National Academy of Sciences: Research Priorities for Airborne Particulate Matter, March 24, 2004
On March 24, 2004, the National Research Council of the National Academies released its fourth and final report — Research Priorities for Airborne Particulate Matter: IV. Continuing Research Progress. The report summarizes the salient findings from six years and over $300 million in federal research funding. It concludes that significant progress has been made in understanding the health risks posed by particle pollution in the air, and identifies areas for further research is needed.
When EPA set new National Ambient Air Quality Standards for fine particles in 1997, Congress established and funded a major new research program to reduce scientific uncertainties about particles in the air and their health effects. Congress also directed that a committee of the National Academy of Sciences be established to provide guidance in planning the research program, and then in monitoring research progress. The Committee on Research Priorities for Airborne Particulate Matter identified ten priority topics for research, and has periodically tracked research progress on these topics.
The final report:
– confirms the serious risks from exposure to particle pollution, including the most dangerous risk, premature death;
– cites evidence of new risks including negative effects on cardiac and reproductive health;
– underscores concern for susceptible populations, such as those with preexisting lung and heart disease, and diabetes, children, and older adults; and
– cites findings from clinical and toxicological studies to explain the sickness and early death from lung and heart disease observed in earlier community health studies.
Below, we present direct quotations from the report on some of the most significant new recent advances in our knowledge about particulate matter.
Research Confirms that PM is Responsible for Adverse Health Outcomes
“It is becoming more evident from clinical and toxicological studies that ambient fine PM induces respiratory and cardiovascular events that in susceptible, compromised people can explain the morbidity and mortality observed in epidemiological studies. Research has documented that components of hypothesized mechanistic sequences do actually take place, supplying a biological basis for explaining some effects of PM observed in susceptible subpopulations.”
“Results from animal models and clinical studies have reinforced epidemiological findings for susceptible subpopulations, increasing the coherence of the body of available evidence.”
“Recent research has confirmed previously observed adverse health effects and identified new ones. Some of the results, particularly on cardiovascular health effects and for older adults and people with asthma, have increased confidence in the prior findings.”
New Epidemiological Studies Point to Particles as the Culprit
“… newer observational studies that have continued to demonstrate an independent effect of particles that is robust to statistical adjustment for other pollutants.”
“The more recent epidemiological and toxicological studies of PM and health provide clear evidence for an independent effect of PM in increasing risk for several adverse health outcomes.”
Outdoor Air Pollution is Key Determinant of Personal Exposure
“Monitoring studies of groups of individuals measured at successive points in time supported the conclusion that ambient (outdoor) particle concentrations are a key determinant of variation in personal exposure to particles. Such an association of ambient concentrations with personal PM exposures supports the use of ambient concentrations in time-series analyses and as a relevant metric for public health.”
Laboratory Findings are Consistent with Observational Studies
“Animal models are yielding consistent findings. Dogs with coronary occlusion and hypertensive rats demonstrate adverse cardiac and vascular effects when exposed to PM. Studies involving rodent models of aging show enhanced susceptibility to PM and an increase in the effect of PM with infection.”
Particulate Matter Worsens Asthma, Especially in Children
“Since 1997, the number of studies examining the health effects of air pollution on children has increased substantially. The majority of these studies focused on the effects of PM and, in several cases, copollutants on the health of children with moderate to severe asthma. Taken as a whole, these studies confirm the findings of earlier studies regarding the adverse effects of fine particles and possibly coarse particles as well on the exacerbation of preexisting illness in children with asthma.”
New Evidence for Effects on Susceptible Populations, Including Diabetics, Pregnant Women, and Older Adults
“Results that were reported include the following:
– PM exacerbates existing asthma conditions among children and adults;
– acute respiratory infections appear to compound adverse cardiovascular effects following PM exposures;
– cardiovascular and respiratory effects in susceptible and general populations continue to be the health responses of greatest concern in relationship to PM exposures.”
“There have been several new findings relevant to susceptible subpopulations. Research results show that following PM exposures, the following effects can occur:
– persons with diabetes might be at increased risk for adverse health effects, including increased mortality;
– intrauterine growth rates and newborn birth weights might be reduced by maternal PM exposures;
– patients with asthma or COPD have greater deposition of inhaled fine and ultrafine PM, resulting in higher doses and related risks;
– older adults experience adverse cardiac physiological changes;
– older adults show hematological changes (for example, changes in blood coagulation factors); and
– dogs with coronary occlusion and hypertensive rats demonstrate adverse cardiac and vascular impacts.”
Increased Evidence of Adverse Cardiovascular Effects
“Results from epidemiological, clinical and animal studies are converging to indicate that PM exposures, both to PM2.5 and ultrafine particles, have adverse cardiovascular effects…”
“There is growing clinical and epidemiological evidence that ambient air pollution can precipitate acute cardiac events, such as angina pectoris, cardiac arrhythmias, and myocardial infarction, with the majority of excess PM-related deaths attributable to cardiovascular disease.”
Broadened Health Outcomes Include Reproductive Effects
“…The list of particle-related health outcomes has broadened and now includes several adverse cardiac outcomes, such as changes in heart rate variability, cardiac arrhythmias, ischemic events, and congestive heart failure, as well as reproductive outcomes.”
Mechanisms are Better Elucidated
“… an impressive array of findings from in vitro, animal, and human studies have provided a much more robust understanding of the potential mechanisms responsible for particle-induced cardiovascular events. Although a definitive mechanism has not been established to explain higher increases in cardiac arrhythmias or myocardial ischemia, it has become clear that particles are capable of inducing many of the intermediate steps that are linked to adverse cardiac outcomes.”
Lung Disease Patients Receive High Doses of Particles
“The greatest policy-relevant advance is the understanding of PM dosimetry since the committee’s first report is the convergence of evidence from studies in multiple laboratories that demonstrate an increase in the portion of inhaled PM2.5 depositing in the respiratory tracts of people having obstructive lung disease (a highly prevalent condition). The available evidence on dosimetry confirms earlier work suggesting that abnormalities of airway structure or intrapulmonary gas distribution are likely to increase the total deposited dose for a given exposure concentration. The greater deposition fraction and the heterogeneity of deposition in abnormal lungs offer one possible mechanism for increased susceptibility of persons with underlying lung disease to inhaled particles — increased lung dose to localized lung regions — in comparison with persons having normal lungs…Translocation of PM or PM constituents from the lung to other organs has been demonstrated, but this phenomenon has not yet been well characterized.”
Metals are Suspect as Toxic Agents
“The initial toxicological studies are providing promising findings, pointing to possible roles for the ultrafine fraction of PM, metals, and other components of the PM mixture in air.”
“Several studies have found that metals, especially the water-soluble fractions, are associated with health-response indicators…These components have been associated with various effects, including production of reactive oxygen species, pulmonary inflammation, enhanced sensitization to antigens, and increased susceptibility to respiratory tract infection. There is also some indication that these species play a role in cardiac effects as well.”
