Distribution of inorganic mercury in liver and kidney of beluga and bowhead whales through autometallographic development of light microscopic tissue sections

Inorganic mercury was localized through autometallography (AMG) in kidney and liver of free-ranging, subsistence-harvested beluga (Delphinapterus leucas; n = 20) and bowhead (Balaena mysticetus: n = 5) whales. AMG granules were not evident in bowhead tissues, confirming nominal mercury (Hg) concentrations (range = 0.011 to 0.038 ug/g ww for total Hg). In belugas, total Hg ranged from 0.30 to 17.11 and from 0.33 to 82.47 ug/g ww in liver and kidney, respectively. AMG granules were restricted to cortical tubular epithelial cytoplasm in belugas with lower tissue burdens; whales with higher tissue burdens had granules throughout the uriniferous tubular epithelium. In liver, AMG granular densities differed between lobular zones, concentrating in stellate macrophages and bile cannalicular domains of hepatocytes. AMG granules aggregated in periportal regions in belugas with lower hepatic Hg concentrations, yet among whales with higher Hg, AMG granule deposition extended to pericentral and midzonal regions of liver lobules. Mean areas occupied by AMG granules correlated well with hepatic Hg concentrations and age. In beluga livers, AMG staining density was not associated with lipofuscin quantity (an index of oxidative damage). Occasionally, AMG granules and lipofuscin were colocalized, but more often were not, implying that Hg was not a prominent factor in hepatic lipofuscin deposition in belugas.