Dietary intake of inorganic mercury: bioaccumulation and oxidative stress parameters in the neotropical fish Hoplias malabaricus.

This study evaluated the effects of trophic and subchronic exposure to inorganic mercury (Hg) on the oxidative stress biomarkers and its bioaccumulation potential in the liver, gills, white muscle and heart of the freshwater top predator fish, Hoplias malabaricus, fed with contaminated live juveniles of matrinxã, Brycon amazonicus, as prey vehicle. Inorganic mercury increased superoxide dismutase, catalase (CAT), glutathione peroxidase (GPx), glutathione S-transferase, and glutathione reductase (GR) activities in the liver, white muscle and heart. Gills CAT activity remained unchanged while GPx and GR values showed a significant decrease. In the liver and gills, Hg induced significant increase in the reduced (GSH) and oxidized (GSSG) glutathione content, concomitantly with a significant decrease in [GSH]/[GSSG] ratio. Differently, in cardiac tissue, the Hg caused an increase in GSH level and increase in [GSH]/[GSSG] ratio. Lipid and protein oxidation and metallothionein levels were significantly higher after Hg trophic exposure in the liver, gills and heart, but remained at control values in the white muscle. Tissue-specific responses against oxidative stress were observed, and the liver and gills were the most sensitive organs, showing signs of redox homeostasis failure. At the end of the experiment, dietary inorganic mercury accumulated through food chain levels. In order, Hg bioaccumulation was: gills > liver >> white muscle = heart. These results pointed out the potential of inorganic Hg to bioaccumulate in aquatic systems. Taken together, our findings suggest that Hg, even in the inorganic form and sublethal amounts, is a risk factor for aquatic biota.