Defining a Defensible NOAEL from the CLARITY-BPA Core Study

Bisphenol A (BPA), used in certain plastics and resins and still present in some consumer and industrial products, remains one of the most extensively studied chemicals in toxicology. However, scientists still debate how to interpret findings from large, complex studies. The Consortium Linking Academic and Regulatory Insights on BPA Toxicity (CLARITY-BPA) Core Study is one of the most comprehensive evaluations of the chemical ever conducted in rodents, yet the study authors did not clearly identify a no-observed-adverse-effect level (NOAEL).

In their article "Determining a NOAEL for the Consortium Linking Academic and Regulatory Insights on BPA Toxicity (CLARITY-BPA) Core Study," Exponent's Noor Aly, Ph.D., and co-authors evaluate the BPA exposure findings reported in the Core Study to assess whether they support a NOAEL determination. The identification of NOAELs is important for assessing potential human health risks from real-world exposures, such as potentially from consumer products. Their analysis focuses on effects in the female reproductive system and male pituitary gland observed only at the highest dose in the Core Study rats, using a structured approach to assess relevance to human health.

The authors examine statistically significant findings reported at the highest administered dose in rats, assessing the consistency of findings across treatment groups and timepoints, persistence, and potential to indicate adverse outcomes in humans, including ovarian weight changes and follicular cysts, uterine epithelial apoptosis, vaginal epithelial hyperplasia, and pars distalis hyperplasia. 

Across all endpoints, the evaluation finds limited evidence of consistent dose-response, no persistence between interim and terminal assessments, and no progression to neoplastic outcomes. Several findings are interpreted as non-adverse, age-related, or within expected biological variability. In this context, and consistent with prior guideline-compliant studies, the authors conclude that 25,000 μg/kg-bw/day is an appropriate NOAEL for BPA and human health risks.

This work underscores the importance of integrating statistical results with biological context in complex chronic toxicity datasets. For risk assessors, it illustrates how weight-of-evidence approaches grounded in study design, internal consistency, and progression of effects can clarify whether observed findings are adverse and inform dose-setting decisions with greater confidence.

From the publication: "There is no evidence that these observations are toxicologically relevant or adverse based on the present evaluation."