Structure-activity relationship (SAR) and quantitative structure-activity relationship (QSAR) models, collectively referred to as (Q)SARs, are mathematical models that can be used to predict the physicochemical, biological and environmental fate properties of compounds from the knowledge of their chemical structure. In the context of plant protection products under Regulation (EC) No 1107/2009 and the Biocidal Products Regulation (BPR) Regulation (EU) 528/2012, QSARs are mainly used in the assessment of the equivalence of technical materials (for plant protection products see the guidance document SANCO/10597/2003 – rev. 10.1 of 13 July 2012). The level of hazard posed for health and environmental protection must be comparable for different sources of technical material.
A two-tiered approach is considered to assess technical equivalence – if equivalence cannot be established on the basis of the Tier I data, further mammalian toxicity/ecotoxicity consideration is necessary which will form the requirements of Tier II. In all cases of new/increased levels of impurities, a (Q)SAR analysis should be conducted in order to predict the toxicity of the impurity based on its chemical structure, if a reliable prediction is possible and can be supported scientifically. QSARs used should be well-documented in terms of their applicability domain, validated at the EU level and suitable for predicting the endpoints of interest. While commercially available models are available for toxicity (e.g. DEREK, TOPKAT), the use of SAR and QSAR approaches for ecotoxicity is more limited by the lower availability of reliable models for the whole spectrum of taxonomic groups occurring in the environment.