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. 2015 Sep 29;112(39):12058-62.
doi: 10.1073/pnas.1506520112. Epub 2015 Sep 8.

Mercury offloaded in Northern elephant seal hair affects coastal seawater surrounding rookery

Jennifer M Cossaboon  1 , Priya M Ganguli  2 , A Russell Flegal  3
Affiliations

Mercury offloaded in Northern elephant seal hair affects coastal seawater surrounding rookery

Jennifer M Cossaboon et al. Proc Natl Acad Sci U S A. .

Abstract

Methylmercury (MeHg) is a potent neurotoxin that is biomagnified approximately 1-10 million-fold in aquatic carnivores such as the Northern elephant seal (Mirounga angustirostris), whose excreta and molted pelage, in turn, constitute a source of environmental MeHg contamination at the base of marine food chains. The potential for this top-down contamination is greatest in coastal areas with productive marine ecosystems that provide ideal habitats for large marine mammal colonies that can number in the thousands. This recycling of MeHg was evidenced by comparing total mercury (HgT) and MeHg concentrations in seawater, and HgT in molted pelage of M. angustirostris, at the Año Nuevo State Reserve pinniped rookery with concentrations at neighboring coastal sites in Central California. Seawater MeHg concentrations around the rookery (average = 2.5 pM) were markedly higher than those at the comparison coastal sites (average = 0.30 pM), and were as high as 9.5 pM during the M. angustirostris molting season. As a consequence, excreta and molts from this marine mammal colony, and presumably other marine predator populations, constitute a major source of MeHg at the base of the local marine food chain.

Keywords: biogeochemistry; biomagnification; environmental toxicology; marine mammals; mercury.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Nearshore seawater sampling locations. (A) Locations of Año Nuevo and comparison sites along the Central California coast. (B) Detailed map showing the sampling stations at the south end of the Año Nuevo mainland breeding rookery during the 2012 Northern elephant seal molting season (M1–M6) and 2013 breeding season (B1–B6), as well as the Cove Beach Año Nuevo State Reserve sampling site.
Fig. 2.
Fig. 2.
MeHg and HgT in nearshore unfiltered seawater samples. (A) MeHg concentrations for the Año Nuevo mainland rookery during the 2012 molting season (M1–M6), 2013 breeding season (B1–B6), and Central California comparison sites. (B) HgT concentrations for the rookery during the 2012 molting season, 2013 breeding season, and Central California comparison sites. Error bars (±1 SD) indicate the sample was analyzed at least three times. HgT for B5 (1,650 pM) was considered contaminated and is not graphed.
Fig. 3.
Fig. 3.
Illustration of the conversion of inorganic mercury [Hg(II)] to MeHg by anaerobic bacteria, biomagnification of MeHg at successive marine trophic levels, and then reintroduction of MeHg to the base of the food chain via top-down contamination. Images are courtesy of the Environmental Molecular Sciences Laboratory (EMSL), a Department of Energy Office of Science user facility at the Pacific Northwest National Laboratory (anaerobic bacteria); Richard R. Kirby, Secchi Disk project (phytoplankton); Maria Grazia Mazzocchi, Stazione Zoologica Anton Dohrn, Italy (zooplankton); and FishWatch, National Oceanic and Atmospheric Administration (prey fish).
See this image and copyright information in PMC

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