Exposure to ambient nitrogen-oxides in air pollution may increase acute bronchitis episodes in children from birth to 4½ years, according to a new study appearing in the journal Environment International.

The association between nitrogen oxides exposure and acute bronchitis was found to increase with age in the first 2 years. In other words, those between 1 and 2 years showed a stronger association compared to those below 1 year of age. A similar trend, however, was not observed in children between 2 and 4½ years of age.

“Acute bronchitis is relatively common in preschool children,” said Irva Hertz-Picciotto, professor and chief of the environmental and occupational health division at the UC Davis Department of Public Health Sciences and the study’s principal investigator. “We found an exposure of approximately 35 micrograms per cubic meter of nitrogen oxides increased incidence of acute bronchitis by about 30%.”

Nitrogen dioxide is known to be a deep lung irritant and is regulated by the US Environmental Protection Agency (EPA). The standard is no more than 188 micrograms per cubic meter for any 1-hour average and no more than 100 micrograms per cubic meter as an annual average.

The study was conducted in two districts in the Czech Republic, Teplice and Prachatice, where ambient levels of nitrogen oxides were regularly monitored. The mixture of gases, consisting mainly of nitrogen dioxide and nitric oxide, are pollutants that result from burning fossil fuels in industrial installations such as power plants and automobiles.

For the study, the researchers looked at daily ambient nitrogen-oxide levels starting in May 1994 through June 2003. A total of 1,133 children were followed from birth up to 4½ years of age. The children’s respiratory health information was obtained from medical records. Additional information was collected using maternal questionnaires.

The researchers also examined what fuels were used in the children’s homes for heating and cooking—gas, electricity, or coal—and other potential exposures, such as second-hand cigarette smoke. The increased association found solely from air pollution persisted even after accounting for these other factors.

"Although our results are not directly comparable, because the current regulatory standards are for nitrogen dioxide, and we investigated a mix of nitrogen oxides, the standards are much higher than the levels associated with increased incidence of respiratory illnesses in this study. This means that levels considered safe actually may pose a risk of elevated rates of respiratory disease in young children," said Hertz-Picciotto.

Source: UC Davis School of Medicine