Pattern of Mercury Allocation into Egg Components is Independent of Dietary Exposure in Gentoo Penguins

Abstract

Avian eggs have become one of the most common means of evaluating mercury contamination in aquatic and marine environments and can serve as reliable indicators of dietary mercury exposure. We investigated patterns of mercury deposition into the major components of penguin eggs (shell, membrane, albumen, and yolk) using the Gentoo penguin (Pygoscelis papua) as a model species. Eggs were collected from both wild and captive populations of Gentoo penguins to compare the allocation of mercury into individual egg components of birds feeding at disparate trophic positions as inferred by stable isotope analysis. Mercury concentrations in captive penguins were an order of magnitude higher than in wild birds, presumably because the former were fed only fish at a higher trophic position relative to wild penguins that fed on a diet of 72-93% krill (Euphausia spp.). Similar to previous studies, we found the majority of total egg mercury sequestered in the albumen (92%) followed by the yolk (6.7%) with the lowest amounts in the shell (0.9%) and membrane (0.4%). Regardless of dietary exposure, mercury concentrations in yolk and membrane, and to a lesser degree shell, increased with increasing albumen mercury (used as a proxy for whole-egg mercury), indicating that any component, in the absence of others, may be suitable for monitoring changes in dietary mercury. Because accessibility of egg tissues in the wild varies, the establishment of consistent relationships among egg components will facilitate comparisons with any other study using eggs to assess dietary exposure to mercury.

Multi-tissue analyses reveal limited inter-annual and seasonal variation in mercury exposure in an Antarctic penguin community

“…Eggshells were cleaned of organic debris in the field and stored in individually labeled plastic bags until preparation for mercury and stable isotope analysis. While eggshell membrane can reliably document mercury exposure in female birds in the absence of other tissues (Morera et al 1997;Akearok et al 2010;Brasso et al 2012b), the timing of egg formation must be considered when interpreting these data. As migratory species, mercury concentrations in egg tissues in Adélie and Chinstrap penguins are reflective of late-winter, prebreeding dietary exposure to mercury away from the breeding colony.…”

“…Mercury concentrations in feathers of adult Pygoscelis penguins averaged \0.50 ppm, fw; the highest mercury concentration was 2.39 ppm (Gentoo penguin). Using relationships described by Brasso et al (2012b), eggshell membrane mercury concentrations were found to be associated with whole egg mercury concentrations within the background (low) risk category for potential adverse effects of maternally deposited mercury (Evers et al 2003). Chicks with down mercury concentrations \13.0 ppm, fw have been suggested to be at minimal risk of adverse impacts of maternally deposited mercury into the egg (Ackerman and Eagles-Smith 2009); average mercury concentrations in chick down in the present study were \0.30 ppm, fw.…”

Mercury concentrations in eggshells of the Southern Ground-Hornbill (Bucorvus leadbeateri) and Wattled Crane (Bugeranus carunculatus) in South Africa

“…It is, therefore, needful to rely on the available information in the literature to predict Hg distribution in the different components of the egg of avian species. One of such studies is that recently reported for Gentoo penguins where up to 92.0% of the total Hg in their eggs were allocated to the albumen, 6.7% in the yolk, 0.4% in the membrane and 0.9% in the eggshell (Brasso et al, 2012).…”

Effect of laying sequence on egg mercury in captive zebra finches: An interpretation considering individual variation

“…Because the eggs have a consistent structure and composition, their mercury levels potentially reflect the status of mercury exposure in the females. Egg laying, therefore, may provide an important mechanism for eliminating methylmercury from the body of female birds [7,15]. Methylmercury is the primary form of mercury in eggs [14] and is deposited into various egg components including albumen, yolk, shell, and membrane.…”

“…Egg sampling is relatively easy and minimally invasive to the population and is used widely in studies of avian toxicology [13]. Because egg mercury levels are correlated with mercury concentration in the blood of female birds, and mercury concentrations in different egg components are mutually correlated, whole eggs are believed to provide reliable information on recent mercury exposure [5,7,15,16]. Egg laying, therefore, may provide an important mechanism for eliminating methylmercury from the body of female birds [7,15].…”