Auto Pollution's Carbon Particulates Harms Kids' Lung Function

LEICESTER, England, July 5 ? Carbon spewed by cars and trucks is responsible for lowered lung function in otherwise healthy children, according to researchers here.

For the first time, there's evidence of a strong dose-dependent link between carbon in airway macrophages - used as marker for exposure to automobile air pollution -- and declines in lung function, said Neeta Kulkarni, M.D., of the University of Leicester. The link fortified hints from population-based studies.

"Our data strengthen the evidence for a causal association between the inhalation of carbonaceous particles and impaired lung function in children," Dr. Kulkarni and colleagues concluded in the July 6 issue of the New England Journal of Medicine.

The researchers studied airway macrophages obtained from 64 healthy Leicestershire children through sputum induction and measured the macrophage area occupied by carbon; the lung function of the children was measured by spirometry. At the same time, Dr. Kulkarni and colleagues looked at how much primary particulate matter of less than 10 micrometers in diameter - so-called PM₁₀ - was in the air at or near each child's home address. Measurement of PM₁₀ was used as a proxy for environmental carbon exposure as it is a major component of particulate matter of that size.

The study found that each increase in primary PM₁₀ of one microgram per cubic meter near a child's home was associated with an increase of 0.10 micrometer squared in the carbon content of the child's airway macrophages.

In terms of lung function, each increase of one micrometer squared in carbon content was associated with:

• A 17% reduction in forced expiratory volume in one second (FEV₁). The decrease was statistically significant at P=0.004.
• A 12.9% reduction in forced vital capacity (FVC). The decrease was statistically significant at P=0.03
• A 34.7% reduction in the forced expiratory flow between 25 and 75% of the forced vital capacity (FEF_25-75). The decrease was statistically significant at P=0.004.

The modeling of PM₁₀ in each child's environment may under-estimate the amount of carbon exposure, the researchers noted, because they did not take into account such factors as time spent indoors, background exposures to PM₁₀ blown into the study area from other areas, and PM_2.5 - the tiny PM particles that contains the most elemental carbon.

It was also possible, Dr. Kulkarni and colleagues noted, that impaired lung function somehow increased the amount of carbon in macrophages. To look at that possibility, they studied nine children with severe asthma; carbon was not detected in the airway macrophages of eight of the nine, although they lived in areas with higher levels of PM₁₀ than the healthy children.

The implication, the researchers said, is that lung dysfunction does not lead to increased carbon in macrophages and, on the contrary, "phagocytosis of carbon particles by airway macrophages may be impaired in severe asthma."

The research is important because impaired lung development in children leads to poor lung function in adulthood, said James Gauderman, Ph.D., of the University of Southern California in Los Angeles.

"Reduced lung function later in life has been described as second only to the exposure to tobacco smoke as a risk factor for death," Dr. Gauderman wrote in an accompanying editorial.

He noted that air quality in many major cities has improved in recent years, as a result of such things as emission controls on automobile exhausts, but that individual exposures may still be high, depending where people live.

Even in areas with relatively low levels of pollution, he argued, "children living or going to school near a busy road may be exposed to unacceptably high levels of air pollution."

The best course is to reduce air pollution even more: "Our children's health depends on it," he said.