Seems like a typo. Half-life of Pu-239 is ~24,000 years, and of Pu-242 ~374,000 years.
I'm guessing Pu-239 was intended as 1) an extra "0" digit is the more likely typo, and 2) Pu-239 is (AFAIU) the principal Plutonium byproduct of typical Uranium fission reactors.
Half life means that radioactivity is reduced by half, not eliminated. A single particle of plutonium is enough to cause cancer and kill a person. This is why nuclear fuel rod storage (the waste products) must be guarded for hundreds of thousands of years.
Half life is inversely proportional to radioactivity. Hundreds of thousands of years = no worries, you only live up to 1e-3 that amount.