Controlled Human Inhalation-Exposure Studies at EPA (2017) / Chapter Skim
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6 Characterizing Risks to Subjects in Controlled Human Inhalation Exposure Studies
6 Characterizing Risks to Subjects in Controlled Human Inhalation Exposure Studies
Pages 77-86
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From page 77... ...
and the health status or risk profile of the individual participants. In this chapter, the committee provides guidance on methods for characterizing risk levels associated with participation in CHIE studies.
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From page 78... ...
. FACTORS THAT MIGHT TRIGGER AN ADVERSE OUTCOME As indicated in Chapter 4, risks of adverse events temporally associated with a subject's participation in a CHIE study might be affected by one or more of the following: Air pollutant exposures occurring independently from the CHIE study, several days prior to or during the multiday experimental protocols; Intended pollutant exposures during the experiments; Preexisting medical conditions or sensitivities of subjects to the CHIE study pollutant(s)
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From page 79... ...
As CHIE studies typically impart a very small increase in the cumulative exposure to ambient air pollution over an individual's lifetime, there is no credible evidence to suggest that chronic effects be considered among the reasonably foreseeable risks of those studies. However, because of associations between long-term exposure to air pollution and chronic effects, concerns have been expressed about whether CHIE study exposures pose an elevated risk of cancer and other chronic diseases (for example, see EPA, 2014a)
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From page 80... ...
Also, if a particular exposure regimen has been used numerous times in previous CHIE studies, without the occurrence of adverse effects, the accrued experience from those studies could be useful in developing a reasonable exposure comparator. We provide examples of comparative scenarios for exposure to diesel exhaust and PM2.5.
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From page 81... ...
Using the same terminating procedure as in KINGCON when the exposure concentration exceeded 600 µg/m3, actual achieved concentrations were as high as 470 µg/m3. Thus, the highest possible 2-hour exposure concentrations of PM2.5 in the OMEGACON and KINGCON CHIE studies were exceeded numerous times recently in Beijing.
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From page 82... ...
TABLE 6-1 Largest Concentrations in 1-Hour PM2.5 samples in 2014 and 2015 in EPA Air Data with Corresponding 2- and 4-Hour Average Concentrations 82 State County Year Day Hour of Day Sample Value (µg/m3) 2-Hour Average (µg/m3)
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From page 83... ...
) , as will be done in this study." "Previous controlled human exposure studies have utilized NO2 concentrations equal to or higher (up to 2000 ppb)
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From page 84... ...
Even if validated, a given cumulative exposure spread out over 24 hours might not involve the same risk as the same cumulative exposure occurring over only 2 hours. WOODSIE compared the planned exposure concentration of 500 μg/m3 wood smoke PM to a number of exposure situations, including forest firefighters, people who use biomass fuels for cooking, people indoors in houses heated by wood burning, and people out of doors in cities where wood is used for heating.
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From page 85... ...
RECOMMENDATIONS The committee recommends that risk-characterization objectives be addressed by using an ESC approach in which the risk associated with a CHIE study exposure is likely to be lower than the risk to the comparative population. To illustrate that the risk associated with the participation in a CHIE study is likely lower that the risk to the comparative population, the comparative scenario involves a documented ambient exposure concentration that is higher than the exposure concentration in the CHIE study and an exposure duration in the comparative scenario that is at least as long as the experimental exposure duration.
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From page 86... ...
Such considerations in comparing study subjects with specific populations and experimental exposures with ambient pollutant concentrations also would be required in attempting to develop quantitative risk estimates. Alternatively, if a particular exposure regimen has been used numerous times in previous CHIE studies, without the occurrence of adverse effects, the accrued experience from those studies could be useful in developing a reasonable exposure comparator.
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