New health research on particulates sheds light on possible mechanism Initial results from new particulate matter (PM) research provide a preliminary explanation for the biological mechanisms responsible for human health effects from exposure to fine particles. Several projects are using "real-world" particles for the first time in order to observe how humans respond to particles they would encounter in their everyday activities. Papers presented in April at conferences of the American Thoracic Society and the Health Effects Institute reveal preliminary links to PM exposure and effects on heart rates in humans and canines. Uncertainty about die mechanism of action was a key issue in the debate over EPA's final standard for particulate matter 2.5 microns or less in diameter (PM2 5), published in luly 1997. While the agency based its standard on epidemiological data linking PM levels with increased mortality and morbidity, toxicological and controlled human exposure studies in the laboratory
do not produce physiological changes, said Carl Shy, professor of epidemiology, University of North Carolina, who reviewed EPA's criteria document supporting the new standard. Working with EPA's National Health Effects and Environmental Research Laboratory, a team of researchers conducted a pilot study designed to examine physiological changes in elderly people exposed to concentrated outdoor air at varying PM levels. The study group, all ambulatory individuals living in a retirement home in Baltimore, underwent a daily battery of tests that measured factors such as lung function and heart rate to name a few, over a three week period. Preliminary analysis of the data shows that individuals with underlying cardiovascular disease exposed to fairly moderate levels of PM had lower heart rate variability than those exposed to the same PM concentrations but had no heart disease.
DRINKING WATER California proposes tighter MTBE standard The California Environmental Protection Agency's Office of Environmental Health Hazard Assessment has tentatively identified the fuel additive methyl terf-butyl ether (MTBE) as a possible human carcinogen, based on animal studies. As a result, it has proposed a public health goal to limit levels of the chemical in drinking water to 14 ppb, a much tighter level than the state and the U.S. EPA have been considering to date. California public health officials have recently become alarmed to find MTBE, a common gasoline oxygenate used to produce cleaner-burning fuel, in drinking water supplies (ES&T, June 1997, p. 269A). The new California report released in April did not present new toxicological data but presented a risk assessment based on a literature review of approximately 300 studies. The proposed public health goal is a scientific target to be used by the state's Department of Health Services in setting the actual tolerance levels, which take into account such factors as economic impacts and technical feasibility. At a May 15 hearing on the report, representatives of petroleum and chemical industries argued that the proposed standard is unnecessarily stringent. Donald Brown of the California citizens group Communities for a Better Environment, argued that improvements in automobile design mean that MTBE is no longer necessary to reduce emissions and should not be tolerated in drinking water in any quantity. The draft MTBE report is on a fast track for public comment and review since the Department of Health Services is under mandate from the state legislature to produce a final tolerance rule by July 1999. —RICHARD A. LOVETT
3 0 4 A • JULY 1, 1998 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS
The difference in heart rate variability, a well-established factor in sudden death from cardiac arrest, provides a tentative explanation for how PM causes negative health effects, said Shy, who worked on the pilot. A healthy newborn has a highly variable heart rate, said Shy. As an individual ages, heart rate variability normally decreases. "We have found a potential mechanism that needs to be explored a lot more," Shy said. An expanded study is being launched this month to a larger sample of elderly people with cardiopulmonary disease. Similar work is underway at the Harvard School of Public Health, where researchers are studying the effects of inhaled ambient particles of Boston air concentrated about 30 times with the Harvard Ambient Particle Concentrator on the heart rate and heart variability of test dogs. The Boston air study found that a significant increase in breathing rate and a change in heart rate variability as an effect from concentrated air particle exposure. "We've been studying inhaled particles for years, looking at ambient particles. Now we are using concentrated, real-world particles as a new direction," said Harvard's John Godleski, associate professor of physiology, who is heading the Boston study on canines. "I think what our studies are showing is that diere clearly are plausible mechanisms. We are just starting in this area, and I think we are at die stage where we are fairly early in testing hypotheses," said Godleski. The Harvard studies, partially funded by EPA, the National Institute of Environmental Health Sciences, and the Health Effects Institute, the latter funded by EPA and industry groups, are expected to characterize particle exposure, size, sulfate, nitrate and elemental constituents, pulmonary inflammation, and cardiac responses. Congress approved $49 million for PM research in 1998, which EPA is using to study mechanisms and to identify vulnerable population groups.— CATHERINE M. COONEY
