Mechanically damaged capacitor leaked liquid - is it toxic?
Yes it's toxic; No it's not mercury; Yes you'll live :)

If it was a "wet" capacitor type, then most likely that was sulfuric acid or some organic or inorganic solvent. If it was a solid, then perhaps manganese dioxide. 

Whatever it was it isn't good for you so don't breath it, take a bath in it, or move to a planet full of it. But... one capacitor one time in your life will not make a difference in your overall health.