Ecosystem matters: fish consumption, mercury intake and exposure among fluvial lake fish-eaters

Many studies use the number of fish meals as an estimate of Hg intake, although fish Hg concentrations, even within the same species, can greatly vary. Furthermore, most freshwater advisories only refer to local catch, while market fish advisories only focus on market fish, although both can contribute to Hg body burden. The present study, carried out in lakeside communities from 2 ecosystems in Quebec, Canada, sought to (i) estimate Hg intake from local freshwater sources, hunted waterfowl and market fish and seafood, and (ii) examine the relations between fish consumption, estimated Hg intake and biomarkers of exposure. A total of 238 adults (18-74 years), who had consumed local catch within the past three months, responded to an extensive interview-administered fish and waterfowl frequency questionnaire. Anthropometric measures were taken and a self-administered questionnaire was used to obtain socio-demographic information. Hg intake was estimated as microg Hg/kg body weight/day. Blood and hair samples were analyzed for Hg content. Results showed that persons from one ecosystem ate significantly more fish compared to those from the other (median: 52.1 g/day vs 38.9 g/day), but presented significantly lower concentrations of hair Hg (median: 448.0 ng/g vs 730.5 ng/g), blood organic Hg (median: 1.1 microg/L vs 3.4 microg/L) and inorganic Hg (median: 0.4 microg/L vs 0.8 microg/L). Median daily total Hg intake was 0.080 microg/kg bw/day for the former community and 0.141 microg/kg bw/day for the latter. Overall, 59.5% from the first ecosystem and 41.0% from the other, exceeded the US EPA RfD (0.1 microg/kg bw/day), while 13.2% and 6.0%, respectively, exceeded the Canadian tolerable daily intake (0.47 microg/kg bw/day) for adults. For the two groups, freshwater fish consumption frequency, but not total fish, was positively associated with bioindicators of Hg while estimated Hg intake from freshwater catch as well as from total fish consumption were positively related to Hg biomarkers. There was a positive relation between consumption and estimated Hg intake from freshwater fish and blood inorganic Hg. These findings indicate that the number of fish can be a poor surrogate for Hg exposure. The differences observed here for Hg intake and exposure reflect ecosystem disparities in fish diversity and Hg bioaccumulation. Studies and advisories need to consider Hg fish concentrations and fish-eating patterns in different ecosystems, as well as the contribution of market fish. The relation between fish consumption and inorganic Hg exposure, reported as well in other studies, needs to be further investigated.