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Description of key information

There were no hints for a possible bioaccumulation of indigo; the oral absorption rate is ca. 20%.

Key value for chemical safety assessment

Bioaccumulation potential:
no bioaccumulation potential
Absorption rate - oral (%):
20

Additional information

The toxicokinetic properties of Indigo have been investigated in male rats (Research Triangle Institute: Absorption, Distribution, Metabolism and Excretion of CI Vat Blue #I; Indigo; RTI/2227/00-04P, September 1983). For this purpose, radioactive labeled (14C) Indigo (radiochemical purity ca. 70%) was administered as a single intravenous injection (0.23 mg/kg bw), a single oral gavage (3.0; 31; 305 mg/kg bw) and a single dermal application (1.5 and 3.7 mg/kg bw).

Intravenous injection: 25% of the administered radioactivity was detected in the bile within 7 hours after injection. 35% and 43% of the administered radioactivity were found in the urine and feces of the rats, respectively, within 240 hours after intravenous injection. Excretes via urine, bile and feces contained only 0.5% to 2% unchanged Indigo; 98% of the excreted radioactivity were metabolites.

Oral administration: 9% to 11% and 77% to 87% of the administered radioactivity were excreted with urine and feces, respectively, within 72 hours after gavage. Less than 1% was detected in the exhaled fraction. Comparison with IV data led to an oral bioavailability of approximately 33% to 58%.

After oral administration of the purified indigo 4% and 78% of the radioactivity were found in the urine and feces, respectively, after 72 hours. Taking into account the results with purified indigo, as well as after standardization of the IV data would lead to an oral absorption of about 20%.

The highest tissue levels after oral administration were found in liver and kidneys

Dermal administration: After dermal application of the ointment, 0.8% of the administered radioactivity was found in urine, feces and cage washes; after application of the dry powder, only 0.3% was found, leading to a very limited dermal absorption of indigo.

There were no hints for a possible bioaccumulation of indigo.