Air pollution: traffic fumes go straight into your bloodstream

Written by Liam Kirkaldy on 19 September 2017 in Feature

The growing evidence of how particulate matter in air pollution is damaging our health

Air pollution -  stock

When the High Court ordered the UK Government to publish its air pollution plan back in April, Theresa May could have been forgiven for letting out a sigh of frustration.

After all, with the general election looming, the court’s decision to reject the government’s defence and order it to release its draft plans a month before the vote presented a headache the Prime Minister could have done without.

But the issue had been looming on the agenda for some time. From environmental organisations to health campaigners, air quality concerns have grown in recent years, particularly as evidence mounted over the damage pollution does to human health.


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The European Environment Agency describes air pollution as the single biggest health threat in Europe. Across the continent, it attributes more than 430,000 premature deaths each year to the problem, which is largely caused by transport emissions.

Meanwhile a Royal College of Physicians’ report, released last year, estimated that around 40,000 deaths can be attributed to outdoor air pollution in the UK each year. In Scotland, this means outdoor air pollution could contribute to as many as 2,500 premature deaths each year.

Evidence from the World Health Organisation suggests that globally, around 3.7 million premature deaths annually can be attributed to outdoor air pollution, with about 80 per cent of those deaths due to heart disease and stroke.

Professor David Newby, BHF John Wheatley Professor of Cardiology at the BHF Centre of Research Excellence at the University of Edinburgh, has been researching the health problems caused by air pollution for the last 15 years, using controlled exposure to pollution to measure its effects.

He told Holyrood: “We put people in a chamber and expose them to diluted diesel exhaust, with the exposure inside around the level you would get on the roadside on a polluted day. When we did that we looked at how the blood vessels in the body responded – essentially, they don’t relax as much, they are more likely to form blood clots, and if a blood clots forms it is less likely to dissolve.

When these things come together they can cause heart attacks and strokes. There is a lot of data out there proving there is a link between air pollution and chronic heart disease and cardiovascular disease, as well as precipitating acute strokes and heart attacks.

“If you look at the global burden of disease, air pollution is three out of the top five or six causes of death and disability across the world that is avoidable. From what we have learned, it seems to be the particle matter in the air pollution that causes these bad health effects in the body. Actually, when we put people with heart disease into these chambers, they also have a lot more strain in the heart.”

And while gases such as nitrogen dioxide, contained in exhaust fumes, are likely to cause health issues – especially for those with existing respiratory problems – it is the particulate matter released into the air which is most closely linked to heart disease and stroke.

Dr Mark Miller is a Senior Research Fellow within the BHF Centre for Cardiovascular Science, University of Edinburgh, who has researched how particulate matter moves through the body.

He told Holyrood: “We know air pollution is responsible for many millions of deaths around the world every year, but when you talk about the actual deaths – rather than disease – what people tend to die from is cardiovascular disease, disease of the heart, as opposed to disease of the lungs. So it is really important to try and study how air pollution causes damage to the heart and blood vessels. It’s quite clear how things inhaled into the lungs could cause lung disease and asthma, but it’s not quite as clear how it affects these distant parts of the body.

“There are lots of things that are dangerous about air pollution. But when you look at the cardiovascular system, it is the particles which are the most harmful. That is not to say things like nitrogen dioxide aren’t harmful – they are certainly harmful to the lung and in the long term will be harmful to the cardiovascular system. But if you just look at the very immediate effects of air pollution, it tends to be particles that are harming the heart and blood vessels.”

In an effort to learn more, Dr Miller’s research examined how the smallest type of particulate matter, called Nano particles – emitted by exhausts and even smaller than PM 2.5 – could pass into the blood. In an attempt to find a way to measure their movement, the team used gold.

Dr Miller said: “We can get these [gold Nano particles] at the same size as diesel exhaust particles, and importantly, we can track these around the body with very low concentrations. We exposed people to these gold diesel exhaust Nano particles and then we took their blood and urine afterwards to measure for the gold.”

The gold began to appear in the subjects’ blood around 15 minutes after the end of their exposure, then slowly increased in concentration over the next 24 hours. After 24 hours, every volunteer had gold in their blood. In fact, when the researchers invited them back they were shocked to find there was still gold in their blood and their urine three months later.

Dr Miller explained that while only a small number of particles are likely to get into the blood, the effect is still significant. 

“It’s important because if these particles get to areas where they can cause harm then even small amounts of these particles could be dangerous. What we did in the second part of the study was to look at where they went in the blood, and whether they went to areas of disease. With studies in both animals and patients – who had to have a two-year history of a stroke – we started to look and see if we could measure gold Nano particles in the blood vessels themselves.

"What we found was that the Nano particles seemed to preferentially go into areas of disease. So not only did they get into the blood but they accumulated in areas of disease. So it seems as though these particles can go anywhere in the body, but they selectively go to areas where they can cause the most harm.”

The study increased understanding of how particulate matter can damage different parts of the body. In particular, it showed that it is the smallest particles which are the most harmful. The obvious answer is for regulation to attempt to reduce levels of these pollutants. 

As Professor Newby put it: “The smaller particles are generally generated by combustion in traffic. There are several levels where we can change things. One is legislation, which obviously government can help with. Two is industry – they could make cleaner engines, and they are doing that. Then the third is based in active transport – people should get on their bikes and walk more.”

In this sense, air quality regulation is key. But while the UK is obliged to meet EU air quality standards, the prospect of Brexit has raised questions over the future of regulation.

In fact, the UK’s future membership status aside, the relevant EU air quality directives are due to be reviewed. The process will start at the end of this year, with a consultation expected in the middle of 2018, and a recommendation on future targets due before 2019.

Anna Heslop, a lawyer at ClientEarth – the group which brought the case against the UK Government – told Holyrood: “The [European] Commission has a rolling programme where they review directives that are a few years old. Sometimes they look at them and say, ‘yes, this is fit for purpose, let’s keep it’ and other times they look at them and say, ‘actually, this isn’t working properly’. 

“But the World Health Organisation has more ambitious guidelines for PM than the existing EU directive does, and we know the WHO is going to look at those again, so we might find they come down even more. We would expect the commission to take that into account when they review the directive, because the limits in the current directive are not the same as in the WHO guidelines. But if you open the directive up [to review], the limits could go up or down, depending on the political negotiation.”

But while campaigners are concerned over what Brexit could mean for air quality, the picture in Scotland looks somewhat different to the rest of the UK. 

Updating the Scottish Government’s Cleaner Air for Scotland strategy earlier this year, Roseanna Cunningham highlighted how Scotland became the first country in Europe to adopt in law WHO guidelines on fine particulate matter, while creating four new Air Quality Management Areas, bringing the total to 38 in Scotland. In doing so, Scotland now has more ambitious targets than those demanded by the EU.

And in this sense, rather than leading to weaker regulation, Brexit could potentially provide an opportunity for the rest of the UK to adopt the tougher standards established by WHO. Amid growing concern over the effect of PM on human health – particularly on the heart – campaigners will hope for action, no matter how it comes about.  

In association with the British Heart Foundation

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