The U.S. Environmental Protection Agency (EPA) has recently issued a new draft Technical Support Document (TSD) aimed at enhancing the risk assessment of six phthalates under the Toxic Substances Control Act (TSCA).
The six phthalates under review, including Di(2-ethylhexyl) phthalate (DEHP), Benzyl butyl phthalate (BBP), Dibutyl phthalate (DBP), Dicyclohexyl phthalate (DCHP), Diisobutyl phthalate (DIBP), and Diisononyl phthalate (DINP), are of concern due to their similar toxicological properties and potential health risks. These compounds have been identified as endocrine disruptors, particularly affecting testosterone levels in fetal testes.
The main contents of the TSD include:
- Joint hazard assessment: By calculating Relative Potency Factors (RPFs) based on shared endpoints and datasets, this evaluates health endpoints related to fetal testis testosterone, using DBP as the index chemical, providing a solid foundation for dose-response assessment.
- Scenario-based phthalate exposure: Describes the relevant frequency and duration of exposure, and provides a qualitative analysis of co-exposure. Additionally, it offers a quantitative analysis of cumulative risk under specific use conditions for workers and consumers.
- National cumulative exposure and risk: Utilizes reverse dosimetry from urinary biomonitoring data from the National Health and Nutrition Examination Survey (NHANES) to show the average overall exposure of the U.S. population to the assessed phthalates. These data, combined with RPFs, provide a common understanding of nonspecific exposure and risk for susceptible populations in the U.S., including women of reproductive age and male children.
- Example of calculating cumulative risk: Details how exposure data from individual chemical risk assessments are combined to calculate cumulative risk, with a particular emphasis on considering cumulative occupational exposure values (OEV).
The document summarizes how RPFs can be used to supplement the hazard assessment of various phthalates and integrates them with NHANES data for risk characterization in individual risk assessments. This document will play a key role in guiding the risk assessment process for various phthalates and provide crucial support and basis for risk management strategies under the TSCA framework.
