Abstract
Over decades, the airline industry has published considerable documentation on the potential for inhalation exposure to organophosphates and other toxins sourced to engine oil fumes supplied by “bleed air” systems, which are used on most commercial and military aircraft. Case studies on the subsequent development of neurological and other symptoms reported by crewmembers have also been widely documented. However, airline industry reviews tend to define toxicity of engine oil fumes according to a single toxicological endpoint - Organo Phosphate Induced Delayed Neuropathy (OPIDN) – which is acknowledged to be the result of a very high dose of exposure to a specific chemical, Tri-Ortho Cresyl Phosphate (TOCP). Industry reviews typically argue that the low levels of TOCP in aviation engine oils justifies the safety of continuing to use unfiltered engine bleed air to ventilate civil and military aircraft cabins. In fact, this approach ignores the routine presence and toxicity of a complex mixture of OPs in oil fumes supplied by engine bleed air systems and ignores the type of neurological symptoms that crews report (i.e., not OPIDN). The industry approach also ignores the scientific literature on repeated low-dose exposure to OPs over extended periods (particularly relevant for airline crewmembers) and the variable susceptibility of individuals to toxicological damage. This paper reviews the above-mentioned studies and presents the scientific literature that should be considered to make a realistic risk assessment of the hazards of aircraft engine bleed air.
Highlights
Lubrication oils in gas turbine aero engines require the presence of synthetic lubricants, which include additives, to minimize engine wear at the high temperatures encountered in normal operation [1,2,3]
The majority of the lubricants utilised in turbine engines add cresyl phosphates, generally termed Tricresyl Phosphate (TCP) at approximately 3%
There are in addition many other compounds in the cresyl phosphate TCP commercial formulations
Summary
Lubrication oils in gas turbine aero engines require the presence of synthetic lubricants, which include additives, to minimize engine wear at the high temperatures encountered in normal operation [1,2,3]. The 2nd paragraph of Section 4 contains the core of the risk assessment: “Based on the detection limit of ToCP (0.5 ng/m3) maximum uptake via inhalation with a 100% bioavailability would amount up to 0.02 ng/kg body weight per day for a crew member of 70 kg (Step 1), (Figure 2) This level of exposure was compared with the available lowest No-Observed Adverse Effect Level (NOAEL) of ToCP that was established in chickens and amounts to 1.25 mg/kg/ d after a repeated daily oral dose for 90 days (Craig and Barth) [27]. The paper avoids citing of the latest science on low dose repeat exposure to OPs. the use of OPIDN as the toxicological endpoint represents, at best, a failure of hazard assessment and at worst a complete misunderstanding of the clinical picture presenting in aircrew. The failures of risk assessment illustrated in these three examples are repeated in the majority of the other studies listed in (Table 3)
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