Maternal transfer of contaminants in birds: Mercury and selenium concentrations in parents and their eggs

Abstract

We conducted a detailed assessment of the maternal transfer of mercury and selenium to eggs in three bird species (n = 107 parents and n = 339 eggs), and developed predictive equations linking contaminant concentrations in eggs to those in six tissues of the mother (blood, muscle, liver, kidney, breast feathers, and head feathers). Mercury concentrations in eggs were positively correlated with mercury concentrations in each of the mother's internal tissues (R(2) ≥ 0.95), but generally not with feathers. For each species, the proportion of mercury transferred to eggs decreased as mercury concentrations in the mother increased. At the same maternal mercury concentration, the proportion of mercury transferred to eggs differed among species, such that Forster's tern (Sterna forsteri) and black-necked stilt (Himantopus mexicanus) females transferred more methylmercury to their eggs than American avocet (Recurvirostra americana) females. Selenium concentrations in eggs also were correlated with selenium concentrations in the mother's liver (R(2) = 0.87). Furthermore, mercury and selenium concentrations in tern eggs were positively correlated with those in the father (R(2) = 0.84). Incubating male terns had 21% higher mercury concentrations in blood compared to incubating females at the same egg mercury concentration. We provide equations to predict contaminant concentrations in eggs from each of the commonly sampled bird tissues.

Avian mercury exposure and toxicological risk across western North America: A synthesis

“…No adjustments were necessary for methylmercury concentrations in kidney, because THg concentrations were always available when methylmercury concentrations in kidneys were reported. Fifth, to make the mercury data comparable across bird tissues, all tissue concentrations were converted into blood-equivalent THg concentrations (μg/g) in wet weight (ww) using multiple equations from Eagles-Smith et al (2008) and Ackerman et al (2016a) detailed below. Before using these equations, it was necessary to convert THg concentration data from each tissue compartment into the same units, and thus all muscle, liver, kidney, and feather data were converted into dry weight THg concentrations (μg/g dw) using the reported percent moisture in the sample.…”

“…5) from Ackerman et al (2016a), that was developed using 83 females and their full clutches for 3 species with a broad range of tissue THg concentrations, was used: $$(R^2=0.95):ln\left(\mathit{Female}\mathit{Bird}\mathit{Blood}{\mathrm{italicTHg}}_{\frac{\mathrm{normal\mu }g}{g}ww}\right)=1.0734\times ln\left(\mathit{Egg}{\mathrm{italicTHg}}_{\frac{\mathrm{normal\mu }g}{g}\mathit{fww}}\right)+0.8149$$…”

“…Bird THg concentrations in whole blood are highly correlated to THg and methylmercury concentrations in internal tissues that require more invasive sampling procedures (Eagles-Smith et al, 2008). Additionally, the THg concentration in a female’s blood is highly correlated to THg concentrations in her eggs (Ackerman et al, 2016a), providing THg concentrations in blood with a strong link to the numerous toxicity benchmarks that have been developed for egg hatchability. Eggs are a high-priority sampling tissue because they are relatively easy to sample, and relate directly to many toxicity benchmarks, including impaired reproduction.…”

Trophic ecology drives contaminant concentrations within a tropical seabird community

“…Since seabirds are able to excrete Hg in feathers (Dauwe et al, 2003), blood Hg in adults reflects the short term Hg contamination of individuals (Fort et al, 2015), and therefore provides information for the sampling period, usually the breeding season in seabirds (Goodale et al, 2008). In nestlings, concentrations usually reflect the Hg exposure since hatching and maternal transfer of Hg (Ackerman et al, 2016), even if the latter can be also excreted in the down.…”

“…Over the past years, given its involvement in some crucial physiological functions (Rayman, 2012), the knowledge on the relationship between Se bioavailability and health status and on the important role that Se supplementation plays in diseases has radically increased in humans (Rayman, 2012;Tinggi, 2008). One of the aspects that has been well studied is the "protective effect" of Se against Hg toxicity (Ackerman et al, 2016;Polak-Juszczak and Robak, 2015;Sørmo et al, 2011). Indeed, because of the high affinity between these two elements, Hg binds to Se to produce insoluble tiemannite in the liver of many mammals and certain birds (Ikemoto et al, 2004).…”