EV-595 Fall 1997

Readings (old):


Calculated Risks
Chapter 2 - Exposures- All
Chapter 3 - Into the Body - pp. 25 to 31
Chapter 4 - Assessing Risks - All

Risk Assessment Guidance for Superfund
Chapter 1 - Introduction - All
Chapter 2 - Statutes, Regulations, Guidance and Studies Relevant to Human Health Evaluation - All
Chapter 6 - Exposure Assessment - All

Guidelines for Exposure Assessment (Supplemental Reading)
Federal Register; Vol. 57; No. 104; pp. 22888 - 22938 (May 29, 1992)

Readings (New):

Risk Assessment Guidance for Superfund: Volume I - Human Health Evaluation Manual
(Part B, Development of Preliminary Remediation Goals) - All

Exposure Assessment:

* Three step process - Interrelated

- Values selected for exposure parameters determines "type" of dose calculated.
- "Types" of dose:

- Reasonable Maximum Exposure (RME) - Highest exposure that is reasonably expected to occur.

- Maximum Exposure - Upper bound estimate of all possible exposures.

- Average Exposure - Estimate using average exposure parameters.

- Use RME (per EPA) because:

- Average dose calculations give values lower than those to which much of the population is exposed; maximum dose calculations give values higher than is plausible.

- Using consistent RME dose approach makes it easier to identify those variables that contribute the most to the uncertainty in the dose estimates.

- Can calculate own RME parameters following EPA rules:

CR All terms together should approximate the 95^th percentile of the joint distribution.

EFD All terms together should approximate the 95^th percentile of the joint distribution.

BW The average (median, mean) of body weight for the term of exposure

AT Toxicity parameter and end-point specific

- Sources of Exposure Parameters that can be used to replace EPA defaults:

- Survey information

- EPA documentation:

• - Exposure Factors Handbook. 1996. EPA/600/P-95/002B - New version in SAB draft
• - Exposure Factors Handbook. 1989. EPA/600/8-89/043 - Old, approved version

- About AT:

- Values used for AT determines the "type" of dose being calculated

• - For estimates of systemic toxicity always use ED × 365 days/year
  • - Results in average daily dose adjusted for body weight
• - For estimates of lifetime excess cancer risk always use 70 years × 365 days/year
  • - Results in average daily dose over lifetime adjusted for body weight

2) Have equations for:

- Residential scenario ^@

- Recreational scenario ^@

- Industrial scenario ^@

- Excavation scenario ^@

- Concentration in various foods - Use these only if don't have sampling results!

3) Have equations for chemical intake (or radionuclide intake) and for absorbed dose

- "intake" used for ingestion, consumption, and inhalation exposures = administered dose

- "absorbed dose" used for dermal contact or exposure to ionizing radiation

4) All equations for chemicals end up with dose in units of mg/(kg × day), but not appropriate to sum doses.

- Will eventually sum "risks" and "hazards" for decision-making though.