Mercury stable isotopes in flying fish as a monitor of photochemical degradation of methylmercury in the Atlantic and Pacific Oceans

Motta, Laura C.; Popp, Brian N.; Drazen, Jeffrey C.; Close, Hilary G.

doi:10.1016/j.marchem.2020.103790

Cited by 17 publications

(29 citation statements)

References 67 publications

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“…As photodegradation proceeds both the Δ 199 Hg and δ 202 Hg values of the remaining MMHg (that eventually enters the foodweb) increase in magnitude with a slope of ∼2.4 ( 29 , 57 ). Flying fish have been used as a monitor of the maximum values of Δ 199 Hg and δ 202 Hg attained in the near-surface open ocean ( 58 ). As MMHg sinks through the photic zone and into the OMZ (∼400–800 m in the central Pacific) it has been suggested that microbial production of MMHg occurs on particles ( 11 ) and in so doing dilutes the pool of MMHg with MMHg that is devoid of a positive Δ 199 Hg value ( 26 ).…”

Section: Discussionmentioning

confidence: 99%

Mercury isotopes identify near-surface marine mercury in deep-sea trench biota

Blum

Drazen

Johnson

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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Mercury isotopic compositions of amphipods and snailfish from deep-sea trenches reveal information on the sources and transformations of mercury in the deep oceans. Evidence for methyl-mercury subjected to photochemical degradation in the photic zone is provided by odd-mass independent isotope values (Δ199Hg) in amphipods from the Kermadec Trench, which average 1.57‰ (±0.14,n= 12, SD), and amphipods from the Mariana Trench, which average 1.49‰ (±0.28,n= 13). These values are close to the average value of 1.48‰ (±0.34,n= 10) for methyl-mercury in fish that feed at ∼500-m depth in the central Pacific Ocean. Evidence for variable contributions of mercury from rainfall is provided by even-mass independent isotope values (Δ200Hg) in amphipods that average 0.03‰ (±0.02,n= 12) for the Kermadec and 0.07‰ (±0.01,n= 13) for the Mariana Trench compared to the rainfall average of 0.13 (±0.05,n= 8) in the central Pacific. Mass-dependent isotope values (δ202Hg) are elevated in amphipods from the Kermadec Trench (0.91 ±0.22‰,n= 12) compared to the Mariana Trench (0.26 ±0.23‰,n= 13), suggesting a higher level of microbial demethylation of the methyl-mercury pool before incorporation into the base of the foodweb. Our study suggests that mercury in the marine foodweb at ∼500 m, which is predominantly anthropogenic, is transported to deep-sea trenches primarily in carrion, and then incorporated into hadal (6,000-11,000-m) food webs. Anthropogenic Hg added to the surface ocean is, therefore, expected to be rapidly transported to the deepest reaches of the oceans.

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Section: Discussionmentioning

confidence: 99%

Mercury isotopes identify near-surface marine mercury in deep-sea trench biota

Blum

Drazen

Johnson

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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“…Biological demethylation is clearly important in MeHg degradation in water and sediments, particularly below the photic zone. However, abiotic demethylation has long been recognized (Figure ), although most studies so far have focused on photochemical demethylation, which is thought to be responsible for as much as 80% of MeHg degradation in some freshwater lakes. − A recent study suggests that dark abiotic demethylation may contribute equally to biological demethylation in some swamps in Sweden . Additionally, MeHg is shown to be degraded through the formation and decomposition of the binuclear bis(methylmercuric(II)) sulfide complex, (CH 3 Hg) 2 S, in sulfide-rich environments. ,,,, The presence or absence of sulfide or sulfide minerals is thus considered as a key factor behind the variability in rates of MeHg formation and demethylation reported for different environmental settings .…”

Section: Abiotic Demethylationmentioning

confidence: 99%

“…The strong relationship observed between the Hg MIF and energy of incident radiation suggests that MIF signatures may be used as a tool for quantifying photochemical cycling of Hg. Indeed, MIF has been demonstrated in tracing the source and degradation of MeHg in marine biota, ,,,− and it is estimated that about 56–80% of MeHg could be photodegraded prior to entering the food web . MIF has also been used in studying the effects of DOM and its chemical-structural properties on photodemethylation of MeHg, but additional studies are warranted to understand the links between MIF and photoreduction and photodemethylation before this tool can be fully utilized.…”

Section: Abiotic Demethylationmentioning

confidence: 99%

Demethylation─The Other Side of the Mercury Methylation Coin: A Critical Review

Barkay

2021

ACS Environ. Au

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The public and environmental health consequences of mercury (Hg) methylation have drawn much attention and considerable research to Hg methylation processes and their dynamics in diverse environments and under a multitude of conditions. However, the net methylmercury (MeHg) concentration that accumulates in the environment is equally determined by the rate of MeHg degradation, a complex process mediated by a variety of biotic and abiotic mechanisms, about which our knowledge is limited. Here we review the current knowledge on MeHg degradation and its potential pathways and mechanisms. We describe detoxification by resistant microorganisms that employ the Hg resistance (mer) system to reductively break the carbon− mercury (C−Hg) bond producing methane (CH 4 ) and inorganic mercuric Hg(II), which is then reduced by the mercuric reductase to elemental Hg(0). Very recent research has begun to elucidate a mechanism for the longrecognized mer-independent oxidative demethylation, likely involving some strains of anaerobic bacteria as well as aerobic methane-oxidizing bacteria, i.e., methanotrophs. In addition, photochemical and chemical demethylation processes are described, including the roles of dissolved organic matter (DOM) and free radicals as well as dark abiotic demethylation in the natural environment about which little is currently known. We focus on mechanisms and processes of demethylation and highlight the uncertainties and known effects of environmental factors leading to MeHg degradation. Finally, we suggest future research directions to further elucidate the chemical and biochemical mechanisms of biotic and abiotic demethylation and their significance in controlling net MeHg production in natural ecosystems.

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“…Our data suggest that precipitation (i.e., atmospheric wet deposition) is the primary Hg exposure pathway for this portion of the southern Tropical Eastern Pacific Ocean food web due to the prevalence of positive Δ 200 Hg observed in the Galápagos Marine Reserve and Ecuadorian mainland coast populations. Motta et al (2020) also concluded that precipitation is an important source tied to sinking particulates. Even though the tuna samples from the Galápagos Marine Reserve are from a region thought to be impacted by volcanism, no isotopic anomalies were observed in this population compared with that of the Ecuadorian mainland coast.…”

Section: Differences In Hg Processing Within Yellowfin Tuna Populationsmentioning

confidence: 99%

Elevated Mercury Concentrations and Isotope Signatures (N, C, Hg) in Yellowfin Tuna (Thunnus albacares) from the Galápagos Marine Reserve and Waters off Ecuador

Muñoz‐Abril

Valle

Alava

et al. 2022

Enviro Toxic and Chemistry

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We examined how dietary factors recorded by C and N influence Hg uptake in 347 individuals of yellowfin tuna (Thunnus albacares), an important subsistence resource from the Galápagos Marine Reserve (Ecuador) and the Ecuadorian mainland coast in 2015–2016. We found no differences in total Hg (THg) measured in red muscle between the two regions and no seasonal differences, likely due to the age of the fish and slow elimination rates of Hg. Our THg concentrations are comparable to those of other studies in the Pacific (0.20‐9.60 mg/kg wet wt), but a subset of individuals exhibited the highest Hg concentrations yet reported in yellowfin tuna. Mercury isotope values differed between Δ199Hg and δ202Hg in both regions (Δ199Hg = 2.86 ± 0.04‰ vs. Δ199Hg = 2.33 ± 0.07‰), likely related to shifting food webs and differing photochemical processing of Hg prior to entry into the food web. There were significantly lower values of both δ15N and δ13C in tuna from Galápagos Marine Reserve (δ15N: 8.5–14.2‰, δ13C: −18.5 to −16.1‰) compared with those from the Ecuadorian mainland coast (δ15N: 8.3–14.4‰, δ13C: −19.4 to −11.9‰), of which δ13C values suggest spatially constrained movements of tuna. Results from the pooled analysis, without considering region, indicated that variations in δ13C and δ15N values tracked changes of Hg stable isotopes. Our data indicate that the individual tuna we used were resident fish of each region and were heavily influenced by upwellings related to the eastern Pacific oxygen minimum zone and the Humboldt Current System. The isotopes C, N, and Hg reflect foraging behavior mainly on epipelagic prey in shallow waters and that food web shifts drive Hg variations between these populations of tuna. Environ Toxicol Chem 2022;41:2732–2744. © 2022 SETAC

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Mercury stable isotopes in flying fish as a monitor of photochemical degradation of methylmercury in the Atlantic and Pacific Oceans

Cited by 17 publications

References 67 publications

Mercury isotopes identify near-surface marine mercury in deep-sea trench biota

Mercury isotopes identify near-surface marine mercury in deep-sea trench biota

Demethylation─The Other Side of the Mercury Methylation Coin: A Critical Review

Elevated Mercury Concentrations and Isotope Signatures (N, C, Hg) in Yellowfin Tuna (Thunnus albacares) from the Galápagos Marine Reserve and Waters off Ecuador

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