Mercury Stable Isotopes in Seabird Eggs Reflect a Gradient from Terrestrial Geogenic to Oceanic Mercury Reservoirs

Abstract

Elevated mercury concentrations ([Hg]) were found in Alaskan murre (Uria spp.) eggs from the coastal embayment of Norton Sound relative to insular colonies in the northern Bering Sea-Bering Strait region. Stable isotopes of Hg, carbon, and nitrogen were measured in the eggs to investigate the source of this enrichment. Lower δ(13)C values in Norton Sound eggs (-23.3‰ to -20.0‰) relative to eggs from more oceanic colonies (-20.9‰ to -18.7‰) indicated that a significant terrestrial carbon source was associated with the elevated [Hg] in Norton Sound, implicating the Yukon River and smaller Seward Peninsula watersheds as the likely Hg source. The increasing [Hg] gradient extending inshore was accompanied by strong decreasing gradients of δ(202)Hg and Δ(199)Hg in eggs, indicating lower degrees of mass-dependent (MDF) and mass-independent Hg fractionation (MIF) (respectively) in the Norton Sound food web. Negative or zero MDF and MIF signatures are typical of geological Hg sources, which suggests murres in Norton Sound integrated Hg from a more recent geological origin that has experienced a relatively limited extent of aquatic fractionation relative to more oceanic colonies. The association of low δ(202)Hg and Δ(199)Hg with elevated [Hg] and terrestrial δ(13)C values suggested that Hg stable isotopes in murre eggs effectively differentiated terrestrial/geogenic Hg sources from oceanic reservoirs.

Quantifying mercury isotope dynamics in captive Pacific bluefin tuna (Thunnus orientalis)

“…Using a York regression (York, 1966) Hg values of the dietary mixture were within the ranges of this estimated slope (Figure 3). This slope is consistent with the photochemical degradation of MMHg observed in many marine food webs (∼1.2) (Senn et al, 2010;Gehrke et al, 2011;Laffont et al, 2011;Point et al, 2011;Day et al, 2012;Blum et al, 2013).…”

“…Hg values observed in mammals, birds, and human hair (Laffont et al, 2011;Day et al, 2012;Perrot et al, 2012;Kwon et al, 2014Kwon et al, , 2015Li et al, 2014 (Wiederhold et al, 2010). Given that MMHg in muscle tissues is most often associated with thiol-ligands (Olson et al, 1978;Schultz and Newman, 1997), we presume that MMHg with higher d…”

“…199 Hg values have been used to estimate the extent of photochemical degradation of IHg and MMHg in natural ecosystems (Senn et al, 2010;Gehrke et al, 2011;Point et al, 2011;Day et al, 2012;Blum et al, 2013;Kwon et al, 2013Kwon et al, , 2014. We found that d…”

“…By combining MDF and MIF, previous studies have identified sources and gained insight into complex biogeochemical processes governing MMHg in many natural ecosystems (Gantner et al, 2009;Senn et al, 2010;Gehrke et al, 2011;Point et al, 2011;Day et al, 2012;Perrot et al, 2012;Tsui et al, 2012Tsui et al, , 2013Tsui et al, , 2014Blum et al, 2013;Demers et al, 2007;Kwon et al, 2014Kwon et al, , 2015.…”

Tracing mercury pathways in Augusta Bay (southern Italy) by total concentration and isotope determination

“…This signature is generally well mirrored in marine organisms Perrot et al, 2013) and retained in the food web (Senn et al, 2010;Blum et al, 2014). Positive MIFs were also observed in human hair (Point et al, 2011;Day et al, 2012) and they are generally related to seafood consumption (Laffont et al, 2011;Blum et al, 2014). On the other hand, MDF has been revealed in human hair, resulting in a~þ2‰ d 202 Hg offset with respect to the consumed seafood (Laffont et al, 2009;.…”