Total mercury, methylmercury, and selenium in aquatic products from coastal cities of China: Distribution characteristics and risk assessment

Abstract

This study analyzed total mercury (THg), methylmercury (MeHg) and selenium (Se) in 114 aquatic product samples (representing 39 species) from eight coastal cities of China. The THg and MeHg levels in different parts of the same sample species were in the order of muscle ≥ skin/shell > roe, whereas Se levels were much higher in roe. Concentrations of THg, MeHg, and Se in the muscles were between 2.27-154, 0.36-135, and 57.8-1.20 × 10³ ng g^-1 wet weight (ww), respectively. Although significant differences in analyte concentrations were not observed among cities, they existed among three species; marine fish, freshwater fish, and shellfish. Shellfish had generally lower Hg content (mean: 20.2 ng g^-1 ww THg, 6.71 ng g^-1 ww MeHg, and 30.9% MeHg/THg ratio); however it had higher Se content (528 ng g^-1 ww) than the other types of fish (mean: 33.3 ng g^-1 ww THg, 28.2 ng g^-1 ww MeHg, and 79.2% MeHg/THg ratio, 257 ng g^-1 ww Se). In addition to species, the individual growth and HgSe interaction influenced Hg distribution. Evident correlations were observed between several individual body features and Hg content, and between Se and THg concentrations (p < 0.05). The greater correlation coefficient between two elements for fish indicated stronger HgSe antagonism through HgSe compound formation in fish. Relatively low THg daily intakes (mean 0.013-0.080 μg kg^-1 day^-1) and MeHg daily intakes (0.006-0.065 μg kg^-1 day^-1) along with Se:Hg molar ratios >1 and positive HBV_Se values suggest that aquatic products from these sites will not pose immediate health problems to consumers. Fish was the dominating contributor for MeHg intake whereas shellfish was the dominating contributor for Se intake. To safeguard against mercury exposure, residents in these areas can appropriately increase shellfish intake (especially bivalves), rather than exclusively consuming marine fish.

Keywords: Fish; Methylmercury (MeHg); Selenium (Se); Shellfish; Total mercury (THg).