No, this was not an issue during WW1.

Mass, compulsory sterilization. However, that would be impossible to implement.

It was the compulsory sterilization program, based on the "Law for the Prevention of Hereditarily Diseased Offspring" of 1933. In regulated the enforced sterilization of the mentally handicapped, the blind and the physically deformed among others. The law resulted in 400,000 sterilizations. Although you might not expect it, the idea - and practice - of enforced sterilization of the mentally handicapped first came up in the US, but was discontinued there after a number of years for ethical reasons.

Yes. Chemical sterilization and cold sterilization are the same thing.

This is a procedure of sterilization using a gas.