International Agency for Research on Cancer (IARC) - Summaries & Evaluations


VOL.: 29 (1982) (p. 295)

CAS No.: 1937-37-7
Chem. Abstr. Name: 2,7-Naphthalenedisulfonic acid, 4-amino-3- {[4'-((2,4-
diaminophenyl)azo)(1,1'-biphenyl)-4-yl]azo}-5-hydroxy-6-(phenylazo)-, disodium salt

5. Summary of Data Reported and Evaluation

5.1 Experimental data

Direct Black 38 was tested by oral administration in mice and rats and by bladder implantation in mice. In one study in mice, the compound produced hepatocellular carcinomas and mammary carcinomas following its administration in drinking-water. The other study in mice was inadequate for evaluation. Oral administration to rats of one commercial sample of Direct Black 38 resulted in hepatocellular carcinomas in males and neoplastic nodules in males and females sacrificed 13 weeks after start of exposure to the highest dose at which animals survived. Lower doses produced only liver-cell changes such as foci of cellular alteration. In another study in rats, sacrificed after 60 weeks' exposure to the dye in drinking-water, mucosal hyperplasia and carcinoma of the bladder and carcinomas of the liver and colon were seen.

One study has shown that Direct Black 38 and the urine of hamsters given this compound are mutagenic to Salmonella typhimurium with metabolic activation.

One limited study in rats has shown it to be embryolethal but not teratogenic.

5.2 Human data

Occupational exposure to Direct Black 38 has and probably still does occur during its production and its use for the dyeing of textiles, leather and paper. Benzidine and its metabolic derivatives have been detected in the urine of workers exposed to direct azo dyes.

No data were available to assess the mutagenicity or chromosomal effects of this compound to man.

No study of exposure to Direct Black 38 alone was available to the Working Group. An epidemiological study of silk dyers and painters who had multiple exposure to benzidine-based and other dyes indicated that those exposures were strongly associated with the occurrence of bladder cancer. Case reports and other epidemiological studies support the existence of such a relationship.

5.3 Evaluation

There is sufficient evidence that commercial Direct Black 38 is carcinogenic to rats.

Although the epidemiological data were inadequate to evaluate the carcinogenicity in man of Direct Black 38 alone, they, together with the presence of benzidine in the urine of exposed workers, provide sufficient evidence that occupational exposure to benzidine-based dyes represents a carcinogenic risk to man.

For definition of the italicized terms, see Preamble Evaluation.

Subsequent evaluation: Suppl. 7 (1987)


Last updated: 9 April 1998

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