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Categories

Category name:
Stilbene fluorescent whitening agents

Justifications and discussions

Category definition:
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’-disulfonic acid, each with one anilino and one alkyl amino moiety at the triazine ring. The anilino moiety can also be mono- or di-sulfonato anilino. With the exception of CAS Nos. 4404-43-7 and 70942-01-7 all substances are sodium salts. The molecular structures of CAS Nos. 4404-43-7, 70942-01-7 and 4193-55-9 are the same except that the first one is the free sulfonic acid and the second one the potassium/sodium salt.
Category order description:
The category comprises three sub-groups, di-, tetra and hexa-sulfonates.
Category rationale:
The category members display similar physicochemical and environmental fate properties. Since category members are all organic salts or internal salts, they exhibit high degree of dissociation in water, very low octanol/water partition coefficients, high melting points, do not boil without decomposing and do not exert vapour pressure. In addition, category members are stable to hydrolysis. 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 photo-degradation in the hydrosphere. All category members tested are appreciably soluble in water. Water solubility tends to increase with increasing numbers of sulfonate groups on the molecule. Existing data for the substances indicate that they exert similar effects with respect to aquatic and mammalian toxicology. Available studies suggest that the category members are of low toxicity to fish, aquatic invertebrates, algae, soil macroorganisms, and bacteria. With respect to mammals, the category members are of low acute or repeated dose oral toxicity, are not mutagenic or clastogenic, and are not reproductive or developmental toxicants. They are generally not irritating or sensitizing to skin and eyes.

Because these substances exhibit similarity in their physicochemical, eco-toxicological and toxicological properties they can be considered to constitute a chemical category. Data gaps for mammalian toxicity, eco-toxicity and environmental fate can be addressed by read-across applying the category and analogue approach.

Category members possess similar use, release and exposure profiles. They are used as fluorescent whitening agents which are incorporated in preparations (e.g. detergents) and articles (paper and textiles) with low incorporation rates (< 1%).