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Dr. Tim Adams Food and Drug Administration

The concept of the Threshold of Toxicological Concern (TTC) uses the principles of chemical grouping and read-across to prioritize the relative toxicity of chemical substances. Chemical Groups and exposure thresholds in TTC are largely based on the Cramer 1978 Decision Tree. To leverage the scientific knowledge accumulated since 1978, more than 15,000 scientific studies were reviewed to determine the effects of species, strain, sex, and target organ on toxicity and metabolic fate. These studies provided no-observed-effect-levels for more than 1,900 substances that were then organized according to their structure, metabolic fate, and toxic potential. Analysis of this database resulted in the development of refined DT questions leading to an increased

number of classes of toxic concern. These classes of toxic potential can be applied to a vast group of chemicals, including food packaging materials, for prioritization for future evaluation.