OEHHA Issues a Safe Use Determinant for Exposure to Crystalline Silica from the Use of Wood Filler Products

Posted on Behalf of  Melinda Donnell


On February 21, 2020, the California Office of Environmental Health Hazard Assessment (OEHHA) issued a Safe Use Determination (SUD) for exposures to crystalline silica in four Design Hardwood Products, Inc. (DHPI) WOODWISE® wood filler products that are designed for use on hardwood floors. Each product contains 0.2% respirable crystalline silica by weight, and either 0.6% or 2.0% total crystalline silica by weight. In 1988, OEHHA listed respirable crystalline silica on the Proposition 65 list as a chemical known to the state to cause cancer. However, OEHHA has not yet adopted a No Significant Risk Level (NSRL) for the chemical.

In their analysis, OEHHA identified professional hardwood flooring installers and refinishers as the user group with the highest exposure potential to respirable crystalline silica. DHPI provided OEHHA with a “worst-case” analysis of inhalation exposure to crystalline silica from the use of WOODWISE® wood filler products. This worst-case analysis used personal and area samples collected while professional flooring installers used the WOODWISE® product with the highest expected exposure potential (i.e., quantity used, tasks performed). While respirable crystalline silica was not quantified in any sample, OEHHA estimated a screening-level lifetime average exposure concentration by conservatively using the maximum measured respirable particle concentration and the product’s respirable crystalline silica content.

Because there is no NSRL for respirable crystalline silica, OEHHA compared the estimated lifetime exposure to concentrations based on cancer potency values. In prior SUDs, OEHHA estimated that the exposure concentrations associated with a lifetime cancer risk of 1 in 100,000 ranged from 0.54 to 15 µg/m3 crystalline silica. OEHHA’s screening-level estimate fell below the lower end of the air concentration range, and therefore, OEHHA determined that respirable crystalline silica exposures from using the four WOODWISE® wood filler products over a lifetime average fall below the level posing a significant cancer risk for professional hardwood flooring installers, “do-it-yourself” users of the products, and occupants of homes and other buildings in which these wood filler products have been used. As such, OEHHA does not require a Proposition 65 warning on these four products.

While the SUD is specific to only the products and exposure scenarios defined in the assessment, a similar risk comparison approach may be used when assessing carcinogens without established NSRLs. However, several considerations must be taken when using such an approach, including the anticipated pathway and route of exposure, as well as the quality of the cancer potency values. An alternative, yet more complex approach is deriving an NSRL based on the modeling specifications in Title 27, Article 7 (California Code of Regulations).

Cardno ChemRisk has assisted companies in understanding potential product exposures and risks. Our scientists have evaluated diverse scenarios for Proposition 65 compliance, ranging from a single product to entire product lines. For more information regarding Cardno ChemRisk’s Proposition 65 capabilities, please contact Ms. Jennifer Bare or Dr. Ania Urban.