Medical Effects: Fine Particulate Pollution: Low Birth Weight

EHN: Yale study links bad air to low birth weight and health problems

[Once again 'bad air' is not including wood smoke. Perhaps one of the problems is that the researchers have not had the hands on experience of monitoring fine particulate from different sources, including wood smoke sources: barbeques, wood burning restaurants, fireplaces, wood stoves, wood boilers, etc. A pregnant woman would not have to be burning herself, wood smoke is a shared experience so to speak. 

Because wood smoke is missed, it means that proposed solutions will miss the mark. New diesel engines are an important and expensive priority. Wood smoke prevention costs very little, but the benefits in cleaning up PM2.5 can be quite large, as much as 30 to 60% in some seasons.  Mary J. Rozenberg, Editor,]

Bad Air Linked to Low Birth Weight

Abram Katz, Register Science Editor

A groundbreaking Yale University study

Connecticut air that meets federal pollution limits still contains enough harmful chemicals to stunt babies before they are born.

The Yale study found that emissions from cars, diesel engines and power plants increase the frequency of low-birth weight babies, who face a multitude of medical problems, including cognitive ability, infection, heart disease and stroke.

"It is very worrisome and a tremendous public health problem," said David Brown, public health toxicologist and adjunct professor at Fairfield University.

"If you look at people with neurological difficulties, the predominant link is low birth weight," he said.

Occupational health experts and environmentalists said the study represents more evidence that air pollution standards need to be tightened, and that current limits are too lax to protect the population.

Yale researchers, led by Michelle L. Bell, assistant professor of environmental health at the Yale School of Forestry and Environmental Studies, analyzed 358,504 births from 1999 to 2002 in 15 Connecticut and Massachusetts counties.

They then correlated maternal location, weather and pollution levels over the previous nine months, and the weight of the women's infants.

The study is the first to measure air pollution and birth weight in the Northeast.

Similar research has been conducted in California, Nevada and Georgia, with inconsistent results.

Bell and colleagues found that exposure to pollution, even at low levels, apparently increases the risk of low birth weight. Black women were effected more strongly than whites.

The scientists examined maternal exposure to nitrogen dioxide, sulfur dioxide, carbon monoxide, and soot particles 2.5 and 10 microns in diameter.

A human hair is about 70 microns across.

Pollutants reduced birth weight by up to an average of 16.2 grams, or about half an ounce.

However, because this is an average, an infant at the low end of the statistical curve might weigh substantially less, specialists said. Imagine a bell curve. A 16-gram difference would be more significant for the lower weight infants, and less of a factor for the heavier ones.

Babies who weigh less than 2,500 grams, or about 5C pounds, are considered to be at low birth weight.

In the Yale study sample, 4 percent of the infants were low birth weight. That would correspond to about 164,500 infants born in the United States every year, including around 1,684 in Connecticut.

"All of the counties in the study are in compliance (with federal clean air standards) so the lower levels are dangerous," Bell said.

The study showed that different pollutants had varying effects when breathed by the mother at different time in the pregnancy.

For example, lowered birth weight was associated with exposure to 10-micron particles in the third trimester. Carbon monoxide created its greatest effect in the first and third trimesters, and 2.5-micron particles in the second and third trimesters.

Most low birth weight babies do well, said Dr. Robert Herzlinger, chief of neonatology at Bridgeport Hospital.

Infants who are affected may experience poor growth, growth failure later in life, neurodevelopmental problems, cardiovascular disease and diabetes, he said.

Many factors determine birth weight, Herzlinger said, including poor nutrition, exposure to alcohol and drugs, smoking and prematurity.

The Yale researchers corrected for extremely low-weight infants, along with infants whose mothers smoked, level of education, lack of early prenatal care, and older and younger mothers.

Why breathing air pollutants while pregnant should influence the weight of the full-term infant is not well understood.

Bell and fellow researchers said air pollution could affect a fetus directly through the placenta, or indirectly by degrading the mother's health. The same mechanism at work in smoking, premature rupture of membranes, may be to blame.

Inhaling smog may disrupt endocrine and nervous systems, and soot particles could reduce the amount of oxygen reaching the fetus.

Brown said a link between air pollution and birth weight, although obscure, shows that the population is responding to the pollutants.

Carbon monoxide, nitrogen and sulfur oxide particles tend to travel together, making the task of figuring out which ones cause lower infant weight difficult.

Other unmeasured pollutants may also exert a bad influence, he said. Vanadium, a toxic metal, is often generated along with the ambient pollutants recognized by the U.S. Environmental Protection Agency, yet it is neither tested for nor recorded, Brown said.

"We don't want to repeat the cigarette smoke situation," he said. For many years tobacco companies denied that smoking caused lung cancer because researchers could not explain how.

Industries could again argue that since none of the pollutants has been shown to cause lower birth weight, that no extra measures need be taken, Brown said.

"The question is, what will it take for people to understand this in such a way that they take action?" he said.

In fact, the EPA and states are working to reduce air pollution, said Roger Smith, campaign director for Clean Water Action in Hartford. The organization also works on air pollution.

"There has been some progress. In 2007, 2.5-micron particles must be reduced by 90 percent," he said. New diesel engines will be required to meet the more stringent standard, and Congress enacted a bill to spend $200 million on retro-fitting older engines with catalytic converters and filters to remove most fine soot particles.

However, the money has not been allocated.

"We're slowly getting there, but too slowly," Smith said.

Also, under amendments to the federal Clean Air Act, all states must produce acceptable plans to reduce nitrogen oxides and particulates. These plans should be required to meet lower limits, he said.

The Connecticut General Assembly passed "An Act Establishing a Connecticut Clean Diesel Plan" in 2005.

The goal is to cut diesel exhaust from school buses, transit buses and construction equipment working on state jobs by 2010.

Whether these measures are sufficiently stringent, or even attainable, is not clear.

L. Bruce Hill, senior scientist with the Clean Air Task Force, a nonprofit organization based in Boston, said the Yale study suggests that current National Ambient Air Standards are too weak.

"It also suggests that there is no lower threshold for levels of particulates. It's a cause for concern," Hill said.

Meanwhile, no single study will be sufficient to answer public health questions about air pollution and birth weight, said Dr. John Meyer, assistant professor in the division of occupational and environmental medicine at the University of Connecticut Health Center.

"These kinds of studies are extremely hard to do," said Meyer, whose research focuses on occupational reproductive hazards.

As for the Yale study, Meyer said that county weather records are not specific enough. Pollution is higher in urban centers than in rural areas, which may lead to underestimating the birth weight effect in cities.

Parsing out all of the contributing factors of living in impoverished areas is also extremely difficult, Meyer said. "One would like to see additional studies of smaller areas," he said.

"The study makes another good step in understanding the issue. It's helpful in adding to the base of knowledge. Should we be doing something about it? You'd have to compare the effects of poor pre-natal care and lack of access to medical care, to the effects of pollution," Meyer said.

Bell said she wants to continue her research with another study including more detailed information on each pregnancy.

"It's useful for us to know," she said.

(c)New Haven Register 2007

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