Weight of Evidence Approach for Chemicals with Limited Toxicity Data (silanes and siloxanes)

Last Updated: 1 month ago Bredfeldt, Grant, Jones, Lee
Bredfeldt, T.G., Lee, J.S., Jones, R., Grant, R.L., Toxicology Division, Texas Commission on Environmental Quality, Austin, TX

During the air permit review process, the Toxicology Division (TD) from the Texas Commission of Environmental Quality (TCEQ) frequently evaluates chemicals with limited toxicity data (LTD chemicals) in order to generate an effects screening value (ESL) upon which to regulate those chemicals (see text in question 2 below for a description of ESLs). In this case study, we review the procedures used to set health-protective concentrations for LTD chemicals based on approaches discussed in our guidance for derivation of toxicity factor document (TCEQ, 2012), using silanes as example chemicals.
In simple terms, the approach used for ESL derivation for LTD chemicals is driven by available data, as well as time and resource constraints. Possible approaches include the following:
· Surrogate
· Category (i.e., Threshold of Concern (TOC))
· N-to-L (NOAEL-to-LC50) ratio
· Route-to-route extrapolation
· Relative Toxicity/Potency
· POD/UF (acute or chronic)
· BMD/UF (acute or chronic)

Downloads

• Case Study
• Excerpts from the TCEQ Guidelines that describe LTD (low toxicity data) Chemical
• Presentation