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About the 2015 TCEQ Guidelines to Develop Toxicity Factors

A technical guide written and used by the TCEQ's Toxicology Division (TD) to develop health- and welfare-based inhalation toxicity values, and health-based oral toxicity values.
Background

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)
Intended Use

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

ESLs 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)Exit the TCEQ Exit the TCEQ . 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 Adobe Acrobat PDF Document [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.

Responses to Public Comments Adobe Acrobat PDF Document

POSITION PAPER:

This position paperAdobe Acrobat PDF Document was included as Section 2.2 of the 2015 updated RG-442Adobe Acrobat PDF Document .

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 commentsAdobe Acrobat PDF Document addresses comments received on both of these documents. The list of odor valuesMicrosoft Excel Document 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 paper.

Please query the Toxicity Factor Database to search for toxicity factors (including AMCVs and ESLs) to see which value is to be used for permitting purposes (i.e., odor or short-term health).

WHITE PAPERS:
This WhitepaperAdobe Acrobat PDF Document supplements the 2015 Texas Commission on Environmental Quality (TCEQ) Guidelines to Develop Toxicity Factors [hereafter referred to as the 2015 updated RG-442]Adobe Acrobat PDF Document.

The TCEQ proposed these guidelines for public comment in April 2017 and posted the final white paper along with the response to public comments in December 2017.This document is not intended to be an explicit instruction manual, but rather a guide to use for any chemical evaluation.

Response to Public CommentsAdobe Acrobat PDF Document
This WhitepaperAdobe Acrobat PDF Document was included as section 4.6 in the 2015 updated RG-442]Adobe Acrobat PDF Document.

The TCEQ sought public comments on a white paper about its guidelines for developing chemical-specific 24-hour inhalation reference values—a supplement to the 2012 version of publication RG-442. Reference values are used in air monitoring as comparison values. The 24-hour guidelines went through an external peer review, as discussed in the document description and intended use. The TCEQ posted these guidelines for a second public comment period; the document was finalized in June 2014. Please refer to the White Paper to review the final draft.

Response to Public CommentsAdobe Acrobat PDF Document
This WhitepaperAdobe Acrobat PDF Document was updated in section 3.9.1 in the 2015 updated RG-442]Adobe Acrobat PDF Document.

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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