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

6) All residential and recreational tables (1-14 & 15-25) have parameters for multiple cohorts.

Multiple cohorts considered in exposure equations because of importance of relationship between intake rate and body size. Ratio of child intake rate to child body size is greater than that of adults for some routes.

- Routes where important are incidental ingestion of soil (or sediment) and consumption of milk. For dose used to estimate cancer risk (ELCR) for these routes, calculate dose for child (ED = 6 years) and adult (ED = 34 or 24 years) and sum for lifetime dose.

- For dose used to estimate hazard for these routes, calculate dose for child (ED = 6 years) and adult (ED = 34 or 24 years) separately. Cannot sum child and adult dose for these.

- For all other routes, can simply calculate using adult exposure parameters (ED = 40 or 30 years).

7) Do not have exposure equations that allow for calculation of inhalation dose from air concentration.

To use air concentration, need to modify equation by deleting those terms that estimate emissions from soil (sediment) or water.

- Terms used in inhalation dose from soil equation are:

• PEF - Particulate Emission Factor - enables estimation of mass of particulates < 10 microns in diameter emitted from soil. Site-specific parameter.

• VF - Soil to Air Volatilization Factor - enables estimation of mass of vapors emitted from soil. Site- and chemical-specific parameters.

- Term used in radiation inhalation dose from water equation is:

• IEF - Inhalation Exposure Factor - non-zero values for tritium and radon, only.

8) For all dermal absorption dose equations, have chemical-specific values that allow estimation of chemical's ability to cross skin and enter into tissues.

- For soil and sediment have ABS - Absorption Factor - estimates fraction of chemical in soil that partitions to skin and is taken into tissues. Have defaults for most chemicals. Some chemical-specific values.

- For water have P_c and K_p - Permeability Constant - estimates equilibrium partitioning between water and skin. Have chemical-specific values.

- Additional information about estimation of dose from dermal absorption can be found in:

Dermal Exposure Assessment Principals and Applications, EPA/600/8-91/011B, January 1991.

* Human Health Risk-Based Concentrations - Using exposure equations to calculate "acceptable chemical concentrations."

- Defined as values calculated by rearranging the exposure and risk equations so that a concentration in a medium that yields a "target" risk is calculated.

- Various names but really all the same:

• PRG - Preliminary Remediation Goal
• RBC - Risk-Based Concentrations
• RGO - Remedial Goal Option
• SSL - Soil Screening Level
• MCL - Maximum Contaminant Limit (Risk portion only. There is a technology component to these as well.

- All risk-based concentrations are:

• Medium-specific
• Chemical-specific
• Scenario-specific

Normally, all are calculated using de minimis risk as target. These targets are:

• 1 × 10^-6 for excess lifetime cancer risk (ELCR)
• 0.1 for systemic toxicity hazard

- When calculating these, can combine multiple-cohorts (and multiple-routes) to develop a single target for a medium.