Closing the research loop: a risk-based approach for communicating results of air pollution exposure studies - Research

Environmental Health Perspectives, Jan, 2004 by Devon C. Payne-Sturges, Margo Schwab, Timothy J. Buckley

We assessed cumulative noncancer risks by aggregating the His across the VOCs that affect the same target organ. Aggregation in this way produces a "target-organ-specific hazard index" (TOSHI), defined as the sum of His for individual VOCs that affect the same organ or organ systems (U.S. EPA 2001).

Interpretation

Our approach for interpreting the results from the risk analysis was based on the recent air toxics work by the U.S. EPA and others, specifically the U.S. EPA's Cumulative Exposure Project and National Air Toxics Assessment (Caldwell et al. 1998; U.S. EPA 2001; Woodruff et al. 1998, 2000) in which VOC exposures posing a one-in-a-million cancer risk or more were interpreted as posing possible public health concerns. A one-in-a-million cancer risk as a health benchmark is consistent with provisions in the 1990 Clean Air Act Amendments, sections 112(f) and 112(c), which allow hazardous pollutant emission source categories to be exempted from regulation when posing less than a one-in-a-million lifetime risk to the most exposed individual (Clean Air Act of 1990).

For noncancer hazards, HIs > 1 were flagged to indicate that the VOC concentration exceeded the RfC and may be of public health concern. If the HI was [less than or equal to] 1, no harm was expected because the exposure was below the threshold for an adverse effect (Caldwell et at. 1998).

Whereas the Clean Air Act establishes a one-in-a-million cancer risk benchmark for single chemical pollutant emissions, there is no guidance for interpreting cumulative risk resulting from multiple pollutant emissions. We used the one-in-a-million cancer risk benchmark to interpret risk from exposure to multiple VOCs because the CAC position was that exposures should pose negligible risk to be protective of the vulnerable members of the community (e.g., children, the elderly, impoverished, those without health care).

Presentation Format

Individual-level results communication. We communicated the exposure measurement results and risk interpretation to the study participants during home visits to deliver the written reports and discussed the findings with each participant. The individual-level reports included seven types of information: a) actual personal exposure concentrations that we measured, b) exposure comparisons of individual results with results from other studies reported in the literature, c) risk-based interpretation based on the individual exposure results, d) general information on potential health effects of VOCs, e) general information on VOC sources, fly individual-level indoor:outdoor ratios, and g) local, state, and federal resources for understanding and reducing exposure and risk. Examples of some of the actual written materials that were distributed to the study participants are shown in Table 1 and Figures 1-3.

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Individual reports were prepared using a narrative, tables, and graphs. Exposure results were presented in concentration units (micrograms per cubic meter), as shown in Table 1. In presenting individual risk estimates, we explained in writing and orally the limitations of the exposure data and the risk estimates. The major uncertainties and underlying assumptions associated with estimating risk that we discussed with study participants included the following: