Isotopic and Chemical Characteristics of Mercury in Organs and Tissues of Fish in a Mercury-Polluted Lake: Evidence for Fractionation of Mercury Isotopes by Physiological Processes

Organs and tissues of whitefish and trout from mercury (Hg)-polluted Lake Ontario were analyzed for Hg isotopes, methylmercury (CH3Hg+), and inorganic Hg to investigate possible mass-dependent fractionation (MDF) and mass-independent fractionation (MIF) of Hg isotopes by physiological processes of the fish. Isotope signatures of different body parts were defined by delta-values of Hg-198/Hg-202, Hg-199/Hg-202, Hg-200/Hg-202, and Hg-201/Hg-202 ratios and by Delta-values representing effects of MIF on Hg-199/Hg-202 and Hg-201/Hg-202 ratios. The research yielded the following evidence for MDF and MIF, including MIF of isotopes with even as well as odd mass numbers, by metabolic activities: 1) anomalously low delta-values for whitefish kidneys but not for trout kidneys; 2) widely varying differences between the delta-values of different body parts of whitefish but practically uniform differences for those of trout; 3) different relationships between Delta Hg-199 and Delta Hg-201 for whitefish than for trout; 4) nonlinear correlation between delta Hg-198 and delta Hg-200 for whitefish but linear correlation for trout; 5) an inverse correlation between the delta Hg-199 values and CH3Hg+ concentrations of whitefish and trout; 6) an inverse correlation between the delta Hg-201/delta Hg-199 and CH3Hg+/inorganic Hg ratios of trout kidneys and gills (and lipids of trout near the sources of pollution) but a positive correlation for muscle, liver, and gut; and 7) inverse correlations between Delta Hg-199 and the CH3Hg+/inorganic Hg ratio for trout liver, kidneys, and gut. (C) 2017 SETAC