Van den Heuvel says she is a victim of what is known as aerotoxic syndrome, described by campaign group the Aerotoxic Association as “acquired acute and chronic ill health caused by exposure to toxic oil fumes present in the breathing air of most commercial jets”.
In the majority of commercial airliners, the air supply is sucked into the cabin via the engines, from where it can sweep up a host of toxic chemicals including oil fumes, organophosphates (in particular tricresyl phosphates), halogenated flame retardants and other volatile and semi-volatile substances, particularly if there is an engine leak of some kind.
The Aerotoxic Association, founded by pilots, says that the air is making people seriously, chronically ill, “unaware, thousands of people suffer every day, without knowing about this hidden health and safety hazard”.
Van den Heuvel started flying with KLM in 2008 and by 2011 started to “develop headaches, tiredness and cramps in the legs and arms” around two to three hours into a flight.
It began with the headaches and tiredness, which she initially put down to jet lag until she began to experience tremors and “couldn’t feel my hands and legs… at night I couldn’t walk up the stairs…this is not jet lag”.
Despite her symptoms, van den Heuvel said the airline kept pushing her to work and eventually dismissed her in 2016 when she refused to keep full-time hours. After a protracted legal battle, she was awarded the right to claim disability benefit at the Dutch Central Appeals Court in June. Her legal problems may have ended but her physical ones have not – today she still suffers from “very heavy headaches” and has to sleep for around two hours every afternoon.
Damage to the central nervous system
Neurologist Gerard Hageman included the flight attendant alongside two pilots in his 2019 study, Three patients with probable aerotoxic syndrome, in which he concluded that there was “objective evidence of damage to the central nervous system”, but not of causation. “Whether the autoantibody profile is specific to engine oil emissions needs to be addressed in future studies,” states the paper.
Similar symptoms have been described in other studies of air crew, “although objective evidence of exposure is lacking in most of these studies”, according to Hageman. “Reduced levels of butyrylcholinesterases in one of our cases is suggestive of causation and elevated neuronal and glial autoantibodies provide objective evidence of damage to the central nervous system. We consider further research is warranted.”
A growing number of cabin crew, passengers and pilots are reporting the symptoms associated with the syndrome. The body of scientific research examining it is also increasing, but so far has not proven a solid causal link between a specific chemical and the disease.
'Evidence of occupational risk'
In a bid to make sense of the evidence, David Megson, associate director of the ecology and environment research centre at Manchester Metropolitan University (MMU) and Kevin Hayes, his PhD student at MMU and Mount Royal University, led a systematic review of 138 papers on the disease - the largest and most comprehensive to date.
Megson and Hayes, in their resulting paper, Occupational risk of organophosphates and other chemical and radiative exposure in the aircraft cabin: A systematic review, state that there was “evidence of occupational risk” and that there was also “evidence that those who work in the aircraft cabin are at an increased risk of neurological injury or disease due to their profession”.
But with around 70 chemicals of concern being identified in the body of work, what remains elusive is a single “contaminant or mixture of contaminants in sufficient concentration proven to be capable of the symptomology”, states the paper, recommending more work is done to determine whether it exists.
Megson said the “research and the testimonies of many air crew clearly suggests that there is a problem that is impacting the health of these workers” and that although much of the data “pointed towards poor air quality in the cabin... it was not possible to link this to a specific chemical or event and it is considered more likely that there are several factors working together”.
He added: “One key aspect is repeated short term exposure to chemicals such as organophosphates, however there are also many other toxic chemicals that air crew are exposed to. This in combination with other factors such as shift patterns, working hours and an individual’s capacity to break down pollutants can all make matters worse. More should be done to help understand this problem and protect these people to enable them to conduct their jobs safely.”
Organophosphates are neurotoxins and form the basis of Sarin gas, which was released on the Tokyo underground in the terrorist attack of 1995. The chemicals were also used in government-mandated sheep dip until 1992, leaving hundreds of farmers with debilitating illnesses.
Hayes agrees there are lage evidence gaps. “The sum of exposures to multiple contaminants concurrently has not been adequately explored” and “not all contaminant sources have been examined and the chemical exposome onboard aircraft has not been adequately characterized,” he said.
“What someone ingests, breathes in, or touches in an aircraft cabin may result in a low dose exposure that could happen many many times,” he added. “This could potentially lead to illness.”
Another recent study found that concentrations of ultrafine particles in an aircraft cabin increased during take off, which could lead to ill health. A further paper states that engine hydraulic fumes are more harmful than engine oil fumes and that there are potential health risks associated with fume events.
'Governments and regulators do nothing'
Tristan Loraine, a former airline captain turned film director and campaigner, is the spokesperson for the Global Cabin Air Quality Executive (GCAQE), a global coalition of health and safety advocates set up to “raise awareness and find solutions to poor air quality on aircraft”.
It has been calling on regulators and governments globally to mandate the introduction of effective 'bleed air' filters and contaminated air warning sensors on passenger aircraft for years.
Loraine says the “American military first became aware of the problem in the 1950s when they first started using synthetic jet engine oils” but that it was masked on commercial aircraft by cigarette smoke.
He is continually frustrated at the lack of action.
“The British Air Accidents Investigations Branch has twice recommended to the regulators and the government that every aeroplane should have warning systems to protect flight safety – the last one was over 10 years ago – and the government and the regulators do nothing,” said Loraine.
“Twelve air accident departments around the world have made 50 recommendations and findings and still nobody fixes the problem,” he added.
John Hoyte, a founder of the Aerotoxic Association and former BAe 146 training captain who was grounded prematurely due to sickness, says “there is now more than enough published evidence to absolutely confirm that aerotoxic syndrome does exist”. He says the disease has been “systematically covered up for the past 20 years by governments who put the health and wellbeing of the aviation industry above the cost of human health”.
Former BA cabin crew member Dee Passon, who has chronic fatigue, has set up Angel Fleet, a website that lists the names of crew members that have died, such as 29-year old Matt Bass, whose death was attributed to an unintentional sleeping pill overdose and whose post mortem showed damage to his heart and nervous system. His family say toxic air could have been the cause.
'Neuroactive products are present'
But despite the growing body of evidence and proof that “neuroactive products are present” in cabin air, the existence of the chronic syndrome is contested by the aviation industry.
The regulator the Civil Aviation Authority (CAA) on its website, concedes that “fume events – abnormal odours, smoke, haze or fumes in the cabin – may arise from various internal or external sources, and some are due to contamination of the bleed air supply, for example as a result of a failure of an oil seal in the engine”.
It notes that, “In recent years concerns have been expressed about possible adverse health effects of exposure to contaminants in cabin air”, and says there is “strong evidence that some people experience acute symptoms as a consequence of fume events... and may cause itching or soreness of the eyes, nasal discharge, sore throat or coughing”.
But the CAA is not convinced that the fumes can create the long-term health problems described by the Aerotoxic Association and van den Heuvel. “It is currently unclear whether any form of long-term illness occurs to excess in people with such exposures,” it concludes.
The CAA did not respond to a request for comment but did provide the number of fume events that had taken place on Airbus and Boeing aircraft between 2013 and 2020, a total of 3,226, ranging from minor “smoke from a coffee maker” to “strong fumes causing cabin crew and flight crew illness” to “smoke and fumes in all areas of aircraft, MAYDAY declared and aircraft returned”.
The data reveals that more than half of the events took place on Airbuses A319 and A320, on which 844 and 775 were recorded respectively. Events were recorded on Airbuses A319, A320, A321 and A380 and Boeing models 737, 747, 757, 767 and 777.
Safety is paramount
A spokesperson for Boeing said safety is the firm’s top priority and that cabin air inside commercial airplanes is safe. “While no indoor environment is free from contaminants, several independent studies have found that air quality on Boeing aircraft compares favorably to other indoor air environments like schools, office buildings, and homes,” they said, adding that cabin air is exchanged every two to three minutes and that all Boeing airplanes use hospital-grade HEPA filters to remove essentially all particles from air that is re-circulated to the cabin. HEPA filters are not designed to remove heated engine oil or hydraulic fumes.
The spokesperson said that “independent researchers, universities, industry groups, and government agencies have conducted extensive research on cabin air quality.
“The results repeatedly demonstrate that contaminant levels generally are low and that health and safety standards are met. Based on that research, the world's five leading aerospace medical associations have rejected a connection between cabin air and significant health effects, and no aviation regulator has determined that additional safety regulations are required. Nevertheless, Boeing continues to work with scientists to improve our understanding of cabin environmental factors and to study potential technologies such as sensors and advanced filtering.”
Airbus did not respond to a request for comment.
KLM said the health of passengers and employees and the safety of the operation are paramount.
“Exposure to oil vapors (containing tricresyl phosphates) in the cabin air and its possible effect on health, is a focus of attention for KLM and other airlines,” a spokesperson for the firm said. “To this end, measurement results and research data are exchanged in a national (including in the National Cabin Air Advisory Group) and international context (including within European Aviation Safety Agency) with various parties involved, including scientists, aviation authorities, aircraft manufacturers, engine suppliers and unions of flying and technical personnel. In the many scientific studies that have been done to date, no indications have been found that there is an increased risk of health problems during the flight as a result of exposure to tricresyl phosphates.”
However, the spokesperson said KLM will “continue to monitor all developments in terms of research and publications. When passengers or employees report complaints, they are of course taken seriously and possible causes are looked into. There are protocols in place to adequately respond, ask questions and investigate complaints related to cabin air.”
A spokesman for British Airways said the firm would “never operate an aircraft if we believed it posed any health or safety risk to our customers or crew” and pointed to research commissioned by the European Aviation Safety Agency concluded that the “air quality on board aircraft was similar or better than that observed in normal indoor environments”.
“We always encourage our colleagues to tell us about any concerns they have, with reports passed onto the Civil Aviation Agency. Safety is our first priority and every report is thoroughly investigated, with typically 151 engineering checks before an aircraft is cleared to continue flying. Fume or odour reports have been found to be caused by a wide range of issues, including burnt food in the oven, aerosols, strongly-smelling food in cabin bags, and de-icing fluid,” the BA spokesperson said.
Easyjet said it has a modern Airbus fleet, that fume events are “fairly infrequent” and that its aircraft are all fully compliant with the latest standards of air quality and air conditioning.
“The health and wellbeing of our passengers and crew is our highest priority,” said the spokesperson. “Whilst we acknowledge that smell events occur there is no evidence that these events are linked to long term health and independent medical research has found no evidence for any such link. Additionally, aviation regulators and manufacturers around the world have looked at this issue and found no proof that long term health issues arise from cabin air quality.” Its fleet is fitted with “high performance carbon recirculation filters”.
A spokesperson for Virgin Atlantic said: “Creating a safe and secure environment for our people and our customers is always a priority at Virgin Atlantic and we work closely with the authorities on all matters of health and safety. As with all British airlines we operate to the strict regulations set out by the UK CAA and European Aviation Safety Agency.”
For the government’s part, the Department for Transport noted that “conclusions drawn from research suggest that long term ill health due to any toxic effect from cabin air is understood to be unlikely”, but added that it would “continue to monitor instances of fumes entering cabins on flights and consult with agencies both national and international”.
“All UK airlines are legally required to report any occurrences that did or, if uncorrected or addressed, could endanger aircraft, its occupants or any other person to the CAA within 72 hours of becoming aware of the occurrence. Airlines are also required to carry out appropriate levels of analysis of a potential incident and determine any further action that may help improve aviation safety. This applies to all types of occurrences including those relating to fire, smoke, fumes or smells,” it added.
But there is some progress, according to Hoyte, who is please to see that Teledyne Technologies has just released a new certified aircraft cabin environment sensor, to address what it calls the “need for accurate and comprehensive data” which is “essential to understand air quality onboard an aircraft and ensure a safe flying experience for both passengers and cabin crews”.
At present there is no air quality monitoring for the chemicals thought to cause aerotoxic syndrome with airliner cabins.
So the evidence continues to build, but government and the industry remain unconvinced. Meanwhile, many people continue to suffer from long-term debilitating sickness without answers, such as van den Heuvel, who is trying to move on with her new and limited life. She has advice for anyone who suspects they may be experiencing symptoms.
“Stop flying, the sooner the better, and try to contact people who know more about aerotoxic syndrome and to read about it. The less damage to your brain and nervous system the better, of course. Maybe if you stop flying in time the chronic damage will not be as bad as mine.”