Scientists at the University of Göttingen say they have found dangerous chemicals in blood and urine samples from aircrew, suggesting that they have been exposed while working on board.
The team led by Dr Astrid Heutelbeck said that as well as organophosphates – chemicals known to have a negative effect on enzymes in the human body – they also found traces of volatile organic compounds (VOCs).
Scientists tested 140 patients who reported symptoms, mostly aircrew members.
"These are all substances that are forbidden in consumer products," Dr Heutelbeck said.
She added that until now, there have been no official guidelines on the amount of these compounds it is safe to breathe in – in fact, the only guidance has been for workers who deal directly with the dangerous chemicals in their jobs.
Now Heutelbeck's team say they have identified which substances cause which medical symptoms, in detailed results which they plan to release in detail over the coming weeks at conferences and in journal articles.
The substances they identified could attack the nervous system, circulation and airways of people affected.
VOCs are described by the US National Institutes of Health (NIH) as "organic compounds that easily become vapours or gases... released from burning fuel".
The NIH further adds that the health effects of VOCs "can vary greatly according to the compound, which can range from being highly toxic to having no known health effects".
In Göttingen, the researchers suggest that the VOCs found in aircrew could have been released from kerosene, oils or antifreeze used in the engines that leaked into the cabin air supply.
Air drawn from engines
In almost all passenger aircraft, cabin air is drawn from the engines – and is regularly found to be contaminated with oil or antifreeze.
Such "Fume Events" have been recorded since the 1950s, with 663 cases recorded by the German Air Accident Investigation Authority (BFU) between 2006 and 2013 alone.
In one famous case in Cologne in 2010, the crew of a Germanwings plane were forced to put on their oxygen masks during landing after they reported a burning smell that made them feel unwell. The aircraft was able to land safely.
But despite repeated incidents like this, there was no scientific evidence to show that cabin air could cause illness – a much bigger risk for aircrew than for passengers.
Closer to answers
Following the Göttingen scientists' results pilots' union Cockpit called on aircraft manufacturers and the European Aviation Safety Agency (EASA) to find a technical solution.
They suggest adding separate turbines to draw in cabin air – a feature that was common in the early jet age, but was gradually phased out as it made aircraft heavier and more expensive to build.
Only Boeing's 787 among modern passenger jets does not draw cabin air directly from the propulsion system.
The union demands that the EASA and manufacturers must finally end the practice.
And researcher Dr Heutelbeck and her team say that those affected by possible VOC inhalation have usually been forgotten about after a few days – as have the laboratory checks ordered after events like the 2010 incident at Cologne airport.
Union Verdi, meanwhile, argues that "people on the ground are also placed in a high degree of danger" by toxic air in aircraft, and called for a specialist medical centre to be set up to treat people affected by VOCs inhaled in-flight.
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