Contrasting Food Web Factor and Body Size Relationships with Hg and Se Concentrations in Marine Biota

Abstract

Marine fish and shellfish are primary sources of human exposure to mercury, a potentially toxic metal, and selenium, an essential element that may protect against mercury bioaccumulation and toxicity. Yet we lack a thorough understanding of Hg and Se patterns in common marine taxa, particularly those that are commercially important, and how food web and body size factors differ in their influence on Hg and Se patterns. We compared Hg and Se content among marine fish and invertebrate taxa collected from Long Island, NY, and examined associations between Hg, Se, body length, trophic level (measured by δ15N) and degree of pelagic feeding (measured by δ13C). Finfish, particularly shark, had high Hg content whereas bivalves generally had high Se content. Both taxonomic differences and variability were larger for Hg than Se, and Hg content explained most of the variation in Hg:Se molar ratios among taxa. Finally, Hg was more strongly associated with length and trophic level across taxa than Se, consistent with a greater degree of Hg bioaccumulation in the body over time, and biomagnification through the food web, respectively. Overall, our findings indicate distinct taxonomic and ecological Hg and Se patterns in commercially important marine biota, and these patterns have nutritional and toxicological implications for seafood-consuming wildlife and humans.

Mercury, cadmium, zinc and copper concentrations and stable isotope ratios of carbon and nitrogen in tiger sharks (Galeocerdo cuvier) culled off Ishigaki Island, Japan

“…Marine predators, particularly long-lived species such as sharks, tuna, swordfish, and cetaceans, accumulate high levels of mercury (Hg) via the food web, and the hepatic Hg concentration in marine cetaceans is greater than the Hg concentration in the muscle (Honda et al, 1983;Andre et al, 1991;Holsbeek et al, 1998;Zhou et al, 2001) as the hepatic Hg concentration increases greatly after maturation due to the formation of Hg-Se complexes (Endo et al, 2002(Endo et al, , 2006Lailson-Brito et al, 2012;Karimi et al, 2013;Gui et al, 2014). In contrast to cetaceans, there are only limited data available on Hg concentration in the shark liver because most Hg surveys on shark species were undertaken for the edible part of the muscle.…”

Mercury and Selenium in Muscle and Target Organs of Scalloped Hammerhead Sharks Sphyrna lewini of the SE Gulf of California: Dietary Intake, Molar Ratios, Loads, and Human Health Risks

“…The organisms that occupy high trophic positions in marine ecosystems, such as tuna, billfishes, and sharks, are particularly exposed to toxic elements like Hg through food intake (Kojadinovic et al 2007;Damiano et al 2011;McMeans et al 2015). In addition, the influence of chemical factors on trace element bioavailability in water, and factors like length, body size, growth rate, and age can strongly influence trace elements accumulation (Karimi et al 2013;Jardine et al 2013). Mercury is well known for its toxicity; however, the most abundant and toxic Hg species is the organic form methylmercury (MeHg), which is bioaccumulated by aquatic organisms and biomagnified through the food chain.…”

Application of stable isotope mixing models for defining trophic biomagnification pathways of mercury and selenium

“…Se maintained a molar excess over Hg in all species examined in this study, with Se concentrations never reaching those considered to be a toxic threat (Lemly 1996). Exceptionally large Se molar advantages have been recorded through lower trophic groups (Chen et al 2001;Belzile et al 2006, Karimi et al 2013), but these molar advantages tend to decrease up the food chain to higher organisms (Yang et al 2008;Kehrig et al 2009;Fang et al 2011). This relationship was also evident in the present study, with the reduced molar advantage with increasing trophic level being the result of the biomagnification of Hg across trophic levels, as Se concentrations showed either no biomagnification or weak reductions with increasing d 15 N. The stability of the Se concentrations across the food web may be the result of a metabolic balancing act in which Se molar advantage over Hg is offset against maintaining Se concentrations at a level that does not cause toxicity problems (Lemly 1996).…”

“…Total mercury (THg) and methylmercury (MeHg) concentrations typically increase with trophic level (Beneditto et al 2012), as can Se concentrations (Besser et al 1993;Wang 2002;Hamilton 2004). The role of Se in mitigating Hg toxicity (Yang et al 2008;Kehrig et al 2009;Peterson et al 2009) has led to recent work quantifying Hg and Se concentration against trophic position (Campbell et al 2005;Hong et al 2013;Karimi et al 2013). Consumers' tissues are ultimately derived from the food they eat; consequently, stable isotope ratios of carbon (d 13 C) and d 13 C nitrogen (d 15 N) offer an effective quantitative measure of trophic structure, providing time-integrated tracers of energy flow, dietary history, and trophic position (Post 2002;Phillips and Gregg 2003).…”