Aerotoxic
Basically all the industry denials are commercial & legal liability issues. BALPA massed an impressive collection of scientists and experts and were going into bat over it until someone (BA?) drew their attention to the impact of them proving the case; since then it has been deny & rule.
There have been too many well documented instances of tests, victims and investigations for it to be challenged realistically but the system makes it hard to budge any of the players. However, Boeing mysteriously decided that the 787 should have engine free air con and pressure and cited efficiency as the reason. Really? When "efficiency" was the reason engine bleed air was used in the first place.
If it walks like a duck & quacks like a duck etc