Looks like the original Sani-Flush was still being sold until 2009 or so. With its main ingredient being sodium bisulfate, when some people didn’t follow directions and mixed it with chlorine bleach (drain cleaners like Liquid-Plumr or Drano), it created chlorine gas, which can be fatal.
And then there’s the whole thing about DDT and raptors and shell thinning and OMG they’re still fighting about that so I’m not going to link to anything about it.