Bioaccessibility of mercury from traditional northern country foods measured using an in vitro gastrointestinal model is independent of mercury concentration Brian D. Laird a , Christopher Shade b , Nikolaus Gantner c , Hing Man Chan d , Steven D. Siciliano e, ⁎ a Graduate Program of Toxicology, University of Saskatchewan, Saskatoon, SK, Canada b Quicksilver Scientific, Denver, CO, USA c Water & Climate Impacts Research Centre, Environment Canada, Victoria, BC, Canada d Community Health Sciences Program, University of Northern British Columbia, Prince George, BC, Canada e Department of Soil Science, Toxicology Group, University of Saskatchewan, Saskatoon, SK, Canada abstract article info Article history: Received 9 March 2009 Received in revised form 16 July 2009 Accepted 7 August 2009 Available online xxxx Keywords: Contaminants Dietary exposure Gastrointestinal uptake Speciation Gastrointestinal microbes Human health risk assessment of dietary mercury (Hg) exposure in Canada assumes that all Hg from fish consumption is in the form of methylmercury (MeHg), the more bioavailable and hazardous form of Hg. In contrast, the risk assessment of dietary Hg to Inuit in northern Canada assumes that no more than two-thirds of dietary Hg is MeHg since mammal organs consumed by Inuit contain substantial concentrations of inorganic Hg. In vitro gastrointestinal models (e.g., the Simulator of the Human Intestinal Microbial Ecosystem) are often used for the evaluation of soil contaminant bioaccessibility, i.e., the fraction solubilized into gastrointestinal fluids, for use in site-specific human health risk assessment. In this research, we digested northern country foods using the SHIME for the measurement of Hg bioaccessibility, a novel approach for the assessment of dietary Hg bioavailability. We demonstrated that small intestinal Hg bioaccessibility from 16 fish, wild game, and marine mammal samples consumed by Inuit in northern Canada ranged between 1 and 93% and was independent of food HgT (MeHg + Hg II ) concentration. Additionally, we demonstrated that gastrointestinal microbes may affect Hg bioaccessibility of the 16 country foods, either increasing or decreasing bioaccessibility depending upon the type of food. These results indicate that gastrointestinal absorption of Hg is not likely limited by the concentration of Hg in the food, which is in agreement with in vivo Hg bioavailability studies. Furthermore, these in vitro results support the hypothesis that the gastrointestinal absorption of Hg from Inuit country foods is dependent upon food type. © 2009 Published by Elsevier B.V. 1. Introduction Traditional country foods offer tremendous social, health, and economic benefits to Inuit in northern Canada (NCP, 2003); however, the presence of environmental contaminants such as mercury (Hg) in country foods may also present health risks. The risk assessment of ingested Hg by the Canadian public is calculated under the assumption that 100% of the Hg in fish flesh is in the form of methylmercury (MeHg) (BCS, 2007). The hazard of MeHg makes this assumption both conservative and protective (BCS, 2007). The assumption that dietary mercury is 100% MeHg is realistic for southern Canadians (i.e., those consuming typical western diets of cereals, legumes, dairy products, fruits, vegetables, and meat) since fish is their primary source of Hg exposure (BCS, 2007) and the majority of Hg in fish is MeHg (Wagemann et al., 1997; ATSDR, 1999; BCS, 2007). Although fish consumption rates of Inuit can be substantially higher relative to southern Canadians (BCS, 2007), fish consumption constitutes a small proportion of the Inuit Hg exposure (NCP, 2003). The dietary Hg risk assessment of Inuit could be improved by systemically evaluating the concentration, speciation, and bioavailability of Hg from a variety of traditional country foods. Although both Hg II and MeHg are primarily absorbed in the small intestine, toxicokinetic differences exist between Hg II and MeHg (Nielsen, 1992; ATSDR, 1999; Clarkson et al., 2007). For example, only a fraction of ingested Hg II is absorbed across the gastrointestinal (GI) tract (Nielsen, 1992; Kamijo et al., 2004). In contrast, both human and animal studies demonstrated nearly complete absorption of Hg when ingested as MeHg contaminated fish, or as MeHg spiked into water, oils, or fish muscle homogenates (ATSDR, 1999; Clarkson et al., 2007). The absorption of MeHg across the intestinal epithelium is mediated by brush border dipeptide transporters due to the structural homology of L-cysteine–MeHg complexes and methionine (Clarkson et al., 2007). In contrast, the mechanisms of Hg II absorption are not yet completely understood (Hoyle and Handy, 2005). In vitro GI models are useful tools in the measurement of Hg bioaccessibility, i.e., the fraction of ingested Hg that is solubilized into gastrointestinal fluids (Ruby, 1999). In contrast, Hg bioavailability refers to the fraction of ingested Hg that is absorbed across the Science of the Total Environment xxx (2009) xxx–xxx ⁎ Corresponding author. Tel.: +1 306 966 4035; fax: +1 306 966 6881. E-mail address: steven.siciliano@usask.ca (S.D. Siciliano). STOTEN-11476; No of Pages 6 0048-9697/$ – see front matter © 2009 Published by Elsevier B.V. doi:10.1016/j.scitotenv.2009.08.014 Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv ARTICLE IN PRESS Please cite this article as: Laird BD, et al, Bioaccessibility of mercury from traditional northern country foods measured using an in vitro gastrointestinal model is independent of mercury concentration, Sci Total Environ (2009), doi:10.1016/j.scitotenv.2009.08.014