Entrance of monomethylmercury into marine phytoplankton and mercury dynamics and accumulation in the food web along the West Antarctic Peninsula

Mercury (Hg) is a contaminant of global concern due to its volatile gas phase (Hg0) and toxicity both in its inorganic (Hg2+) and most importantly the organic form, monomethylmercury (MeHg), a developmental neurotoxin capable of crossing the blood brain barrier that increases in concentration at higher levels of marine food webs. Although the threat of MeHg upon exposure to humans is well known, knowledge of its behavior and accumulation in temperate marine ecosystems is in early stages of development and the accumulation of MeHg at the base of the West Antarctic Peninsula (WAP) food web lacks even baseline data. To assess the entrance of MeHg into marine food webs and subsequent accumulation and magnification of the toxin, cellular MeHg uptake rates were examined in temperate and polar marine phytoplankton cultures in artificial and natural seawater with varying concentrations of dissolved organic carbon (DOC). Along with lab incubations, Hg concentrations were measured in seawater, particulate organic matter (POM), and juvenile and adult Antarctic krill (Euphausia superba) in coastal, shelf, and slope waters along the WAP, and Hg and stable carbon (δ13C) and nitrogen (δ15N) isotope ratios were measured in feathers of three Pygoscelis penguin species (Adélie-P. adeliae, gentoo-P. papua, and chinstrap-P. antarctica) breeding sympatrically near Anver’s Island (~65°S). Results showed that the maximum MeHg uptake rates in temperate (7.9 to 20.6 attmol/cell/hr) and Antarctic (14.3 to 249 attmol/cell/hr) marine phytoplankton were observed at low DOC concentrations. Methylmercury concentrations in northern (~65°S) WAP krill collected near Anver’s Island were low (0.3 to 2.9 ng g-1), while high and variable concentrations of dissolved (0.06 to 0.92 pM) and particulate (0.07 to 7.49 ngMeHg/gtotbio) MeHg were measured at neighboring sites. Concentrations of total Hg (sum of inorganic and organic forms) and MeHg in northern WAP krill were significantly higher in juveniles than adults (p < 0.005 and p < 0.001, resp.). Mean concentrations of Hg in feathers were significantly (p < 0.05) higher in chinstrap (0.80±0.20 µg g-1) than sympatric breeding Adélie (0.09±0.05 µg g-1) and gentoo (0.16±0.08 µg g-1) penguins. These findings suggest that the WAP ecosystem receives inputs of Hg from ocean water masses and potentially glacial meltwater. Although krill accumulate MeHg at low levels depending on developmental stage and location, such accumulation still has the potential to support much higher MeHg accumulation in WAP top predators.Ph.D.Includes bibliographical referencesby Philip Tighe Sonta