TCEQ Air Target Risk Level Policy
Sunset Advisory Commission’s Management Recommendation 1.2: Commission Vote on Acceptable Level of Health-Based Risk
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About The TCEQ Target Risk Level Policy
On September 25, 2024, the Texas Commission on Environmental Quality (TCEQ or commission) adopted the executive director’s Air Target Risk Level Policy, which sets a target cancer risk level of 1 in 100,000 (1 x 10-5) for developing screening levels that are used in TCEQ’s air permitting program and that are compared to ambient air monitoring data. The proposal for the policy was initially published for public comments in the September 1, 2023, issue of the Texas Register (48 TexReg 4882). The final Air Target Risk Level Policy describes the basis for the TCEQ Toxicology, Risk Assessment, and Research Division’s use of 1 in 100,000, or 1 x 10-5, as a target cancer risk level in setting screening levels for use in TCEQ’s air permitting program and for comparison to ambient air monitoring data. The Air Target Risk Level Policy will be used in conjunction with the TCEQ Guidelines for Developing Toxicity Factors (RG-442).
The TCEQ Executive Director proposed that the Commission of the TCEQ set a target cancer risk level of 1 in 100,000. The Commission approved the request to post the proposal for 30 days of public comment. The public comment period began on September 1, 2023, and ended on October 3, 2023. Public comments that were received can be found here.
Background
The Sunset Advisory Commission Staff Report with Commission Decisions on the Texas Commission on Environmental Quality (TCEQ) (2022-23, 88th Legislature) contains the Sunset Advisory Commission’s statutory recommendations to the Legislature and management recommendations for TCEQ to implement. Management Recommendation 1.2 from the report states “[d]irect TCEQ’s commission to vote in a public meeting on the acceptable level of health-based risk used in the development of toxicity factors for permitting and other regulatory actions.” The referenced “acceptable level of health-based risk” is interpreted to mean the acceptable individual-chemical excess cancer risk, or target risk level, used in permitting and other regulatory actions.
This policy specifically addresses the acceptable target cancer risk level used to develop toxicity factors that are used in the TCEQ air permitting program, and for comparison to air monitoring data. Although the Sunset Management Recommendation 1.2 could be read to more broadly apply to any toxicity factor used for permitting and other regulatory actions, all non-air-related toxicity factors have a target risk level specified in a TCEQ rule (30 TAC Chapters 307, 334, 335, and 350) that has already been approved by the Commission in a public meeting.
Target Risk Levels and The Development of Toxicity Factors
A target cancer risk level is the amount of cancer risk from a lifetime exposure to a chemical that can cause cancer (called a carcinogen). This is a theoretical risk, and it is in addition to the actual average lifetime cancer risk in the United States of about 1 in 3.
Many factors influence whether a person exposed to a carcinogen will develop cancer. These factors include how much of the chemical a person is exposed to and for how long, as well as other risk factors such as lifestyle choices (e.g., smoking), family history of cancer, etc.
Target risk levels describe cancer risk as a chance or probability, like 1 in 10,000 or 1 in 100,000. This is the same way that the odds of other events are described, like the chances of being struck by lightning (about 1 in 15,000). In the case of a target cancer risk level of 1 in 100,000, this means that for every 100,000 people exposed to a certain amount of chemical over their lifetime, 1 person may get cancer from that chemical exposure. This is written in different ways, such as 1 in 100,000, one in one hundred thousand, or 1×10-5. The United States Environmental Protection Agency (EPA) accepts a range of these cancer risk levels between 1 in 10,000 and 1 in 1,000,000. Figure 1 provides a simple comparison of what is meant by various risk levels.
Figure 1. Diagram showing the chances of different events occurring over a person’s lifetime, together with the range of cancer risks that the United States Environmental Protection Agency (EPA) considers acceptable and the TCEQ’s target cancer risk level of 1 in 100,000.
Relevant Considerations for Setting a Target Risk Level
The concept of acceptable target risk levels has been used in regulatory decision-making by various federal and state agencies for decades. The commonly used acceptable risk range of 1 in 1,000,000 to 1 in 10,000 (1×10-6 to 1×10-4) has been applied to multiple types of environmental exposure, such as to soil and water via the EPA the National Contingency Plan (NCP; 40 CFR Section 300.430), as well as to air, via the EPA National Emissions Standards for Hazardous Air Pollutants (NESHAPs) rules (at least as far back as the Benzene NESHAP, 54 FR at 38044–38045, September 14, 1989).
In addition, Texas has consistently set a target risk level of 1 x 10-5, using it for the Texas Risk Reduction Program (TRRP) rule for site remediation, and for the Texas Surface Water Quality Standards (30 TAC Chapter 307). Consistency within and across agency programs and/or rules helps provide clarity and stability regarding the level of excess risk considered to be acceptable (e.g., for each chemical in each environmental medium).
Used in conjunction with a chemical’s toxicity factor (e.g., inhalation unit risk factor) to calculate a health-protective media concentration (e.g., in ambient air), the target risk level of 1 in 100,000 (1 x 10-5):
- Represents the logarithmic center of EPA’s acceptable excess risk range of 1 in 10,000 to 1 in 1,000,000.
- Accounts for potential exposure to multiple carcinogens while remaining below the upper end of EPA’s acceptable risk range (1 in 10,000 or 1 x 10-4). TCEQ looked at the theoretical cancer risks from chemicals measured by TCEQ’s air monitors and found that total cancer risk from multiple chemicals together (cumulative risk) is less than 1 in 10,000.
- Allows for prompt response to pollutants monitored by the TCEQ that exceed the concentration and duration associated with the target risk level, (e.g., under the Air Pollutant Watch List program to reduce emissions in an area) well before reaching the upper end of EPA’s acceptable risk range.
- Insignificantly contributes to an individual’s lifetime cancer risk. For example, a 1 in 100,000 excess cancer risk, when added to the background lifetime cancer risk of approximately 1 in 3 (or 33,000 in 100,000), generates a theoretical total cancer risk of 33,001 in 100,000, a de minimis increase of 0.001% (one one-thousandth of a percent).
These considerations, evaluated when first drafting the TCEQ’s Guidelines to Develop Toxicity Factors (RG-442) and re-evaluated now, support the conclusion that a target risk level of 1 in 100,000 (1×10-5) is protective of human health and is reasonable to use in agency programs, rules, and guidance.