A scientific study published online on November 10, 2014 in the peer-reviewed journal Food and Chemical Toxicology assesses the reliability of the Threshold of Toxicological Concern (TTC) approach. A group of four European scientists compared experimental toxicological data on 328 pesticide active substances to threshold values obtained after using the TTC approach. Based on the results of expert judgment and software-aided classification, 279 and 43 pesticides were assigned to Cramer class III (highest concern) and to the class of organophosphates and carbamates, respectively. The no-observed effect levels (NOELs) of these two classes were plotted as distribution curves and the 5th percentile NOEL values were determined according to the work by Munro et al. (1996). The authors compared the 5th percentile NOEL values of the pesticide database with previously published data. They concluded that the threshold values of the pesticides were higher or equal to the values determined in previous studies for other chemicals. This means that the experimental toxicological data for the pesticides do not result in lower, thus more conservative threshold values. Additionally, the acceptable daily intakes (ADIs), which were based on experimental toxicity studies, were related to the assigned threshold values. The toxicity of 17 substances in the pesticide database was underestimated by the TTC approach. Feigenbaum and colleagues evaluated each of these 17 pesticides by including their bioaccumulation potential and judging whether the ADI could be considered as justified, cautious or overly cautious. The authors concluded that only 10 pesticides (2.8%) seem to be underestimated using the TTC approach.
It is important to mention that the study was not performed to propose a new application of the TTC approach for the risk assessment of pesticides, but to improve the reliability of the concept. In the EU, the TTC approach is currently used for the risk assessment of flavoring agents and it is discussed to be potentially used for food contact materials in the future.
Feigenbaum, A. et al. (2015). “Reliability of the TTC approach: Learning from inclusion of pesticide active substances in the supporting database.” Food and Chemical Toxicology, 75, 24-38.
Munro, I.C. et al. (1996). “Correlation of structural class with no-observed-effect levels: a proposal for establishing a threshold of concern.” Food and Chemical Toxicology, 34, 829-67.