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Updated: Aug 9, 2026

Screening for Endocrine Activity in Water Using Commercially-available In Vitro Transactivation Bioassays
Published on: December 4, 2016
Threshold analysis of selected dose-response data for endocrine active chemicals
1Division of Genetic and Reproductive Toxicology, National Center for Toxicological Research, U.S. Food and Drug Administration, Jefferson, AR 72079, USA.
This study used the Michaelis-Menten equation to analyze endocrine-disrupting chemical data, finding that biological responses often lack a threshold dose. The modified model effectively describes dose-response curves for these chemicals.
Area of Science:
- Pharmacology and Toxicology
- Mathematical Biology
- Endocrinology
Background:
- Endocrine-active chemicals can disrupt normal hormonal functions.
- Determining safe exposure levels requires understanding dose-response relationships, particularly the existence of thresholds.
Purpose of the Study:
- To investigate whether dose-response curves for endocrine-active chemicals exhibit a no-threshold phenomenon.
- To assess the applicability of a modified Michaelis-Menten equation to analyze such data.
Main Methods:
- Utilized published data from studies on endocrine-active chemicals.
- Applied a modified Michaelis-Menten equation incorporating background response and estimated key parameters (Bnh, Rmax, D0, ED50) via non-linear regression.
- Normalized response and dose data and combined them into a composite dataset for analysis.
Main Results:
- Analyzed 31 datasets (24 endpoints) across 9 chemical/hormone treatments.
- Twenty-six datasets showed a strong fit (r>0.90) to the modified Michaelis-Menten equation.
- The normalized composite data also demonstrated a good fit, supporting the no-threshold model.
Conclusions:
- The modified Michaelis-Menten equation effectively models dose-response relationships for various biological responses to endocrine-active chemicals.
- Findings suggest that for many endocrine-active chemicals, there may be no safe threshold dose, implying potential risks even at low exposure levels.
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