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New international research has shown that particulate air pollution (or soot) is a significant cause of low birth weight in infants. The study is actually a meta-analysis of 14 studies done in nine countries, with a total sample of over 3 million births. A meta-analysis is an analysis of analyses, or a way of statistically combining the results of several studies to arrive at an overall estimate of the significance of an effect. The fact that the studies were done by different researchers, at different sites, using slightly different research methods is generally seen as increasing our confidence in the outcome.

Pollution at the study sites varied from 10 to 70 micrograms per cubic meter of air. The effect was small but consistent. Two ways of summarizing the results are:

• For every 10 microgram increase in pollution, average birth weight declines by 8.9 grams, or roughly one-third of an ounce.
• For every 10 microgram increase, the probability that an infant will be of low birth weight—less than 5 pounds, eight ounces—increases by 3%.

The effect was highly significant when controlling for the socioeconomic status of the mother and other confounding variables.

The two major sources of particulate pollution are industrial plants, especially power plants, and vehicle emissions. Exposure has been shown to be associated with health problems such as asthma, heart disease, stroke and diabetes. It's not clear why particulate pollution reduces birth weight, but one possibility is that it, and the diseases with which it is associated, place stress on the mother's body, which affects fetal growth. Low birth weight is a risk factor for infant mortality, and for heart, lung and behavior problems in later life.

A recent article in The Lancet attempted to quantify the major causes of premature death in the world. Air pollution was #7, contributing to 3.2 million deaths per year. (In case you're wondering, high blood pressure is #1, smoking #2, and alcohol consumption #3.) As David Pettit of the Natural Resources Defense Council notes:

Fortunately there are many actions that can be taken to address outdoor air pollution. The technology is readily available at a fraction of the investment cost compared to the health costs that the public bears.

Obviously, the availability of clean air technology is of little consequence if the corporations responsible for most of the pollution control a corrupt political system.

As if to show how obsolete our political system is, last August, the U. S. Court of Appeals struck down an Environmental Protection Agency rule intended to reduce emissions crossing state borders, partially on grounds that the rule was a violation of states' rights.