Evaluation of the Interaction-Based Hazard Index Formula Using Data on Four Trihalomethanes from U.S. EPA's...

Area of Science:

• Environmental Toxicology
• Risk Assessment
• Chemical Mixtures

Background:

• Characterizing toxicologic interactions in chemical mixtures is complex.
• The interaction-based hazard index (HI_INT) is a novel approach for mixtures assessment.
• Trihalomethanes (THMs) are regulated contaminants often found in mixtures.

Purpose of the Study:

• To demonstrate and statistically evaluate the interaction-based hazard index (HI_INT).
• To assess HI_INT performance using single, binary, and quaternary THM mixture data.
• To identify potential improvements for the HI_INT method.

Main Methods:

• Statistical analysis of toxicologic data from a multipurpose study on four THMs.
• Application of the HI_INT formula to relative liver weight and alanine aminotransferase endpoints.
• Evaluation of HI_INT's ability to adjust the additive hazard index (HI).

Main Results:

• HI_INT generally adjusted the HI in the correct direction for relative liver weight, predicting greater than dose-additivity.
• Results for alanine aminotransferase were mixed, with HI_INT generally predicting less than dose-additivity.
• A methodological improvement was made in calculating maximum interaction magnitude.

Conclusions:

• The HI_INT provides valuable insights into toxicologic interactions when mixture data are available.
• Refinements, including mixture-specific parameters and quantitative uncertainty descriptions, are suggested for HI_INT.
• Further research is needed to fully validate and optimize the HI_INT for regulatory applications.