High-resolution imaging of Hg/Se aggregates in the brain of small Indian mongoose, a wild terrestrial species: insights into intracellular Hg detoxification

Human activities result in the emission of 2000 metric tons of mercury compounds annually. Mercury (Hg) biomagnification has been characterized in marine mammals and predatory fish; however, little is known about mercury accumulation in brains of wild terrestrial species. Elevated Hg content, of 1.27 mu g/g wet wt.-found in the brain of wild small Indian mongoose, prompted us to use synchrotron X-ray fluorescence imaging for simultaneous, quantitative mapping of biologically relevant and neurotoxic elements with high spatial resolution. X-ray fluorescence combined with immunohistochemistry revealed similar to 0.5-1.9 micron Hg-rich aggregates in cells of the choroid plexus and astrocytes of the subventricular wall in the mongoose brain. Hg content within aggregates correlated with selenium. Hg aggregates did not co-localize with lysosomes. The low Hg density inside aggregates indicated diffuse Hg binding to a Se-containing biomolecule, rather than much denser HgSe nanoparticles proposed to form in other species. Our data show the susceptibility of the small Indian mongoose population to Hg pollution and highlight the vulnerability of the brain as an organ targeted by mercury. Data also provide evidence on the adaptation in the form of a Se-based detoxification mechanism sequestering Hg into intracellular aggregates.

Automated summary

Human activities result in the annual emission of 2000 metric tons of mercury compounds. While mercury biomagnification has been studied in marine mammals and predatory fish, little is known about mercury accumulation in the brains of wild terrestrial species. This study found elevated mercury content in the brain of wild small Indian mongooses, prompting the use of synchrotron X-ray fluorescence imaging to map biologically relevant and neurotoxic elements. The results showed the presence of mercury-rich aggregates in the cells of the mongoose brain, and these aggregates correlated with selenium. The study highlights the vulnerability of the mongoose brain to mercury pollution and provides evidence of a Se-based detoxification mechanism.