The term "mixture" has different meanings in the context of substance definitions. In general, a mixture consists of two or more constituents, which are not considered as additives or impurities. Depending on whether the mixture is prepared intentionally or not, it is distinguished between:
Preparations, which according to the definition given in REACH are intentional mixtures of substances gained by blending of two or more constituents. The components retain their own chemical identity and properties and do not react. The composition of a preparation can be fully characterised. In the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) preparations are referred to as "mixtures".
Unintentional mixtures consisting of more than one constituent as a result of the manufacturing process and/or the source. These include:
Multi-constituent substances, which are mixtures consisting of several main constituents present in a certain range of concentrations (e.g. => 10 and < 80% (w/w));
Complex mixtures including Unknown or Variable composition, Complex reaction products or Biological materials (UVCB substances), or process stream.
The IUCLID feature Mixture only relates to the mixtures as described under bullet 1, i.e. preparations. These include for example biocidal products.
To fulfill REACH obligations (e.g. registration of substances) or within the OECD HPV programme the data should not be entered under the mixture section. REACH encompasses substances (mono-constituent, multi-constituent and UVCB substances) which all should be addressed as substances.