Particulate Air Pollution, Sulfur Dioxide, and Daily Mortality: A Reanalysis of the Steubenville Data

The effects of particulate and ozone pollution on mortality in Moscow, Russia

The objectives of this study were (1) to evaluate how acute mortality responds to changes in particulate and ozone (O(3)) pollution levels, (2) to identify vulnerable population groups by age and cause of death, and (3) to address the problem of interaction between the effects of O(3) and particulate pollution. Time-series of daily mortality counts, air pollution, and air temperature were obtained for the city of Moscow during a 3-year period (2003-2005). To estimate the pollution-mortality relationships, we used a log-linear model that controlled for potential confounding by daily air temperature and longer term trends. The effects of 10 mug/m(3) increases in daily average measures of particulate matter </=10 mum in aerodynamic diameter (PM(10)) and O(3) were, respectively, (1) a 0.33% [95% confidence interval (CI) 0.09-0.57] and 1.09% (95% CI 0.71-1.47) increase in all-cause non-accidental mortality in Moscow; (2) a 0.66% (0.30-1.02) and 1.61% (1.01-2.21) increase in mortality from ischemic heart disease; (3) a 0.48% (0.02-0.94) and 1.28% (0.54-2.02) increase in mortality from cerebrovascular diseases. In the age group >75 years, mortality increments were consistently higher, typically by factor of 1.2 - 1.5, depending upon the cause of death. PM(10)-mortality relationships were significantly modified by O(3) levels. On the days with O(3) concentrations above the 90th percentile, PM(10) risk for all-cause mortality was threefold greater and PM(10) risk for cerebrovascular disease mortality was fourfold greater than the unadjusted risk estimate.

Health effects of particulate air pollution

In the 1980's it was generally felt that particulate air pollution concentrations in the United States were not a hazard to the public health. However, in the early 1990's the application of econometric time-series studies and prospective cohort studies suggested increased mortality associated with acute (daily) and chronic (decades) exposures to particulate air pollution commonly observed in the developed world. The epidemiologic evidence was not supported by evidence of causal associations from other disciplines. Nevertheless, the EPA moved to tighten controls on fine particulate air pollution. The debate over the science was played out in public hearings and the courts. The experience provides lessons on the use of epidemiologic data in setting public policy.

A new longitudinal design for identifying subgroups of the population who are susceptible to the short-term effects of ambient air pollution

A longitudinal design is proposed to investigate the short-term effects of air pollution on health status. The study design exploits a new statistical methodology developed by Dewanji and Moolgavkar (2000, 2002) that makes use of a Poisson counting process for the incidence of events in a longitudinal cohort study. The methodology allows for modeling of subject-specific baseline hazards of multiple events and time-dependent ecological (i.e., daily levels of air pollution and weather conditions) and individual covariates (e.g., comorbid conditions, indices of declines in health status). The study will determine the association between short-term changes in air pollution and incidence of hospitalization, emergency department visits, "intermediate health conditions" (e.g., changes in health status reflected by changes in filled prescriptions), and mortality. Data from the universal Quebec medicare system are used, including data for residents of Montreal age 65 yr and above. The cohorts include individuals who have at baseline airways disease, chronic coronary artery disease, congestive heart failure, hypertension, cerebrovascular disease, atherosclerosis, dysrhythmias, and diabetes, and these will be followed for the incidence of the already mentioned adverse outcomes, adjusting for time-dependent individual and ecological covariates. This type of study will provide findings that can be used to confirm or refute results of time series analyses. Using a different methodology that includes subject-specific information will greatly increase our understanding as to whether short-term exposures to ambient air pollution cause serious changes in health status among subgroups of the population. These results will also help in understanding mechanisms by identifying groups that are susceptible to the effects of air pollution.

Mortality displacement and distributed lag models

Numerous time-series studies have investigated the association between daily mortality and daily ambient particulate air pollution concentrations (PM). The consensus from these studies is that increases in PM are associated with increases in daily mortality. However, it may be that increases in PM only hasten the deaths of individuals in a small, frail subset of the population whose longevity is short even in the absence of particulate air pollution. This hypothesis has been termed mortality displacement or harvesting. Distributed lag models (DLM) have been used to explore mortality effects of air pollution that are spread over multiple days, and DLM coefficients have been proposed as indicators of mortality displacement. We investigate statistical properties of DLM coefficients in the context of mortality displacement using simulation studies with frail population models. Our simulations use actual PM time series, as well as actual weather time series included as confounders. Our simulations show that DLM coefficients can have large bias when the mean lifetime of individuals in the frail subset of the population is more than a few weeks, and that the magnitude of this bias increases as the mean lifetime of individuals in the frail subset of the population increases. We conclude that DLM coefficients may be misleading as an indicator of mortality displacement, in the context of the frail population models that we explored.

Health-related benefits of attaining the 8-hr ozone standard

During the 2000-2002 time period, between 36 and 56% of ozone monitors each year in the United States failed to meet the current ozone standard of 80 ppb for the fourth highest maximum 8-hr ozone concentration. We estimated the health benefits of attaining the ozone standard at these monitors using the U.S. Environmental Protection Agency's Environmental Benefits Mapping and Analysis Program. We used health impact functions based on published epidemiologic studies, and valuation functions derived from the economics literature. The estimated health benefits for 2000 and 2001 are similar in magnitude, whereas the results for 2002 are roughly twice that of each of the prior 2 years. The simple average of health impacts across the 3 years includes reductions of 800 premature deaths, 4,500 hospital and emergency department admissions, 900,000 school absences, and > 1 million minor restricted activity days. The simple average of benefits (including premature mortality) across the 3 years is 5.7 billion dollars [90% confidence interval (CI), 0.6-15.0] for the quadratic rollback simulation method and 4.9 billion dollars (90% CI, 0.5-14.0) for the proportional rollback simulation method. Results are sensitive to the form of the standard and to assumptions about background ozone levels. If the form of the standard is based on the first highest maximum 8-hr concentration, impacts are increased by a factor of 2-3. Increasing the assumed hourly background from zero to 40 ppb reduced impacts by 30 and 60% for the proportional and quadratic attainment simulation methods, respectively.

Interactions between particulate air pollution and temperature in air pollution mortality time series studies

In many community time series studies on the effect of particulate air pollution on mortality, particulate air pollution is modeled additively. In this study, we investigated the interaction between daily particulate air pollution and daily mean temperature in Cook County, Illinois and Allegheny County, Pennsylvania, using data for the period 1987-1994. This was done through the use of joint particulate air pollution-temperature response surfaces and by stratifying the effect of particulate air pollution on mortality by temperature. Evidence that the effect of particulate air pollution on mortality may depend on temperature is found. However, the results were sensitive to the number of degrees of freedom used in the confounder adjustments, the particulate air pollution exposure measure, and how the effects of temperature on mortality are modeled. The results were less sensitive to the estimation method used--generalized linear models and natural cubic splines or generalized additive models and smoothing splines. The results of this study suggest that in community particulate air pollution mortality time series studies the possibility of an interaction between daily particulate air pollution and daily mean temperature should be considered.

The particulate air pollution controversy

Scientists, regulators, legislators, and segments of industry and the lay public are attempting to understand and respond to epidemiology findings of associations between measures of modern particulate air pollutants (PM) and adverse health outcomes in urban dwellers. The associations have been interpreted to imply that tens of thousands of Americans are killed annually by small daily increments in PM. These epidemiology studies and their interpretations have been challenged, although it is accepted that high concentrations of air pollutants have claimed many lives in the past. Although reproducible and statistically significant, the relative risks associated with modern PM are very small and confounded by many factors. Neither toxicology studies nor human clinical investigations have identified the components and/or characteristics of PM that might be causing the health-effect associations. Currently, a massive worldwide research effort is under way in an attempt to identify whom might be harmed and by what substances and mechanisms. Finding the answers is important, because control measures have the potential not only to be costly but also to limit the availability of goods and services that are important to public health.

The association between daily mortality and ambient air particle pollution in Montreal, Quebec. 1. Nonaccidental mortality

This study was undertaken to determine whether variations in concentrations of particles in the ambient air of Montreal, Quebec, during the period 1984 to 1993, were associated with daily variations in nonaccidental mortality. Fixed-site air pollution monitors in Montreal provided daily mean levels of various measures of particulates and gaseous pollutants. Total sulfates were also measured daily (1986-1993) at a monitoring station 150 km southeast of the city (Sutton, Quebec). We estimated associations for PM(2.5), PM(10), total suspended particles, coefficient of haze (COH), extinction coefficient, and sulfates. We used coefficient of haze, extinction coefficient, and Sutton sulfates to predict fine particles and sulfates for days that were missing. To estimate the associations between nonaccidental mortality and ambient air particles, we regressed the logarithm of daily counts of nonaccidental mortality on the daily mean levels for the above measures of particulates, after accounting for seasonal and subseasonal fluctuations in the mortality time series, non-Poisson dispersion, weather variables, and gaseous pollutants. There were 140,939 residents of Montreal who died during the study period. We found evidence of associations between daily nonaccidental deaths and most measures of particulate air pollution. For example, the mean percentage increase (MPC) for an increase of total suspended particles of 28.57 microg/m(3) (interquartile range, IQ), evaluated at lag 0 days, was 1.86% (95% confidence interval (CI): 0.00-3.76%), and for an increase of coefficient of haze (IQ=18.5 COH units per 327.8 linear m) the MPC was 1.44% (95% CI: 0.75-2.14%). These results are similar to findings from other studies (the mean percentage increase in nonaccidental deaths for a 100 microg/m(3) increase in daily total suspended particles was 6.7%). We also found increases for fine particles and for inhalable particles, but the confidence intervals included unity. All measures of sulfates showed increased daily mortality; e.g., the MPC for sulfates from fine particles (IQ=3.51 microg/m(3)) was 1.86% (95% CI: 0.40-3.35%). We generally found higher excesses in daily mortality for persons 65 years of age and for exposures averaged across lags 0, 1, and 2 days. The slope of the association between daily mortality and ambient air particles in Montreal, which has lower levels of pollution than most major urban centers, is similar to that reported in most other industrialized cities. This study therefore provides further evidence that the association is linear and that any threshold effect, should it exist, would be found at lower levels of air pollution than those found in Montreal.

Daily mortality in relation to weather and air pollution in Christchurch, New Zealand

OBJECTIVE

To investigate the relationship between the daily number of deaths, weather and ambient air pollution.

METHOD

An ecological study. We assembled daily data for the city of Christchurch, New Zealand (population 300,000) from June 1988 to December 1993. We used Poisson regression models, controlling for season using a parametric method.

RESULTS

Above the third quartile (20.5 degrees C) of maximum temperature, an increase of 1 degree C was associated with a 1% (95% CI: 0.4 to 2.1%) increase in all-cause mortality and a 3% (0.1 to 6.0%) increase in respiratory mortality. An increase in PM10 of 10 micrograms/m3 was associated (after a lag of one day) with a 1% (0.5 to 2.2%) increase in all-cause mortality and a 4% (1.5 to 5.9%) increase in respiratory mortality. We found no evidence of interaction between the effects of temperature and particulate air pollution.

CONCLUSIONS

High temperatures and particulate air pollution are independently associated with increased daily mortality in Christchurch. The fact that these results are consistent with those of similar studies in other countries strengthens the argument that the associations are likely to be causal.

IMPLICATIONS

These findings contribute to evidence of health consequences of fuel combustion, both in the short term (from local air pollution) and in the long term (from the global climatic effects of increased atmospheric CO2).

Pulmonary retention and clearance of inhaled biopersistent aerosol particles: data-reducing interpolation models and models of physiologically based systems--a review of recent progress and remaining problems

During the last 40 years, most models of long-term clearance and retention of biopersistent particles in the pulmonary region of the lung were phenomenologically oriented and accounted for only a small portion of the growing insight into lung dynamics by pulmologists, histologists, and biochemists. In this review, theoretical developments of modeling pulmonary dynamics for biopersistent particles during or after inhalation exposure are discussed. Several characteristic examples are given of the present state of the art. Most of the models presently in use are pragmatical compartmental models with a single compartment for the pulmonary region. They relate to observed data and facilitate an interpolation within the range covered by observation. Occasionally, these models are unjustifiably used for extrapolations in efforts to derive hypothetical risk assessments. Modeling efforts aiming at models of physiologically based pulmonary systems with a potential for extrapolations are not common and were published only during the last decade. Of this kind of approach, the review covers four examples. Promising progress has been made, but scarcity of supporting experimental data slows validation and extension. The two most recent model developments are based on a hypothesis by P.E. Morrow. According to Morrow, alveolar clearance is accomplished by mobile alveolar macrophages after phagocytosis of particles on the alveolar surface. The macrophage mobility, however, and thus the efficiency of the transport to the mucociliary escalator of the tracheobronchial tract will eventually decline towards total loss of mobility after the particle burden of the macrophages exceeds a critical value. The POCK model has been evaluated for a variety of chronic and subchronic rat exposure studies with noncytotoxic aerosols and gave good simulation results. The model by Tran et al. appears to be still in the developing stage of facilitating simulations for cytotoxic aerosols, but the combination of both model approaches seems to be a sound route of future efforts.

Air pollution and respiratory health in Mexico City

To determine the effect of air pollution in Mexico City on respiratory health, patient visits for upper respiratory tract infections were monitored in five clinics. Levels of ozone, nitrogen dioxide, carbon monoxide, and sulfur dioxide, and climatological variables were collected. Correlations of filtered data revealed an association between NO2 and O3 with an increase in visits to clinics because of respiratory problems. Autoregressive analysis indicated that pollutant levels/respiratory visits associations remained significant even after simultaneous inclusion of temperature, suggesting that air pollution was associated with 10 to 16% of the clinic visits. The relative risk indicated that high levels of O3 and NO2 could increase the total number of clinic visits to between 19 and 43% above average. The other pollutants and the control group did not demonstrate significant associations.