Methylation of mercury compounds increases their ability to enter the CNS and
also prolongs their stay in the body. Since mercuric ions can be biomethylated
by cobalamins, persons taking large doses of folate and B12 may be more likely
to be harmed by mercury should they contact it. (p. 51-52)
The irony here is pretty spectacular.
Snodgrass, S. R. (1992). Vitamin neurotoxicity. Molecular Neurobiology, 6, 41-73.