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Reference
Endpoint:
basic toxicokinetics
Type of information:
other: expert statement
Adequacy of study:
key study
Study period:
2010-07-28
Reliability:
2 (reliable with restrictions)
Reason / purpose:
reference to same study
Reason / purpose:
reference to other study
Qualifier:
no guideline followed
GLP compliance:
no
Remarks:
Doses / Concentrations:
Not applicable
Details on absorption:
Oral absorption is favoured for molecular weights below 500 g/mol which is the case for all three components. The substance is soluble in water. The log Pow values of 1.3 and 1.31 for the monomer and MIBK are favourable for absorption by passive diffusion. The dimer with a log Pow of 4.2 may be taken up by micellular solubilisation. As the substance is water soluble and the molecular weight is low, the test item may pass through aqueous pores or be carried through the epithelial barrier by the bulk passage of water. The test item revealed NOAELs of 150 mg/kg bw/day, 200 and 75 mg/kg bw/day in repeated dose and reproduction toxicity studies. Administered in an acute oral study test item leads to a LD50 of 1575.3 mg/kg bw/day. Therefore, it can be assumed that the substance becomes systemically available and direct absorption across the gastrointestinal tract epithelium will occur when applied orally. When administered orally the test item is expected to rapidly hydrolyze.

The highest vapour pressure of MIBK (2.9E+003) assumed a moderate availability for inhalation as a vapour. The vapour pressure of the two other constituents assumed less availability for inhalation. If the substance reaches the lung, the test item may be absorbed. The test item showed toxic effects after inhalation administration, in an acute inhalation toxicity study (LC50 = 1500 mg/m3). Together, this indicates systemic availability after inhalation and if bioavailable, acute toxicity via this route of administration.

Based on physical – chemical properties the dimer component is not likely to penetrate skin to a large extent as the high log Pow value of 4.2 does not favour dermal penetration. The two other components with log Pow values of 1.31 and 1.3 favour dermal penetration. Furthermore the substance is a skin corrosive and applied to the skin of guinea pigs, sensitizing effects were observed. This indicates the substance is dermal available.

Details on distribution in tissues:
When reaching the body the test item will be widely distributed due to low molecular weight and high water solubility. Based on its low BCF and log Pow values the test item is not considered to bioaccumulative in the human body. The 90-day repeated dose toxicity study revealed in necropsy findings (dark colored or dark reddish mottled lungs, dark red liver) and in histological examinations in both cases acute catarrhal-purulent tracheitis accompanied with abundant fibrinous exudation into the lumen and diffuse congestion and edema in the lungs as cause of the death. These lesions were probably due to intra-tracheal applications of the test item in both animals. A slight and reversible elevation of the percentage of reticulocytes was observed in a dose related manner in male and female animals at 150 and 50 mg/kg bw/day at the termination of the treatment period. Although all values were lying well within the historical background range, the slight elevation correlated with the slight changes in the splenic weight, therefore a test item influence cannot be excluded. These findings indicate that the molecules of the test item are well distributed in the body through the bloodstream.
Details on excretion:
Based on the water solubility and the molecular weight value, excretion via the urine is likely. As discussed above the test item will hydrolyse rapidly, and will thus not be excreted in its unhydrolysed form.


Metabolites identified:
no
Details on metabolites:
Neither in the in-vitro nor in the in-vivo studies, the test substance induced genetic toxicity effects in the presence of metabolic activation. The chromosome aberration test showed clastogenic effects in the absence of metabolic activation. The other studies showed no effects in the absence of metabolic activation. Cytotoxic effects were observed in all studies in the absence and in the presence of metabolic activation. No difference was found between cytotoxic effects with and without metabolic activation. Based on these results it can be assumed that the test substance is not enzymatically activated (toxified) during the metabolism as the metabolized substances showed no higher toxicity compared to the parent compound. Based on the structure of the molecule and its nature, metabolism in the human body will mainly consist of phase-II metabolising steps, leading to an even better water solubility for excretion.
Conclusions:
Based on physical-chemical characteristics, particularly water solubility, octanol-water partition coefficient and vapour pressure absorption may occur by the dermal and inhalation routes. This assumption is further supported by inhalative and dermal toxicity studies. Also the oral route uptake of the test item or its hydrolysis products is relevant. Bioaccumulation of the test item and the hydrolysis products is not likely to occur based on the physical-chemical properties. Excretion is expected to occur mainly via urine.

Description of key information

Based on physical-chemical characteristics, particularly water solubility, octanol-water partition coefficient and vapour pressure absorption may occur by the dermal and inhalation routes. This assumption is further supported by inhalative and dermal toxicity studies. Also the oral route uptake of the test item or its hydrolysis products is relevant. Bioaccumulation of the test item and the hydrolysis products is not likely to occur based on the physical-chemical properties. Excretion is expected to occur mainly via urine.

Key value for chemical safety assessment

Bioaccumulation potential:
no bioaccumulation potential

Additional information

Toxicological profile

An acute oral toxicity study with rats revealed a LD50-value of 1575.3 mg/kg bw. An acute inhalation toxicity study with rats revealed a LC50-value of 1500 mg/m3(solvent: DIP). In an acute dermal toxicity study with rats a LD50 of > 2000 mg/kg bw was determined.

In a skin irritation study corrosive effects were observed in rabbits. An eye irritation test showed that MIKP causes severe damage to the rabbit’s eye. A guinea pig maximization test revealed that MIKP induces skin sensitization cat. 1 (solvent: DIP).

MIKP was not mutagenic in a bacterial mutagenicity test (a reverse mutation test - Ames test) and in an in vitro read across HPRT study to MEKP (Methyl-ethylketone peroxide, CAS 1338-23-4) all in the presence and absence of metabolic activation (solvent used in the assays: acetone, TXIB/Diacetonalkohol). Clastogenic effects were observed in an in vitro chromosome aberration test in the absence of metabolic activation (solvent DIP). In the absence of S9-mix at the 48 h continuous exposure time test concentrations of 100 and 125 µg/mL caused statistically significant, dose related increases in the number of cells with chromosome aberrations both when gaps were included and excluded. In the presence of S9 mix, the test item did not induce a statistically significant or biologically relevant increase in the number of cells with chromosome aberrations. An in-vivo micronucleus test in bone marrow cells of the mouse with the test item showed no clastogenic effects with and without metabolic activation.

A 90 day oral toxicity read across study was performed with MEKP (solvent: TXIB/diacetone alcohol) in male and female Fischer, F344/DuCrl rats according to OECD guideline 408. Although all values remained within the historical control ranges, along with the elevated percentage of reticulocytes a test item effect might be supposed. There were no histological lesions related to the test item effect.One male and one female animal administered with 150 mg/kg bw/day died on Day 76 and 36 of the study, respectively. Decreased activity, dyspnea or cyanotic skin were noted for these animals 1-2 days before the death. In accordance with necropsy findings (dark colored or dark reddish mottled lungs, dark red liver), histological examinations revealed in both cases acute catarrhal-purulent tracheitis accompanied with abundant fibrinous exudation into the lumen and diffuse congestion and edema in the lungs as cause of the death. These lesions were probably due to intra-tracheal applications of the test item in both animals. Toxic signs related to the test item were not detected at any dose level (150, 50 or 20 mg/kg bw/day) at the daily and detailed weekly clinical observations and in the course of the functional observation battery. The body weight development of male and female animals was not affected by the test item. No test item related body weight, or body weight gain changes were observed with respect to controls at any dose level during the course of the study (150, 50 or 20 mg/kg bw/day).The daily mean food consumption was similar in animals of the control and test item treated groups (150, 50 and 20 mg/kg bw/day).There were no abnormalities in the eyes of animals in the high dose group at termination of the treatment (150 mg/kg bw/day).A slight and reversible elevation of the percentage of reticulocytes was observed in a dose related manner in male and female animals at 150 and 50 mg/kg bw/day at the termination of the treatment period. Although all values were lying well within the historical background range, the slight elevation correlated with the slight changes in the splenic weight, therefore a test item influence cannot be excluded. Clinical chemistry examinations did not reveal test item related toxic changes in the evaluated parameters (150, 50 and 20 mg/kg bw/day).A test item influence on the estrous cycle was not detected (150, 50 and 20 mg/kg bw/day).Sperm analysis did not reveal test item influence on the sperm cells (count, motility and morphology) at 150 mg/kg bw/day dose. Specific macroscopic alterations related to treatment with the test item were not observed at the terminal necropsy or at the end of the recovery period.A test item influence cannot be excluded in changes of the weights of spleen (absolute and relative to body and brain weight) in male and female animals at 150 mg/kg bw/day and in female animals at 50 mg/kg bw/day. Based on these observations the no observed adverse effect level (NOAEL) for Methyl-ethylketone peroxide (MEPK) was 150 mg/kg bw/day for male and females rats.Also a 28 -day oral (gavage) toxicity read across study was performed with MEKP (solvent: TXIB/diacetone alcohol) in male and female Fischer, F344/DuCrl rats according to OECD guideline 407. The test substance caused a series of unspecific and minor alterations in general appearance (reduced well-being), in body weights, feed consumption, haematology, clinical biochemistry and organ weights. None of the alterations gives a clear evidence for a target organ; none bears severe or life-threatening effects. Alterations partly returned to normal during the follow-up period. No test substance related findings were made in the low and mid dosed groups (20 and/or 65 mg/kg bw/day). There was no clear sex difference in the response to the test substance. At necropsy no test substance related or uncommon spontaneous findings were observed. There was no test substance related alteration noted histopathologically.Therefore, the No-observed-adverse-effect-level (NOAEL) of methyl-ethylketone peroxide was 200 mg/kg bw/day for male and female animals.

A reproduction/developmental toxicity screening test with the read across substance methyl-ethylketone peroxide (solvent: TXIB/DMP) was performed according to OECD 421. This study was conducted to provide preliminary information on the potential adverse effects of methyl-ethylketone peroxide on male and female reproductionBased on the results of this study, F0 parental systemic toxicity was observed at 100/75 mg/kg/day as mortality/moribundity, reductions in body weight and food consumption, and macroscopic and microscopic findings in the stomach. No signs of parental systemic toxicity were observed at 25 and 50 mg/kg/day; therefore, the no-observed-adverse-effect level (NOAEL) for parental systemic toxicity was 50 mg/kg/day.No effects on F0 reproduction were noted in animals administered methyl-ethylketone peroxide at dosage levels of 25, 50 or 100/75 mg/kg/day, therefore the NOAEL for F0 reproductive toxicity was 75 mg/kg/day. F1 growth and survival were unaffected by parental test article administration; however, because mean F1 pup body weights in the 100/75 mg/kg/day group were lower than control values, the NOAEL for F1 neonatal toxicity was 50 mg/kg/day. There were no differences between the vehicle control groups when F0 and F1 parameters were evaluated; therefore, the toxicity observed at the 100/75 mg/kg/day dosage level was due to the methyl-ethylketone peroxide and not to the diluent components.

A reproduction/developmental toxicity screening read across study with the read-across substance methyl-ethylketone peroxide (solvent: TXIB/diacetone alcohol) was performed according to OECD guideline 414. The read across substance was examined for its possible prenatal developmental toxicity.The death of one as well as clinical signs of three further pregnant females (squish breath, dyspnoea and breath with open mouth started in all cases immediately after drawing the gavage out of the esophagus) in the 200 mg/kg bw/day group were suspected to be due to an aspiration or inhalation of the test item hence as a consequence of a technical reason probably due to the properties of the test item at this concentration. The stomach and intestines of the dam which died before scheduled necropsy were empty and filled with gas. The necropsy findings (reddish mottled lungs, dark red liver) of the non-pregnant female in the 200 mg/kg bw/day group that died before scheduled termination might confirm the suspect of aspiration/asphyxia. There was no mortality and treatment related clinical signs and necropsy findings in the 65 and 20 mg/kg bw/day dose groups. A slight, but statistically significant reduction in the body weight gain was observed in the food consumption and body weight gain of the dams in the 200 mg/kg bw/day group between gestation days 11 and 17 which was attributed to an effect of the test item. There were no treatment related differences in the food consumption and body weight of the animals in the 65 and 20 mg/kg bw/day groups. The mean number of implantations, intrauterine mortality and sex distribution of the fetuses was not influenced by the treatment. There were no test item related differences in the fetal- and placental weight, body weight retardation and other external, visceral and skeletal variations. There were no fetal malformations found at external and skeletal examination. External hydrocephaly was found in one fetus as a malformation at visceral examination in the 200 mg/kg bw/day dose group which was judged to be unrelated from the treatment based on the historical control data. As a conclusion, based on these observations the No Observed Adverse Effect Level (NOAELs) were determined as follows: NOAEL (maternal toxicity): 65 mg/kg bw/day, NOAEL (developmental toxicity): 200 mg/kg bw/day

Toxicokinetic analysis

The test item is a colourless liquid at room temperature. The substance consists of 3 components 4-methylpentane-2,2-diyl dihydroperoxide (44865-41-0, monomer), dioxybis-4-methylpentane-2,2-diyl dihydroperoxide (53151-88-5, dimer), 4-Methyl-2-Pentanon (108-10-1, MIBK) with a molecular weight of 266.34 g/mol (dimer), 100.16 g/mol (MIBK) and 150.18 g/mol (Monomer). The substance is soluble in water (252 mg/L). The log Pow of the monomer was 1.3. The log Pow of the dimer was determined to be 4.2. The log Pow of MIBK was determined to be 1.31. Based on this log Pow a log BCF of 0.525 for the monomer and of 2.438 for the dimer was calculated. The log BCF of MIBK was calculated to be 0.531. The test item has a vapor pressure of 12.8 Pa (monomer), 2.9E+003 Pa (MIBK) and 0.0129 Pa (dimer) at 25 °C (estimated by QSAR). The KOC values were calculated to be 4413 L/kg (dimer, log Koc=3.6448), 70.03 L/kg (MIBK, log Koc=1.8453) and 13.42 L/kg (Monomer, log Koc=1.1279). Based on the physical chemical characteristic of organic peroxides, the test item can be expected to hydrolyse rapidly. The substance is readily biodegradable. The constituens of the test item have low BCF values. The highest log BCF value was calculated to be 2.438. The highest log Pow value of 4.2 is under the threshold of 4.5 for the B criterion in PBT assessment (according to Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.11: PBT/vPvB)

Absorption

Oral absorption is favoured for molecular weights below 500 g/mol which is the case for all three components. The substance is soluble in water. The log Pow values of 1.3 and 1.31 for the monomer and MIBK are favourable for absorption by passive diffusion. The dimer with a log Pow of 4.2 may be taken up by micellular solubilisation. As the substance is water soluble and the molecular weight is low, the test item may pass through aqueous pores or be carried through the epithelial barrier by the bulk passage of water. The test item revealed NOAELs of 150 mg/kg bw/day, 200 and 75 mg/kg bw/day in repeated dose and reproduction toxicity studies. Administered in an acute oral study the test item leads to a LD50 of 1575.3 mg/kg bw/day. Therefore, it can be assumed that the substance becomes systemically available and direct absorption across the gastrointestinal tract epithelium will occur when applied orally. When administered orally the test item is expected to rapidly hydrolyze.

The highest vapour pressure of MIBK (2.9E+003) assumed a moderate availability for inhalation as a vapour. The vapour pressure of the two other constituents assumed less availability for inhalation. If the substance reaches the lung, the test item may be absorbed. The test item showed toxic effects after inhalation administration, in an acute inhalation toxicity study (LC50 = 1500 mg/m3). Together, this indicates systemic availability after inhalation and if bioavailable, acute toxicity via this route of administration.

Based on physical – chemical properties the dimer component is not likely to penetrate skin to a large extent as the high log Pow value of 4.2 does not favour dermal penetration. The two other components with log Pow values of 1.31 and 1.3 favour dermal penetration. Furthermore the substance is a skin corrosive and applied to the skin of guinea pigs, sensitizing effects were observed. This indicates the substance is dermal available.

Distribution

When reaching the body the test item will be widely distributed due to low molecular weight and high water solubility. Based on its low BCF and log Pow values the test item is not considered to bioaccumulative in the human body. The 90-day repeated dose toxicity study revealed in necropsy findings (dark colored or dark reddish mottled lungs, dark red liver) and in histological examinations in both cases acute catarrhal-purulent tracheitis accompanied with abundant fibrinous exudation into the lumen and diffuse congestion and edema in the lungs as cause of the death. These lesions were probably due to intra-tracheal applications of the test item in both animals. A slight and reversible elevation of the percentage of reticulocytes was observed in a dose related manner in male and female animals at 150 and 50 mg/kg bw/day at the termination of the treatment period. Although all values were lying well within the historical background range, the slight elevation correlated with the slight changes in the splenic weight, therefore a test item influence cannot be excluded. These findings indicate that the molecules of the test item are well distributed in the body through the bloodstream.

Metabolism

Neither in the in-vitro nor in the in-vivo studies, the test substance induced genetic toxicity effects in the presence of metabolic activation. The chromosome aberration test showed clastogenic effects in the absence of metabolic activation. The other studies showed no effects in the absence of metabolic activation. Cytotoxic effects were observed in all studies in the absence and in the presence of metabolic activation. No difference was found between cytotoxic effects with and without metabolic activation. Based on these results it can be assumed that the test substance is not enzymatically activated (toxified) during the metabolism as the metabolized substances showed no higher toxicity compared to the parent compound. Based on the structure of the molecule and its nature, metabolism in the human body will mainly consist of phase-II metabolising steps, leading to an even better water solubility for excretion.

Excretion

Based on the water solubility and the molecular weight value, excretion via the urine is likely. As discussed above the test item will hydrolyse rapidly, and will thus not be excreted in its unhydrolysed form.

Summary

Based on physical-chemical characteristics, particularly water solubility, octanol-water partition coefficient and vapour pressure absorption may occur by the dermal and inhalation routes. This assumption is further supported by inhalative and dermal toxicity studies. Also the oral route uptake of the test item or its hydrolysis products is relevant. Bioaccumulation of the test item and the hydrolysis products is not likely to occur based on the physical-chemical properties. Excretion is expected to occur mainly via urine.

References

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ECHA (2008), Guidance on information requirements and chemical safety assessment, Chapter R.7c: Endpoint specific guidance.

IPCS & IOMC (2000). Concise International Chemical Assessment Document 26. Benzoic

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JECFA, 2002. Safety evaluation of certain food additives and contaminants. Fifty-seventh meeting of the Joint FAO/WHO Expert Committee on Food Additives, WHO Food Additives Series: 48. IPCS, WHO, Geneva.

Marquardt H., Schäfer S. (2004). Toxicology. Academic Press, San Diego, USA, 2nd Edition 688-689.

Mutschler E., Schäfer-Korting M. (2001). Arzneimittelwirkungen. Lehrbuch der Pharmakologie und Toxikologie. Wissenschaftliche Verlagsgesellschaft, Stuttgart, 2001

ECETOC Guidance (2002) Recognition of and Differentiation between, Adverse and Non-adverse effects in Toxicoloigal studies. Technical Report No. 85.

Nielsen, N.M., Bundgaard, H. (1987). Prodrugs as drug delivery systems. 68. Chemical and plasma catalayzed hydrolysis of various esters of benzoic acid: a reference system for designing prodrug esters of carboxylic acid agents. International Journal of Pharmaceutics, 39: 75-85.