C.I. Direct Blue 15 is one of five chemicals being evaluated in 2-year carcinogenicity and toxicity studies as part of the NTP's Benzidine Dye Initiative. This Initiative was designed to evaluate representative benzidine congeners, benzidine congener-derived dyes, and benzidine-derived dyes. The dye, industrial grade C.I. Direct Blue 15, was chosen for study as a product to which workers are potentially exposed. Because of the high salt content, the dye was desalted prior to use. The purity was determined to be approximately 50%, with high-performance liquid chromatography indicating one major peak and approximately 35 impurities. Toxicology and carcinogenesis studies were conducted by administering the dye, C.I. Direct Blue 15, in drinking water to groups of F344/N rats of each sex for 14 days, 13 weeks, or 22 months. Planned as 24-month studies, the 22-month studies were terminated early because of rapidly declining animal survival, which was due primarily to neoplasia. These studies were performed only in rats because studies of benzidine congeners were being performed in mice at the National Center for Toxicological Research (NCTR). Genetic toxicology studies were conducted in Salmonella typhimurium and Chinese hamster ovary cells.
Rats were given C.I. Direct Blue 15 in drinking water at doses of 1,250, 2,500, 5,000, 10,000, or 30,000 ppm. All control and treated rats survived. Body weight gain in high-dose females was less than that in controls. Water consumption declined as the dose increased. Male and female rats receiving 30,000 ppm had slight degeneration and necrosis of individual hepatocytes in the liver, and females also had mild to moderate renal tubule degeneration and thymic lymphoid depletion.
C.I. Direct Blue 15 was administered in drinking water at doses of 0, 1,250, 2,500, 5,000, 10,000, or 30,000 ppm to male rats, and at doses of 0, 630, 1,250, 2,500, 5,000, or 10,000 ppm to female rats. Seven of 10 male rats receiving 30,000 ppm died; all rats in the other groups survived until the end of the studies. Mean final body weights of males receiving 10,000 or 30,000 ppm were 92% and 69% of those of controls, and mean final body weights of females receiving 5,000 or 10,000 ppm were 97% and 94% of those of controls. Tissues from treated animals were stained blue. Compound-related lesions were seen in the kidney and liver of male rats given 30,000 ppm and in the kidney of males and females given 10,000 ppm. The renal lesions included necrosis, degeneration, pigmentation and regeneration of the tubule epithelium, and tubule mineralization. Liver lesions included centrilobular hepatocellular degeneration, fatty metamorphosis, and individual cell necrosis with slight periportal hepatocellular hypertrophy. Lymphoid depletion in the thymus was also seen in the high-dose males. Based on the results of the 14-day and 13-week studies, the high dose chosen for the 22-month studies was 2,500 ppm.
At study initiation, 70 rats of each sex were given 0 or 2,500 ppm C.I. Direct Blue 15, 45 rats of each sex were given 630 ppm, and 75 rats of each sex were given 1,250 ppm. Interim evaluations were made at 9 and 15 months. The average amounts of compound consumed per day by the six dose groups after week 52 of the studies were estimated to be 45, 90, and 215 mg/kg for male rats and 50, 100, and 200 mg/kg for female rats.
Survival and Body Weights: The studies were terminated at 22 months due to extensive mortality associated with chemical-related neoplasia. Survival of control, 630, 1,250, and 2,500 ppm males at 22 months was 37/50, 8/35, 11/65, and 2/50; survival of females was 40/50, 13/35, 22/65, and 4/50. At 22 months, the mean final body weights of the 630, 1,250, and 2,500 ppm groups were 95%, 91%, and 81% of those of the control for male rats and 91% of those of the control for all female dose groups.
Histopathologic Effects in the 22-Month Studies
At the 9-month interim evaluations, one adenoma of the Zymbal's gland was seen in a high-dose male rat, and three carcinomas of the clitoral gland were seen in the high-dose females. At the 15-month interim evaluations, Zymbal's gland neoplasms were seen in low- and high-dose males and all treated female dose groups. Mid- and high-dose males and females also had preputial or clitoral gland neoplasms, and a few neoplasms were present in the skin, small and large intestine, liver, and oral cavity of treated animals at 15 months.
At the end of the study, neoplasms related to chemical administration were found in the Zymbal's gland, skin, oral cavity, and the preputial or clitoral gland in both male and female rats. Neoplasms related to chemical administration were also seen at other sites including the small and large intestine, liver, uterus, and brain. The incidence of mononuclear cell leukemia was also increased in treated rats.
C.I. Direct Blue 15 was not mutagenic in Salmonella typhimurium strains TA100, TA1535, TA1537, and TA98 when tested in a standard preincubation protocol with or without exogenous metabolic activation; however, when a specialized reductive metabolism protocol was used, C.I. Direct Blue demonstrated mutagenic activity in Salmonella strain TA1538. C.I. Direct Blue 15 did not induce sister chromatid exchanges or chromosomal aberrations in Chinese hamster ovary cells with or without S9 activation; reductive metabolism was not used in these cytogenetic tests.
Under the conditions of these 22-month drinking water studies, there was clear evidence of carcinogenic activity of C.I. Direct Blue 15 (desalted industrial grade) in male F344/N rats, as indicated by benign and malignant neoplasms of the skin, Zymbal's gland, preputial gland, liver, oral cavity, and small and large intestine. Increased incidences of mononuclear cell leukemia and neoplasms of the brain may have been related to chemical administration. There was clear evidence of carcinogenic activity of C.I. Direct Blue 15 in female F344/N rats, as indicated by benign and malignant neoplasms of the skin, Zymbal's gland, clitoral gland, liver, oral cavity, small and large intestine, and uterus, and by mononuclear cell leukemia.