Blood dynamics of mercury and selenium in northern elephant seals during the lactation period

Abstract

a b s t r a c tThe effects of reproduction and maternal investment (i.e., milk transfer) on trace element levels remain poorly understood in marine mammals. We examined the blood dynamics of mercury (Hg) and selenium (Se) during lactation in the northern elephant seal (Mirounga angustirostris), a top predator from the North Pacific Ocean. Total Hg and Se levels were measured in whole blood and milk of 10 motherepup pairs on days 5 and 22 of lactation. Both Hg and Se were transferred to offspring through the milk. Results suggested that the maternal transfer of Se was prominent during lactation, whereas the Hg transfer was larger during gestation. The lactation period affected Hg and Se levels in the blood of elephant seal mothers and pups. Physiological processes and their relationship to body condition should be considered carefully when interpreting trace element levels in the framework of biomonitoring.

How are trace elements mobilized during the postweaning fast in Northern elephant seals?

“…Therefore, an increase of hemoglobin concentration contributes to the increase of Fe and Hg levels in the blood. Interestingly, blood concentrations of Hg, Se, and Cu in weaned pups of the present study were totally in continuity with those previously determined in northern elephant seal suckling pups [13]. Values in the early postweaning fast were very close to values in late lactation (respectively, 0.066 and 0.077 mg/kg wet wt for Hg, 1.5 and 1.3 mg/kg wet wt for Se, and 0.98 and 0.93 mg/kg for Cu) in following the increasing or decreasing trend observed during lactation (Fig.…”

“…Only levels of Hg and Se were analyzed in northern elephant seal females and their pups during lactation (reaching 0.3 and 1.1 mg/kg wet wt, respectively, in blood of females from early lactation [13]). That study showed that fasting associated with milk production in lactating females, as well as suckling in pups, induced rapidly significant changes in Hg and Se blood levels over the lactation period.…”

“…Contaminants such as organ chlorines [8][9][10] and trace elements [11][12][13] concentrate in marine organisms at higher levels than those measured in their surrounding environment. Some studies focused on anthropogenic organic chemicals in pups of northern [9] and southern [14,15] elephant seals.…”

Marine foraging ecology influences mercury bioaccumulation in deep-diving northern elephant seals

“…Following the annual moult, female elephant seals return to the ocean for the long foraging trip, at which time gestation occurs. Maternal offloading of methylmercury in marine mammals occurs mostly via the placenta during gestation and to a much lesser extent during lactation [50,51]. For elephant seals arriving from the short foraging trip, there has been no recent maternal transfer of methylmercury and the greatest amount of time has elapsed since the prior moult ( figure 1).…”

“…Lastly, the increased mass and body condition (i.e. growth dilution effect due to increase in body mass) of seals at the end of the long foraging trip, in preparation for the extended lactation and fasting period associated with breeding, probably reduces mercury concentrations in internal tissues because changes in body condition can influence mercury concentrations in vertebrates [51,52]. Thus, the higher mercury concentrations we observed in seal blood and muscle after the short foraging trip (about 150 days shorter than the long foraging trip) were probably caused by decreased body mass (mass approx.…”