Quote Originally Posted by john_s
I'm not so sure, though, about developing agents with benzene rings (hydroquinone, pyrocatechol, pyrogallol).
The phenols we use in developing aren't a proper benzene ring, first -- benzene has three double bonds distributed along all six of the carbon-carbon bonds; the phenols we use have single bonds all around the ring AFAIK. And those phenols (metol, HQ, catechols, pyrogallol, p-aminophenol, etc.) all oxidize very quickly once the developed is diluted out to the point where there isn't a significant presence of preservative (like sodium sulfite) present. By the time they reach a treatment plant or spend any time in a septic tank, developing agents have turned into tannins or similar staining/tanning agents.