The chemicals might have a short-half life that only affects people in direct contact with the active agent.
They have no-fly zones over all of their dens of iniquity for a reason.
It may be a lock and key system. The chemicals they spread might only become fully activated when it encounters another chemical. They can run lab studies proving chemical X is safe to ingest, never introduce chemical Y to the test subjects, and get it approved for use. As long as they avoid running a study including both chemical X and chemical Y, they can claim both are safe, and spread them all over with wild abandon. Meanwhile, in practice, chemical X and chemical Y cause cancer when in the body. One is a lock, the other is a key. As long as they avoid the "key" chemical, they are safe. Fluoride would be a good candidate for that.
I'm not claiming the above are good explanations, but they are possible.
They probably have an antidote.
The chemicals might have a short-half life that only affects people in direct contact with the active agent.
They have no-fly zones over all of their dens of iniquity for a reason.
It may be a lock and key system. The chemicals they spread might only become fully activated when it encounters another chemical. They can run lab studies proving chemical X is safe to ingest, never introduce chemical Y to the test subjects, and get it approved for use. As long as they avoid running a study including both chemical X and chemical Y, they can claim both are safe, and spread them all over with wild abandon. Meanwhile, in practice, chemical X and chemical Y cause cancer when in the body. One is a lock, the other is a key. As long as they avoid the "key" chemical, they are safe. Fluoride would be a good candidate for that.
I'm not claiming the above are good explanations, but they are possible.