Registration Dossier

Administrative data

Description of key information

The substance is included in the category of Stilbene Fluorescent Whitening Agents (SFWA) comprising of 14 member substances in total. The category of Stilbene Fluorescent Whitening Agents is defined as a structurally related group of substances that are derivatives of 4,4’-bis(1,3,5-triazinyl-2-yl)amino)stilbene-2,2’-disulphonic acid, each with one aniline and one alkyl derivative amino moiety at the triazine ring. The aniline moiety can also be mono- or di-sulfonic aniline. With the exception of 3a-A (free acid) and OB 3a-A (NaK) all substances are sodium salts. The molecular structures of 3a-A (free acid), OB 3a-A (NaK) and OB 3a-A (Na) are the same except that the first one is the free sulfonic acid and the second one the potassium/sodium salt. The chemical structures are highly symmetric with an extended chromophor system. Substituents have little influence on the chromophor system; they affect the application properties and substantivity. To be included in the defined category of SFWA a substance must have the following characteristics:

 •           All substances are derivatives of 4,4’-bis(1,3,5-triazinyl-2-yl)amino)stilbene-2,2’-disulphonic acid, each with one aniline derivative (R1) and one alkyl derivative amino moiety at the triazine ring (R2).

•            The substances have all negative calculated log Pow(<-1), due to the fact that except from the acid form, they are all salts.

•            Molecular weights range from ca. 872 to ca. 1369 g/mol.

•            All category members are very soluble, with an individual solubility ranging from ca. 1 to >200 g/l. Water solubility tends to increase with the degree of sulfonation. They are all very stable and do not hydrolyze.

•            As a result of the stilbene portion of the molecule, common to all category members, these fluorescent whitening agents have an UV absorption maximum between 340 to 360 nm in water, which makes them subject to direct photo-degradation in the hydrosphere. The structural differences between the substances are determined by the presence of two moieties (R1 and R2) bound to both triazine rings. Each substance is characterized by a combination of two of these moieties to each triazine ring and by the cations of the sulfonic acid group present, which in almost all cases is Na+, in one case it is Na+ and K+; instead of these cations a proton (H+) is present for one substance. R1 is bound to the 3 position of the triazine ring and is described as an aniline function, which may have one or two sulfonate functions. Based on the variability related to R1 or R2 two different sub-categorizations can be considered - Sub-categorization based on R1 or Grouping based on R2. R2 can be constituted by the following:

•            morpholino

•            methyl (2-hydroxyethyl)amino,

•            2-hydroxyethylamino,

•            bis(2-hydroxyethyl)amino,

•            diethylamino,

•            (2-carbamoylethyl)(2-hydroxyethyl)amino,

•            bis(2-hydroxypropyl)amino,

For read-across both of these structural differences in moiety R1 and R2 are taking into account. Therefore, read-across to OB 2 -A having an identical structure in moiety R2 and to OB 3a-DSA having an identical structure in R1 is applied.

Skin sensitization is a systemic endpoint; therefore skin absorption is required to express the effect. Dermal absorption is estimated to be negligible for all members of the category based on physicochemical properties (see Table 19 of the category justification) and also measured for OB 2 -A and OB 3b-A. No dermal metabolism is indicated with the OECD QSAR Toolbox.

The available data on the substances in the category show that they are all negative regarding skin sensitization. Therefore, based on structural similarities, lack of specific alerts, and predicted specific endpoint results, a read across approach for the substances that have not been tested is justified, hence, as all results were consistently negative there is no evidence for skin sensitization properties of any category member.


Justification for read-across:

1)     The substance is part of the Group 2, in which the members share the common organic functional group morpholino derivative, with different sulfonation degrees: bisulfonated (OB 2 -A) tetrasulfonated (OB 2 -MSA) and hexasulfonated (OB 2 -DSA).

2)     The studies performed on OB 1 -DSA, harvesting inorganic functional group diethylamino derivativeinstead of the morpholino derivative but sharing the same residue in R1, are also considered as supporting reference. Both substances (OB 1 -DSA and OB 2 -DSA) are hexasulfonated sodium salts, very similar according to Tanimoto rules.

3)     Within the whole category no substance showed concern about skin sensitization potential.

4)     OECD QSAR Toolbox previsions suggest no skin sensitization potential for the substance, based on no alert found for protein binding by OASIS v. 1.2, protein binding by OECD, protein binding potency, and protein binding alerts for skin sensitization.

5)     Skin sensitization is a systemic effect and dermal adsorption needs to provide the effect. Very low dermal absorption based on predicted values calculated with DERMWIN and confirmed by measured dermal absorption on a similar substances of the category (OB 3b-A).

6)     No dermal metabolism has been proposed by the dermal metabolism simulator in the OECD QSAR Toolbox.

In summary, OB 2 -DSA is expected to have no skin sensitization potential which is in line with results obtained in various in vivo tests among the category members. Therefore, also with respect to animal health and welfare, read-across to OB 2 -A and OB 2 -MSA is applied and no further testing in vivo is considered.

Key value for chemical safety assessment

Skin sensitisation

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed (not sensitising)

Respiratory sensitisation

Endpoint conclusion
Endpoint conclusion:
no study available

Justification for classification or non-classification

The substance was considered to be a non sensitiser, hence does not warrant classification as per the CLP (Regulation EC No. 1272/2008) criteria.