In vitro estimation of exposure of Hong Kong residents to mercury and methylmercury via consumption of market fishes

In order to evaluate effects of exposure to mercury (tHg) and methylmercury (MeHg) of Hong Kong residents via consumption of fish, total and bioaccessible concentrations of tHg and MeHg were measured in 10 freshwater and 10 marine fishes collected from markets in Hong Kong. Concentrations of tHg and MeHg in fishes ranged from 27.2 to 311ngg^-1 (median 88.9ngg^-1) and ND to 116ngg^-1 (median 45.0ngg^-1), respectively. Concentrations of MeHg in marine fishes (64.4±28.5ngg^-1) were significantly greater than those in freshwater fishes (40.3±26.0ngg^-1). Bioaccessibility tHg and MeHg was predicted for edible flesh of twenty fishes by use of an in vitro gastrointestinal assay. Bioaccessibilities of tHg and MeHg ranged from 21.4 to 51.7% (mean 37.4%) and 19.5 to 59.2% (mean 43.7%), respectively. Based on total concentrations, diets of 36% of adults and 51% of children exceeded the reference dose (RfD, 100ngkg^-1bodymass(bm)d^-1) for MeHg, but when bioaccessibility was considered, consumption of local market fish would not result in an EDI_bio exceeded the RfD of MeHg for Hong Kong adults. These contradictory results suggested that risk assessments based on total concentrations would overestimate exposure because not all of contaminants consumed are bioaccessible. Furthermore, 9% of children had EDI_bio for MeHg that exceeded the RfD, which suggests that more attention should be paid to consumption of local fish on health and development of children in Hong Kong.