Public health protection from air pollution can be achieved more effectively by shifting from a single-
pollutant approach to a multi-
pollutant approach. To develop such multi-
pollutant approaches, identifying which
air pollutants are present most frequently is essential. This study aims to determine the frequently found carcinogenic air toxics or hazardous
air pollutants (HAPs) combinations across the United States as well as to analyze the health impacts of developing
cancer due to exposure to these HAPs. To identify the most commonly found carcinogenic air toxics combinations, we first identified HAPs with
cancer risk greater than one in a million in more than 5% of the census tracts across the United States, based on the National-Scale Air Toxics Assessment (
NATA) by the U.S. EPA for year 2005. We then calculated the frequencies of their two-component (binary), and three-component (ternary) combinations. To quantify the
cancer-related health impacts, we focused on the 10 most frequently found HAPs with national average
cancer risk greater than one in a million. Their
cancer-related health impacts were calculated by converting lifetime
cancer risk reported in
NATA 2005 to years of healthy life lost or Disability-Adjusted Life Years (DALYs). We found that the most frequently found air toxics with
cancer risk greater than one in a million are
formaldehyde,
carbon tetrachloride,
acetaldehyde, and
benzene. The most frequently occurring binary pairs and ternary mixtures are the various combinations of these four air toxics. Analysis of urban and rural HAPs did not reveal significant differences in the top combinations of these chemicals. The cumulative annual
cancer-related health impacts of inhaling the top 10 carcinogenic air toxics included was about 1,600 DALYs in the United States or 0.6 DALYs per 100,000 people.
Formaldehyde and
benzene together contribute nearly 60 percent of the total
cancer-related health impacts. Our study shows that although there are many carcinogenic air toxics, only a few of them affect public health significantly at the national level in the United States, based on the frequency of occurrence of air toxics mixtures and
cancer-related public health impacts. Future research is needed on their joint toxicity and cumulative health impacts.