The latest studies suggest that airborne pollution could pose a greater risk to health than previously thought. Sean Ottwell reports.

Combustion of fossil fuels results in the production of complex mixtures of chemicals that are released into the environment and potentially affect millions of people globally. However, although such particulate air pollution is widespread, there is as yet little understanding of the long-term health implications associated with exposure.

Now a group of Canadian researchers have taken a step forward in our understanding with an investigation into the genetic damage caused to male mice exposed to particular pollution in an industrial/urban environment.

Previous work demonstrated that the offspring of wild birds breeding near integrated steel mills on the North American great lakes inherited increased numbers of tandem repeat DNA sequence mutations compared with those from areas without steel mills.

The Canadian scientists, writing in the 15 January issue of the Proceedings of the National Academy of Sciences (PNAS), described how they exposed mice to ambient air near two integrated steel mills and a major highway, alongside control mice breathing high-efficiency air particulate (HEPA) filtered ambient air.

The scientists found a significant increase in germ-line mutation rate in mice housed in the industrial environment compared with the reference site. The majority of mutations were transmitted through the paternal germ line. High-efficiency HEPA filtration of the ambient air resulted in a significant reduction in mutation frequency, down to levels measured at a reference location.

From this the scientists concluded that the particulate fraction of air in this industrial location was largely responsible for the mutagenic hazard. “These findings show that chemical pollutants may cause heritable mutation,” they say, while cautioning that further research is required to confirm the results, and to evaluate the potential risk to humans exposed to particulate air pollution.

Foetus size

Meanwhile, work carried out at the Queensland University of Technology in Australia has found that exposure to air pollution significantly reduces foetus size during pregnancy.

Run over ten years, the study compared the foetus sizes of more than 15 000 ultrasound scans in Brisbane to air pollution levels within a 14 km radius of the city.

“The study found that mothers with a higher exposure to air pollution had foetuses that were, on average, smaller in terms of abdominal circumference, head circumference and femur length,” said senior research fellow Adrian Barnett.

Commenting further on the results, which have just been published in the international journal Environmental Health Perspectives, he added: “To our knowledge this is the first study of its kind as it uses ultrasound measurement as a direct estimate of growth, rather than using birth weight as a delayed measure of growth.”

When analysing scans from women at different distances to monitoring sites, the researchers found that there was a negative relationship between pollutants such as sulphur dioxide found in diesel emissions, and ultrasound measurement.

“If the pollution levels were high the size of the foetus decreased significantly … birth weight is a major predictor of later health, for example, bigger babies have been shown to have higher IQs in childhood and lower risk of cardiovascular disease in adulthood,” he said.

Barnett concluded that more data was needed from individual mothers to be more certain about the effects of air pollution on foetal development, but recommended in the mean time that where possible pregnant women reduce their exposure to air pollution.

Improved heavy metal

Air quality in the UK has improved significantly over the past 25 years according to a report published by the National Physical Laboratory (NPL). Monitoring at 17 testing sites around the UK shows a fall in the presence of harmful airborne heavy metals such as lead, iron and copper.

Results show a 70 per cent reduction in the average presence of all heavy metals tested over the period. The total average concentration has fallen from 1873 ng/m3of air in 1980 to just 568 ng/m3 in 2006 for the nine elements monitored. Lead has seen a particularly sharp decline falling from 556 ng/m3 in 1980 to 19.95 ng/m3 last year - a reduction of 96.5 per cent.

The decrease in air pollution reflects a move to greener industrial and household processes and advances in environmentally focused technology such as unleaded petrol.

Richard Brown, principal research scientist at NPL, explained: “Taking lead as an example, the steady decline of emissions from coal and oil combustion along with the change in fuel usage, and reductions in industrial output, has resulted in a significant reduction of lead in the atmosphere. We expect to see this decline continuing across the board until levels finally bottom out and become close to those occurring naturally.”

Air quality is measured on a monthly basis by collecting filters provided to the participating sites by NPL. These are returned to the laboratory where the results are analysed and collated. Results show that levels of all 13 harmful elements monitored are below those demanded by European directives and all are already well inside the UK’s air quality objectives for 2009.