Stage of development affects dry weight mercury concentrations in bird eggs: Laboratory evidence and adjustment method

Abstract

Bird eggs are often used to monitor levels and trends of mercury (Hg) in the environment. Logistical issues in such studies sometimes require the use of eggs at different stages of development. Therefore, it is important to understand how embryonic age may affect egg Hg concentrations. Studies using dry weight Hg concentrations in eggs assume that dry mass (e.g., lipids) does not change through embryonic development and thus expressing concentrations on a dry weight basis adjusts for any changes that may occur in egg mass throughout development. That assumption is tested in the present study by injecting chicken eggs with Hg and measuring Hg concentrations in embryonic contents at different stages of artificial incubation. The results indicate that dry weight Hg concentrations in eggs at later stages of development are statistically greater than in undeveloped eggs. To address this issue, we developed a method of standardizing egg Hg concentrations for embryonic age based on egg contents density (egg contents mass/egg contents volume). A combined dataset (n = 225) from precocial and semi-precocial birds was used to demonstrate that egg contents density declines with increasing embryonic development. Based on this finding, we applied a formula to adjust egg dry weight Hg concentrations for stage of development: adjusted egg [Hg] = unadjusted [Hg] × (egg contents density). The application of this approach to adjust data from the chicken egg Hg injection study resulted in there being no statistically significant difference in dry weight Hg levels in eggs at different stages of embryonic development. The adjustment approach described in the present study is a straightforward method to account for stage of development when assessing Hg levels in avian eggs and should be widely applicable to studies of this nature. Environ Toxicol Chem 2018;37:1168-1174. © 2017 SETAC.

Spatial trends in a biomagnifying contaminant: Application of amino acid compound–specific stable nitrogen isotope analysis to the interpretation of bird mercury levels

“…Methods used to process egg samples and measure THg levels in egg contents were identical to those of Dolgova et al (). In eggs, approximately 97% of THg is methyl Hg (MeHg; Ackerman et al ), so measuring THg is an efficient, cost‐effective way to estimate MeHg levels in eggs.…”

“…The limit of detection for THg was 0.006 μg/g (dry wt). Individual egg THg concentrations (micrograms per gram, dry wt) were corrected for increasing Hg levels with stage of development using an adjustment factor based on individual egg morphological parameters (egg contents mass/egg volume; see Dolgova et al ).…”

Methylmercury Effects on Birds: A Review, Meta‐Analysis, and Development of Toxicity Reference Values for Injury Assessment Based on Tissue Residues and Diet

“…Instead, we advise sampling whole blood from adult birds and/or their eggs and comparing the measured Hg concentrations with the toxicity reference values that have specifically been developed on an adult blood‐equivalent (µg/g wet wt) and egg‐equivalent basis (µg/g fresh wet wt). If eggs are used, especially eggs that are sampled after incubation has already begun, appropriate egg measurements and calculations would need to be performed to ensure that the estimated egg Hg concentrations are adjusted to a fresh wet weight basis (Ackerman et al, 2013; Dolgova et al, 2018; Stickel et al, 1973).…”

Advances in science and applications of air pollution monitoring: A case study on oil sands monitoring targeting ecosystem protection

“…Colonial waterbird eggs from gull and tern colonies in downstream receiving environments of the LAR were therefore used to assess spatial and temporal trends in Hg, arsenic (As), and PACs in eggs (Campbell et al 2013;Hebert, Nordstrom, and Shutt 2010;Hebert et al 2011). A key methodological development enabled this assessment, namely, the ability to standardize concentrations across space and species through the use of compoundspecific amino acid stable isotope analyses (Dolgova et al 2018a(Dolgova et al , 2018b. This approach can account for different embryonic developmental stages across different colonial waterbird species at different trophic positions.…”

“…In addition, Hg concentrations in gull and tern eggs are sufficiently high in northern Alberta to require an advisory restricting their consumption by indigenous harvesters and traditional land-users (My WildAlberta 2017). Although higher Hg levels in gull and tern eggs have been found in receiving environments downstream of the OS region (Dolgova et al 2018a), and potential mechanisms and Hg transport pathways exist that could help explain these higher Hg levels downstream (Hebert 2019), additional research is required to understand the role of the LAR in transporting Hg to downstream environments, and more research involving Hg in air, in aquatic and terrestrial systems, and in biota in the region is necessary to assess the relative Figure 23. Geometric mean (± 95% confidence intervals) total mercury (THg) concentrations in gull eggs collected from three regions: south (<58°N, sites 1-5), downstream of the Athabasca River (58.9°N-59.4°N, sites 6-8), and north (>59°N, sites 9-12).…”