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Clarification to degradation and mutagenicity testing under REACH

ECHA clarifies the rules on accepting adaptations to degradation testing and requiring combined studies for mutagenicity. Companies need to take these changes into account when deciding whether to update their registrations.

Helsinki, 24 August 2021 - ECHA considers that the chemical safety assessment does not allow registrants to omit submitting standard information on degradation from column 1 under REACH (Annex IX, section 9.2., column 2). Instead, this provision is a legal basis for registrants to propose, and ECHA to require, further testing on degradation if the substance’s chemical safety assessment indicates such a need. 

To adapt degradation tests listed in column 1, companies can still apply the specific rules for adaptation listed in REACH Annex IX, sections and 9.2.3, column 2, as well as the general rules for adaptations, listed in Annex XI. 

Exposure-based adaptations can be considered if human or environmental exposure is absent or so low that additional hazard information will not lead to improved risk management (Annex XI, section 3 or Annex IX, sections, column 2). The legal basis for such an adaptation must be clearly defined. For all adaptations, adequate justification and documentation is needed, taking the whole lifecycle of the substance into account.

For mutagenicity, a combined comet assay and micronucleus test may also be required for substances registered above one tonne per year under Annex VII to REACH. This combined test can also be required from substances registered at REACH annexes VIII, IX and X.

The combination study will be requested if there is:

  • a positive Ames test – which checks the potential of chemicals to create mutations in bacteria;
  • an indication of a chromosomal aberration concern; and
  • no other adequate and appropriate in vivo genotoxicity data in the registration.

The combined study can help reduce animal testing while providing useful information on the potential of a substance to induce chromosomal aberrations or gene mutation in vivo.


Further biotic degradation testing has to be proposed by companies if the chemical safety assessment indicates the need to further investigate the degradation of the substance and its degradation products. The choice of the appropriate tests depends on the results of the chemical safety assessment. See REACH Annex IX, section 9.2, column 2.

Further mutagenicity studies shall be considered in case of a positive result. See REACH Annex VII, section 8.4., column 2.