ZZS-similarity tool Risico's van Stoffen


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Enter the SMILES or the CAS-number of a substance to find structural similar ZZS substances. Explanation

You can only use one search field at a time.

Batch search

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You can enter multiple SMILES and/or CAS-numbers here. The results will be saved as a tab-separated-values .txt file. Explanation

A maximum of 100 items will be processed.

These should be divided by a space, a comma, a vertical line (|) or by a new line.

For each item, the most similar ZZS substance will be found.

Model description

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The ZZS structural similarity model is an online tool designed to predict whether a chemical is structurally similar to a ZZS. Structural similarity could be an indication of similar toxicity profiles. Therefore, this model could be used for screening purposes.

The model was initially based on the methodology as analyzed and evaluated by Wassenaar et al. (2019) (with slight variances to facilitate implementation), and was updated based on suggestions made by Wassenaar et al. (2021).

Details on the implementation of the methodology, the required input and the interpretation of the output can be found on the ZZS-Similarity tool page.


A SMILES-code or a CAS-number of a chemical structure needs to be provided.


Structural similar ZZS are shown for the input structure. The results are categorized into similarity to ZZS with CM, R, PBT/vPvB and ED properties according to REACH, CLP or POP-regulations In addition, a category of substances with other ZZS properties is included. This includes substances that are identified as ZZS based on other hazard properties (like sensitizing properties), or are derived from other sources than REACH, CLP or POP-regulations. The most similar substance per category is shown on top. Generally, the three most comparable ZZS are shown per category. ZZS that are considered to be structurally similar to the input structure according to the computer model are shown in 'orange'. Furthermore, a score is provided that indicates the model’s confidence in the structural similarity, with a confidence score equal to or above 50% when the model considers the structures to be structurally similar.

It should be noted that the absence of structural similarity to a ZZS does not per definition means no concerns. Vice versa, similarity does not per definition mean that a substance exerts a specific effect, it is a trigger for further inspection and analysis.


Simplified Molecular Input Line Entry System
Dutch Substance of Very High Concern (in Dutch: Zeer Zorgwekkende Stoffen)
Carcinogenic, Mutagenic
Persistent, Bioaccumulative and Toxic / very Persistent and very Bioaccumulative
Endocrine disruptor
Persistent, Mobile and Toxic
Resp. Sens.
Respiratory sensitizer