Mercury
Mercury Toxicity is one of the most frequently documents heavy metal poisonings. Mercury Poisoning is a very serious and potentially life threatening illness.
Mercury comes in a variety of forms: Organic Mercury, Elemental Mercury, and Inorganic Mercury.
| Methylmercury | Elemental Mercury | Inorganic Mercury | |
|---|---|---|---|
| Sources | Fish, poultry, pesticides | Industry, dental amalgams, fossil fuels, old latex paint, thermometers, incinerators. | Demethylation of methylmercury by intestinal microflora; biological oxidation of elemental mercury |
| Absorption | 95-100 percent in intestinal tract; 100 percent of inhaled vapor | 75-85 percent of vapor absorbed | 7-15 percent of ingested dose absorbed; 2-3 percent of dermal dose absorbed in animals |
| Distribution | Lipophilic, distributed throughout body; readily crosses bloodbrain barrier and placental barrier; accumulates in brain, kidney. | Lipophilic, distributed throughout body; crosses blood-brain and placental barriers; accumulates in brain, kidney | Does not cross blood-brain or placental barrier; found in brain of neonates; accumulates in kidney |
| Metabolism | Cysteine complex necessary for intracellular absorption; slowly demethylated to inorganic mercury in brain by tissue macrophages, fetal liver, and free radicals | Oxidized intracellularly to inorganic mercury by catalase and hydrogen peroxide | Methylated by intestinal microflora; binds and induces metallothionein biosynthesis |
| Excretion | 90 percent in bile,feces; 10 percent in urine | Urine, feces, sweat and saliva | Urine, bile, feces, sweat, saliva |
| Cause of Toxicity | Demethylation to inorganic (divalent) mercury; free radical generation; binding to thiols in enzymes and structural proteins. | Oxidation to inorganic (divalent) mercury | Binding to thiols in enzymes and structural proteins |
Thimerosal — Thimerosal, or thiomersal, is a thiolate ethylmercury derivative. Ethylmercury is the primary metabolite of Thimerosal. Thimerosal was primarily used as an antiseptic and as a preservative in vaccines. It was removed from childrens vaccines in the U.S. in 2001.
Thimerosal has toxicity similair to methylmercury. In Vitro finds their toxicity to be fairly identical, where as In Vivo studies of thimerosal toxicity studies finds that it has a third of the toxicity of methylmercury, with the discrepency likely being due to differences in metabolization and excretion.
Refrences:
1. Mercury toxicity and antioxidants: Part 1: role of glutathione and alpha-lipoic acid in the treatment of mercury toxicity. Patrick L.
2. Zimmermann LT, Santos DB, Naime AA, et al. Comparative study on methyl- and ethylmercury-induced toxicity in C6 glioma cells and the potential role of LAT-1 in mediating mercurial-thiol complexes uptake. Neurotoxicology. 2013;38:1-8. doi:10.1016/j.neuro.2013.05.015
3. Burbacher TM, Shen DD, Liberato N, Grant KS, Cernichiari E, Clarkson T. Comparison of blood and brain mercury levels in infant monkeys exposed to methylmercury or vaccines containing thimerosal. Environ Health Perspect. 2005;113(8):1015-1021. doi:10.1289/ehp.7712
4. Sanfeliu, C., Sebastià, J., Cristòfol, R. et al. Neurotoxicity of organomercurial compounds. neurotox res 5, 283–305 (2003). https://doi.org/10.1007/BF03033386