Epidemiological evidence linking fine particulates in air to increases in deaths from respiratory or vascular illness has accumulated rapidly over the last four years. The mechanisms are not fully understood, but in 1995 the Government's Expert Panel on Air Quality Standards (EPAQS) was sufficiently sure of the link to propose a 50µg/m3 standard, expressed as a 24-hour running average, for PM10 - particulates less than 10µm in diameter (ENDS Report 250, pp 17-21 ).
Most of the evidence has come from studies of mortality and hospital admission figures during pollution episodes - leading to arguments over whether PM10 exposure leads to significant shortening of life expectancy or merely brings forward deaths from pre-existing acute illness. The new study suggests that the impact is significant, and is likely to stimulate further investigation of the impacts of pollution on the young.
Researchers from the US Environmental Protection Agency (EPA) and the National Center for Health Statistics examined data for about four million infants born between 1989 and 1991 which were cross-referenced with local PM10 levels. Deaths of infants over 27 days old due to sudden infant death syndrome (SIDS), respiratory illness and "other" causes were considered.
PM10 exposure was defined by mean local levels over the first two months of life, and infants were divided into low, medium and high exposure groups for statistical comparison. The low exposure group experienced particulate levels of 11.9-28µg/m3, while high exposures were at 40-68.8µg/m3.
After adjusting for confounding variables such as maternal education and smoking, the researchers found that infants with high PM10 exposure were 10% more likely to die than those with low exposure. Babies with normal body weights exposed to high PM10 levels were 40% more likely to succumb to respiratory ailments, and 26% more likely to die of SIDS, than those exposed to low levels. There was no correlation between PM10 exposure and other causes of death, leading the authors to conclude that particulates were associated with an increased risk of infant mortality.
The researchers note that the idea that air pollution affects young children is not new. In 1954, a report on the London smog episode of December 1952 found increased mortality in children less than a year old.
The study was published as President Clinton approved an EPA proposal to tighten air quality standards for particulates. For the first time, a standard has been set for particulates of less than 2.5µm in diameter (PM2.5). The standard will be 50µg/m3 as a daily average - weaker than the UK standard for PM10 - and 15µg/m3 as an annual average.
The study, carried out under the European Commission's APHEA project, concludes that the consistent results in the western cities support a causal association between exposure to particulates and SO2 and mortality from all causes.