Aerotoxic syndrome: are jet engine oil compounds turned toxic by aircraft air-con?

Dr David Megson, Senior Lecturer in Chemistry and Environmental Forensics, discusses the aerotoxic syndrome research with Frank Cannon, left, aviation lawyer and research funder, and Lucía Rodríguez Armesto, right

University researchers investigating the disputed phenomenon of aerotoxic syndrome in aeroplanes have established that low toxicity components in jet engine oil do not undergo a conversion into more harmful chemicals during their journey through the aircraft air conditioning system.

Proponents of aerotoxic syndrome believe that fresh air sucked into the cabin of commercial airliners via jet engines – known as bleed air – may be contaminated by engine lubricant vapours and could be breathed in by those on board, allegedly causing headaches, nausea and long-term health problems.

It is contested whether aerotoxic syndrome exists and is the source of an ongoing debate.

Cabin air contaminants?

The ventilation relies on a mixture of bleed air and re-circulated cabin air, and the limited research undertaken to date has indicated that cabin air generally meets health and safety standards, with contaminant levels normally low.

Those who believe that aerotoxic syndrome occurs say an aircraft's crew may risk greater exposure to airborne contaminants because of the specific conditions within the space-constrained flight deck.

It is a far from resolved scientific issue but existing literature suggests the substances involved may be organophosphates – the main components of herbicides, pesticides and insecticides – and the focus by chemists has been on one particular group of organophosphates called tricresylphosphates (TCPs), found in oil.

Testing for transisomerisation

The team from Manchester Metropolitan University’s Ecology and the Environment Research Centre investigated if low toxicity TCP components in jet engine oil could undergo a transformation in an aircraft’s air conditioning system and end up as more harmful poisonous TCP particulates in the cabin and flight deck.

They used a catalytic converter at a university laboratory to replicate the kind of heat – as much as 400°C – the oil would face during a flight to see if they could realise the hypothesised effect.

The results are published in the Chemosphere journal.

Effects not fully understood

Lead academic Dr David Megson, Senior Lecturer in Chemistry and Environmental Forensics, said:

This is a highly important and emotive issue for many people.

From the evidence provided to date it appears clear that something is causing significant harm to air crew.

Most of the focus has been on TCPs present in aircraft oil although there are many different factors at play here.

For example, there are many other potential sources of organophosphates on planes and many other toxic compounds that air crew may be exposed to.

We do not yet fully understand the potential cumulative effects of these compounds and how they affect different people in a high altitude cabin environment.

The most important thing is to identify what is causing the reported symptoms and implement some effective mitigating measures

Laboratory testing

Previous research conducted by Dr Megson and his team confirmed aircraft oil does not contain toxic ortho-substituted TCPs (ooo-TCPs), one type of organophosphate that has been the focus of many studies.

The Manchester Metropolitan team wanted to test if other less harmful TCP isomers – TCP molecules with the same number of atoms but in a different arrangement – in aircraft oil could undergo a conversion process, known in organic chemistry as transisomerisation, in the palladium catalytic systems of aircraft cabins and become the toxic ooo-TCP.

This testing was carried out in a laboratory under the supervision of Dr Aidan Doyle, Senior Lecturer in Industrial Chemistry, and the experiments confirmed transisomerisation did not take place.

More focus on other potential sources

Dr Megson said: “ooo-TCP has been previously found in aircraft cabins but it was not clear what this source of the ooo-TCP was.

“It was therefore important for our study to establish that the oil does not appear to be the source of ooo-TCP and more focus should be placed on investigating other potential sources.”

The study was funded and co-authored by Frank Cannon, an aviation lawyer, former pilot and former airline owner who has represented ex-pilots and ex-members of cabin crew who have launched legal claims with airlines over aerotoxic syndrome.

Another co-author was environmental chemist Dr Jean-Christophe Balouet, who has previously independently researched aerotoxic syndrome.