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Exposure Assessment

Exposure Parameters

The Supplemental Guidance states:  When developing quantitative estimates of cancer risk, EPA recommends integration of age-specific values for both exposure and toxicity/potency where such data are available and appropriate.

To assist with the computation of age-specific values in exposure estimates, exposure parameters from current US EPA guidance (including EPA's Exposure Factors Handbook, Child-Specific Exposure Factors Handbook, Age-Grouping Guidance) were compiled.  These values can be downloaded from the following links:

The original references for the exposure parameters in the above files can be accessed through links on the Resources section of the Handbook.

Note:  In applying the Supplemental Guidance to risk assessments, risk assessors should decide the age-specific exposure assessment that makes the most sense for their site.

Age Bins

The Supplemental Guidance further indicates that any grouping of ages in the exposure assessment will need to be integrated with the default Age-Dependent Adjustment Factor (ADAF) age groupings (if applicable) to derive age group-specific risk estimates.

For example, under current Superfund guidance, exposure factors for humans are divided into two age intervals:

Child = age 1 - 6
Adult = age 7 - 30

Thus, exposure to a chemical or compound to which the default ADAFs are applied may be estimated by dividing the exposure into four intervals:

Age
(years)
Exposure
Factors
Exposure
Duration
(years)
ADAF
(unitless)
0 - <2 Child 2 10
2 - <6 Child 4 3
6 - <16 Adult 10 3
16 - <30 Adult 14 1
Note:  Alternate age bins may be considered to address site-specific scenarios.

Sensitivity Analysis of Exposure Parameters and Age Bins

A sensitivity analysis was conducted to evaluate the effect of various age-specific exposure parameters and age bins on cancer risk estimates and Preliminary Remediation Goals (PRGs) for a 30-year resident using the new Supplemental Guidance (e.g., applying ADAF potency adjustments).  This analysis can be viewed in the following file:

As seen, the effect of applying age-specific exposure parameters and refined (smaller) exposure age bins results in cancer risks calculated using the new Supplemental Guidance that are less than 2-fold higher than cancer risks calculated using the exposure parameters and age bins for a resident under current Superfund Guidance.  PRGs are less than 2-fold lower.

Waste and Cleanup Risk Assessment | Superfund Risk Assessment | Superfund Human Health: Toxicity | Risk Assessment Topics


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