UC Davis     UC Davis Health System   •  Department of Public Health Sciences   



Ranking Cancer Risks of Organic Hazardous Air Pollutants in the United States

This study compares cancer risks from organic hazardous air pollutants (HAPs) based on total personal exposure summed across different microenvironments and exposure pathways.

We developed distributions of personal exposure concentrations using field monitoring and modeling data for inhalation and, where relevant, ingestion pathways. We calculated risks for a non-occupationally exposed and non-smoking population using US Environmental Protection Agency (EPA) and California Office of Environmental Health and Hazard Assessment (OEHHA) unit risks. The contribution to risk from indoor versus outdoor sources was determined using indoor/outdoor ratios for gaseous compounds and the infiltration factor for particle-bound compounds.

Using OEHHA's unit risks, the highest ranking compounds based on the population median and 1,3-butadiene, formaldehyde, benzene, and dioxin, with risks on the order of 10-4 - 10-5. The highest risk compounds using the EPA unit risks were dioxin, benzene, formaldehyde, and chloroform, with risks on a similar order of magnitude. While indoor exposures are responsible for nearly 70% of risk using OEHHA's unit risks, when infiltration is accounted for, inhalation of outdoor sources contributed 50% to total risk, on average. Additionally, 15% of risk resulted from exposures through food, mainly due to dioxin.

Most of the polycyclic aromatic hydrocarbon, benzene, acetaldehyde, and 1,3-butadiene risk came from outdoor sources, while indoor sources were primarily responsible for chloroform, formaldehyde, and naphthalene risks. The infiltration of outdoor pollution into buildings, emissions from indoor sources, and uptake through food are all important to consider in reducing overall personal risk to HAPs.


The chart to the right is a baseline risk ranking using OEHHA toxicity estimates. X indicates the distribution medians if the EPA risk estimates were used (where available). 1,3-Dicholoropropene does not have a unit risk value from OEHHA, therefore the EPA risk estimate was used. *Formaldehyde cancer potency value is undergoing reassessment, and will likely drop this risk by a couple orders of magnitude.


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