2011
Volume 11, Number 4, pp. 152–164
The scientific adequacy of the present state of knowledge concerning neurotoxins in aircraft cabin air
Jeremy J. Ramsden
Cranfield University, Bedfordshire, MK43 0AL, UK
It is known that organophosphates (tricresyl phosphates) are present in jet engine lubricating oil. Oil may leak into the aircraft cabin if its air supply is bled off the engine. Depending on the type of oil seal, this may always occur to a small degree. The amount of leakage may increase due to faulty maintenance (including during the interval immediately preceding a scheduled maintenance intervention). If there is actual failure of a component of the seal, leakage may be considerable. In any case, leakage tends to be greater when the engine is cold and when the engine is working hard. Furthermore, some oil is pyrolysed in the engine, and the complex mixture of pyrolysis products may also be present in the bleed air. Tricresyl phosphates are potent neurotoxins. This has been most extensively established through animal testing (mainly cats, chickens and rabbits). The effects of human exposure have mainly been deduced by extrapolation from animal exposure and from observing cases of accidental human exposure. Any agent that damages the nervous system is prima facie expected to have a very broad spectrum of effects, given the pervasive nature of the nervous system in the control of any large multicellular organism. The proposition examined in this paper is that certain substances, namely tricresyl phosphates and their derivatives, if present in aircraft cabin air and hence inhaled, cause neural degeneration. Sufficient evidence would appear to have accumulated to make this a definite aviation hazard. The frequency of occurrence of acute “fume events”, in which a high concentration of neurotoxins is likely to be released into the cabin, cannot be estimated with a high degree of certainty but would appear to be around one in a thousand commercial flights. These constitute a safety hazard. Evidence for almost omnipresent low concentrations of neurotoxins suggests an occupational health hazard for aircrew and frequently flying business passengers, since the tricresyl phosphates accumulate in the body. Priority actions are needed to ensure that especially vulnerable people do not travel in jet aircraft that use bleed air to pressurize the cabin and to develop an appropriate sensor for continuously monitoring cabin air quality.