Recent publication comparing the Threshold of Toxicological Concern (TTC) values and oral reference dose (RfD) values

ToxStrategies’ scientists have proposed potential expansions of the use cases for the threshold of toxicological concern (TTC) in human health risk assessment applications. Analyses indicate that conservative TTC values for chemicals are, on average, approximately six-fold lower than IRIS derived reference dose (RfD) values for noncancer effects. The findings have three potential applications: (1) serve as provisional toxicity values estimated from TTC Cramer Classifications in data-poor or emergency situations, (2) serve as a comparator for toxicity criteria derived by multiple agencies or stakeholders, and (3) identify RfD values that might warrant reanalysis when they are substantially lower than their corresponding TTC value. Importantly, the findings reaffirm the health protective nature of TTC values, with the majority of TTC values being lower than their corresponding RfD values.

The open-access article was published in Regulatory Toxicology and Pharmacology.

ToxStrategies scientists at the Toxicology Forum Winter Meeting

ToxStrategies scientists attended the 44th Annual Winter Meeting of the Toxicology Forum January 27–29, where they presented on a wide range of topics, including the use of New Approach Methods (NAMs) in the risk characterization of PFAS; advances, opportunities, and challenges in using NAMs in toxicological evaluations; expanding the use and chemical space of the TTC; and challenges and opportunities in assessing the safety of sunscreen active ingredients. The following ToxStrategies scientists were participants at the meeting:

Dr. Laurie Haws,
session co-chair and presenter

Session/Presentation: “Use of New Approach Methods in Risk Characterization of PFAS: Challenges and Opportunities — Introduction”
Jan 27 8:00 to 8:05 am

Dr. Grace Chappell,
session co-chair

Session: “High-Throughput Screening Data and Use of Other In Vitro NAMs in Toxicological Evaluations-Advances, Opportunities, and Challenges 20 Years into the 21st Century”
Jan 28 8:00 am to noon

Dr. Sarah Vater,

Presentation: “Update: New Data Requirements for Sunscreen Over the Counter Additives—Challenges and Opportunities”
Jan 28 at 4:00 pm

Dr. Susan Borghoff,
session co-chair

Session: “Advances in Thresholds of Toxicological Concern (TTC): Expansion of Databases to Support New Chemical Space”
Jan 29 8:00 am to 10:00 am

These scientists are all active in The Center of Excellence for 21st Century Toxicology, a division of ToxStrategies, Inc.


ToxStrategies at First EPA Conference on Reducing Animal Testing

Dr. Susan Borghoff, Director of ToxStrategies’ Center of Excellence for 21st Century Toxicology, was invited to participate in the inaugural Conference on Reducing Animal Testing for Chemical Safety, convened on December 17, 2019, by EPA’s Office of Pesticide Programs. Approximately 60 scientists from government, academia, and industry were present at the full-day meeting, and were joined by more than 600 individuals in the morning session via teleconference. The gathered experts in environmental and chemical safety research discussed advancements in New Approach Methods (NAMs), to assess the current state of chemical safety research and discuss scientifically valid alternatives to animal testing. According to EPA, “This event, which will take place annually, is a major step in implementing [the Agency’s vision] to aggressively pursue reductions in animal testing.”


Dr. Borghoff brought her expertise in study design and managing research and regulatory-driven toxicology to the breakout group that discussed “Variability and Relevance of Current Animal Tests and Expectations of NAMs.” In her 30-year career, Dr. Borghoff has managed diverse research programs for both industry and government clients. Recent efforts have been focused on the development and implementation of a framework to evaluate both in vitro and in vivo mechanistic data into hazard characterization.