particularly among lower-income populations, research suggests.
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A study published in PLOS Medicine used vital registration and population data from across the United States for 1999-2015 to estimate the number of deaths and loss of life expectancy associated with four different models of concentrations of fine particulate matter pollution, and examine how that has changed over time.
While the current national ambient air quality standard for particle pollution is 12 mcg/m3 in almost all counties, the study found that in 1999, 59% of the 1,339 county units had concentrations above this level. At that time, the population-weighted average fine particulate matter pollution concentration for the entire country was 13.6mcg/m3. The highest level was seen in Fresno county in California, which had a fine particulate pollution concentration of 22.1 mcg/m3.
By 2015, national concentrations had declined to 8.0 mcg/m3, and the lowest observed concentration was 2.8 mcg/m3.
The investigators wrote, “Each model was applied to county-level cardiorespiratory death rates separately by sex and age group (5-year age groups from birth to 85 years and 85 years and older) because death rates vary by age group and sex, as might their associations with air pollution. From each model we estimated age-specific proportional increases in death rates (i.e. rate ratios) for each 1 mcg/m3 of PM2.5 [fine particulate matter].” The analysis revealed that fine particulate matter pollution above the lowest observed concentration of 2.8 mcg/m3 was associated with higher death rates from cardiorespiratory diseases.
Overall, researchers estimated that these higher levels contributed to 15,612 deaths from cardiorespiratory diseases in women and 14,757 deaths in men, representing 2.8% and 2.7% of all cardiorespiratory deaths, respectively. This amounted to 0.15 years of life expectancy lost in women and 0.13 years lost in men.
There was significant variation in the cost to life expectancy around the country. In the midwestern and Rocky Mountain counties in states such as New Mexico, Colorado, and Arizona, which had lower levels of air pollution, life expectancy loss was less than 0.05 years. But in southern states where the air pollution levels were highest, such as Arkansas, Oklahoma, Alabama, and around Los Angeles, the life expectancy loss was greater than 0.3 years.
“While current PM2.5 pollution is responsible for a significant mortality burden and loss of longevity, reductions in pollution since the late 1990s have benefited virtually the entire country, with the exception of 14 counties where PM2.5 increased slightly over this period,” wrote James E. Bennett, PhD, of the School of Public Health at Imperial College London and coauthors.
The primary limitation of the study is that this association between air pollution and cardiorespiratory health or life expectancy cannot be shown to be causal. Other pollutants and other environmental and behavioral factors that impact cardiorespiratory health may be significant. For example, including ozone and nitrogen dioxide levels in the models could result in different results in terms of the impact of PM2.5 on cardiorespiratory health.
The data highlighted that life expectancy loss associated with air pollution was larger in lower-income counties, those where a higher proportion of the population had a family income below the poverty line, and those where a higher proportion of the population were black or African American.
“This inequality in mortality burden occurs because lower-income counties, those with more poverty, with a greater proportion who are of black or African American race, or with a lower proportion who have graduated high school tend to have higher baseline death rates at any pollution level because of conditions associated with these covariates and hence experience a larger absolute number of deaths as a result of air pollution,” the authors wrote.
The study was funded by the U.S. Environmental Protection Agency and the Wellcome Trust. One author declared grants and personal fees from private industry, outside the submitted work.
SOURCE: Bennett JE et al. PLoS Med. 2019 Jul 23. doi: 10.1371/journal.pmed.1002856.