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Select Committee on Science and Technology Minutes of Evidence

Memorandum by Dr Sarah MacKenzie Ross MA, MPhil, C.Psychol, DPsychol, AFBPsS

RE: AIR TRAVEL AND HEALTH—SUBMISSION OF NEW EVIDENCE

1.1 I am a Consultant Clinical Neuropsychologist based at University College London and I would like to submit new evidence that has been produced since 2000 on the health effects of air travel. In particular, health effects associated with exposure to engine oil fumes in the aircraft cabin.

1.2. Throughout 2005 and 2006 I examined a number of pilots who complained of ill health following reported exposure to contaminated air on commercial aircraft. I prepared a report detailing my findings for the Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment, entitled Cognitive function following reported exposure to contaminated air on commercial aircraft: An audit of 27 airline pilots seen for clinical purposes.

SUMMARY OF MY REPORT[1]

2.1 I identified a profile of cognitive deficits in pilots which involves under functioning on tests of working memory, verbal memory, attention, mental flexibility and information processing speed. These deficits can not be attributed to factors such as mood disorder, anxiety disorder, malingering or chance.

2.2 My findings are of obvious concern as they pose a risk to flight safety. A pilot's job involves complex three dimensional thought processing and a need to accurately interpret, shift attention between and respond to changing information presented to them by flight instruments, navigation systems and air traffic controllers.

2.3 The pilots I examined were tested during the day and were asked to perform to the best of their ability, yet deficits were identified. These deficits may be magnified under particular working conditions, such as when a pilot is fatigued after a long shift at work or under stress in a complex emergency situation.

2.4 My report has been considered by the Committee on Toxicity (COT), and they arranged for it to be peer-reviewed by an independent expert and Professor of Neuropsychology who concluded that my study was well designed, had been conducted with an appropriately high level of expertise; and that the deficits/abnormalities identified were striking and of sufficient severity to cause concern about the functioning of implicated aircrew.

SUMMARY OF A SCIENTIFIC PAPER DESCRIBING A SINGLE CASE STUDY, RECENTLY PUBLISHED IN THE JOURNAL OF OCCUPATIONAL HEALTH AND SAFETY, AUSTRALIA AND NEW ZEALAND IN 2006[2]

3.1 In this paper we conclude that: Potential contamination of aircraft cabin air by engine oil fumes is a serious aviation safety concern for both crew and passengers and further research is needed to determine the potential toxicity of pyrolised engine oil under aviation conditions (ie at altitude, in a reduced oxygen environment, after being subjected to extreme temperature). The medical profession should develop internationally agreed medical protocols for the evaluation and treatment of affected individuals. Aircrew who report ill health following exposure to contaminated air should be referred for further investigations, including psychology, neurology, neurophysiology, neuroimaging and respiratory. Diagnoses such as "industrial hysteria" and "psychosomatic disorder" are unhelpful and misleading and should only be made if there is clear evidence that psychological factors are involved in the aetiology of a patient's complaints. Absence of underlying pathology following medical examination is not proof of an actual non organic condition, particularly in the context of a history that might reasonably account for the symptoms.

FURTHER RESEARCH HAS BEEN PUBLISHED SINCE 2000 THAT MAY INVALIDATE THE CONCLUSIONS DRAWN BY THE COMMITTEE IN 2000

4.1. For example, the Committee focused heavily on the presence of one chemical isomer of Tricresyl phosphate, namely, Tri-orth-cresyl phosphate (TOCP) to ascertain the potential risk to passengers and crews of developing ill health following exposure to engine oil fumes. The Committee concluded that the low levels of TOCP that might be found following an oil leak would not pose a "significant risk to the health of passengers and crew".

4.2 However, it is important to consider (a) other more toxic TCP isomers which are present in much higher concentrations than TOCP and have higher toxicity;[3] and the combined, synergistic effects of all of the chemicals present in engine oil (see below).

4.3 Recent research has shown that adverse effects may be caused by impurities and/or other constituents of the formulated products (eg solvents), as opposed to the active ingredients; and there may be synergistic effects of chemical combinations.[4] Combined exposure to other chemicals which cause oxidative stress can decrease the level required to produce neuronal damage following exposure to organophosphates.[5] Animal studies have shown that when two chemicals are combined (eg an OP plus DEET) severe neurotoxic effects were seen in the peripheral and central nervous system and increased mortality even though safe levels of each chemical were chosen. In other words when certain chemicals are combined, even at safe levels, the end product can be more toxic than what would be predicted from the known properties of each chemical which makes up the mixture.[6] Furthermore, toxicological testing needs to consider health outcomes other than the extremely rare condition known as OPIDN. Physical, cognitive and emotional consequences of exposure should be considered first.[7]

4.4 It is also important to consider the possibility that genetic differences between individuals may render some people more susceptible to the toxic effects of certain chemicals than others. A number of papers have been published since 2000 which find an association between genetically determined polymorphisms and the development of ill health following exposure to organophosphate pesticides.[8], [9], [10], [11]

RECOMMENDATIONS—GAPS IN THE EVIDENCE BASE

5.1 Given the scientific uncertainty regarding the potential hazards of inhalation of pyrolised engine oil, further research into the full range of health effects from inhalation of heated or pyrolised synthetic jet oils is definitely warranted. This research should consist of:

(a) On board monitoring to determine the contaminants and level of each contaminant that enters the aircraft. The Committee recommended in 2000 that airlines carry out cabin atmosphere sampling (see paragraphs 1.25 and 1.26) and undertake real time monitoring of air quality (see paragraph 1.43 (c);

(b) An Epidemiological Survey to determine the incidence and prevalence of ill health in aircrew and any association there might be with exposure to contaminated air. A sub-sample of aircrew should also undergo clinical examinations by a multi-disciplinary group of healthcare professionals to explore the nature of any symptoms identified in more depth, determine severity and impact on life, ascertain whether there are subgroups of people at particular risk (eg the elderly, pregnant women, children, persons of less than average health). The House of Lords Science and Technology Select Committee recommended in 2000 that maximum value should be extracted from the medical records of aircrew concerning any long-term effects from exposure to the aircraft cabin environment—see paragraph 1.43 (f);

(c) A survey needs to be undertaken to determine whether passengers are affected by exposure to engine oil fumes on board aircraft;

(d) Toxicological testing needs to be undertaken that takes account of the potential synergistic effects of the range of different chemicals found in engine oil; and this research should consider health outcomes other than OPIDN, such as physical, cognitive and emotional disorder;

(e) The current edition of the Department of Health book aimed at professionals should contain information about the potential health effects of exposure to engine oil fumes;

(f) Whilst this research is being undertaken, the Government and regulators should re-consider (a) supplying only fresh air to the flight deck (see paragraph 1.24) and/or (b) installing filters to minimise the risk to aircrew and passengers of engine oil fumes.

7 June 2007

References

Haley, R W, Billecke, S, La Du, B N (1999). Association of low PON1 Type Q (Type A) arylesterase activity with neurologic symptom complexes in Gulf War veterans. Toxicology and Applied Pharmacology, 157, 227-233.

Richter R J and Furlong, C E (1999). Determination of paraoxonase (PON1) status requires more than genotyping. Pharmacogenetics, 9: 745-753.