The assumption of a threshold is false in risk assessments for endocrine disrupting chemicals (EDCs) when endogenous hormones being disrupted are already above any possible threshold: a policy failure by the US FDA.

The US FDA continues to assure the public that if they are exposed to an endocrine disrupting chemical (EDC), there is a threshold daily exposure level below which everyone is safe throughout the lifespan (the Acceptable or Tolerable Daily Dose). This assurance is false when the endogenous hormone systems being disrupted by EDCs are already above a threshold for producing adverse effects or there are cumulative effects of mixtures of similar chemicals. Decades of published experimental research, and multiple mathematical analyses, demonstrate the absence of a threshold (safe) dose for hormones, hormonal drugs or EDCs. However, this entire literature has been rejected in decision making by the US FDA food safety division. We review experiments directly falsifying the threshold hypothesis for hormones, drugs and EDCs. Our analysis includes application to hormone and EDC experimental data sets of the Michaelis–Menten (MM) equation, which explains mathematically hormone (or EDC)-receptor binding that mediates normal as well as adverse effects at extremely low exposures. The MM equation regresses to zero at zero hormone or EDC dose, i.e., there is no threshold dose. We derive the MM equation in Supplemental Materials for those interested in the math. We also identify that hormone and EDC potency is the consequence of a number of cell-specific mechanisms not included in the MM equation. We begin by reviewing the history of the now falsified assumption that a threshold exists for EDCs that are generally classified as systemic toxicants. In particular, the threshold hypothesis is problematic during fetus/infant/child development during which homeostatic defense systems have not yet fully developed, rendering them largely defenseless against the disruptive effects of EDCs. Published findings implicate EDC exposures at very low environmentally relevant doses with every non-communicable disease, which are all increasing in incidence on a global scale. We identify here the empirical and endocrinological evidence falsifying the determination by chemical regulatory agencies that there are safe daily exposure levels for EDCs below an estimated threshold that is not actually experimentally examined. These findings indicate that current human exposures to EDCs are harming the general population as well as causing widespread environmental harm.