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Air Toxicology and Epidemiology

Adoption of Chronic Reference Exposure Levels (RELs) for Airborne Toxicants, April 2000

In accordance to Health and Safety Code, Section 44300 et seq. (The Air Toxics Hot Spots Information and Assessment Act, AB 2588, Connelly as amended by SB 1731, Calderon), the Office of Environmental Health Hazard Assessment (OEHHA) hereby adopts Chronic Reference Exposure Levels (RELs) for 16 chemicals (attachment).

OEHHA is mandated to develop risk assessment guidelines to be used by state and local agencies in implementing the Air Toxics Hot Spots program. Development of these guidelines is proceeding in stages. There are four technical support documents, three of which have been adopted, and the fourth is currently being reviewed by the Scientific Review Panel (SRP) on Toxic Air Contaminants. These describe the scientific basis for (respectively) acute RELs, cancer potency factors, chronic RELs, and exposure assessments. The fifth document is a guidance manual based on the four technical support documents.

The third technical support document, Air Toxics Hot Spots Program Risk Assessment Guidelines. Part III. The Determination of Chronic Reference Exposure Levels for Airborne Toxicants, was adopted on February 23, 2000. A chronic REL is an airborne level that would pose no significant health risk to individuals indefinitely exposed to that level. RELs are based solely on health considerations, and are developed from the best available data in the scientific literature. This technical support document provided chronic RELs for 22 chemicals, with a summary for each describing its chemical and physical properties, its chronic health effects, and the data used to calculate the REL.

The SRP had initially reviewed a number of other proposed chronic RELs at previous meetings, beginning in September 1999. At its April 13, 2000 meeting, the SRP endorsed 16 additional RELs, bringing the total number of chemicals for which chronic RELs are provided to 38. The expanded list and supporting summaries will be available on our Web site. Additional RELs are currently undergoing review by the public and the SRP, and revision by OEHHA; these will be presented in due course.

Follow the link to download a PDF copy of this memorandum.

Follow the link to view the Chronic Reference Exposure Levels adopted in April 2000. You may also download individual chemical summaries from this table.

Follow the link to download a PDF copy of all Chronic Reference Exposure Levels adopted in April 2000.