Exposure to large airborne pollutants also linked to asthma in children says new study

New US research has found that children exposed to airborne coarse particulate matter -- a mix of dust, sand and non-exhaust tailpipe emissions -- are more likely to develop asthma and need hospital care than children who are unexposed.

Carried out by researchers at The Johns Hopkins University, the results of the large-scale study has highlighted some of the the long-term dangers of coarse particulate matter, a type of air pollution created by physical processes such as tire and brake wear, agricultural tilling, salt spray and dust created in manufacturing.

Also known as PM 10-2.5, coarse particle matter measure from 2.5 to 10 micrometers. Fine particulate matter (PM 2.5) is defined as particles measuring 2.5 micrometers or smaller. By comparison, a human hair is between 50 and 70 micrometers thick.

There is already a large body of evidence to show that PM 2.5 has a negative effect on respiratory and cardiovascular health, with levels of fine particulate pollution now monitored and regulated by the Environmental Protection Agency (EPA).

However, there is less data on the relationship between respiratory health and coarse particle matter, with lead author Corinne A. Kent, explaining that, "We did this study to understand whether, in addition to PM2.5, coarse particulate matter contributes to asthma development and morbidity. The most recent assessment by the EPA concluded that there wasn't enough data to say one way or another whether PM10-2.5 causes negative health effects."

For the new research the team looked at data on asthma-related diagnosis and treatment gathered from 7,810,025 children ages 5 to 20 years across 34 states.

To estimate the levels of coarse PM in each zip code the team used measurements of particulate matter collected in the EPA's Air Quality System database.

After taking into account differences in race and ethnicity, sex, age, poverty level, education and urban density of the children's neighborhoods, the team found that for each microgram/cubic meter increase in coarse particulate matter, asthma diagnosis increased by 0.6 percent, emergency room visits for asthma by 1.7 percent and hospitalizations for asthma by 2.3 percent.

The association between coarse particulate matter and asthma was even stronger for children 11 years old and younger, with the team finding that in this group diagnosis increased by 1.3 percent, emergency room visits by 3.3 percent and hospitalizations by 4.5 percent, possibly because younger children spend more time outdoors and their immature lungs are also more vulnerable to air pollution.

The researchers acknowledged that the study was limited by the fact that there are few locations that monitor PM10-2.5, with most only monitoring PM2.5.

However, Keet added that, "More research is needed, but these findings add to evidence that exposure to PM 10-2.5 may contribute to asthma, and that regulation and monitoring of this part of air pollution may need to be considered."

The findings can be found published online in the American Journal of Respiratory and Critical Care Medicine.