The ZZS Similarity Tool compares the chemical structure of a substance with the structure of Dutch Substances of Very High Concern (In Dutch: Zeer Zorgwekkende Stoffen, ZZS). This tool can be used for substances for which little is known about potential properties of concern. A similarity in structure to a ZZS may indicate similar properties. RIVM uses this instrument when providing advice on substance properties.

The ZZS Similarity Tool is developed based on scientific research on structure similarity (Wassenaar et al. 20192021 & 2022). More details on the application and the underlying methodology are available in the user manual ZZS Similarity Tool.
We greatly appreciate comments and additions from your application of this instrument in practice. You can send these to the 
helpdesk of this website.


The results of the ZZS Similarity Tool provide a prediction of potential ZZS-properties. Absence of structural similarity to a ZZS does not necessarily mean that there is no ZZS-concern. Conversely, similarity to a ZZS does not necessarily mean that a substance is ZZS. It is a trigger to further evaluate a substance. New knowledge or insights can lead to changes and updates of the tool. Changes to a new version will be published on this website.