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Air Toxicology and Epidemiology

Exposure Assessment and Stochastic Analysis Guidelines Public Workshop, Review and Comment Period - comment period closed
[12/31/96]

Dear Interested Party:

The Office of Environmental Health Hazard Assessment (OEHHA) is releasing for public review and comment the Technical Support Document for Exposure Assessment and Stochastic Analysis as part of the Air Toxics "Hot Spots" Program Risk Assessment Guidelines. In 1992, Senate Bill (SB) 1731 amended the Air Toxics "Hot Spots" Information and Assessment Act of 1987 (Assembly Bill 2588 as codified in Health and Safety Code Section 44300 et seq.) to require OEHHA to prepare risk assessment guidelines for facilities subject to the Act. SB 1731 also requires OEHHA to conduct public workshops and seek review and comment by the public, regulated community, and the Air Resources Board's Scientific Review Panel on Toxic Air Contaminants prior to formal adoption of the guidelines. OEHHA has a strong commitment to an open process in the development of risk assessment guidelines and is seeking your written comments on this document. Through scientific peer review and open public discussions of OEHHA's draft health assessments and risk assessment guidelines, we ensure that the most up-to-date and widely accepted science is incorporated into our workproducts.

Consistent with SB1731, OEHHA is developing risk assessment guidelines for use in the "Hot Spots" program. The guidelines will describe the preferred approaches for conducting risk assessments of facility emissions, including a "likelihood of risks" approach. The technical support document, Exposure Assessment and Stochastic Analysis, contains the data and methods used to characterize probability distributions for key exposure intake variates needed to conduct a "likelihood of risks" analysis. It also describes a tiered approach to risk assessment that allows facility operators to include supplemental site-specific information in the assessment of risks from their facilities. The tiered approach begins with point estimates of risk and progresses to the likelihood of risks approach, or stochastic analysis of risks. Once approved and adopted, the data and values proposed in this technical support document will be incorporated into the guidelines for conducting facility-specific risk assessments.

The technical support document will be available for public review by December 31, 1996. The publishing of this notice will commence a 60-day comment period ending March 10, 1997. Due to the size of the document and the cost of duplication and mailing, OEHHA will not be sending out a mass mailing of the document. Instead, the document will be posted on the Internet.

Public workshops to discuss the document will be held in February at the following locations:

Tuesday, February 4, 1997
Continental Plaza
601 North 7th Street
Sacramento, CA 94243-7320

Thursday, February 6, 1997
Air Resources Board Auditorium
9528 Telstar Ave
El Monte, CA 91731

While public comment is encouraged on the entire document, there are some general and technical issues on which we are specifically requesting comment. The general issues are:

1. the use of a tiered approach to risk assessment for the "Hot Spots" program (described in Chapter 1);

2. the consistency of this document with the recommendations found in "A Review of the California Environmental Protection Agency's Risk Assessment Practices, Policies, and Guidelines" a report of the Risk Assessment Advisory Committee, October, 1996 (available on OEHHA's home page);

3. the adoption of U.S. EPA's "central tendency" and "high-end" point estimates of exposure parameters for developing a range of risks to improve risk characterization in Tier 1 risk assessments;
   and

4. identification of any exposure or modeling issues for future analysis and evaluation, should resources become available.

We are also requesting comments specifically on several technical issues as follows:

1. how dominant pathways are determined in the exposure assessment (described in Chapter 1);

2. how to identify central tendency or average values for point estimates for certain exposure variates (e.g., soil ingestion rates for children and adults in Chapter 4 and exposure duration for the breastmilk pathway described in Chapter 5) ;

3. the overall impact on total risk of evaluating human exposures based on three "age" groups: infants (0 - 1 year), children (aged 1 to 6 years) and "adults" (greater than 7 years) as done by U.S. EPA as compared to using additional age groups such as adolescents (e.g., 7 to 18 years);

4. whether the weighting factor (w(t)) for genotoxins in the mother's milk pathway (see Chapter 5) is an exposure parameter which should be included in the exposure document or is an issue of chemical potency;

5. if a default value for the weighting factor (w(t)) for the potency of genotoxic carcinogens should be applied to early-in-life exposures when inadequate data exist to empirically determine a "true" value (see Chapter 5);

6. should the weighting factor (w(t)) be applied to the total dose of receptor- or carrier-mediated chemicals like "dioxins" and dioxin-like chemicals (PCBs) which may have only limited genotoxic (DNA-damaging) activity;

7. information useful to identify half lives (t1/2 ) for the various PAHs listed in Appendix G, or a range of half lives that might be relevant to humans;

8. information to evaluate the gastrointestinal relative absorption factor (GRAF) for chemicals assessed by the incidental soil ingestion pathway (described in Chapter 4);

9. information useful for evaluating exposure to metals through breastmilk;

10. information regarding dermal absorption of chemicals listed in Table E-2 for which values are not readily available;
    and

11. information useful for evaluating children's consumption rate of fisher-caught fish (e.g., recreationally caught sport fish).

We are most interested in your written comments and suggestions and you may address them directly to me. If you do not have access to the Internet and have questions regarding the availability of documents, or would like details of the upcoming workshops, or have specific technical questions, please contact Dr. Robert Blaisdell at (510) 540-3324.

Sincerely,

William A. Vance, Ph.D.
Acting Deputy Director for Scientific Affairs
Office of Environmental Health Hazard Assessment
P.O. Box 942732
Sacramento, CA 94234-7320

cc:

George V. Alexeeff, Ph.D., Chief
Air Toxicology and Epidemiology Section


Melanie Marty, Ph.D., Chief
Air Risk Assessment Unit


Robert Fletcher, Chief
Emissions Assessment Branch
Air Resources Board


Stew Wilson, Secretary
California Air Pollution control Officers Association

IMPORTANT NOTE: For more detailed information on the times and locations of the meetings regarding this document, please see the Notice To Interested Parties re: Air Toxics Hot Spots Program Risk Assessment Guidelines. Printed copies may be obtained for a fee from Copy World, 2154 University Ave., Berkeley, CA 94704 and can be reached at (510) 849-9701, fax (510) 849-9704.