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Man made mercury pollution is reaching even deep ocean organisms


Mercury is a naturally occurring element, but more than 2,000 metric tons of it are emitted into the atmosphere each year from human activities. This inorganic mercury can travel thousands of miles before being deposited onto land and ocean surfaces, where microorganisms convert some of it to methylmercury, a highly toxic organic form that can accumulate in fish to levels that are harmful to humans and wildlife. Anthropogenic mercury enters the oceans via rainfall, dry deposition of windblown dust, and runoff from rivers and estuaries.

Effects on humans can include damage to the central nervous system, the heart and the immune system. The developing brains of fetuses and young children are especially vulnerable.

While mercury emissions have declined in recent years in North America and Europe, China and India continue to expand their use of coal, and global-scale mercury emissions are rising. To determine how seafood is likely to be impacted, researchers rely on global models. And refining those models requires the clearest possible understanding of how mercury cycles within the oceans and between the oceans and the atmosphere.

The new study:
A University of Michigan-led research team that analyzed the isotopic composition of mercury in fish and crustaceans collected at the bottom of two deep-sea trenches in the Pacific. The team reports its findings in a study scheduled for publication Nov. 16 in Proceedings of the National Academy of Sciences.

Blum and his colleagues collected snailfish and crustaceans called amphipods at depths of up to 33,630 feet in the Mariana Trench in the northwest Pacific, southwest of Guam. Other samples were collected at depths of up to 32,800 feet in the Kermadec Trench in the southwest Pacific, northeast of New Zealand.

Foto: A snailfish collected from the Kermadec Trench in the southwest Pacific Ocean.
(Photo credit: Paul Yancey)

“These samples were challenging to acquire, given the trenches’ great depths and high pressures,” said study co-author Jeffrey Drazen, a University of Hawaii oceanographer. “The trenches are some of the least studied ecosystems on Earth, and the Mariana snailfish was only just discovered in 2014.”

Mercury has seven stable (nonradioactive) isotopes, and the ratio of the different isotopes provides a unique chemical signature, or fingerprint, that can be used as a diagnostic tool to compare environmental samples from various locations. The researchers used these fingerprinting techniques—many of which were developed in Blum’s lab—to determine that the mercury from deep-sea-trench amphipods and snailfish had a chemical signature that matched the mercury from a wide range of fish species in the central Pacific that feed at depths of around 500 meters (1,640 feet). Those central Pacific fish were analyzed by Blum and his colleagues during a previous study.

"Mercury that we believe had once been in the stratosphere is now in the deepest trench on Earth,” said U-M environmental geochemist Joel Blum, lead author of the PNAS paper and a professor in the U-M Department of Earth and Environmental Sciences.

“It was widely thought that anthropogenic mercury was mainly restricted to the upper 1,000 meters of the oceans, but we found that while some of the mercury in these deep-sea trenches has a natural origin, it is likely that most of it comes from human activity.”

At a scientific meeting in June, Blum’s team and a Chinese-led research group independently reported the detection of human-derived mercury in deep-sea-trench organisms.

The Chinese researchers, who published their findings July 7 in the journal Nature Communications, concluded that the mercury gets to the deep-sea trenches by hitching a ride on microscopic particles of sinking organic matter—including fecal material and dead plankton—that constantly rain down from the upper oceans.

But in their PNAS paper, Blum and his colleagues reported that the isotopic composition of the mercury in sinking particles of detritus, the delivery mechanism favored by the Chinese team, does not match the chemical signature of mercury in the trench organisms. They concluded that most of the mercury in the trench organisms was transported there in the carcasses of fish that feed in sunlit near-surface waters, where most of the mercury comes from anthropogenic sources.

“We studied the trench biota because they live in the deepest and most remote place on Earth, and we expected the mercury there to be almost exclusively of geologic origin—that is, from deep-sea volcanic sources,” Blum said. “Our most surprising finding was that we found mercury in organisms from deep-sea trenches that shows evidence for originating in the sunlit surface zone of the ocean.”

“Deep-sea trenches have been viewed as pristine ecosystems unsullied by human activities. But recent studies have found traces of anthropogenic lead, carbon-14 from nuclear weapons testing, and persistent organic pollutants such as PCBs in organisms living in even the deepest part of the ocean, which is known as the hadal zone,” Drazen said.

The latest mercury findings provide yet another example of human activities impacting food webs in the most remote marine ecosystems on Earth.

This article has been republished from the material presented by the University of Michigan. Note: material may have been edited for length and content.

The original study:

Joel D. Blum, Jeffrey C. Drazen, Marcus W. Johnson, Brian N. Popp, Laura C. Motta, and Alan J. Jamieson, Mercury isotopes identify near-surface marine mercury in deep-sea trench biota, Proc. Nat. Acad. Sci. U.S.A., published November 16, 2020; DOI: 10.1073/pnas.2012773117

Related studies (newest first)

A.Y. Kurz, J.D. Blum, L.E. Gratz, D.A. Jaffe, Anthropogenic impacts on the atmosphere contrasting controls on the diel isotopic variation of Hg0 at two high elevation sites in the Western United States. Environ. Sci. Technol., 54 (2020) 10502–10513. DOI: 10.1021/acs.est.0c01918

R. Sun, J. Yuan, J.E. Sonke, Y. Zhang, T. Zhang, W. Zheng, S. Chen, M. Meng, J. Chen, Y. Liu, X. Peng, C. Liu,  Methylmercury produced in upper oceans accumulates in deep Mariana Trench fauna.  Nat. Commun., 11 (2020) 3389. DOI: 10.1038/s41467-020-17045-3

  Maodian Liu, Wenjie Xiao, Qianru Zhang, Linlin Shi, Xuejun Wang, Yunping Xu, Methylmercury Bioaccumulation in Deepest Ocean Fauna: Implications for Ocean Mercury Biotransport through Food Webs, Environ. Sci. Technol. Lett., 7/7 (2020) 469–476. DOI: 10.1021/acs.estlett.0c00299

L.C. Motta, J.D. Blum, B.N. Popp, J.C. Drazen, H. Close, Mercury stable isotopes in flying fish as a monitor of photochemical degradation of methylmercury in the atlantic and Pacific oceans. Mar. Chem., 223 (2020) 103790. DOI:  10.1016/j.marchem.2020.103790

L.C. Motta, J.D. Blum, M.W. Johnson, B.P. Umhau, B.N. Popp, S.J. Washburn, J.C. Drazen, C.R. Benitez-Nelson, C.C.S. Hannides, H.G. Close, C.H. Lamborg, Mercury cycling in the North Pacific Subtropical Gyre as revealed by mercury stable isotope ratios. Global Biogeochem. Cycles, 33 (2019) 777–794. DOI: 10.1029/2018GB006057

  D.J. Madigan, M. Li, R. Yin, H. Baumann, O.E. Snodgrass, H. Dewar, D.P. Krabbenhoft, Z. Baumann, N.S. Fisher, P. Balcom, E.M. Sunderland, Mercury Stable Isotopes Reveal Influence of Foraging Depth on Mercury Concentrations and Growth in Pacific Bluefin Tuna, Environ. Sci. Technol., 52/11 (2018) 6256–6264. DOI: 10.1021/acs.est.7b06429

C.J. Welty, M.L. Sousa, F.M. Dunnivant, P.H. Yancey. High-density element concentrations in fish from subtidal to hadal zones of the Pacific Ocean. Heliyon 4 (2018) e00840. DOI: 10.1016/j.heliyon.2018.e00840

J.D. Blum, M.W. Johnson, Recent developments in mercury stable isotope analysis. Rev. Mineral. Geochem., 82/1 (2017) 733−757. DOI: 10.10231/rmg.2017.82.17

D.K. Sackett, J.C. Drazen, B.N. Popp, C. Anela Choy, J.D. Blum, M.W. Johnson, Carbon, nitrogen, and mercury isotope evidence for the biogeochemical history of mercury in Hawaiian marine bottomfish. Environ. Sci. Technol., 51 (2017) 13976–13984. DOI: 10.1021/acs.est.7b04893

  B.P. DiMento, R.P. Mason, Factors controlling the photochemical degradation of methylmercury in coastal and oceanic waters. Mar. Chem., 196,  (2017) 116–125. DOI: 10.1016/j.marchem.2017.08.006

  S.E. Janssen, J.K. Schaefer, T. Barkay, J.R. Reinfelder, Fractionation of mercury stable isotopes during microbial methylmercury production by iron- and sulfate-Reducing bacteria. Environ. Sci. Technol., 50 (2016) 8077–8083. DOI: 10.1021/acs.est.6b00854

H. Cai, J. Chen, Mass-independent fractionation of even mercury isotopes. Sci. Bull. (Beijing) 61 (2016) 116–124. DOI: 10.1007/s11434-015-0968-8.

M.L. Li, A.T. Schartup, A.P. Valberg, J.D. Ewald, D.P. Krabbenhoft, R.S. Yin, P.H. Balcom, E.M. Sunderland, Environmental origins of methylmercury accumulated in subarctic estuarine fish indicated by mercury stable isotopes. Environ. Sci. Technol. 50 (2016) 11559–11568. DOI: 10.1021/acs.est.6b03206

M. Štrok, P. A. Baya, H. Hintelmann, The mercury isotope composition of Arctic coastal seawater. C. R. Geosci., 347 (2015) 368–376. DOI: 10.1016/j.crte.2015.04.001

Zhuhong Wang, Jiubin Chen, Xinbin Feng, Holger Hintelmann, Shengliu Yuan, Hongming Cai, Qiang Huang, Shuxiao Wang, Fengyang Wang, Mass-dependent and mass-independent fractionation of mercury isotopes in precipitation from Guiyang, SW China, C.R. Geoscience, 347/7–8 (2015)  358-36. DOI: 10.1016/j.crte.2015.02.006

  P. Chandan, S. Ghosh, B. A. Bergquist, Mercury isotope fractionation during aqueous photoreduction of monomethylmercury in the presence of dissolved organic matter. Environ. Sci. Technol. 49 (2015) 259–267. DOI:  10.1021/es5034553

Kathleen M. Munson, Carl H. Lamborg, Gretchen J. Swarr, Mak A. Saito, Mercury speciesconcentrations andfluxes in the CentralTropical Pacific Ocean,Global Biogeochem. Cycles, 2 (2015) 656-676. DOI: 10.1002/2015GB005120

J.D. Blum, B.N. Popp, J.C. Drazen, C. Anela Choy, M.W. Johnson, Methylmercury production below the mixed layer in the north Pacific Ocean. Nat. Geosci., 6 (2013) 879–884. DOI: 10.1038/ngeo1918

  J.B. Chen, H. Hintelmann, X.B. Feng, B. Dimock, Unusual fractionation of both odd and even mercury isotopes in precipitation from Peterborough, ON, Canada. Geochim. Cosmochim. Acta, 90 (2012) 33–46. DOI: 10.1016/j.gca.2012.05.005

  D.B. Senn, E.J. Chesney, J.D. Blum, M.S. Bank, A. Maage, J.P. Shine, Stable isotope (N, C, Hg) study of methylmercury sources and trophic transfer in the northern gulf of Mexico. Environ. Sci. Technol.,44 (2010) 1630–1637. DOI: 10.1021/es902361j

P. Rodríguez-González, V.N. Epov, R. Bridou, E. Tessier, R. Guyoneaud, M. Monperrus, D. Amouroux, Species-specific stable isotope fractionation of mercury during Hg(II) methylation by an anaerobic bacteria (Desulfobulbus propionicus) under dark conditions, Environ. Sci. Technol., 43/24 (2009) 9183-8. DOI: 10.1021/es902206j.

E.M. Sunderland, R.P. Mason, Human impacts on open ocean mercury concentrations. Global Biogeochem. Cycles, 21 (2007) GB4022. DOI: 10.1029/2006GB002876.

B. A. Bergquist, J. D. Blum, Mass-dependent and -independent fractionation of hg isotopes by photoreduction in aquatic systems. Science, 318 (2007) 417–420.  (2007). DOI: 10.1126/science.1148050

R. P. Mason, G. Sheu, Role of the ocean in the global mercury cycle. Global Biogeochem. Cycles, 16 (2002) 1093-1107. DOI: 10.1029/2001GBC001440

Related EVISA News

January 21, 2011: Arctic Mercury Cycling May Be Linked to Ice Cover
June 28, 2010: New Study Examines Why Mercury is More Dangerous in Oceans
September 8, 2009: Inorganic Mercury Level in US Women increases
August 21, 2009: USGS Study Reveals Mercury Contamination in Fish Nationwide
May 3, 2009: Ocean mercury on the rise
February 11, 2009: Mercury in Fish is a Global Health Concern
March 11, 2007: Methylmercury contamination of fish warrants worldwide public warning
October 9, 2006: Linking atmospheric mercury to methylmercury in fish
February 9, 2006: Study show high levels of mercury in women related to fish consumption
January 12, 2005: Number of fish meals is a good predictor for the mercury found in hair of environmental journalists
April 27, 2004: FDA/EPA recommends pregnant women to restrict their fish consumption because of methylmercury content

last time modified: November 24, 2020


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