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EURL ECVAM Recommendation on the 3T3 NRU Assay for Supporting the Identification of Substances Not Requiring Classification for Acute Oral Toxicity

1. EURL ECVAM Recommendation, ESAC Opinion and ESAC WG Report

On 02.05.2013 EURL ECVAM published its recommendation on the 3T3 Neutral Red Uptake (3T3 NRU) Cytotoxicity Assay for the Identification of Substances not Requiring Classification for Acute Oral Toxicity According to the EU Classification, Labelling and Packaging System (CLP) implementing categories 1 to 4 of the UN Globally Harmonised System:

pdf icon EURL ECVAM Recommendation. Annex 1: ESAC Opinion. Annex 2: EURL ECVAM request for ESAC advice
pdf icon ESAC WG Consensus Report


2. Relevant validation study reports

pdf icon Follow-up study on the predictive capacity of the 3T3 Neutral Red Uptake cytotoxicity assay to correctly identify substances not classified for acute oral toxicty under the EU CLP system (LD50 > 2000 mg/kg b.w.); Annexes to the study report                             


3. Summary of the changes made in response to public comments received 


The recommendation was open for public comments from 18.12.2012 to 31.1.2013. In total four parties submitted comments to EURL ECVAM. In response to these comments the following key changes were introduced in the document together with further editorial improvements:

  • Before public commenting, the recommendation referred to EU CLP only in view of the regulatory framework for non-classification. However, as EU CLP implements the majority of the UN GHS classes for the classification of acute oral toxicity (apart from class 5 which is however subject to specific requirements as stipulated in UN GHS), a reference to the UN GH system has been added with an accompanying explanatory footnote. Further, references to other international regulatory systems using, like EU CLP, the UN GHS Category 4 threshold of 2000 mg k.g. b.w. as cut-off for non-classification has been added, specifically reference to the US Department of Labor's OSHA system for classifying substances in the context of occupational health.
  • The usability of data from the 3T3 NRU test method under the REACH Regulation has been further clarified. In particular, explanations were added referring to Annex XI of the REACH legislation which allows, already now to use data from the 3T3 NRU assay for adapting the standard information requirements within a Weight of Evidence approach in conjunction with other information.
  • Additional recommendations for follow-up activities have been added, relating to the development of integrated approaches (e.g. Weight of Evidence & Integrated Testing Strategies) that make use of the 3T3 NRU method. Moreover, in this context, the applicability domain of industrial chemicals (i.e. substances not designed to act via specific mechanisms/pathways) has been emphasized. The recommendation to further explore the applicability, limitations of the assay and to investigate other key mechanisms of acute oral toxicity (apart from general toxicity) has been maintained.
  • Throughout the text, the term "general purpose chemicals" has been replaced by "industrial chemicals". The intended meaning is: substances not designed to interact with biological systems or act on specific biological (molecular) targets (as distinct from, for example, pharmaceuticals, biocides, pesticides, herbicides which are designed to act through specific mechanisms) but to fulfil other purposes in a wide variety of applications.