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About the 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.

 

New Information A New Public Comment Period Has Begun for 2 DSDs!

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Hot Topic A New Public Comment Period Has Begun: WHITE PAPER – TCEQ Guidelines to Develop 24-Hour Inhalation Reference Values!

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Background

This document is an update of and replacement for the previous TCEQ Regulatory Guidance-442 (RG-442), Guidelines to Develop Effects Screening Levels, Reference Values, and Unit Risk 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),
        • chronic oral reference dose (RfD) and slope factor (SFo) values.

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 TCEQ Guidelines to Develop Toxicity Factors (hereafter referred to as Guidelines) has been finalized.

In June of 2001, the draft Guidelines underwent a letter peer review and public comment period which was organized by Toxicology Excellence for Risk Assessment (TERA)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 Guidelines incorporated comments from the Peer Review Report and the two rounds of public comments that increased its scientific and technical merit and clarity. The Texas Commission on Environmental Quality Responses to Peer Review ReportAdobe Acrobat PDF Document and the Texas Commission on Environmental Quality Responses to Public CommentsAdobe Acrobat PDF Document documents are available on the TCEQ Web page.

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