Photochemical behaviors of mercury (Hg) species in aquatic systems: A systematic review on reaction process, mechanism, and influencing factor

Luo, Huimin; Cheng, Qianqian; Pan, Xiangliang

doi:10.1016/j.scitotenv.2020.137540

Cited by 61 publications

(36 citation statements)

References 122 publications

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“…Additionally, reduction of Hg(II) in the presence of DOC has been observed under sunlight in many different types of natural waters ( Costa and Liss, 1999 ). This activity is affected by many factors such the chemistry and molecular weight of the DOC pool, the availability and wavelength of light, pH, dissolved oxygen, and the composition and abundance of cations and anions ( Luo et al, 2020 ). Photoreduction of Hg(II) by intracellular algal components has also been documented ( Kritee et al, 2018 ); however, the relevance of this process in mitigating the intracellular toxicity of Hg(II) produced from MeHg remains to be determined in species whose genomes encode MerB but not MerA.…”

Section: Resultsmentioning

confidence: 99%

Expanded Diversity and Phylogeny of mer Genes Broadens Mercury Resistance Paradigms and Reveals an Origin for MerA Among Thermophilic Archaea

2021

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Mercury (Hg) is a highly toxic element due to its high affinity for protein sulfhydryl groups, which upon binding, can destabilize protein structure and decrease enzyme activity. Prokaryotes have evolved enzymatic mechanisms to detoxify inorganic Hg and organic Hg (e.g., MeHg) through the activities of mercuric reductase (MerA) and organomercury lyase (MerB), respectively. Here, the taxonomic distribution and evolution of MerAB was examined in 84,032 archaeal and bacterial genomes, metagenome assembled genomes, and single-cell genomes. Homologs of MerA and MerB were identified in 7.8 and 2.1% percent of genomes, respectively. MerA was identified in the genomes of 10 archaeal and 28 bacterial phyla previously unknown to code for this functionality. Likewise, MerB was identified in 2 archaeal and 11 bacterial phyla previously unknown to encode this functionality. Surprisingly, homologs of MerB were identified in a number of genomes (∼50% of all MerB-encoding genomes) that did not encode MerA, suggesting alternative mechanisms to detoxify Hg(II) once it is generated in the cytoplasm. Phylogenetic reconstruction of MerA place its origin in thermophilic Thermoprotei (Crenarchaeota), consistent with high levels of Hg(II) in geothermal environments, the natural habitat of this archaeal class. MerB appears to have been recruited to the mer operon relatively recently and likely among a mesophilic ancestor of Euryarchaeota and Thaumarchaeota. This is consistent with the functional dependence of MerB on MerA and the widespread distribution of mesophilic microorganisms that methylate Hg(II) at lower temperature. Collectively, these results expand the taxonomic and ecological distribution of mer-encoded functionalities, and suggest that selection for Hg(II) and MeHg detoxification is dependent not only on the availability and type of mercury compounds in the environment but also the physiological potential of the microbes who inhabit these environments. The expanded diversity and environmental distribution of MerAB identify new targets to prioritize for future research.

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Section: Resultsmentioning

confidence: 99%

Expanded Diversity and Phylogeny of mer Genes Broadens Mercury Resistance Paradigms and Reveals an Origin for MerA Among Thermophilic Archaea

2021

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“…However, even within the relatively small range in DOC concentrations between study locations (2.2–3.8 mg/L), these differences were still a significant contributor to observed differences in photodemethylation rates (GLM p = 0.018, df = 26). Although the changes in DOC concentrations may be relatively small, there may also be differences in organic carbon quality that also exist within the reservoir (e.g., Figure 3), which have been shown to impact photodemethylation rates (Luo et al 2020). In general, photodemethylation rates increased with increasing DOC concentrations, which is consistent with other studies showing that water chemistry (such as DOC) can play an important role in demethylation through the production of reactive species such as hydroxyl radicals (Girard et al 2016; Luo et al 2020).…”

Section: Resultsmentioning

confidence: 99%

Methylmercury Production and Degradation under Light and Dark Conditions in the Water Column of the Hells Canyon Reservoirs, USA

Eckley

Luxton

Knightes

et al. 2021

Enviro Toxic and Chemistry

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Methylmercury (MeHg) is a highly toxic form of mercury that can bioaccumulate in fish tissue. Methylmercury is produced by anaerobic bacteria, many of which are also capable of MeHg degradation. In addition, demethylation in surface waters can occur via abiotic sunlight-mediated processes. The goal of the present study was to understand the relative importance of microbial Hg methylation/demethylation and abiotic photodemethylation that govern the mass of MeHg within an aquatic system. The study location was the Hells Canyon complex of 3 reservoirs on the Idaho-Oregon border, USA, that has fish consumption advisories as a result of elevated MeHg concentrations. Our study utilized stable isotope addition experiments to trace MeHg formation and degradation within the water column of the reservoirs to understand the relative importance of these processes on the mass of MeHg using the Water Quality Analysis Simulation Program. The results showed that rates of MeHg production and degradation within the water column were relatively low (<0.07 d -1 ) but sufficient to account for most of the MeHg observed with the system. Most MeHg production within the water column appeared to occur in the spring when much of the water column was in the processes of becoming anoxic. In the surface waters, rates of photodemethylation were relatively large (up to -0.25 d -1 ) but quickly decreased at depths >0.5 m below the surface. These results can be used to identify the relative importance of MeHg processes that can help guide reservoir management decisions.

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“…Here we assumed that both reactions involve the entire Hg II and MMHg pools (Ortiz et al, 2015;Schaefer and Morel, 2009;Zhang et al, 2019) (Zhang et al, 2014a). MMHg photodegradation is assumed to yield both Hg 0 and Hg II (k phdm {MMHg DOC +MeHgCl}) due to the contrasting results in experimental studies (Luo et al, 2020).…”

Section: Biogeochemical Dynamics In the Hg Modelmentioning

confidence: 99%

Assessing the spatial and temporal variability of MeHg biogeochemistry and bioaccumulation in the Mediterranean Sea with a coupled 3D model

Rosati

Canu

Lazzari

et al. 2022

Preprint

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Abstract. Human exposure to mercury (Hg) is a cause of concern, due to the biomagnification of the neurotoxic species monomethylmercury (MMHg) in marine ecosystems. Previous research revealed that commercial fish species in the Mediterranean Sea ecosystems are particularly enriched in Hg, due to a combination of physical and ecological factors. Since the fate of Hg depends on the interactions among several biogeochemical and physical drivers, biogeochemical modelling is crucial to support the integration and interpretation of field data. Here, we develop and apply a coupled transport-biogeochemical-metal bioaccumulation numerical model (OGSTM-BFM-Hg), to simulate the biogeochemical cycling of the main Hg species (HgII, Hg0, MMHg, and DMHg) in seawater, organic detritus, and through the planktonic food web. The model is applied to a 3D domain of the Mediterranean Sea to investigate the spatial and temporal variability of MeHg distribution and bioaccumulation. Model results reproduce the strong vertical and zonal gradients of MeHg concentrations related to primary production consistently with the observations, and highlight the role of winter deep convection and summer water stratification in shaping the MeHg vertical distribution, including sub-surface MeHg maximum. The modelled bioaccumulation dynamics in plankton food webs are characterized by a high spatial and temporal variability that is driven by plankton phenology, and are in agreement with available field data of concentrations in plankton and with other indicators, such as bioconcentration factors (BCFs) and trophic magnification factors (TMFs). Model results pointed out that the increment in water temperature linked to a decline of deep convection can cause an increase in water MeHg concentrations with cascading effects on plankton exposure and bioaccumulation.

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Photochemical behaviors of mercury (Hg) species in aquatic systems: A systematic review on reaction process, mechanism, and influencing factor

Cited by 61 publications

References 122 publications

Expanded Diversity and Phylogeny of mer Genes Broadens Mercury Resistance Paradigms and Reveals an Origin for MerA Among Thermophilic Archaea

Expanded Diversity and Phylogeny of mer Genes Broadens Mercury Resistance Paradigms and Reveals an Origin for MerA Among Thermophilic Archaea

Methylmercury Production and Degradation under Light and Dark Conditions in the Water Column of the Hells Canyon Reservoirs, USA

Assessing the spatial and temporal variability of MeHg biogeochemistry and bioaccumulation in the Mediterranean Sea with a coupled 3D model

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