Subacute oral toxicity of tri-n-butyl phosphate in the Sprague-Dawley rat

Effects of TRI-n-butyl phosphate on pregnancy in rats

A teratological study was carried out on the plasticizer tri-n-butyl phosphate (TBP). Pregnant Wistar rats were treated orally on days 7-17 of gestation with TBP at 0, 100, 200, 400 or 800 mg/kg/day in the dose-finding study and 0, 62.5, 125, 250 or 500 mg/kg/day in the subsequent teratological study. Caesarean sections were performed on day 20 of gestation. In the dose-finding study, all of the pregnant rats were killed by the treatment with TBP at 800 mg/kg/day. In the teratological study, salivation and depression of body weight gain, adjusted body weight gain and food consumption were observed at the higher doses of TBP. There were no significant differences between the groups in the incidence of dead or resorbed foetuses, the number of living foetuses and the body weights of living foetuses of both sexes. The incidence of rudimentary lumbar rib increased significantly at 500 mg/kg/day. There were two cases of malformation: a foetus with deformity of fore- and hind-limbs at 400 mg/kg/day in the dose-finding study and conjoined twins exhibiting three fore-limbs and four hind-limbs at 125 mg/kg/day in the teratological study. These malformations were rare in the background data of teratology, and the incidence of foetuses with malformations was not increased significantly. Therefore, TBP was considered not to be teratogenic in this study.

Assessment of the delayed neurotoxicity of tributyl phosphate, tributoxyethyl phosphate, and dibutylphenyl phosphate

There industrial organophosphorus compounds were tested for their ability to cause organophosphorus compound-induced delayed neurotoxicity (OPIDN) in the adult hen. The compounds tested were tributyl phosphate (TBP), tributoxyethyl phosphate (TBEP), and dibutylphenyl phosphate (DBPP). The acute oral LD50 of TBP and DBPP were estimated to be 1,863 and 1,500 mg/kg, respectively, and the dose equal to the LD50 was used as a test dose. The acute oral LD50 of TBEP was greater than 5,000 mg/kg and 5,000 mg/kg was used as a test dose. An oral dose of 750 mg tri-o-cresyl phosphate (TOCP) was used as a positive control. For the acute delayed neurotoxicity test, hens were given two test doses of the test materials 21 days apart and killed 21 days after the second dose. None of the hens given TBP, TBEP, or DBPP exhibited nerve damage or clinical signs which distinguished them from untreated control animals. A single dose of TOCP resulted in paralysis and a histopathological profile typical of a distal neuropathy. For the assay of the inhibition of esterases, hens were killed 24 hours after a single dose equal to the greater of either the LD50 or 5000 mg/kg. TOCP administration resulted in over 90% inhibition of brain neurotoxic esterase (NTE), but none of the other three compounds inhibited NTE to an extent (greater than 70%) which would be expected to result in OPIDN. Administration of TOCP, TBEP, or DBPP resulted in approximately a 70% decrease in plasma butyrylcholinesterase (BuChE) activity. TBP caused a 2-3 fold increase in BuChE activity. TBEP administration resulted in about 45% inhibition of acetycholinesterase (AChE) in brain. These results indicate that TBP, TBEP, and DBPP are all unlikely to cause OPIDN with any single sublethal dose.

Induction of urinary bladder hyperplasia in Sprague-Dawley rats orally administered tri-n-butyl phosphate

The effects of tri-n-butyl phosphate (TBP) were investigated in the Sprague-Dawley rat over an 18-wk period. Groups of randomized female (average weight [AW] = 206 +/- 10 g) and male (AW = 294 +/- 13 g) rats were divided into low-dose, high-dose, and control groups (12 rats/sex X group). Tri-n-butyl phosphate was administered by gavage once a day for 5 days/wk over an 18-wk period. Low-dose animals received 0.20 g/kg X day throughout the experiment and high-dose animals received 0.30 g/kg X day for the first 6 wk. For the remaining 12 wk, the high-dose level was increased to 0.35 g/kg X day. Histopathological examination of tissues revealed that all test rats examined developed diffuse hyperplasia of the urinary bladder epithelium. Similar changes were not found in the control animals.