Pollution from traffic may cause, not worsen, respiratory problems

Emissions linked to prevalence of allergic rhinitis and asthma

MUNICH – Studies from Taiwan and Germany show that respiratory problems in children appear to be induced rather than exacerbated by air pollution caused by heavy traffic.

The studies appear in the June edition of the European Respiratory Journal. The two independent studies looked at almost 300,000 children in total.

The larger study, carried out in Taiwan, used data from 800 schools. The eight-month study involved adolescents ages 12 to 15 years. The Chinese version of the standard International Study of Asthma and Allergies in Childhood questionnaire was sent to more than a million students and their parents. Only students from non-smoking homes were ultimately included in the study.

While doctors had already diagnosed allergic rhinitis in 28.6% of boys and 19.5% of girls in that group, the questionnaire responses indicated the rates were much higher, at 42.4% of boys and 34% of girls.

In parallel, the Taiwanese team examined data provided by the 55 air monitoring stations in the areas in which the schools were located.

The hourly sampling data from the stations identified two main types of pollutants: first, those connected directly with vehicles, namely nitrogen oxides, carbon monoxide and ozone; and, second, pollutants emitted by industry, power plants or domestic fossil fuels, especially sulphur dioxide and particulate matter
with a diameter of 10 microns or less, the so-called "PM10."

The team identified a clear connection (with an increased risk of 16% for girls and 17% for boys) between carbon monoxide or nitrogen oxides in ambient air and the prevalence of medically diagnosed allergic rhinitis, after adjustment for climatic factors (temperature and humidity) that also represent risk factors.

However, the Taiwanese researchers could not determine the respective role of each pollutant because certain other traffic-related pollutants were not measured.

For allergic rhinitis diagnosed on the basis of the questionnaire responses, the figures for increased risks were slightly lower at 12% and 9%, respectively.

"While more boys than girls seem to suffer from allergic rhinitis in the general population, traffic pollution seems to have the same impact on both sexes," said Dr. Leon Guo, the lead author of the Taiwan study.

The much smaller German study, involving 4,000 children who lived within 50 m of a busy roadway in Munich, compared child health data with traffic density and levels of certain pollutants.

Traffic-related air pollution (levels of benzene, soot and nitrogen dioxide) was calculated according to a prediction model on the basis of measurements taken at 34 measurement sites in the city, of which 16 had a daily flow of between 17,000 and 33,000 vehicles and the remaining 18 had a flow exceeding 33,000.

Here, as in a previous study, a geographical information system was used to identify where each child's home was situated in relation to street segments, at distances of up to 50 m and between 50 m and 300 m.

The level of the air pollutant exposure was then calculated for each child according to the model created from the site measurements.

Children living within 50 m of very busy roads (with a flow of more than 33,000 vehicles per day) were almost twice as likely to suffer from asthma as the general population (a relative risk of 1.8).

The figures were lower for coughing and wheezing, for which the relative risk was 1.6. Allergy susceptibility was also increased (by between 17% and 56% depending on the allergen), particularly in children who were also exposed to tobacco smoke.

Since the effect appeared to fall off with distance, the researchers emphasize that their figures also suggest a dose-response effect.

An editorial in the journal, written by Bert Brunekreef of the University of Utrecht, and Jordi Sunyer of the Medical Research Institute of Barcelona, struck a cautious note. "Surely," they wrote, "the world variation in the prevalence of asthma is so large that it seems unlikely that traffic-related air pollution is a major determinant of this variation. Nevertheless . . . we are gradually seeing more data suggesting that . . . air pollution may not just be a factor in
triggering attacks in patients who have developed asthma already."