I had thought this was part of a John Brunner novel, like one of the strands in The Sheep Look Up or a "Tracking in Closeups" segment in Stand on Zanzibar, but it doesn't seem to be in either. As I recall it fits with the pessimistic but somewhat absurdist/surrealistic tone of those.
A scientist is studying rats, in particular seeing how they adapt to a massively polluted environment. At the time of the story he has airtight cages with rats thriving while breathing air so toxic it would kill an unprotected human. At this point he runs into a teenage girl who the scientist realizes is also immune to the toxic effects of the pollution. The teenager ends up stuck in her own suite full of equally toxic air. We are shown how toxic the polluted air is when the scientist's assistant accidentally gets exposed to it and his hair starts to fall out.
It comes up that the scientist, or his assistant, has wired up a bell so it rings if one of the experimental subjects has an orgasm. (I believe the explanation was that they wanted to use that to measure the effects on the rats.) The scientist mentions to his assistant that he made the bell ring.
Somehow they find a teenage boy who is also immune to the air. When they put him in the toxic air suite the bell is ringing almost constantly...