About the 2015 TCEQ Guidelines to Develop Toxicity Factors
- Intended Use
- ESLs and AMCVs
- TCEQ Guidelines to Develop Toxicity Factors
- Toxicology Position Paper and White Papers
- Sign Up to Receive ESL List, AMCV List, and Other Toxicology Announcements
This document is an update of and replacement for the previous 2012 TCEQ Regulatory Guidance-442 (RG-442), TCEQ Guidelines to Develop Toxicity Factors. It is a technical guide written and used by the TCEQ to develop the following health- and welfare-based inhalation toxicity values, and health-based oral toxicity values:
- acute and chronic inhalation Reference Values (ReVs),
- chronic inhalation Unit Risk Factor (URF) values,
- acute and chronic inhalation Effects Screening Levels (ESLs),
- acute and chronic inhalation Air Monitoring Comparison Values (AMCVs),
- health-based chronic oral reference doses (RfDs)
Although this document is primarily written as guidance for the TCEQ staff, it also documents (largely by reference) the processes used to develop different toxicity values for any interested person with training in inhalation and oral toxicology and risk assessment.
ESLs and AMCVs
are chemical-specific air concentrations set to protect human health and welfare. ESLs are used in the air permitting program. Short-term ESLs are based on data concerning acute health effects, the potential for odors to be a nuisance, and effects on vegetation, while long-term ESLs are based on data concerning chronic health and vegetation effects. Welfare-based ESLs (odor and vegetation) are set based on effect threshold concentrations.
Health-based ESLs, however, are calculated from ReV and URF toxicity factors. ReVs and URFs are based on the most sensitive adverse health effect relevant to humans. Derivation of a ReV or URF begins with a toxicity assessment involving hazard identification and dose-response assessment based on the chemical’s mode of action. The resulting ReV and URF values are then used to calculate ESLs that correspond to no significant risk levels.
AMCV is a collective term used to describe chemical-specific air concentrations used to evaluate air monitoring data that are set to protect human health and welfare. Short-term AMCVs are based on data concerning acute health effects, odor potential, and acute vegetation effects, while long-term AMCVs are based on data concerning chronic health or vegetation effects. AMCVs may contain health-based ReVs and health- and welfare-based ESL values.
TCEQ Guidelines to Develop Toxicity Factors
The 2012 TCEQ Guidelines to Develop Toxicity Factors [hereafter referred to as the 2012 Guidelines (RG-442)] underwent a letter peer review and public comment period in June of 2011 which was organized by Toxicology Excellence for Risk Assessment (TERA). In April of 2012, the revised draft Guidelines underwent a second public comment period lasting 60 days. The final version of the 2012 Guidelines (RG-442) incorporated comments from the Peer Review Report and the two rounds of public comments that increased its scientific and technical merit and clarity.
The 2015 TCEQ Guidelines to Develop Toxicity Factors [hereafter referred to as the 2015 updated RG-442] incorporated minor updates to the 2012 Guidelines. The 2015 Guidelines was posted for a 90-day public comment period. The final version of the 2015 Guidelines (RG-442) incorporated public comments.
Approaches to Derive Odor-Based Values
The Texas Commission on Environmental Quality revised Section 2.2, Odor-Based ESLs, of Guidelines to Develop Toxicity Factors (publication RG-442) (TCEQ 2012). This position paper was developed to describe how TCEQ toxicologists (1) evaluate available chemical-specific data for chemicals proposed for derivation, and (2) conduct analysis to determine whether development of an odor-based value is needed to prevent odor nuisance conditions. The TCEQ sought public comments on this position paper and a proposed odor ESL list and received several comments. The response to public comments addresses comments received on both of these documents. The list represents the substances that the TCEQ has determined have a need for an odor value (i.e., these substances are a product of following the position pape.
Please refer to the Published ESL List to see which value is to be used for permitting purposes (i.e., odor or short-term health).
TCEQ Guidelines to Develop 24-Hour Inhalation Reference Values
Updated Recommendations for Animal-to-Human Inhalation Dosimetry
The Toxicology Division amended Section 3.9.1, “Default Dosimetry Adjustments for Gases,” in the October 2012 version of RG-442 to include information on animal-to-human inhalation gas-dosimetric adjustments based on recommendations in Advances in Inhalation Gas Dosimetry for Derivation of a Reference Concentration (RfC) and Use in Risk Assessment (U.S. EPA 2012, EPA/600/R-12/044). Please refer to the white paper for a discussion of the changes.
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