Temporal increase in organic mercury in an endangered pelagic seabird assessed by century-old museum specimens

Abstract

Methylmercury cycling in the Pacific Ocean has garnered significant attention in recent years, especially with regard to rising mercury emissions from Asia. Uncertainty exists concerning whether increases in anthropogenic emissions over time may have caused increased mercury bioaccumulation in the biota. To address this, we measured total mercury and, for a subset of samples, methylmercury (the bioaccumulated form of mercury) in museum feathers from an endangered seabird, the black-footed albatross (Phoebastria nigripes), spanning a 120-y period. We analyzed stable isotopes of nitrogen (δ 15 N) and carbon (δ 13 C) to control for temporal changes in trophic structure and diet. In post-1940 and -1990 feathers, we detected significantly higher mean methylmercury concentrations and higher proportions of samples exhibiting above deleterious threshold levels (∼40,000 ng·g −1 ) of methylmercury relative to prior time points, suggesting that mercury toxicity may undermine reproductive effort in the species. We also found higher levels of (presumably curator-mediated) inorganic mercury in older specimens of albatross as well as two nonpelagic species lacking historical exposure to bioavailable mercury, patterns suggesting that studies on bioaccumulation should measure methylmercury rather than total mercury when using museum collections. δ 15 N contributed substantially to models explaining the observed methylmercury variation. After simultaneously controlling for significant trends in δ 13 C over time and δ 15 N with methylmercury exposure, year remained a significant independent covariate with feather methylmercury levels among the albatrosses. These data show that remote seabird colonies in the Pacific basin exhibit temporal changes in methylmercury levels consistent with historical global and recent regional increases in anthropogenic emissions.Asian emissions | ecotoxicology | fisheries | global change | mercury contamination

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

“…Temporal variation in mercury availability in sub-Antarctic marine food webs has previously been examined using seabird tissues covering time periods from decades to centuries (Thompson et al 1993;Scheifler et al 2005;Vo et al 2011). However, caution must be used when interpreting trends at these time scales as averaging mercury values over extended periods can mask inter-annual variability.…”

Rapidly increasing methyl mercury in endangered ivory gull ( Pagophila eburnea ) feathers over a 130 year record

“…Most Hg in feathers is MeHg [15], so total Hg (IHg þ MeHg) is often measured as a proxy; however prior to the 1940s, museum specimen preparation techniques often used IHg (usually as HgCl 2 ) as a preservative, introducing a source of Hg contamination [16,17]. This preservation does not interfere with the selective measurement of MeHg in feathers; as a consequence, MeHg is the only appropriate measure of a birds' Hg body burden when analysing museum specimens with unknown preservation histories [12].…”

“…Once grown, feathers are inert, and the Hg bound within the feather is stable [10]. It is therefore possible to examine temporal trends in feather MeHg (and therefore MeHg body burden) using dated museum specimens, allowing retrospective analyses of more than 100 years [11][12][13][14]. Most Hg in feathers is MeHg [15], so total Hg (IHg þ MeHg) is often measured as a proxy; however prior to the 1940s, museum specimen preparation techniques often used IHg (usually as HgCl 2 ) as a preservative, introducing a source of Hg contamination [16,17].…”

Transformations of mercury in the marine water column

“…Anthropogenic loadings of Hg to marine environments are thought to have increased 3-fold since the Industrial Revolution [Lamborg et al, 2002] Various animal records, such as bird feathers [Vo et al, 2011] and egg shells [Xu et al, 2011] suggest that these THg increases result in subsequent increases in MMHg concentrations within marine food webs. Isotopic signatures of Hg in fish collected from the North Pacific indicate water column methylation as the primary source of MMHg [Blum et al, 2013], although the rate of increase in marine fish is debated [Kraepiel et al, 2003].…”