Draft Chronic Reference Exposure Levels for Silica (Crystalline, Respirable)

The Office of Environmental Health Hazard Assessment (OEHHA) has released a draft document, Chronic Toxicity Summary for Silica (Crystalline, Respirable) for use in implementing the Air Toxics Hot Spots Program (Health and Safety Code Section 44300 et seq.). OEHHA developed four Technical Support Documents (TSDs) and a Guidance Manual pursuant to Health and Safety Code Section 44360, which provided the scientific basis for values used in assessing risk from exposure to facility emissions. The TSD for the Determination of Chronic Reference Exposure Levels (Part III of the TSD series), which has already undergone public and peer review and been adopted by OEHHA, describes the methodology for risk assessment for materials having adverse health impacts following chronic exposures. The present document presents a toxicity summary and chronic REL for crystalline silica, particularly when this material is composed of particles of respirable size, as defined by the current NIOSH method. If approved by the Scientific Review Panel on Toxic Air Contaminants, and adopted by the Director of OEHHA, this document will form a further addendum to the Part III TSD.

An earlier draft of the Chronic Toxicity Summary for Silica became available for public review on the OEHHA Home Page at http://www.oehha.ca.gov on April 25, 2003. OEHHA received a number of comments on this document, which was amended in response. The modified Summary, the comments received and OEHHA's responses to them, were initially presented to the Scientific Review Panel at their meeting on May 19th, 2004.

A number of comments were made at that meeting by the Panel, in response to which OEHHA undertook additional investigations and has now prepared a second draft of the document and responses to public comments, which will be considered at the next Scientific Review Panel meeting scheduled for November 30th, 2004. The materials to be presented to the Panel are available as pdf files. Further information about dates, locations and agenda for meetings of the Scientific Review Panel can be obtained from the ARB web page at http://www.arb.ca.gov/srp/srp.htm.

Please direct any inquiries concerning technical matters, or availability of the Chronic Toxicity Summary for Silica (Crystalline, Respirable), to:

Dr. John Budroe
Chief, Air Toxicology and Risk Assessment Section
Air, Community, and Environmental Research Branch
Office of Environmental Health Hazard Assessment
1515 Clay Street, 16th Floor
Oakland, CA, 94612

E–mail: John.Budroe@oehha.ca.gov

Telephone: (510) 622-3145