Toxicology and Carcinogenesis Studies of C.I. Pigment Red 23 (CAS No. 6471-49-4) in F344 Rats and B6C3F1 Mice (Feed Studies).

C.I. Pigment Red 23 is a bluish red commercial dye used as a coloring agent in paints, inks, rubber, plastics, lacquers, and paper. Toxicology and carcinogenicity studies were conducted by feeding groups of rats and mice diets containing C.I. Pigment Red 23 (greater than 96% pure) for 17 days, 13 weeks, and 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium and in Chinese hamster ovary cells. 17-Day Studies: Groups of five rats and five mice of each sex were fed diets containing 0, 6,000, 12,500, 25,000, 50,000, or 100,000 ppm C.I. Pigment Red 23 for 15 to 17 days. All rats and all female mice lived until the end of the studies. Two male mice in the 12,500 ppm dose group died accidentally. No other deaths occurred among male mice. Final mean body weights of rats and mice receiving C.I. Pigment Red 23 were within 10% of those of the controls. Feed consumption by exposed animals was similar to that of the controls. Hematocrit value, hemoglobin concentration, and erythrocyte count were decreased in the 50,000 and 100,000 ppm groups of rats. A corresponding decrease was not seen in mice. Absolute and relative organ weights of exposed animals were generally similar to those of the controls. No chemical-related gross lesions were seen in rats or mice. 13-Week Studies: Groups of 10 rats and 10 mice of each sex were fed diets containing 0, 3,000, 6,000, 12,500, 25,000, or 50,000 ppm C.I. Pigment Red 23 for 13 weeks. All rats and mice lived until the end of the studies. Final mean body weights of rats and mice receiving C.I. Pigment Red 23 were within 10% of those of the controls. Feed consumption by exposed animals was similar to that of the controls. In 50,000 ppm male rats, hematocrit and hemoglobin concentrations and erythrocyte counts were significantly less than those of the controls. In female rats receiving 3,000, 6,000 and 50,000 ppm C.I. Pigment Red 23, lymphocyte counts were significantly higher than the control values. Leukocyte counts in 3,000 ppm females were also significantly increased. Female mice in the 6,000 ppm dose group had significantly lower hematocrit and hemoglobin concentrations than did untreated females. Hematology parameters in exposed males were similar to those of untreated males. There were no biologically significant differences in organ weights among dosed and control rats. Absolute and relative liver weights of male mice receiving 12,500 ppm C.I. Pigment Red 23 were significantly increased compared to those of the controls. Absolute and relative thymus weights for all but 12,500 ppm female mice were significantly lower than those of the controls. No chemical-related gross or histopathologic lesions occurred in rats or mice. 2-Year Studies: Survival, Body Weights, Feed Consumption, and Clinical Findings Because levels of C.I. Pigment Red 23 as high as 50,000 or 100,000 ppm in the feed did not adversely affect survival and mean body weights in the 17-day and 13-week studies, nor cause any chemical- related lesions, doses of 0, 10,000, 25,000, or 50,000 ppm were selected for the 2-year studies. Doses higher than 50,000 ppm (5%) are not used in 2-year studies because they may lead to excessive dilution of nutrients in feed which in turn could produce nutritional deficiencies. Survival rates of mid- and high-dose male and of high-dose female rats were significantly greater than those of the controls, due primarily to a chemical related decreased incidence of mononuclear cell leukemia in these groups (survival in male rats: control, 22/50, low-dose, 29/50, mid-dose, 36/50, high-dose, 35/51; female rats: 29/50, 34/50, 33/50, 40/50). Survival of mice was not affected by the administration of C.I. Pigment Red 23, although survival of low-dose male mice was significantly lower than that of controls (male mice: 29/51, 17/53, 27/52, 30/51; female mice: 35/50, 34/49, 36/50, 35/49). The decreased survival in the low- dose males was associated with evidence of body trauma and secondary septicemia caused by fighting. From approximately week 20 of the study, the group mean body weight, the group mean body weights of exposed female rats were consistently lower than those of controls; at week 101, mean body weights of mid- dose (25,000 ppm) and high-dose (50,000 ppm) females were 6% and 8% less, respectively. The final mean body weights of exposed male rats and male and female mice were similar to those of controls. Feed consumption values for exposed male and female rats and mice were similar to those of the controls and there were no clinical signs associated with the administration of C.I. Pigment Red 23. Pathology Findings: Renal tubule adenomas occurred in two high- dose male rats. Renal tubule carcinomas occurred in one high-dose male and one mid-dose male rat. No renal tubule neoplasms were seen in the controls. Renal tubule neoplasms are uncommon and have occurred in 8/499 (1.6%) untreated historical controls with a range of 0% to 6%. The residual halves of kidneys from control and high-dose males were step sectioned and examined; renal tubule adenomas were observed in a control male and in two additional high- dose males. Because of the low numbers of renal neoplasms, it is uncertain if they were related to chemical administration. The incidence of renal tubule hyperplasia (3/50, 6/48, 5/50, 8/50) and the mean severity of nephropathy were also slightly increased in high-dose male rats. The incidence of mononuclear cell leukemia occurred with a significant negative trend in exposed male and female rats. No chemical-related increases in the incidence of neoplasms were observed in mice of either sex. There was a chemical-related increase in the incidence of hyperplasia (male mice: 0/49, 1/48, 1/50, 7/48; female mice: 6/49, 14/49, 43/50, 47/49) and hyperkeratosis of the forestomach epithelium attributed to chemical administration. Genetic Toxicology: C.I. Pigment Red 23 was mutagenic in Salmonella typhimurium strains TA100, TA1537, and TA98 with and without exogenous metabolic activation (S9), but it was not mutagenic in strain TA1535. C.I. Pigment Red 23 induced sister chromatid exchanges in Chinese hamster ovary cells in the absence of S9, but not with S9 activation. The pigment was negative for the induction of chromosomal aberrations in Chinese hamster ovary cells both in the presence and absence of S9. Conclusions: Under the conditions of these 2-year feed studies, there was equivocal evidence of carcinogenic activity of C.I. Pigment Red 23 in male F344 rats as evidenced by a marginally increased incidence of renal tubule cell neoplasms. There was no evidence of carcinogenic activity of C.I. Pigment Red 23 in female F344 rats fed diets containing 10,000, 25,000, or 50,000 ppm. Mononuclear cell leukemia occurred with a decreased incidence in male and female rats receiving C.I. Pigment Red 23. There was no evidence of carcinogenic activity of C.I. Pigment Red 23 in male and female B6C3F1 mice fed diets containing 10,000, 25,000 or 50,000 ppm. The severity of kidney nephropathy was increased in exposed male rats. In mice, C.I. Pigment Red 23 caused an increase in hyperkeratosis and epithelial hyperplasia of the fore- stomach. Synonyms: 2-Naphthalenecarboxamide; 3-hydroxy-4-((2-methoxy-5- nitrophenyl)azo)-N-(3- nitrophenyl); 3-hydroxy-4-((2-methoxy-5- nitrophenyl)azo)-3 -2-naphthanilide; Alkali Resistant Red Dark; Calcotone Red 3B; Carnation Red Toner B; CI 12355; Congo Red R- 138; Fenalac Red FKB Extra; Malta Red X2284; Naphthol Red B; Naphthol Red T Toner 35- 6001; Naphthol Red Deep 10459; Pigment Red BH; Rubescence Red MT-21; Sanyo Fast Red 10B; Sapona Red Lake RL-6280; Sengale Light Rubin RG; Textile Red WD-263