though I do remember some measurements being taken many years ago in affected aircraft which must have proved the presence of fumes but which nothing was ever heard of.
There have been numerous studies, none of which (to my knowledge) have seen any meaningful quantities of toxic substances in the cabin air, even during what crews described as fume events.
This report is interesting,
for example. The downside is the lack of any control study, which makes the results interesting, but not particularly robust. The conclusion is particularly interesting:
Therefore, with respect to the conditions of flight that were experienced during this study, there was no evidence for target pollutants occurring in the cabin air at levels exceeding available health and safety standards and guidelines.
A much more widespread investigation (including controls, airport samples, and home samples) is needed in order to draw meaningful conclusions, though.