Di-n-butyl phthalate (DBP) is a phthalate used in the manufacture of consumer products such as plastics and personal care products. Widespread exposure in the population occurs throughout life, including during pregnancy and lactation. Because limited data are available in both animals and humans to evaluate DBP as a human carcinogen, the National Toxicology Program conducted 2‑year studies of DBP in rats and mice. Time-mated female Sprague Dawley (Hsd:Sprague Dawley SD) rats were exposed to 0, 300, 1,000, 3,000, or 10,000 ppm DBP in feed during gestation and lactation. Postweaning, F1 offspring consumed diets with the same exposure concentrations as the dam for 2 years (n = 50/sex/exposure group). Male and female adult B6C3F1/N mice were exposed to 0, 1,000, 3,000, or 10,000 ppm DBP in feed for 2 years (n = 50/sex/exposure group). Estimated average chronic chemical consumption was 16–17, 54–57, 152–169, and 510–600 mg DBP/kg body weight/day (mg/kg/day) in rats in the 300, 1,000, 3,000, and 10,000 ppm groups, respectively, and 105–112, 329–347, and 1,306–1,393 mg/kg/day in mice in the 1,000, 3,000, and 10,000 ppm groups, respectively.
Two-year studies
In rats, no exposure-related effect in mortality between exposed and control groups was observed. DBP did not affect rat reproductive or littering parameters. Marginal F0 weight effects (≤6% difference from the control group) were observed during gestation and by the end of lactation; F1 male and female pup weights in the 10,000 ppm group were significantly decreased by 12% and 13%, respectively, compared to the control groups upon weaning. Throughout the postweaning period, F1 body weights were approximately within 20% of the control animals. At 2 years, the incidence of pancreatic acinus adenomas was slightly higher in the 10,000 ppm group compared to the control group in male rats only. Because pancreatic acinus adenomas and carcinomas are associated with peroxisome proliferator-activated receptor alpha activation—and have been observed with exposure to other phthalates—the marginal increase observed could have been related to chemical exposure. The male reproductive tract was a primary target system of DBP in rats. A high incidence of small or absent organs of the male reproductive tract and undescended testes occurred only in the 10,000 ppm group. Some gross lesions correlated with microscopic lesions in the testes (germinal epithelium atrophy), epididymis (hypospermia), and prostate and seminal vesicles (decreased secretory fluid) in the 10,000 ppm groups. Additional microscopic lesions in the reproductive tract in rats included seminiferous tubule dysgenesis, testicular interstitial cell hyperplasia, testicular edema, and fibrosis and granuloma of the rete testis.
In mice, there were no exposure-related effects on survival, and mean body weights were lower only in the 10,000 ppm groups compared to the control groups. There was no exposure-related increase in neoplasms. No gross lesions were observed in the male reproductive tract, but significantly increased incidences of germinal epithelium degeneration in the testes and exfoliated germ cells in the epididymal duct were observed microscopically. The lesions generally occurred only in the 10,000 ppm group and were fewer and less severe in the mouse study, which did not include perinatal exposure, compared to the rat study.
Other nonneoplastic lesions observed were generally limited to the 10,000 ppm group. These lesions were found in the liver (hepatocyte cytoplasmic alteration in male and female rats and mice and multinucleated hepatocytes in male mice), in the pituitary gland (pars distalis hypertrophy in male rats), and in the kidney (renal tubule hyperplasia in female mice).
Conclusions
Under the conditions of these 2‑year feed studies, there was equivocal evidence of carcinogenic activity of di-n-butyl phthalate (DBP) in male Hsd:Sprague Dawley SD rats based on marginal increases in the incidence of pancreatic acinus adenomas. There was no evidence of carcinogenic activity of DBP in female Hsd:Sprague Dawley SD rats at exposure concentrations of 300, 1,000, 3,000, or 10,000 ppm.
There was no evidence of carcinogenic activity of DBP in male or female B6C3F1/N mice at exposure concentrations of 1,000, 3,000, or 10,000 ppm.
Exposure to DBP increased incidences of gross lesions in the male reproductive system in rats and of nonneoplastic microscopic lesions in the male reproductive system (rats and mice), liver (male and female rats and mice), pituitary gland pars distalis (male rats), and kidney (female mice).
National Toxicology Program (NTP). 2021. NTP technical report on the toxicology and carcinogenesis studies of di-n-butyl phthalate (CASRN 84-74-2) administered in feed to Sprague Dawley (Hsd:Sprague Dawley SD) rats and B6C3F1/N mice. Research Triangle Park, NC: National Toxicology Program. Technical Report 600. https://doi.org/10.22427/NTP-TR-600