Thresholds of Toxicological Concern - Setting a threshold for testing below which there is little concern

Area of Science:

• Toxicology
• Risk Assessment
• Chemical Safety

Background:

• The concept of Thresholds of Toxicological Concern (TTC) addresses chemical safety by defining exposure levels below which risks are considered negligible.
• Traditional risk assessment requires substance-specific data, which can be resource-intensive.

Purpose of the Study:

• To review the history, development, and application of the TTC concept in chemical risk assessment.
• To discuss the utility of TTC as a pragmatic tool for prioritizing chemical testing and managing regulatory concerns.

Main Methods:

• Analysis of chemical distribution of lowest or no-effect doses to define TTC values, often using the 5th percentile with an uncertainty factor.
• Review of historical developments and current applications of TTC across various regulatory frameworks.

Main Results:

• TTC allows for the establishment of a pragmatic threshold below which chemical hazards are unlikely to manifest.
• The concept is actively applied in sectors like food and pharmaceuticals, and shows potential for broader regulatory integration (e.g., REACH).

Conclusions:

• TTC serves as a valuable screening tool to deprioritize testing for chemicals with negligible exposure levels.
• Leveraging large toxicological databases enables the definition of TTC for diverse hazards, supporting a precautionary, tiered approach to risk assessment.