Mercury Trends in Colonial Waterbird Eggs Downstream of the Oil Sands Region of Alberta, Canada

Abstract

Mercury levels were measured in colonial waterbird eggs collected from two sites in northern Alberta and one site in southern Alberta, Canada. Northern sites in the Peace-Athabasca Delta and Lake Athabasca were located in receiving waters of the Athabasca River which drains the oil sands industrial region north of Fort McMurray, Alberta. Temporal trends in egg mercury (Hg) levels were assessed as were egg stable nitrogen isotope values as an indicator of dietary change. In northern Alberta, California and Ring-billed Gulls exhibited statistically significant increases in egg Hg concentrations in 2012 compared to data from the earliest year of sampling. Hg levels in Caspian and Common Tern eggs showed a nonstatistically significant increase. In southern Alberta, Hg concentrations in California Gull eggs declined significantly through time. Bird dietary change was not responsible for any of these trends. Neither were egg Hg trends related to recent forest fires. Differences in egg Hg temporal trends between northern and southern Alberta combined with greater Hg levels in eggs from northern Alberta identified the likely importance of local Hg sources in regulating regional Hg trends. Hg concentrations in gull and Common Tern eggs were generally below generic thresholds associated with toxic effects in birds. However, in 2012, Hg levels in the majority of Caspian Tern eggs exceeded the lower toxicity threshold. Increasing Hg levels in eggs of multiple species nesting downstream of the oil sands region of northern Alberta warrant continued monitoring and research to further evaluate Hg trends and to conclusively identify sources.

Unravelling the complexity of pollution by the oil sands industry

“…The only rapidly increasing source of the element in the area is emissions from the oil sands industry (2,3). Increases in birds are paralleled by increases in naphthalene, also indicating that the likely source is the oil sands industry (12). This parallel suggests that people reliant on fish for protein may be at increasing risk.…”

Honouring indigenous treaty rights for climate justice

“…• The contamination of air, water, game, plants and fish with toxins emitted by the oil sands industry 8 . Fish are high in mercury, so health advisories are in effect for eating some species and consuming the eggs of fish-eating birds 9 . The increasing incidence of fish malformations has also been a complaint of Aboriginal communities for more than 20 years, recently confirmed by scientific analysis 10 .…”

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

“…Bacterial methylation of Hg results in the formation of methylmercury (MeHg), a potent neurotoxin (Clarkson 1992) that biomagnifies, reaching its highest concentrations in top predators. Given that impaired reproduction is a common toxicological endpoint associated with Hg exposure in birds (Scheuhammer et al 2007), many studies focus specifically on eggs (Evers et al 2003;Hebert et al 2013). Egg Hg concentrations are comprised almost entirely of MeHg (Ackerman et al 2013), and are correlated with those in the internal tissues of laying females (Ackerman et al 2016;Evers et al 2003); in addition, eggs are an important pathway for Hg excretion (Heinz 1979).…”