CIIT publishes formaldehyde cancer risk assessment

November 11, 1999

A team of scientists at CIIT, working under the latest draft guidelines for cancer risk assessment established by the U.S. Environmental Protection Agency, have published an up-to-date risk assessment for cancer from inhaled formaldehyde, which occurs in some residential and workplace environments. The comprehensive document integrates the latest mechanistic knowledge on the toxic effects of exposure to inhaled formaldehyde, including site-specific modeling of dose of formaldehyde delivered to the upper respiratory tracts of animals and humans.

An important feature of this assessment is the use of a two-stage clonal growth model of carcinogenesis that incorporates data on the rate of cell division and on the number of cells at risk in different regions of the respiratory tract of rats and humans. Risk predictions obtained with this model are more accurate that predictions obtained with earlier models that were based on much smaller data sets. The new, more accurate model predicts significantly lower risks for various environmental and workplace exposures compared with earlier models. The assessment concludes that the risk of tumors at low levels of exposure is far less because of the lack of regenerative cell proliferation that stimulates the mutation process that causes tumors. CIIT researchers used computational flow dynamics (CFD) algorithms with models of human and rat nasal airways in order to predict regional formaldehyde dose. These regional does predictions were in turn linked to subsequent efforts in nasal tissues. Carcinogenic risk was predicted throughout the respiratory tract of humans by combining CIIT's CFD model for human nasal airways and a typical path model for the lower respiratory tract developed by Dr. John Overton of the U.S. EPA.

The model was used to estimate cancer risk for exposure to varying levels of formaldehyde and for workplace and environmental exposure scenarios. Allowances for changes in breathing patterns related to levels of exertion were incorporated into these risk predictions. The model was also used to predict individually the probability of cancer for more than 2000 workers with occupational exposure to formaldehyde, taking their lifetime exposure history into account.

The updated risk assessment is important, not only because it incorporates and critically analyzes the significance of the latest science on inhaled formaldehyde, but also because the process has been scrutinized by an independent panel of international scientists convened under the auspices of Health Canada and the U. S. EPA. The new assessment is valuable to industry in improving safety for employees in the workplace and for government agencies that establish regulations specifying acceptable exposure limits.

The dosimetry methodologies developed by CIIT for examining formaldehyde can be used to assess the noncarcinogenic effects from exposure to other gases, such as chlorine, ozone, vinyl acetate, and acrylic acid vapors.

In addition to the CIIT team, contributors to the hazard assessment portion of the report include Susan Felter of TERA (Toxicological Excellence in Risk Assessment)(now with Proctor and Gamble), Dr. John Overton of the U.S. EPA, and Health Canada staff.

The Executive Summary of the Formaldehyde Risk Assessment is available on the CIIT web site, .
CIIT is a scientifically independent, not-for-profit research institute supported primarily by the chemical industry. Its peer-reviewed research is published in critical scientific journals.

CIIT - Chemical Industry Institute of Toxicology

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