chemicals in the fluids they use are most likely dangerous and toxic.
Why is this assumed? Offshore, a majority of these fluids are allowed to be dumped in the gulf by BOEMRE or whatever it is now. There are many barrels of leftover fluids in the workstring after a frac job that are reversed out overboard.
The acids are the only toxic chemical you could worry about and these are not pumped in high volume. Frac fluid is mostly water with gelling agents that eventually break down.