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Description of key information

Based on physico-chemical characteristics, particularly water solubility and octanol-water partition coefficient absorption via oral, dermal and inhalation route is likely to occur. Intracellular concentration is likely to be higher than extracellular due to the lipophilicity of TBPPI. Hydrolytic and metabolic conversion into tert-butyl hydroperoxide and pivalic acid is expected and conjugation of Phase I-metabolites may further increase hydrophilicity. Metabolites of TBPPI are considered to be less toxic than TBPPI itself. Excretion via urine is assumed to be the main excretion pathway of metabolites formed due to their molecular weight (<300 g/mol in rat). Bioaccumulation of TBPPI itself and its hydrolysis products is not likely to occur based on their physico-chemical properties.

Key value for chemical safety assessment

Bioaccumulation potential:
no bioaccumulation potential

Additional information

Toxicological profile of tert-butyl peroxypivalate (TBPPI)

An acute oral toxicity study conducted with TBPPI with a purity of 75 % using rats revealed a LD50 value of 4169 mg/kg bw. An acute inhalation toxicity study conducted with TBPPI of a purity of 75 % using rats revealed a LC50 value of 7.8 mg/L. In an acute dermal toxicity study with rats a LD50 of 2500 mg/kg bw was determined for TBPPI with a purity of 75 %.

In an in vivo skin irritation and corrosion study, TBPPI with a purity of 75 % caused skin irritation effects when applied to rabbit skin. No corrosive effects were observed. An eye irritation test performed with 75 % TBPPI on rabbits showed that the substance caused only slight effects on the rabbit’s eye and was not considered to be an eye irritant. Within acute inhalation studies available TBPPI was found to be irritating to the respiratory system. A guinea pig maximisation test revealed that TBPPI can cause skin sensitisation.

TBPPI did induce reverse mutations in a bacterial reverse mutation test (Ames test) with five Salmonella typhimurium strains and two Escherichia coli strains. The mutagenic response was depended on the bacterial strain and on the presence of a metabolic activation system (S9 liver homogenate). The chemical caused an increase in the reverse mutation frequency in the tester strains TA 98, TA 100, TA 1537, TA 102, WP2 uvra (pKM101) and WP2 (pKM101) in the presence of acroclor-induced rat liver S9 and in tester strains TA 100, TA 1537, TA 102 and WP2 (pKM101) in the absence of S9. In a second Ames test no induction of reverse mutations were observed. The chemical did not induce a mutagenic response in an in vitro mammalian cell gene mutation test (HPRT assay) performed on CHO-K1 cells both in the absence and presence of metabolic activation. In a further in vivo micronucleous test TBPPI did not cause an increase in the frequency of micronucleated polychromatic erythrocytes in mice and was therefore considered as not mutagenic in this test.

A 14 day dose range finding study using oral administration of TBPPI was performed in male and female Wistar rats in order to obtain first information on the toxic potential of the test item after long-term administration to allow a dose-setting for a combined repeated dose toxicity study with the reproduction/developmental toxicity screening test. The chemical was administered orally (by gavage) once a day for a total of 14 days at 0 (vehicle control), 50, 250 and 750 mg/kg bw/day. No mortality was observed through this study. The test substance caused a reduced food intake and, in turn, a reduced body weight particularly in male rats treated with the high dose of 750 mg/kg bw/day. Furthermore, a test item influence on renal and/or hepatic function appeared in the high dose group as indicated by a significant increase of activity of alanine aminotransferase and aspartat aminotransferase and elevated concentrations of total protein, total bilirubin, creatinine and urea in the male species only. Also, test item related changes in the organ pathology were found. Increased liver weight in females and adrenal glands weight in males and smaller than normal thymus (male and female) and prostate reflected a test item influence at 750 mg/kg bw/day. Salivation was observed in male and female animals of the mid dose group and no test item related adverse effects were observed in the low dose group. Based on these results the following three doses were selected for the aforementioned combined repeated dose toxicity study with the reproduction/developmental toxicity screening study: 50, 150 and 310 mg/kg bw/day.

 

The main study revealed no mortality of male and female animals/dams exposed to TBPPI. Test item related salivation appeared in the high and mid dose group. A slightly decreased food consumption and, in turn, a reduced body weight in males and in dams during lactation were observed in the high dose group. No adverse effects were found in haematology and clinical chemistry. Furthermore, no macroscopic and histological alterations were observed in any dosage group. An elevated mean weight of kidneys in male rats was observed at 310 mg/kg bw/day without corresponding histological findings. There were no differences between the control and test item treated groups in the reproductive performance of male and female animals and in delivery data of dams. A test item related effect on the offspring development was observed in the significantly higher number and percentage of extra uterine mortality in 310 mg/kg bw/day group between postnatal days 0 and 4, and in the significantly less litter weight and litter weight gain and mean pup’s weight and weight gain at 310 mg/kg bw/day. These effects were probably a consequence of the observed maternal systemic effect (reduced body weight and food consumption during lactation period). However, no structural or visceral malformations were observed in the offspring at any dosage level. Based on these observations the respective NOAEL for systemic effects in male and female rats was set to 150 mg/kg bw/day. The NOAEL for reproductive performance of the male and female rats was evaluated to be 310 mg/kg bw/day and the NOAEL for the offspring was determined to be 150 mg/kg bw/day.

 

In order to assess reversibility, persistence or delayed occurrence of potential toxicological effects a 90-day toxicity study followed by a 28-day recovery period was performed with tert-butyl 3,5,5-trimethylperoxyhexanoate (TBPIN), a structural analogous substance of TBPPI. The test item was administered orally (by gavage) to Hsd.Brl.Han: Wistar rats once a day at 0 (vehicle control), 160, 40 and 10 mg/kg bw/day doses. There was no test item related mortality. Toxic signs related to the test item were not detected at any dose level at the daily and detailed weekly clinical observations and in the course of the functional observation battery. Salivation was observed in the male and female animals of the 160 or 40 mg/kg bw/day groups with variable frequency within a group but in a dose related manner regarding the incidence and onset. The body weight development and the daily mean food consumption of male and female animals was not affected by the test item. A test item influence on the estrous cycle was not detected. No test item-related changes were observed in investigated hematology or blood coagulation parameters. Clinical chemistry examinations did not reveal any pathologic changes in the examined parameters.

Although statistical significant increases of mean liver weights in male animals of all dose groups and of mean kidney weights in male animals of 160 and 40 mg/kg bw/day group were noted, all values remained within the historical control ranges. Sperm analysis did not reveal test item influence on the sperm cells (count, motility and morphology) at 160 mg/kg bw/day dose. Histopathology investigations revealed test item related hyaline–like droplets in the epithel cells of some proximal convoluted tubules in the kidney of male animals treated with 160, 40 and 10 mg/kg bw/day, which was accompanied by dilatation of tubuli in the distal area, at the border of cortical – medullary region at 160 and 40 mg/kg bw/day. The renal lesion was not present at the end of the recovery period and no additional renal lesions or increased cell turnover were determined. Based on immunohistochemistry examinations hyaline-like droplets at 160, 40 and 10 mg/kg bw/day doses in male rats could not be caused byα2u-globulin. However, in accordance with literature data (ECETOC, 2002) the isolated and reversible finding hyaline-like droplets in male rats has to be considered as a toxicological relevant, but not adverse effect. A NOEL of < 10 mg/kg bw/day for male animals and 10 mg/kg bw/day for female animals and a NOAEL of 160 mg/kg bw/day for male and female animals was determined for TBPIN.

 

A read-across justification is provided in IUCLID section 13 demonstrating the reliable use of data from TBPIN (source substance) for the hazard assessment of TBPPI.

 

TBPPI was also examined for its possible prenatal developmental toxicity in an OECD 414 study. Groups of 24 sperm-positive female Hsd. Brl. Han: Wistar rats were treated with TBPPI by oral administration daily at three dose levels of 50, 150 and 450 mg/kg bw/day from day 5 up to and including day 19 post coitum. A control group of 24 sperm positive females was included and these animals were given the vehicle sunflower oil. The treatment volume was 2 mL/kg bw. Reduced activity, piloerection, hypotonicity and hyperventilation of the animals as well as reduced food consumption, weight loss and lower body weight in the 450 mg/kg bw/day group as well as reduced body weight- and corrected body weight gain in the 150 mg/kg bw/day dose group was considered to be in association with the test item. TBPPI did not reveal any adverse effect on the preimplantation loss, early embryonic- and fetal death, number of implantation and the sex distribution of the fetuses moreover did not decrease the number of viable fetuses significantly. TBPPI did not increase the incidence of visceral variations, and caused no external malformations. Based on these observations the No Observed Adverse Effect Level (NOAEL) was determined as follows:

NOAEL (maternal toxicity): 50 mg/kg bw/day

NOAEL (developmental toxicity):150  mg/kg bw/day

  

Toxicokinetic analysis of tert-butyl peroxypivalate (TBPPI)

 

Tert-butyl peroxypivalate (TBPPI) is a colourless liquid at room temperature with a molecular weight of 174.2374 g/mol. The substance is soluble in water (1.5 g/L at 20°C). The log Pow of TBPPI was measured and determined to be 3.7 at 25°C. Based on this log Pow, a BCF of 32.6 L/kg wet-wt was calculated. The vapour pressure of TBPPI is approximately 402 Pa at 38°C. In an aqueous solution, TBPPI is degraded hydrolytically to tert-butyl hydroperoxide and 2,2-dimethylpropionic acid (pivalic acid). The half-life of TBPPI in an aqueous solution at 50°C is 4 h at a pH of 4. The extrapolated half-life at pH = 4, 7 and 9 at 20 °C are 247 hours, 319 hours and 309 hours, respectively.

Both hydrolysis substances have a lower log Pow value than TBPPI itself (approximately 0.846 for tert-butyl hydroperoxide and 1.8 at pH 2.5 for pivalic acid). Also the BCF values are lower as compared to TBPPI (approximately 3.16 L/kg wet-wt for both hydrolysis products). Water solubility of both hydrolysis products is higher than of TBPPI itself (> 691 g/L for tert-butyl hydroperoxide and 27.9 g/L for pivalic acid).

 

Absorption

Generally, oral absorption is favoured for molecular weights below 500 g/mol. This characteristic combined with the moderate lipophilic log Pow value and water solubility allow dissolution of TBPPI in the gastro-intestinal fluids and contact with the mucosal surface.

Administered without a vehicle in an acute oral toxicity study performed on rats, TBPPI (75 % solution) lead to a LD50 of 4169 mg/kg bw/day. Furthermore, long-term administration of TBPPI in a combined repeated dose toxicity study with the reproduction/developmental toxicity screening study indicate that the compound, and to a lower amount, its hydrolysis products became bioavailable.

In this regards, as indicated by the half-life values from the hydrolysis test, a small fraction of TBPPI will hydrolyze to tert-butyl hydroperoxide and pivalic acid following oral administration which is indicated by the relative long half-live in an aqueous solution at acidic to neutral conditions. The results of the hydrolysis tests at a pH range of 4 to 9 are somewhat representative for the conditions found in the GIT with the stomach having an acidic milieu (~ pH 1.4 to 4.5) and the intestine a slightly acidic to slightly alkaline milieu (~ pH 5 to 8).

Due to the lower log Pow values of the hydrolysis products, readily absorption through the GIT epithelium is assumed. Furthermore, molecular weights of the hydrolysis products combined with their relatively high water solubility (> 10 g/L) may allow the direct uptake into the systemic circulation through aqueous pores or via carriage of the molecules across the membrane with the bulk passage of water. 

Based on the vapour pressure of approximately 400 Pa TBPPI might become available for inhalation to a certain extend. If the substance would reach the lungs in its vapour or gaseous state, absorption directly across the respiratory tract epithelium by passive diffusion is likely to occur due to its log Pow value and water solubility. An acute inhalation toxicity study performed on rats using TBPPI in its aerosol form revealed a LC50 of 7.8 mg/L. Since specific effects of systemic toxicity were observed these results indicate systemic availability after inhalation.

Similarly, based on physico–chemical properties of TBPPI the substance is likely to penetrate skin as the logPow value and water solubility favour dermal penetration. It is general accepted that if a compound’s water solubility falls between 100-10000 mg/L, absorption can be anticipated to be moderate to high. Moreover, for substances with a logPow between 1 and 4, both penetration into stratum corneum and partition into the epidermis are likely to occur. These assumptions based on the physico-chemical properties of TBPPI are further supported by the results achieved from an acute dermal toxicity study performed on rabbits. During this study test item related mortality and specific effects of systemic toxicity were observed. The LD50 was 2500 mg/kg bw. However, TBPPI caused skin irritation, edema, and necrosis which in turn may favour direct absorption into the systemic circulation. When applied topically onto the skin of guinea pigs, sensitising effects were observed following an initial intradermal induction phase. This indicates that the substance has penetrated through the skin to initiate the immune response. However, the effects may also be caused by the formation of reaction products between TBPPI and molecules present in the skin (haptenation).

Taken together, physico-chemical properties and experimental data indicate bioavailability of TBPPI via oral, dermal and inhalation route.

 

Distribution

Assuming that TBPPI is absorbed into the body following oral intake, it may be distributed into the interior part of cells due to its lipophilic properties and in turn the intracellular concentration may be higher than extracellular concentration particularly in adipose tissues. However, slow hydrolysis of TBPPI into tert-butyl hydroperoxide and pivalic acid is likely to occur. As mentioned above, the physico-chemical properties especially the lower molecular weight and relatively high water solubility of the hydrolysis products favour systemic absorption. Direct transport through aqueous pores is likely to be an entry route to the systemic circulation. The results from the combined repeated dose toxicity study with the reproduction/developmental toxicity screening test indicate that, following absorption, the liver is the primary target organs affected by the chemical. No embryotoxicity/teratogenicity was observed in the reproduction and developmental performance. However, penetration through the placenta could not entirely be excluded. Postnatal mortality of the offspring observed during lactation is estimated to be a consequence of maternal systemic toxicity. Based on their BCF values both, the parent molecule TBPPI and its hydrolysis products have no potential to bioaccumulate in the human body.

 

Metabolism

Based on the structure of the molecule, TBPPI may be hydrolysed after being in contact with an aqueous solution as well as enzymatically. The first degradation product tert-butyl hydroperoxide may be converted by glutathione peroxidase into tert-butanol which in turn could be conjugated with glucuronic acid or sulfate to increase the compound’s hydrophilicity (Chance, B. et al. 1979). Oxidation of tert-butanol by ADH and AlDH is an alternative metabolic pathway resulting in 2,2-dimethyl-propionic acid (pivalic acid), the second degradation product of TBPPI. Pivalic acid is estimated to be conjugated with glucuronic acid or amino-acids like glutamine in order to ultimately facilitate excretion. Thus, metabolites are assumed to be less toxic than the parent compound which is further supported by the results obtained in the HPRT test in the presence of a metabolic activation system.

 

Excretion

As discussed above, TBPPI will be hydrolysed both after being in contact with an aqueous solution or enzymatically and will probably not be excreted in its unhydrolysed form. The degradation products tert-butyl hydroperoxide and pivalic acid have a low molecular weight (90.12 g/mol and102.132 g/mol, respectively), are miscible in water and thus may either directly be excreted by urine or further metabolised by Phase II enzymes before excretion.