Other answers including Franklin Veaux's very good one mention dimethylmercury
Presented at the American Geophysical Union's Fall Meeting, the study revealed that mesoscale eddies within the California current are transporting the compound dimethylmercury
from the ocean into the fog around San Francisco.
Tragically, she died in 1997 as the result of a laboratory accident in which a few drops of highly toxic liquid dimethylmercury
penetrated her protective latex glove and caused rapidly progressive, fatal neurological impairment.
It leaches out of sediraents, washes in from rivers or is airborne in the form of volatile dimethylmercury
(DMHg), which is degraded to MMHg by ultraviolet light.
Such reactions may involve dimethylmercury
(DMHg), which is present in seawater at very low levels.
Delayed cerebellar disease and death after accidental exposure to dimethylmercury
Now it did occur to me that if a country had 50 litres of dimethylmercury
to play with, they wouldn't need to go to all the bother and expense of becoming a nuclear power anyway.