It’s important to note that substances and mixtures already placed on the market before these dates do not need to be re-labelled or re-packaged immediately. They can continue to be supplied within the supply chain until July 1, 2028, for substances, and January 1, 2029, for mixtures.
Classification Principles for Complex Substances
- Complex substances are treated like mixtures but are classified as single substances.
- Two key approaches are used when no direct test data is available for the entire substance:
- Bridging Principles
- Weight of Evidence Approach
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The classification process follows these key principles:
- Use of Available Data:
- Where experimental data on the whole substance is available, this should be the primary basis for classification.
- If data on the whole substance is lacking or insufficient, classification should be based on known constituents
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- Bridging Principles:
- If test data on the complex substance itself is unavailable, a bridging principle can be applied using data from similar substances.
Bridging principles allow classification based on data from similar substances. The following principles apply:
| Bridging Principle | Application |
| Dilution | If a hazardous substance is diluted, classification is based on the diluted concentration. |
| Batching | If a new batch has a similar composition to a previously classified batch, it can inherit the same classification. |
| Interpolation | If two tested mixtures show consistent hazard levels, an untested intermediate mixture can be classified accordingly. |
| Substantially Similar Mixture | If the hazard profile of a similar tested mixture is known, it can be extended to a new mixture. |
| Concentration Additivity | For substances with additive toxic effects, the concentration of individual hazardous components determines classification |
- Weight of Evidence
- A weight-of-evidence approach (expert judgment considering all relevant data) should be used when applying bridging principles
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Weight of Evidence (WoE) Approach
When bridging principles are insufficient, a weight of evidence (WoE) evaluation is required. This approach considers:
- Test data from individual constituents (e.g., mutagenicity, carcinogenicity, aquatic toxicity).
- Human exposure data, including epidemiological and occupational health reports.
- Mode of action—how the substance interacts at a biological or environmental level.
- In vitro (lab) studies and in vivo (animal) studies, if available.
Computer modeling (Q)SAR—predicting toxicity based on chemical structure similarities
- Individual Constituents vs. Whole Substance:
- If individual constituents are classified as hazardous, the complex substance must be evaluated under mixture classification rules to determine if similar hazards apply.
- In some cases, constituents might have hazardous properties in isolation but not in the complex substance due to interactions that modify their behavior
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- Application of Mixture Classification Rules:
- If the bridging principles do not apply, standard mixture classification rules should be used:
- Summation method (for certain health and environmental hazards).
- Additive effects of similar hazardous components should be considered
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Special Considerations for Certain Complex Substances
- Plant-Derived Substances:
- Some complex substances extracted from plants contain multiple components where individual constituents have potential hazard properties, but these may not apply to the whole extract.
- A temporary derogation has been introduced to allow for a scientific review of classification rules for plant extracts
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- Endocrine Disruptors & PBT Substances:
- If a complex substance shows persistent, bioaccumulative, and toxic (PBT) properties, classification should be based on known individual constituents unless whole-substance data proves otherwise.
- The same applies to endocrine-disrupting effects, where both whole-substance and constituent-based evaluations should be considered
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