"White Carbon" is the litteral translation of the Italian expression "Carbon Bianco", an old fashioned way to indicate hydroelectricity. When Italy was under international sanctions because of the Mussolini regime (1922-1943), electricity was generated worldwide mostly by burning coal. In the same period, to face the difficulty of importing coal and the scarcity of domestic coal resouces, Italy developed several hydro-power plants, and hydro-electricity was said to be generated by "carbon bianco" (with reference to water, in contrast to proper coal, which is black).

Have heard it to be an ingredient in toothpaste.

The toothpaste ingredient is black charcoal, which makes the paste totally black, while promising to act as a whitening agent for the teeth.

I now the medical pills named "white activated carbon" which contains only silica and cellulose but not a carbon.