Barium 4-[(5-chloro-4-methyl-2-sulphonatophenyl)azo]-3-hydroxy-2-naphthoate

Endpoint summary

Description of key information

The organic part of the BONA-based metal laked pigments has no potential for bioaccumulation.

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Absorption rate - oral (%):

50

Absorption rate - dermal (%):

50

Absorption rate - inhalation (%):

100

Additional information

The toxicokinetic properties of BONA based metal laked pigments are derived from acute and subacute toxity studies and physico-chemical data. Repeated-dose toxicity data including a treatment-free recovery element is available for Pigment Red 48:2(Ca), Pigment Red 57:1(Ca) and Pigment Red 57(Sr) salt. The organic part was found to be deprotonized at the sulfonate and the carboxylate function (Kennedy et al. (2000) Angew. Chem. Int. Ed. 2000, 39, No. 3). Protonation of the pigment in stomach acid therefore results in disintegration into the organic acid and the metal cation. The sodium salts of the pigments have an orange colour. For oral application of high doses, both red staining of faeces and orange discolouration of urine are observed starting the first day of dosing and resolving within days after the last dose. From this it is concluded that while a fraction of the pigment passes the intestine without uptake, another fraction is taken up and the organic acid is eliminated via the kidney. Considering the orange discolouration, the azo bond of the chromophore should still be at least partly intact. As the solubility of the sodium salt was measured as 0.3 g/L and 1.5 g/L for the sodium salt of Pigment Red 57 and Pigment Red 48, respectively (unpublished data, Ciba 2009), the organic acid is indeed sufficiently soluble for elimination without further metabolism. Enzymatic cleavage of azo bonds to the respective amines is also possible and this would result in non-coloured soluble metabolites. Azo reduction of 1-amino-2-naphthol-based azo dyes was reported to by catalysed by human intestinal microflora [Xu, H., et al.: Anaerobic metabolism of 1-amino-2-naphthol-based azo dyes (dyes) by human intestinal microflora. Appl Environ Microbiol, 2007.73(23): p. 7759 -7762]

Regarding the dermal and inhalation route, only acute data is available. In none of these studies, discolouration of urine or faeces was noted. No indication of toxicity or uptake was observed in the acute inhalation studies with Pigment Red 57:1(Ca) and Pigment Red 57(Na). Upon acute inhalation of Pigment Red 48:1(Ca), one of ten rats died. The male that died during the study showed swollen and abnormally dark lungs and pink contents in the small intestine at necropsy. No abnormalities were detected in surviving animals at the end of the study.

During studies for acute dermal toxicity, no signs of clinical toxicity and no discolouration of urine or faeces were observed for Pigment Red 48:1(Ba), 48:2(Ca), 48:4(Mn) and 57:1(Ca). Coloured remnants of the test material at the application site were observed at the end of the observation period.

Based on the experimental toxicity data and the physico-chemical properties, the organic part of the BONA-based metal laked pigments has no potential for bioaccumulation.

Pigment Red 48:1(Ba) is of very low solubility. Experimental data on inorganic Barium salts indicates that the solubility increases in the acidic environment of the stomach as Barium chloride is of high solubility in water. To what extent this happens depends on the actual pH in the stomach. Dissolved Ba2+ is detected rapidly in the blood after ingestion. It is eliminated to a higher extent in the feces than in the urine and is also incorporated into the bone and detected in tissues.