Mercury and Methylmercury Stable Isotope Measurements in Giant Petrels

Methylmercury (MeHg) and total mercury (HgT) stable isotope measurements were made by the USGS Mercury Research Lab (MRL) in different organs on the Giant Petrels (Macronectes spp.) to examine internal mercury cycling in these seabirds. These data were collected as a compliment to x-ray spectroscopy measurements made by the University of Grenoble, France. The tissues and feathers of the southern giant petrels exhibit large variability in mercury-202 isotope values (δ202HgT), which are typically used to ascertain Hg sources in the environment. These values follow a pattern across all individuals based on tissue type: feathers (δ202HgT = 2.74 ± 0.16‰, n =5, mean ± standard deviation) > brain (δ202HgT = 1.09 ± 0.77‰, n = 3) > liver (δ202HgT = 0.04 ± 0.11‰, n = 5) > kidneys (δ202HgT= 0.01 ± 0.25‰, n = 5)> muscle (δ202HgT = -0.80 ± 0.23‰, n = 5). The δ202HgT for liver tissues are within the range of literature data for seabirds (−0.64‰ < δ202Hgl < 0.68‰), whereas δ202Hg for feathers are modestly higher than those measured previously for seabirds (1.10‰ < δ202Hgf < 2.35‰). Notably, muscle tissues exhibit considerably lower δ202HgT values than liver tissues (on average 0.84‰), counter to observations to other birds and mammals, and were as much as ~−4‰ enriched in light isotopes compared to feathers. The δ202MeHg values, associated with just the MeHg contents within the tissues, for organs and feathers were constrained between 0.90 and 3.05 ‰ (n =9).