Tricresyl phosphate is an organophosphate plasticizer widely used in vinyl plastics and as a fire retardant additive for hydraulic fluids. Toxicology and carcinogenesis studies were conducted by administering a mixed isomer preparation of 79% tricresyl phosphate esters (consisting of 21% tri- m-cresyl phosphate, 4% tri- p-cresyl phosphate, less than 1% tri- o-cresyl phosphate, and other unidentified tricresyl phosphate esters) by gavage to groups of F344/N rats and B6C3F1 mice for 16 days and 13 weeks, and in feed to groups of F344/N rats and B6C3F1 mice for 13 weeks and 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium and cultured Chinese hamster ovary cells.
Sixteen-day gavage study in rats
Groups of 10 male and 10 female rats received tricresyl phosphate in corn oil by gavage at doses of 0, 360, 730, 1,450, 2,900, or 5,800 mg/kg body weight, 5 days per week, for a total of 13 or 14 doses in a 16-day period. One female receiving 1,450 mg/kg and five males and eight females receiving 2,900 mg/kg died before the end of the study. Final mean body weights of male and female rats that received 1,450, 2,900, or 5,800 mg/kg were significantly lower than those of the controls. Necrosis of the mandibular lymph node, spleen, and thymus occurred primarily in rats receiving 2,900 and 5,800 mg/kg. Diffuse aspermatogenesis occurred in the testes of male rats that received 2,900 and 5,800 mg/kg. Changes in neurobehavioral parameters in groups that received 1,450, 2,900, or 5,800 mg/kg were confounded by mortality and reduced body weights and were not attributed to a direct neurotoxic response.
Sixteen-day gavage study in mice
Groups of 10 male and 10 female mice received tricresyl phosphate in corn oil by gavage at doses of 0, 360, 730, 1,450, 2,900, or 5,800 mg/kg body weight, 5 days per week, for a total of 13 or 14 doses in a 16-day period. Five males and all females that received 1,450 mg/kg, all mice that received 2,900 mg/kg, and four males and one female that received 5,800 mg/kg died before the end of the study. Final mean body weights of male mice that received 1,450 and 5,800 mg/kg were significantly lower than that of the controls. Final mean body weights of female mice that received 360, 730, or 5,800 mg/kg were significantly greater than that of the controls. Necrosis of the mandibular lymph node, thymus, and spleen occurred primarily in mice receiving 2,900 and 5,800 mg/kg. Hindlimb grip strengths of male mice that received 360 and 1,450 mg/kg and male and female mice that received 730 and 5,800 mg/kg were significantly lower than those of the controls at the end of the study.
Thirteen-week gavage study in rats
Groups of 10 male and 10 female rats received tricresyl phosphate in corn oil by gavage at doses of 0, 50, 100, 200, 400, or 800 mg/kg body weight. All rats survived to the end of the study. Final mean body weights of male rats receiving 200, 400, and 800 mg/kg were significantly lower than that of the controls. Cytoplasmic vacuolization of the adrenal cortex occurred in all dosed groups and the severity increased with dose. Ovarian interstitial cell hypertrophy occurred in all dosed groups of females. Atrophy of the seminiferous tubules occurred in male rats that received 400 and 800 mg/kg. There were no biologically significant changes in neurobehavioral parameters in rats.
Thirteen-week gavage study in mice
Groups of 10 male and 10 female mice received tricresyl phosphate in corn oil by gavage at doses of 0, 50, 100, 200, 400, or 800 mg/kg body weight. All mice survived to the end of the study. Final mean body weights of male mice receiving 200 mg/kg and of male and female mice receiving 400 and 800 mg/kg were significantly lower than those of the controls. Cytoplasmic vacuolization of the adrenal cortex occurred in all dosed groups of mice and the severity increased with dose. Ovarian interstitial cell hypertrophy was present in all dosed groups of female mice. Multifocal degeneration of the spinal cord occurred in males and females that received 100, 200, 400, and 800 mg/kg, and multifocal degeneration of the sciatic nerve occurred in males that received 200, 400, and 800 mg/kg and females that received 100, 200, 400, and 800 mg/kg. Hindlimb grip strengths of male mice that received 200, 400, or 800 mg/kg were significantly lower than that of the controls at the end of the study.
Thirteen-week feed study in rats
Groups of 10 male and 10 female rats were fed diets containing 0, 900, 1,700, 3,300, 6,600, or 13,000 ppm of tricresyl phosphate. All rats survived to the end of the study. Final mean body weights of males and females exposed to 6,600 and 13,000 ppm and females exposed to 3,300 ppm were significantly lower than those of controls. Feed consumption by male and female rats exposed to 13,000 ppm was lower than that by controls during the first week of the study. Dietary levels of 900, 1,700, 3,300, 6,600 or 13,000 ppm tricresyl phosphate were estimated to deliver daily doses of 55, 120, 220, 430, or 750 mg/kg body weight (males) and 65, 120, 230, 430, or 770 mg/kg (females). There were no biologically significant changes in neurobehavioral parameters in rats.
Cytoplasmic vacuolization of the adrenal cortex occurred in all exposed groups of rats. Hyperplasia of ovarian interstitial cells and inflammation of the ovarian interstitium occurred in all exposed groups of females. Renal papillary edema and renal papillary necrosis occurred in 13,000 ppm males and females and in 6,600 ppm females. Basophilic hypertrophy of the pituitary gland pars distalis and atrophy of the seminiferous tubules occurred in 6,600 and 13,000 ppm males.
Dose selection for the 2-year study in rats was based on lower mean body weights; toxic responses observed in the kidney, pituitary gland, and testis of males and the kidney of females exposed to 6,600 and 13,000 ppm; the presence of cytoplasmic vacuolization of the adrenal cortex in exposed males and females; and the occurrence of ovarian interstitial cell hyperplasia in females exposed to 900 and 1,700 ppm.
Thirteen-week feed study in mice
Groups of 10 male and 10 female mice were fed diets containing 0, 250, 500, 1,000, 2,100, or 4,200 ppm of tricresyl phosphate. All mice survived to the end of the study. Mean body weights of 4,200 ppm males and of females exposed to 2,100 and 4,200 ppm were lower than those of controls throughout the study. Feed consumption by females exposed to 1,000, 2,100, or 4,200 ppm was lower than that by controls during week 12. Dietary levels of 250, 500, 1,000, 2,100, or 4,200 ppm tricresyl phosphate were estimated to deliver average daily doses of 45, 110, 180, 380, or 900 mg/kg body weight (males) and 65, 130, 230, 530, or 1,050 mg/kg (females). Interpretation of grip strength changes observed in groups receiving 2,100 or 4,200 ppm were confounded by the reduced body weights of these groups.
Cytoplasmic vacuolization of the adrenal cortex occurred in all exposed groups of male and female mice with the exception of 250 ppm males. Papillary hyperplasia of the gallbladder mucosa occurred in male mice exposed to 500 ppm or more and in female mice exposed to 1,000 ppm or more. Axonal degeneration occurred in males and females exposed to 2,100 and 4,200 ppm and females exposed to 1,000 ppm. Renal tubule regeneration occurred in all 4,200 ppm male mice.
Dose selection for the 2-year study in mice was based on the presence of axonal degeneration at concentrations of 1,000 ppm or more and cytoplasmic vacuolization of the adrenal cortex at concentrations of 500 ppm or more in males and in all exposed groups of females.
Two-year feed study in rats
Groups of 95 male and 95 female rats were fed diets containing 0, 75, 150, or 300 ppm of tricresyl phosphate. An additional group of 95 male and 95 female rats were fed diets containing 600 ppm of tricresyl phosphate for 22 weeks and then received only control feed. After 3, 9, and 15 months of chemical exposure, up to 15 males and 15 females per group were evaluated for forelimb and hindlimb grip strength, then necropsied and evaluated for histopathologic lesions.
Survival, mean body weights, and feed consumption
Survival of exposed rats was similar to that of controls. The final mean body weights of all exposed groups of males and females were similar to those of the controls. Feed consumption by exposed groups of male and female rats was similar to that by the controls. Dietary levels of 75, 150, or 300 ppm tricresyl phosphate were estimated to deliver average daily doses of 3, 6, or 13 mg/kg body weight (males) and 4, 7, or 15 mg/kg (females).
Pathology findings
There were no chemical-related increased incidences of neoplasms in rats. Cytoplasmic vacuolization of the adrenal cortex occurred in 600 ppm males and 150, 300, and 600 ppm females at the 3-month interim evaluation. At 9 and 15 months, cytoplasmic vacuolization occurred only in female rats, primarily in the 300 ppm group. Cytoplasmic vacuolization of the adrenal cortex and ovarian interstitial cell hyperplasia occurred in female rats exposed to 300 ppm throughout the 2-year study and the incidence and severity were significantly increased at the end of the study.
Two-year feed study in mice
Groups of 95 male and 95 female mice were fed diets containing 0, 60, 125, or 250 ppm of tricresyl phosphate. After 3, 9, and 15 months of chemical exposure, up to 15 males and 15 females per group were evaluated for forelimb and hindlimb grip strength, then necropsied and evaluated for histopathologic lesions.
Survival, mean body weights, and feed consumption
Survival of exposed groups of male and female mice was similar to that of the controls. The final mean body weights of males and females receiving tricresyl phosphate were similar to those of controls. Feed consumption by exposed groups of male and female mice was similar to that by the controls. Dietary levels of 60, 125, or 250 ppm tricresyl phosphate were estimated to deliver average daily doses of 7, 13, or 27 mg/kg body weight (males) and 8, 18, or 37 mg/kg (females).
Pathology findings
There were no chemical-related increased incidences of neoplasms in mice. Ceroid pigmentation of the adrenal cortex occurred in all groups of mice throughout most of the 2-year study, with the exception of 60 and 125 ppm females at the 3-month interim evaluation; however, the severity was markedly increased in female mice receiving 250 ppm. Incidences of clear cell foci, fatty change, and ceroid pigmentation of the liver were significantly increased in male mice that received 125 or 250 ppm.
Genetic toxicology
Tricresyl phosphate was not mutagenic in Salmonella typhimurium strains TA98, TA100, TA1535, or TA1537, nor did it induce chromosomal aberrations or sister chromatid exchanges in cultured Chinese hamster ovary cells. These in vitro assays were all conducted with and without exogenous metabolic activation (S9).
Conclusions
Under the conditions of these 2-year feed studies, there was no evidence of carcinogenic activity of tricresyl phosphate in male or female F344/N rats that received 75, 150, or 300 ppm. There was no evidence of carcinogenic activity of tricresyl phosphate in male or female B6C3F1 mice that received 60, 125, or 250 ppm.
Nonneoplastic lesions associated with exposure to tricresyl phosphate included cytoplasmic vacuolization of the adrenal cortex and ovarian interstitial cell hyperplasia in female rats, increased incidences of clear cell focus, fatty change, and ceroid pigmentation of the liver in male mice, and increased severity of ceroid pigmentation of the adrenal cortex in female mice.