No link to air toxics in pediatric asthma prevalence

A nationwide US study has found that early exposure to ambient air toxics does not associate with the prevalence of asthma in young children.

The results are somewhat surprising, given that air toxics – a list of 187 pollutants deemed hazardous to human health in the 1990 US Clean Air Act Amendments – have been linked to asthma exacerbations in some previous studies. Additionally, the six criteria pollutants have been shown to strongly correlate with prevalent asthma.

However, the research team, led by Timothy Buckley (Ohio State University, Columbus, USA), found that not only did air toxics like acrolein, diesel emissions, and nitrobenzene not associate with asthma prevalence, they appeared to have a mild, protective effect against the condition.

“We are unaware of a biological basis to explain this observation,” they comment, adding that it could be due to families with children at risk for asthma moving to locations with better air quality, or down to bias or confounding.

The team studied a sample of children born in 2001 and assessed at age 5.5 years via interview with their mothers. Exposure to air toxics was based on the National Air Toxics Assessment according to the child’s residence at age 24 months.

Overall, 17.5% of children had been given a diagnosis of asthma by a healthcare professional and 6.8% had required emergency or inpatient treatment for asthma.

The team found that children who lived in areas with greater exposure to air toxics known to pose a respiratory risk did not have a greater prevalence of asthma or incidence of hospitalization either overall, or when considering emissions specifically from motor vehicles, or those from motor vehicle diesel emissions.

This was true when the authors compared the highest and lowest deciles of exposure, as well as when they looked for a linear trend. However, there was actually a trend for children in the lowest deciles of exposure to have the greatest prevalence of asthma and hospitalizations, although this did not reach significance.

Reporting in PLoS One, Buckley et al say that even though they did not find evidence of a link between air toxics and increased asthma prevalence, they note that children from ethnic minorities and socioeconomically disadvantaged areas bore the highest burden of respiratory air toxics risk.

Therefore, they conclude that “[e]ven in the absence of an association between risk and prevalent disease, identification of this environmental injustice warrants attention.”

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