© 2014 Collegium Basilea & AMSI doi: 10.4024/12RA14L.jbpc.14.03 Journal of Biological Physics and Chemistry 14 (2014) 71–74 Received 13 August 2014; accepted 30 September 2014 71 12RA14L ________________________________________________________________________________________________________ A great deal of attention is currently being paid to the presence of tricresyl phosphate (TCP) in aircraft cabin air [1, 2]. From the mechanical engineering point of view this substance is considered to be an indispensable component of turbine engine oil, which, therefore, contains a few percent of TCP. Wherever the air used to pressurize and heat the aircraft cabin (including the cockpit) is bled off the turbines, which is the case in all modern airliners except the very recently introduced Boeing 787, there is a risk that some of the oil will leak into the air. 1 Unlike the base oil, which is a synthetic ester lubricant (e.g., esters of pentaerythritol and short-chain fatty acids) of low toxicity, TCP is a potent neurotoxin. To make this statement more precise, it must be borne in mind that TCP comprises 10 possible isomers, since each cresyl group can be ortho, para or meta. The ortho isomers, especially tri- ortho-cresyl phosphate (ToCP), have been the most extensively investigated because of many cases of human poisoning during the last hundred years or more [3]. Careful comparison of all the isomers with respect to the neural– behavioural symptoms of intoxication revealed that the mono-ortho isomers are the most toxic, followed by the di- ortho ones [4], possibly because if at least one ortho substituent is present the liver can process the TCP to form cyclic saligenin phosphate (2-[o-cresyl]-4H-1,3,2-benzodiox- aphosphoran-2-one, CBDP) [5], which is a considerably more potent neurotoxin than mono-ortho-cresyl phosphate. Recent studies have shown that para-containing isomers bind to butylcholinesterase in the blood, with unknown physiological consequences [6]. The well known effect of brief, acute exposure to high concentrations of TCP is cholinergic (acetylcholine esterase is inhibited at synapses). This can lead to incapacitation and paralysis (e.g., [7]). High concentrations are, however, only likely to occur in the case of catastrophic failure of the oil seals and are believed to be relatively rare events (occurring less than once per day on average in the entire USA [8]). Of wider interest is the sequela of an acute exposure, typically commencing about 10 days later: organophosphate-induced delayed neuropathy (OPIDN), which is a neurodegenerative disease resulting in demyelination and other consequences [9, 10] and, ultimately, profound behavioural sequelae. Since relatively little is known about the mechanism with which OPIDN is engendered, our knowledge of the conditions necessary for inducing it is still limited. In particular, at present it is not known whether there is some threshold concentration of TCP below which OPIDN is never induced. The answer may depend on an individual’s genetic, epigenetic and metabolic constitution. The absence of, or a low, threshold concentration implies that The potential rôle of aircraft cabin aerial dust for transporting semivolatile organic contaminants into the lungs Jeremy J. Ramsden †, ‡ † Department of Materials, Cranfield University, Bedfordshire, MK43 0AL, UK ‡ Sustainable Aviation Unit, Collegium Basilea (Institute of Advanced Study), Hochstrasse 51, CH-4053 Basel * There is presently concern regarding toxins, especially neurotoxins, which have been detected in aircraft cabin air. Among them, the tricresyl phosphates (TCP) are especially problematical, because of their ability to engender organophosphate-induced delayed neuropathy (OPIDN), leading to lasting damage of the central nervous system. The low volatility of TCP in principle offers some protection, since any contaminants emerging from the jet engines that supply hot compressed air to the cabin will tend to condense on the inner walls of the ducts leading to the cabin, where they have indeed been found. Were it not for that, cabin air concentrations would presumably be considerably higher. Alongside various organic compounds, high levels of fine and ultrafine particles (of unknown composition) have also been detected in aircraft cabin air. This paper firstly examines whether volatilized jet oil could account for the measured particle numbers. Since the two are not well correlated, an alternative hypothesis, that the particles are mineral debris, is examined. If coated with monolayer of TCP, such particles could transport a significant quantity of TCP into the lungs. A definitive evaluation requires more parameters to be measured, such as the chemical nature and distribution of diameters of the particles measured in aircraft cabin air. Keywords: adsorption, metal oxide, nanoparticle, respiration, tricresyl phosphate * Present address. E-mail: J. Ramsden@colbas.org. 1 The oil and air circuits are separated by oil seals but even in the best of cases there is chronic small leakage, which tends to worsen as the interval from last engine maintenance increases.