Estimating risk from ambient concentrations of acrolein across the United States

Abstract

Background: Estimated ambient concentrations of acrolein, a hazardous air pollutant, are greater than the U.S. Environmental Protection Agency (EPA) reference concentration throughout the United States, making it a concern for human health. However, there is no method for assessing the extent of risk under the U.S. EPA noncancer risk assessment framework.

Objectives: We estimated excess risks from ambient concentrations of acrolein based on dose-response modeling of a study in rats with a relationship between acrolein and residual volume/total lung capacity ratio (RV/TLC) and specific compliance (sC(L)), markers for altered lung function.

Methods: Based on existing literature, we defined values above the 90th percentile for controls as "adverse." We estimated the increase over baseline response that would occur in the human population from estimated ambient concentrations of acrolein, taken from the U.S. EPA's National-Scale Air Toxics Assessment for 1999, after standard animal-to-human conversions and extrapolating to doses below the experimental data.

Results: The estimated median additional number of adverse sC(L) outcomes across the United States was approximately 2.5 cases per 1,000 people. The estimated range of additional outcomes from the 5th to the 95th percentile of acrolein concentration levels across census tracts was 0.28-14 cases per 1,000. For RV/TLC, the median additional outcome was 0.002 per 1,000, and the additional outcome at the 95th percentile was 0.13 per 1,000.

Conclusions: Although there are uncertainties in estimating human risks from animal data, this analysis demonstrates a method for estimating health risks for noncancer effects and suggests that acrolein could be associated with decreased respiratory function in the United States.

Figure 1

Example of the response distribution among a baseline or unexposed population (solid line) and an exposed population (dashed line). The arrow indicates the change in mean response between the baseline and the exposed populations. Shaded areas represent the proportion of the population with a response past a level “A” that is considered abnormal.

Figure 2

Summary of data from Costa et al. (1986) and model fit for sC_L (cm³/cm H₂O) (A) and RV/TLC (B) for rats in HEC. Error bars indicate 1 SD. The dashed lines represent regression lines from our fitted models: y(x) = 0.08–0.005x for sC_L; y(x) = 0.136 + 0.0005x^2.63 for RV/TLC.

Figure 3

Distribution of additional estimated adverse response (per 1,000) to ambient acrolein using the three different values for defining adverse response. (A) sC_L (cm³/cm H₂O). (B) RV/TLC. Boxes represent interquartile range, horizontal lines represent median, and whiskers extend to the 10th and 90th percentiles. Values for RV/TLC for rural areas are essentially zero and are not shown.