Effect of selenium and mercury on survival of chick embryos

Formation Mechanism and Toxicological Significance of Biogenic Mercury Selenide Nanoparticles in Human Hepatoma HepG2 Cells

It is widely recognized that the toxicity of mercury (Hg) is attenuated by the simultaneous administration of selenium (Se) compounds in various organisms. In this study, we revealed the mechanisms underlying the antagonistic effect of sodium selenite (Na₂SeO₃) on inorganic Hg (Hg²⁺) toxicity in human hepatoma HepG2 cells. Observations by transmission electron microscopy indicated that HgSe (tiemannite) granules of up to 100 nm in diameter were accumulated in lysosomal-like structures in the cells. The HgSe granules were composed of a number of HgSe nanoparticles, each measuring less than 10 nm in diameter. No accumulation of HgSe nanoparticles in lysosomes was observed in the cells exposed to chemically synthesized HgSe nanoparticles. This suggests that intracellular HgSe nanoparticles were biologically generated from Na₂SeO₃ and Hg²⁺ ions transported into the cells and were not derived from HgSe nanoparticles formed in the extracellular fluid. Approximately 85% of biogenic HgSe remained in the cells at 72 h post culturing, indicating that biogenic HgSe was hardly excreted from the cells. Moreover, the cytotoxicity of Hg²⁺ was ameliorated by the simultaneous exposure to Na₂SeO₃ even before the formation of insoluble HgSe nanoparticles. Our data confirmed for the first time that HepG2 cells can circumvent the toxicity of Hg²⁺ through the direct interaction of Hg²⁺ with a reduced form of Se (selenide) to form HgSe nanoparticles via a Hg-Se soluble complex in the cells. Biogenic HgSe nanoparticles are considered the ultimate metabolite in the Hg detoxification process.

Teratogenic effects of external egg applications of methyl mercury in the mallard, Anas platyrhynchos

The embryotoxic potential of external applications of methyl mercury on mallard eggs was investigated to assess the possible impact of mercury transferred from the plumage of effluent-contaminated aquatic birds to their eggs. Eggs were treated on day 3 of development with microliter applications of methyl mercury that was dissolved with ethyl acetate into an aliphatic hydrocarbon vehicle. Mercury analysis by atomic absorption indicated that almost half of the mercury applied entered the eggs past the shell membranes within several days of treatment. Most mortality occurred within this period at doses of 9 microgram of mercury per egg or higher. Decreased embryonic growth resulted with similar doses. A significant incidence of malformations occurred at a dose of 1 microgram per egg. These malformations were mainly minor skeletal aberrations and incomplete ossification. With higher doses of mercury, defects included gross external ones such as micromella, gastroschisis, and eye and brain defects. Application of the aliphatic hydrocarbon vehicle did not result in any of these defects.

Effect of selenium and mercury on gross morphology and histopathology of chick embryos

Gross lesions of selenium toxicity in chick embryos included webbed, fused, and curled toes; cracked, crooked, and shortened beaks and gastroschisis. Mercury injection on day 3 of incubation caused leg defects but older embryos were much less susceptible. Histopathological studies showed that injection of selenium as selenite caused dissociation of hepatic cells, particularly around the central veins. Glomeruli of affected kidneys were enlarged, and in each glomerulus the lumen of the capillary tuft was dilated and the space of Bowman widened. Epithelial cells of the proximal convoluted tubules were detached from the basement membranes. Injection of mercury as chloride resulted in liver pathology in the late dead embryos which included dilated central veins and sinusoids. The cytoplasm of many hepatic cells was vacuolated. Foci of hemorrhages were observed in all liver lobes. In the kidneys, the renal corpuscles showed either shrinkage or enlargement. They seemed to be in the process of degeneration and disintegration. Sclerotic glomeruli were characterized by disappearance of Bowman's space and clumping of the glomerular tuft. Combined treatment with selenium and mercury resulted in liver pathology similar to that observed in mercury toxicity. The hepatic cell dissociation seen in selenium treated embryos was not observed following the combined treatment. In the kidneys the combined treatment resulted in typical lesions of both selenium and mercury toxicity.