balance suggests net atmospheric Hg deposition to the ocean and that Hg burial in inner-shelf sediments is underestimated (up to >100%), needing seasonal observations of sediment-oceanHg exchange. Terrestrial Hg mobilization pathways from soils and the cryosphere (permafrost, ice, snow and glaciers) remain uncertain. Improved soil, snowpack and glacial Hg inventories, transfer mechanisms of riverine Hg releases under accelerated glacier and soil thaw, coupled atmosphere– terrestrial modelling and monitoring of Hg in sensitive ecosystems such as fjords can help toanticipate impacts on downstream Arctic ecosystems.
|
|
| 3. |
|
|
| 4. |
- Jonsson, Sofi, et al.
(författare)
-
Arctic methylmercury cycling
- 2022
-
Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 850
-
Tidskriftsartikel (refereegranskat)abstract
- Anthropogenic mercury (Hg) undergoes long-range transport to the Arctic where some of it is transformed into methylmercury (MeHg), potentially leading to high exposure in some Arctic inhabitants and wildlife. The environmental exposure of Hg is determined not just by the amount of Hg entering the Arctic, but also by biogeochemical and ecological processes occurring in the Arctic. These processes affect MeHg uptake in biota by regulating the bioavailability, methylation and demethylation, bioaccumulation and biomagnification of MeHg in Arctic ecosystems. Here, we present a new budget for pools and fluxes of MeHg in the Arctic and review the scientific advances made in the last decade on processes leading to environmental exposure to Hg. Methylation and demethylation are key processes controlling the pool of MeHg available for bioaccumulation. Methylation of Hg occurs in diverse Arctic environments including permafrost, sediments and the ocean water column, and is primarily a process carried out by microorganisms. While microorganisms carrying the hgcAB gene pair (responsible for Hg methylation) have been identified in Arctic soils and thawing permafrost, the formation pathway of MeHg in oxic marine waters remains less clear. Hotspots for methylation of Hg in terrestrial environments include thermokarst wetlands, ponds and lakes. The shallow sub-surface enrichment of MeHg in the Arctic Ocean, in comparison to other marine systems, is a possible explanation for high MeHg concentrations in some Arctic biota. Bioconcentration of aqueous MeHg in bacteria and algae is a critical step in the transfer of Hg to top predators, which may be dampened or enhanced by the presence of organic matter. Variable trophic position has an important influence on MeHg concentrations among populations of top predator species such as ringed seal and polar bears distributed across the circumpolar Arctic. These scientific advances highlight key processes that affect the fate of anthropogenic Hg deposited to Arctic environments.
|
|
| 5. |
- Schartup, Amina T., et al.
(författare)
-
Influence of the Arctic Sea-Ice Regime Shift on Sea-Ice MethylatedMercury Trends
- 2020
-
Ingår i: Environmental Science & Technology Letters. - : American Chemical Society (ACS). - 2328-8930 .- 2328-8930.
-
Tidskriftsartikel (refereegranskat)abstract
- Arctic sea ice regulates the air−sea exchange of volatile mercury (Hg) species like dimethylmercury (DMHg) or elemental Hg and is known to host Hg methylating microbes that produce neurotoxic and biomagnifying monomethylmercury (MMHg). Arctic sea ice accounts for 57% of the total primary production in the Arctic Ocean, suggesting that it could be the main source of MMHg to arctic food webs. Despite this, little is known about Hg concentrations and speciation in arctic sea ice. Here, we report Hg species and show the importance of sea-ice composition on sea-ice methylmercury (MeHg = DMHg + MMHg) budgets. We propose that the shift from older sea ice (lower MeHg) to younger sea ice (higher MeHg) resulted in a 40% increase in MeHg (per square meter of sea ice) since 1979 despite a 45% decline in the total sea-ice volume. Approximately 30% of the MeHg sea-ice budget is DMHg, which means that when the seaice melts in the summer it could contribute 0.03−2.7 pmol of DMHg m−2 day−1 to the atmosphere, which is comparable to diffusion from water (0.48−2.8 pmol of DMHg m−2 day−1). This study shows that the MeHg content of rapidly shrinking arctic sea ice and exposure of sea-ice biota may not be declining as previously thought.
|
|
