# Regulation (EC) No 1907/2006 of the European Parliament and of the Council of 18 December 2006 concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH), establishing a European Chemicals Agency, amending Directive 1999/45/EC and repealing Council Regulation (EEC) No 793/93 and Commission Regulation (EC) No 1488/94 as well as Council Directive 76/769/EEC and Commission Directives 91/155/EEC, 93/67/EEC, 93/105/EC and 2000/21/EC (Text with EEA relevance), Division 1.5: Grouping of substances and read-across approach

Extent: E+W+S+N.I.

Substances whose physicochemical, toxicological and eco-toxicological properties are likely to be 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 physicochemical properties, human 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 Agency, after consulting with relevant stakeholders and other interested parties, shall issue guidance on technically and scientifically justified methodology for the grouping of substances ....
When nanoforms are covered by the registration the above approach shall address the nanoforms separately. For grouping different nanoforms of the same substance the molecular structural similarities alone cannot serve as a justification.
If nanoforms covered by a registration are grouped or placed in a ‘ category ’ with other forms, including other nanoforms, of the substance in the same registration the obligations above shall apply in the same manner.
The similarities may be based on:
(1) a common functional group;
(2) the common precursors and/or the likelihood of common breakdown products via physical and biological processes, which result in structurally similar chemicals; or
(3) 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 should:
be adequate for the purpose of classification and labelling and/or risk assessment,
have adequate and reliable coverage of the key parameters addressed in the corresponding test method referred to in Article 13(3),
cover an exposure duration comparable to or longer than the corresponding test method referred to in Article 13(3) if exposure duration is a relevant parameter, and
adequate and reliable documentation of the applied method shall be provided.

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Source: https://www.legislation.gov.uk/eur/2006/1907/annex/XI/division/1/division/1.5 (the official version)
Page: https://openlegislation.uk/eu-regulation-2006-1907/annex-XI/division-1/division-1.5
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.