Spencer Washburn, Ph.D., (Minnesota) coauthored a paper titled “Mercury Isotopic Evidence for the Importance of Particles as a Source of Mercury to Marine Organisms” in Volume 119 of the Proceedings of the National Academy of Sciences published on September 20, 2022.

Spencer’s coauthors were Laura Motta and Joel Blum of the University of Michigan; Brian Popp and Jeffery Drazen of the University of Hawaii at Manoa; Blaire Umhau and Claudia R. Benitez-Nelson of the University of South Carolina; and Hilary Close of the University of Miami.

Spencer is a Scientist based in Minnesota who focuses on the biochemistry of surface water and environmental isotope geochemistry. Before joining Geosyntec this year, Spencer conducted postdoctoral research at the Smithsonian Environmental Research Center and the Oak Ridge National Laboratory.

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Abstract

The origin of methylmercury in pelagic fish remains unclear, with many unanswered questions regarding the production and degradation of this neurotoxin in the water column. We used mercury (Hg) stable isotope ratios of marine particles and biota to elucidate the cycling of methylmercury prior to incorporation into the marine food web. The Hg isotopic composition of particles, zooplankton, and fish reveals preferential methylation of Hg within small marine particles in the upper 400 meters of the North Pacific Ocean. Mass-dependent Hg isotope ratios recorded in small particles overlap with previously estimated values for methylmercury sources to Pacific and Atlantic Ocean food webs. Results of articulate compound-specific isotope analysis of amino acids indicate more-significant microbial decomposition in small particles compared to larger particles. Data also suggest that large particles collected in the equatorial ocean are distinct from small particles and resemble fecal pellets. Additional evidence for Hg methylation within small particles is provided by a statistical mixing model of even mass–independent isotope values, demonstrating that Hg within near-surface marine organisms (0–150 m) originates from a combination of rainfall and marine particles. In contrast, in meso- and upper bathypelagic organisms (200–1,400 m), the majority of Hg originates from marine particles with little input from wet deposition. The occurrence of methylation within marine particles is supported further by a correlation between isotope values, demonstrating greater overlap in the Hg isotopic composition of marine organisms with marine particles than with total gaseous Hg or wet deposition.

More Information

Learn more about the article: Mercury isotopic evidence for the importance of particles as a source of mercury to marine organisms | PNAS.
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For consultation regarding mercury isotopic evidence, contact Spencer Washburn at spencer.washburn@geosyntec.com.
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