A TTC threshold for acute oral exposure to non-genotoxic substances.

To derive an acute TTC threshold, the correlation between Allowable Daily Intakes (ADIs, chronic values) and Acute Reference Doses (ARfDs) of pesticides evaluated in the EU was investigated and their distributions were compared. The correlation between ARfDs and ADIs was significant (p = 0.01), but weak (r2 = 0.051). Consequently, using this approach to derive acute TTC values does not seem valid. Therefore, the distributions of ARfDs and ADIs were compared directly, in order to extrapolate from chronic to acute TTC values. This comparison made for the combined Cramer structural class II and III pesticides showed a ratio ARfD/ADI of approximately 3 at the fifth percentile of the distributions.