CYCLING to work may seem the healthy option, but a study has shown that people riding in cities inhale tens of millions of toxic nanoparticles with every breath, at least five times more than drivers or pedestrians.

The research involved fitting cyclists with devices that could count the particles, mostly emitted by car exhausts, in the air they were breathing.

It showed that urban concentrations of nanoparticles, which measure just a few millionths of a millimetre, could reach several hundred thousand in a cubic centimetre of air.

The particles, when inhaled, have been linked to heart disease and respiratory problems.

Because they are exerting themselves, cyclists breathe harder and faster than other road users. The study found that they suck in about 1,000 cubic cm with each breath, meaning they may inhale tens of millions of the particles each time they fill their lungs, and billions during a whole journey.

“This is the first time anyone has counted the particles while also measuring people’s breathing during city commuting. It showed that cyclists can inhale an astonishing number of pollutant particles in one journey,” said Luc Int Panis of the transport research institute at Hasselt University in Belgium, who led the study.

For the research, just published in the journal Atmospheric Environment, Int Panis and his colleagues asked cyclists to pedal while wearing a mask fitted with instruments that could measure and count the particulates, as such particles are known. All are invisible even in severely polluted air.

The researchers found that in Brussels the cyclists inhaled 5.58m nanoparticles for every metre cycled, dropping to about 1.1m when they tried the experiment in Mol, a much smaller town in Belgium.

They also found the cyclists inhaled four to five times more particles than a car passenger driven along the same route.

Int Panis said: “The air pollution figures in a big city like London or Birmingham are the same as or greater than in Brussels so British city cyclists will experience similar effects.”

For cyclists and other road users, the key question is what the health impact might be of inhaling so many particles.

This has been one of the hardest questions to answer because the time lag between exposure to pollutants and developing an illness is usually long.

Earlier researchers had the same difficulty when studying whether smoking was linked to lung cancer, and it took decades to confirm the connection.

New techniques for gathering and analysing data mean, however, that the health problems caused by particulates are emerging much more quickly.

A study carried out in London, to be published soon in the journal Epidemiology, is expected to show that exposures to high concentrations of nanoparticles are associated with a higher risk of heart disease. It will also show an association between larger particulates and respiratory health.

Other studies have shown that exposure to particulate pollution can have rapid short-term effects too — such as provoking asthma attacks.

In a 2007 study, published in the New England Journal of Medicine, researchers at Imperial College London asked 60 people with mild or moderate asthma to walk along the western end of the busy Oxford Street in central London, where only diesel-powered taxis and buses, plus cyclists, are permitted. The volunteers suffered asthma symptoms such as reduced breathing capacity and lung inflammation.

Diesel vehicles emit far higher levels of pollutant nanoparticles than petrol engines.

What alarms health researchers is that such particles are so small that they penetrate the lungs and circulate in the blood. They are then thought to accumulate in organs such as the heart and brain and cause inflammatory reactions.

Wearing a mask offers little protection as the particles are so small that they pass straight through any shield.

Earlier this year, such fears prompted the House of Commons environmental audit select committee to publish a report warning that air pollution caused about 50,000 premature deaths a year in Britain.

Int Panis’s research has already annoyed cycling groups. He has decided not to attend Velo-city 2010, a conference on cycling to be held in Copenhagen next month, because of the hostility he faced when announcing preliminary results of his research.

Int Panis and his colleagues point out that cycling still brings many health benefits and hope that it may be healthier than driving a car.

Int Panis said: “I am a cyclist and the idea that riding a bike might be less healthy than driving is not pleasant, but I am also a scientist, so I have to look at the data.”

http://www.timesonline.co.uk/tol/news/environment/article7140213.ece