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Results on intestinal absorption and skin penetration of CAS 16090 -02 -1 were reported by Black et al. (1977). Two groups of 6 rats each were treated by oral gavage with 0.5 ml of a solution containing 0.007% tritiated substance in 1% (w/v) detergent (alkyl benzene sulfonate and sodium tripolyphosphate) or in an aqueous solution. All animals were placed in separate metabolic cages and urine and feces samples were collected every 24 hours for up to 4 days. At scheduled necropsies after 24, 48 and 96 hours blood samples were taken by heart puncture and selected organs were sampled for radioanalysis. The bulk of radioactivity from both treatment groups was excreted in the feces, mostly during the first 24 hours. Small amounts were present in the urine. Recovery of radioactivity was essentially complete after 48 hours (total recovery > 92% with 48 hours). No significant amount of radioactivity was found in urine, blood and feces samples from 16 rats treated topically with 0.2 ml of a solution containing 0.007% tritiated substance in 1% aqueous detergent. In two rats, treated topically with 0.5 ml of a solution containing 0.43 mg/ml tritiated test material in ethanol, however, small amounts of radioactivity were detected in feces, large and small intestines and their contents as well as in the content of the stomach. Only minor amounts of radioactivity were found in the liver, bladder, kidneys, and heart of one of the treated animals. Approximately 0.1% of the applied dose (i.e. approximately 0.01 μg/cm²) had been absorbed through the skin during two days.

Forbes (1976) found after application in methanol, 14C-activity was lost from the skin of hairless mice at a constant rapid rate for the first 2 hours; thereafter loss continued at a lesser rate.

These findings are confirmed by absorption, distribution and excretion experiments in rats published by Mücke et al. (1975) (CIBA-Geigy, 1972b). Following an oral dose of 14C-labeled of CAS 16090 -02 -1 in water at 5.9 mg/kg bw to rats of both sexes, rapid and complete excretion of radioactive material was observed, with an excretion half life ranging from 7-13 hours. Feces were practically the only route of excretion (more than 95% of the administered radioactive material was excreted within 48 hours), indicating, in combination with the short half life times, that no significant amounts were absorbed from the gastro-intestinal tract. No radioactivity was found in blood, liver kidney, brain, muscle, or fat 96 hours after dosing (limit of quantification 0.005 - 0.01 ppm equivalents). The total recovery of radioactivity was 97.5% and 95.2% of the orally applied dose for males and females, respectively.

Only very limited information is available on the biotransformation (metabolism) of CAS 16090 -02 -1 in experimental animals. Little or no cis-isomer was produced by Beagle dogs fed with 2000 mg/kg bw of the trans isomer (Burg et al., 1977).

Conclusion: Since all stilbene fluorescent whitening agents of this category show similar physico-chemical parameters it can be stated that after oral exposure, rats excrete stilbene fluorescent whitening agents almost completely in the feces within 48 hours. There was no measurable skin penetration of stilbene fluorescent whitening agents when topically applied in a detergent solution to rats. When applied at 0.43 mg/ml in ethanol, approximately 0.01 μg/cm² penetrated rat skin within 2 days. This shows that all category members and then, reading across, also the substance CAS 371756 -75 -1 are almost completely excreted after oral exposure and that a dermal absorption is poor.