EV-595 Fall 1997

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

- General Equation for Cancer Risk - One Pathway

• Remember to include any additional chemical-specific parameters found in footnotes to Human Intake Factor tables .

- General Equation for Systemic Toxicity Hazard - One Pathway

• Remember to include any additional chemical-specific parameters found in footnotes to Human Intake Factor tables.

- Can combine cohort "risks" and rearrange equation to get risk-based concentration for multiple cohorts by remembering:

For excess lifetime cancer risk:

and:

and rearranging to solve for a concentration.

- Can combine route "risks" from multiple routes and rearrange equation to get risk-based concentration for multiple routes by remembering:

For excess lifetime cancer risk:

and:

For systemic hazard:

and:

- For excess cancer risk can also combine over multiple cohorts and multiple routes, but rearranging equation to solve for risk-based concentration becomes very complex.

- Easier to use linear nature of equations and unit risk approach.

Under unit risk approach, simply solve for the risk or hazard posed through exposure via each route to each cohort by a unit concentration (e.g., 1 mg/kg, 1 mg/l, etc.) and use ratios to solve for risk based concentration.

- To solve for risk-based concentration over cohorts and routes (can do this for excess lifetime cancer risk only!):

(See table for source of values.)

- Best if use table in form of following when organizing this:

- To solve for risk-based concentration for route over cohorts (can do this for excess lifetime cancer risk only!):

- To solve for risk-based concentration for cohort over routes (can do this for both hazard and excess lifetime cancer risk):

==> THIS WORKS AS LONG AS THE EXPOSURE EQUATION USED TO CALCULATE DOSE IS LINEARLY RELATED TO REPRESENTATIVE CONCENTRATION IN MEDIUM.

* Presentation of the Exposure Assessment

- Remember goal is to:

1. provide the dose estimates for the important routes of exposure calculated during the exposure assessment.
2. explain the rationale used to complete the exposure assessment.
   ** IT IS UP TO THE RISK ASSESSOR TO JUSTIFY THE SELECTION OF PATHWAYS QUANTIFIED AND THE EXPOSURE PARAMETERS SELECTED.

- See RAGS, Part A; Chapter 9 for outline and reviewer's check list.

- In the presentation, tables (e.g., Handout #15), figures (e.g., conceptual site model), and text are used.

- Sections of Exposure Assessment are:

1. Characterization of Exposure Setting (May be done by reference if risk assessment is chapter of larger report.)
2. Identification of Exposure Pathways
3. Quantitation of Exposure
4. Identification of Uncertainties (May be moved to larger uncertainty discussion at end of risk assessment.)
5. Summary of Exposure Assessment

* Uncertainties in Exposure Assessment

- Three primary sources.

1. Fate and Transport Modeling
2. Use of RME Dose
3. Development of Conceptual Site Model

* Presentation in Introduction of Risk Assessment

- Need to present:

1. Objectives of Risk Assessment
2. Scope of Risk Assessment
3. Description of Site History (including results of previous risk assessments.
4. Overview of Contamination