New study confirms health risks from smaller particulates

Researchers at the Health Effects Institute, an independent research organisation in Cambridge, Massachusetts, have spent three years re-analysing data from previous investigations and testing dozens of different explanations for the results. The study suggests that tiny particles with a diameter of less than 2.5 micrometers, which are mostly caused by by-products of combustion, are more dangerous than those of 10 micrometers. These smaller particulates may also contain more carcinogens.

Currently, although the US sets air-quality standards for both 2.5 and 10 micrometer particles, Europe only has a standard for 10 micrometer particles, though the European Commission is due to review its particle pollution laws. Tim Brown of Britain’s National Society for Clean Air is reported as calling for more research into how particle composition, not just size, affects health.

Concern about particulate pollution stems mostly from a 1993 study by a team of researchers at the Harvard School of Public Health in Boston, which identified particles with a diameter of less than 10 micrometers as being a threat to public health. Death rates and pollution levels in six cities were compared by following more than 8000 adults for up to 16 years.

In 1995, a seven-year study of 550 000 adults by the American Cancer Society also found a strong link between death rates and particulate pollution, though critics of both studies argued that factors such as poverty might also be responsible for differences in death rates.

Adrian Pope of the Brigham Young University in Provo, Utah, who led the American Cancer Society study, is reported as saying that he hopes that the new analysis will end the controversy.