Guidance of EFSA on risk assessments for active substances of plant protection products that have stereoisomers as components or impurities and for transformation products of active substances that may have stereoisomers

Regulation (EC) No 1107/2009, Regulation (EC) No 396/2005, Regulation (EU) 283/2013, plant protection product, stereoisomers, enantiomers, diastereoisomers, risk assessment
First published in the EFSA Journal
26 August 2019
22 July 2019
Guidance of EFSA

The European Commission will decide the implementation time for the mandatory use of this guidance in the regulatory context


In response to the request of the European Commission to EFSA, this document provides guidance on the information necessary to perform the risk assessment of plant protection active substances that contain stereoisomers in their composition as active components or impurities. The guidance should also be used for active substances that without containing any stereogenic element may generate transformation products or metabolites that do contain them. As a general principle, stereoisomers need to be treated as different chemical components for the risk assessment. Current data requirements in the EU regulatory framework (Regulation (EC) No 1107/2009 and Regulation (EC) No 396/2005) already establish that the substance tested should match the technical specifications (including its isomeric composition) and that formation and effects of metabolites, degradation and transformation products should be investigated (which certainly includes the case when transformation products are stereoisomers). Experience gained during the application of EU pesticides regulation has shown that guidance may be needed to provide applicants and evaluators advice on how to generate and assess the required data. Also, guidance is needed on how to make the best use of the available information to perform the risk assessment of these substances, particularly in situations when the information on individual isomers is not available or difficult to obtain, with a primary objective being to reduce the need for repeating vertebrate animal testing. This guidance does not aim to provide specific technical advice on analytical methods. In this guidance, the Regulation (EU) 283/2013 on the data requirements for the plant protection active substances is analysed and recommendations are given on how to best address and assess data requirements for active substances containing stereoisomers.

European Food Safety Authority
pesticides.mrl [at]
EFSA Journal 2019;17(8):5804
Question Number
On request from
European Commission