Both sodium selenite and selenate are classified as dangerous and toxic to the environment. They can be carcinogenic and genotoxic, and may contribute to reproductive and developmental problems in animals and humans. Nonetheless, they are the primary forms of the mineral sold on the mass market today.
Most mass-market vitamins actually contain chemicals that the EPA has banned from public drinking water at levels above 50 parts per billion. That's the equivalent of a tablespoon of water in an Olympic-size swimming pool.
According to Green Med Info:
"... [T]his is not the first time in American history that such a hoax has been perpetuated on the public. The FDA-approved use of fluoride in our drinking water and the use of radioactive cobalt-60 culled from nuclear reactors for the IRRADIATION OF conventional food illustrates how industrial waste products with known toxicity are eventually converted into commodities or technologies 'beneficial to health.' Whereas initially these substances have very high disposal costs for the industries that excrete them into our environment, the liability is converted -- through the right combination of lobbying, miseducation and "checkbook science" -- back into a commodity".