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Description of key information

BBP has been tested in a number of repeated dose dietary studies in rodents (mainly rats) with durations of between 14 days and 2 years. The lowest NOAEL, 151 mg/kg bw/day, was obtained in a reliable 90-day dietary study in rats, with higher doses of 381 and 960 mg/kg bw/day resulting in histopathological changes in the pancreas of males, gross changes in the liver, and a statistically significant increase in relative kidney weight (Ford, 1981). A similar NOAEL, 160 mg/kg bw/day, was obtained in a 14-day rat study which reported testicular damage from 480 mg/kg bw/day (Lake et al. 1978). In 2-year studies the NOAELs ranged from 240-300 mg/kg bw/day in rats (NTP, 1982, 1997a), while a figure of 780 mg/kg bw/day was determined in an equivalent mouse study (NTP, 1982).
Two reliable GLP-compliant studies have been conducted in Sprague-Dawley rats exposed to BBP by inhalation (6 hours/day on 5 days/week), with no-observed-adverse-effect-concentrations (NOAECs) of 0.218 mg/l in the 13-week study (Roloff, 1982) and 1 mg/l in the 4-week study (Terrill, 1982). The only effect observed after 13 weeks’ exposure at 0.789 mg/l was increased relative liver and kidney weights (but with no accompanying histopathological findings).

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion
Dose descriptor:
NOAEL
151 mg/kg bw/day

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion
Dose descriptor:
NOAEC
218 mg/m³

Mode of Action Analysis / Human Relevance Framework

Additional information

Oral

In a reliable study, groups of 50 B6C3F1 mice of each sex were given BBP in the diet for 103 weeks at concentrations of 0, 6000 or 12000 ppm (providing around 0, 780 or 1560 mg/kg bw/day). The mice were observed daily for clinical signs of toxicity, body weight changes were recorded every 4 weeks, and the animals were sacrificed at 106 weeks. A comprehensive range of organs and tissues was examined for gross and microscopic changes. There was a dose-related decrease in mean body weights of males and females throughout the study. Statistical significance was not reported, but the reduction in body-weight gain appeared to be around 5% and 5-10% in low-dose males and females respectively, and 15% and 10-25% in high-dose males and females respectively. No other compound-related clinical signs were observed and survival was comparable in the control and treated groups. No toxic lesions were evident, and all histological changes observed were similar in both treated and control groups and were within the normal historical incidence limits in B6C3F1 mice. Similarly the neoplastic effects observed were deemed to be unrelated to administration of the test substance and also fell within the range of historical controls. The NOAEL was 6000 ppm (780 mg/kg bw/day) (NTP, 1982).  

The equivalent rat study involved dietary administration of BBP to groups of 50 Fischer 344/N rats of each sex for 103 weeks at concentrations of 0, 6000 or 12000 ppm (providing around 0, 300 or 600 mg/kg bw/day). The rats were observed twice daily for clinical signs of toxicity, body weight changes were recorded every 4 weeks, and the animals were sacrificed at 106 weeks. A comprehensive range of organs and tissues was examined for gross and microscopic changes. Data on male rats were considered unreliable as many of the animals (particularly in the high-dose group) died prematurely from internal haemorrhaging. In the females, there was a slight, dose-related decrease in body-weight gain throughout the study in the treated groups, but the reduction was less than 10% and is not considered of biological significance. Feed consumption was between 70-80% that of the controls. No treatment-related clinical effects were observed and no non-neoplastic adverse effects were evident on histological examination. The NOAEL was 6000 ppm (300 mg/kg bw/day), due to an increased incidence of mononuclear cell leukemia at the top dose (NTP, 1982).

 

In a subsequent 2-year dietary study in the same strain of rats, groups of 60 animals of each sex were given the test substance in the diet at up to 12000 ppm in males (500 mg/kg bw/day) and 24000 ppm in females (1200 mg/kg bw/day); similar groups of animals received the untreated diet. Blood was sampled from 10 animals of each sex at various time intervals for haematology and serum hormone levels. After 15 months of exposure these animals were evaluated for haematology, hormone levels, organs weights (epididymis, kidney, liver and testis) and histopathology. At study termination a comprehensive range of organs and tissues were examined microscopically for both neoplastic and non-neoplastic effects. Survival in all exposed groups was similar to that of the controls. A dose-related decrease in body-weight gain was seen throughout the study; during the later stages of the study the highest dose caused a decrease of about 10% in males and 25% in females, when compared to controls. There was a dose-related increase in the incidence of focal hyperplasia of the pancreatic acinar cells in males (8, 14, 18 and 24% in the control, low-, mid- and high-dose groups, respectively, apparently not statistically significant). The incidence of transitional epithelial hyperplasia of the urinary bladder in the female 24000 ppm group was significantly greater than that in the control group (20% versus 8%). In the kidney the incidences of nephropathy were increased in all treated groups but this was not dose-related, occurring in about the same number of animals for each treated group. Minimal transitional epithelial hyperplasia of the kidney was also increased in the treated females, but only reached statistical significance in the 12000 ppm (mid-dose) females. In males dosed at 12000 ppm, the incidence of pancreatic acinar cell adenomas was 41% (compared with 11% in control males) and one treated male had a pancreatic carcinoma (a neoplasm which apparently had not been observed in 1919 historical control males from NTP 2-year feed studies). In females in the 24000 ppm group, two pancreatic acinar cell adenomas were detected. The incidence of acinar focal hyperplasia was also increased in treated males, but not in females. Transitional epithelial papillomas of the urinary bladder were observed in two females in the 24000 ppm group (exceeding the range of historical controls from NTP 2-year feed studies) and in one control female. The high-dose females also showed a higher incidence of mild to moderate hyperplasia in the urinary bladder. NOAELs of 240 and 600 mg/kg bw/day were established in males and females respectively (NTP, 1997a).

The NTP also assessed the subchronic toxicity of BBP in a 26-week feeding study. Groups of 15 male rats were given 0, 300, 900, 2800, 8300 or 25000 ppm in the diet, equivalent to around 0, 30, 60, 180, 550 or 1660 mg/kg bw/day. Blood was collected for haematological examination at various intervals throughout the study and a comprehensive range of tissues and organs from the high-dose and control groups were examined microscopically on study termination. In addition, the testis, epididymis, seminal vesicle and prostate were examined in the other treated groups. Epididymal spermatozoal parameters were examined in the 0, 300, 8300 and 25000 ppm groups. At study termination, the mean body weight of the 25000 ppm group was 30% less than that of the control group. A minimal to mild macrocytic anaemia was detected at 30 days in the high dose group and continued throughout the study. The absolute weights of the testis, cauda and epididymis were reduced (P <0.01) in the 25000 ppm group, as was the absolute prostate weight, while relative liver and kidney weights were increased (P <0.01). Incidences of hypospermia and atrophy of the seminiferous tubules and hypospermia in the epididymis were significantly greater (P <0.01) in the high dose group, and the concentration of sperm in the cauda epididymal tissue was less than 1% of that in the control group. None of these effects were observed at the next dose down, 8300 ppm (equivalent to around 550 mg/kg bw/day). No insight was provided into the effects of the test substance on other tissues and organs. Thus, in this 26-week study in male rats, BBP given in the diet at 25000 ppm (equivalent to around 1660 mg/kg bw/day) caused degenerative changes to the testis and epididymis. The NOAEL was 8300 ppm (550 mg/kg bw/day) (NTP, 1997b).  

A reliable subchronic study in Wistar rats involved dietary administration of BBP to groups of 27 males and 27 females at concentrations of 2000, 5000 or 12000 ppm (providing mean daily BBP intakes of 151, 381 or 960 mg/kg bw for males and 171, 422 or 1069 mg/kg bw for females). Six of each sex were treated for 2 weeks, 6/sex for 6 weeks and 15/sex for 14 weeks. A control group of 45/sex received plain diet for 2, 6 or 14 weeks (9, 9 and 27/sex per time point respectively). Evaluation included clinical observation, body weight, haematology, clinical chemistry, urinalysis, organ weights, and gross and microscopic examination of a range of organs and tissues. Body weights were reduced in males at all dietary concentrations and in females at 12000 ppm, although this was associated with a reduced food consumption in males at 2000 and 5000 ppm. Relative weights of liver, kidney and caecum were increased at all dietary concentrations. Histopathological findings were observed only in males, at 5000 ppm and above, and included pancreatic lesions and gross pathological changes in the liver. The NOAEL was 2000 ppm (151 mg/kg bw/day) (Ford, 1981).

 

The EU RAR cites other repeated dose toxicity studies: a 90-day study in Sprague-Dawley rats established an NOAEL of 375 mg/kg bw/day, with increased relative liver and kidney weights at 750 mg/kg bw/day (Hammond et al., 1987); a 14-day study in Sprague-Dawley rats determined an NOAEL of 160 mg/kg bw/day, as one out of three males given 480 mg/kg bw/day showed testicular atrophy, while the top dose of 1600 mg/kg bw/day produced severe damage to the testes (Lake et al., 1978); in a 3-month oral study in beagles, the only effect reported was a decrease in body weight at 1852 mg/kg bw/day (Erickson, 1965).

 

Inhalation

Groups of 25 male and 25 female Sprague-Dawley rats were exposed by whole-body inhalation to BBP at concentrations of 0, 0.051, 0.218 or 0.789 mg/l (analytical) for 6 hours/day on 5 days/week. An interim sacrifice was performed on 10/sex/group after 7 weeks of exposure, and the remaining animals were sacrificed after 13 weeks of exposure. Evaluation included clinical observation, body weight, haematology, clinical chemistry, urinalysis, organ weights and macroscopic and microscopic examination of a range of organs and tissues. Urine-stained fur and chromodacryorrhea were observed in both sexes in the mid- and high-exposure groups. Although the investigators described these findings as "seemingly compound and dose-related", the EU RAR made no mention of chromodacryorrhea but stated that urine-stained fur, piloerection and alopecia "were not considered as reliable indicators of the test compound". Increased relative liver and kidney weights were seen at the top dose (although there were no accompanying histopathological findings), and males in this group had a marked decrease in serum glucose at terminal sacrifice, leading the EU RAR to set the NOAEC for this study at 0.218 mg/l (Roloff, 1982).

 

Groups of 20 male and 20 female Sprague-Dawley rats were exposed by whole-body inhalation to BBP at concentrations of 0, 0.36, 1.0 or 2.1 mg/l (analytical) for 6 hours/day on 5 days/week for 4 weeks. Evaluation included clinical observation, body weight and macroscopic examination of a range of organs and tissues. Treatment-related findings were seen only in the high-exposure group, with increased mortality (3 males and 4 females died or were sacrificed in extremis), decreased growth in both sexes, and atrophy of the spleen and reproductive organs in males. Effects on the skin and fur seen in all treatment groups were attributed to direct skin contact with large particles rather than a systemic effect from inhaling the test compound. The NOAEC was 1 mg/l (Terrill, 1982).

The Roloff study was used to derive DNELs for long-term systemic effects of inhalation exposure (0.78 mg/m3 for the general population, and 4.36 mg/m3 for workers). In addition, in route-to-route extrapolation from this inhalation study and the Tyl 2 -generation oral reproductive toxicity study to determine possible DNELs for the systemic effects of long-term dermal exposure, it was the Roloff study that provided the lowest figures (with DNELs of 4.5 and 12.6 mg/kg bw/day for the general population and workers, respectively).


Repeated dose toxicity: via oral route - systemic effects (target organ) digestive: liver; digestive: pancreas

Repeated dose toxicity: inhalation - systemic effects (target organ) digestive: liver; urogenital: kidneys

Justification for classification or non-classification

The results from repeated dose toxicity studies indicate that BBP does not need to be classified as a specific target organ toxicant following repeated oral or inhalation exposure, under the EU CLP regulations.