1.5. Grouping of substances and read-across approach

Substances whose physico-chemical, toxicological and ecotoxicological properties are similar or follow a regular pattern as a result of structural similarity may be considered as a group or ‘category’ of substances. Application of the group concept requires that physico-chemical properties, human and animal health effects, and environmental effects or environmental fate may be predicted from data for reference substance(s) within the group by interpolation to other substances in the group (read-across approach). This avoids the need to test every substance for every endpoint. The similarities may be based on: a common functional group indicating the presence of dangerous properties; common precursors and/or the likelihood of common breakdown products via physical and biological processes, which result in structurally similar chemicals and indicates the presence of dangerous properties; or a constant pattern in the changing of the potency of the properties across the category. If the group concept is applied, substances shall be classified and labelled on this basis. In all cases results shall: be adequate for the purpose of classification and labelling and risk assessment, have adequate and reliable coverage of the key parameters addressed in the corresponding test method, and cover an exposure duration comparable to or longer than the corresponding test method if exposure duration is a relevant parameter. In all cases, adequate and reliable documentation of the applied method shall be provided. The Agency shall, in collaboration with the Commission, Member States and interested parties, develop and provide guidance on technically and scientifically justified methodology for the grouping of substances.

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Source: EUR-Lex (Cellar) · retrieved 2026-10-29 · Text as adopted (Official Journal); later amendments are not incorporated in this text.