Table 1.

Summary of the chemical characterization needs for UVCB that are registered and evaluated under REACH in the European Union.

Information Needed	Substance Identification for Registration (REACH Annex VI, Section 2)	Hazard Characterization for Evaluation (REACH Annex XI, Section 1.5)
		Read-Across Assessment Framework: Considerations on multi-constituent substances and UVCBs (ECHA, 2017c)		Advice on Using Read-Across for UVCB substances (ECHA, 2022)
		Category Approach	Analogue Approach
Overall Substance Identification	Substance name [from a trade association and/or nomenclature system] Substance identifiers [source, manufacturing process, carbon and boiling range, phys-chem properties, etc.]	Substance(s) to be grouped in a category Compositions to be included Manufacturing process description	Source substance(s) and target substance Compositions to be included Manufacturing process description	Similarity may be established based on: (i) presence of identical constituents OR (ii) variation in concentration and variability in constituents Constituents present at >1% must be identified; lower thresholds if constituents of concern are present (>0.1% for carcinogenic/mutagenic, >0.3% for repro/developmental) >80% of constituents in the substance must be identified
Composition Characterization	Constituents present >10% Constituents <10% that may be impacting hazard classification	Category “domain” needs to be defined (constituent-specific concentration determination not specified)	Source substance(s) Target substance (constituent-specific concentration determination not specified)	Must be characterized up to 100% When full characterization is impractical/impossible need to provide (i) justification AND (ii) demonstration of similarity “by other means”
Variability	Not Required	Structural similarity for category based on worst-case scenario Determine if quantitative differences or patterns in predicted properties may be reflected in structural similarity	Structural Similarity between source & target based on worst-case scenario Determine if quantitative differences or patterns in predicted properties may be reflected in structural similarity	Structural similarity explained based on quantitative and qualitative comparison of composition When full characterization is impractical/impossible need to provide (i) comparison of constituents AND (ii) demonstration of similarity “by other means” (e.g. analytical information for >95% constituents, constituents of high concern, high resolution for confidence fingerprinting) Analysis of at least 5 independent (i.e., production batches) samples analyzed from ALL registrants of a substance