Reaction mass of 2,6-dimethylheptan-4-ol and 4,6-dimethylheptan-2-ol

Repeated dose toxicity: inhalation

Administrative data

Endpoint:

chronic toxicity: inhalation

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

A detailed justification for the grouping of these surrogate substances for the purposes of read across is provided in the 'read across justification' attached to section 13 of the IUCLID dossier.

Cross-reference

Cross-reference 1

Reason / purpose for cross-reference:

read-across source

Reference

Endpoint:

chronic toxicity: inhalation

Type of information:

experimental study

Remarks:

Supporting read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Study period:

2008

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study without detailed documentation

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

equivalent or similar to guideline

Guideline:

other: OECD Guideline 451 (Carcinogenicity Studies)

Deviations:

no

GLP compliance:

yes

Limit test:

no

Specific details on test material used for the study:

Read-across source substance

Species:

rat

Strain:

other: F344/N

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Taconic Laboratory Animals and Services (Germantown, NY)
- Age at study initiation: approximately 6 weeks old
- Housing: Individually housed
- Diet (e.g. ad libitum): NTP-2000 non-purified diet (irradiated wafers; obtained from Zeigler Brothers, Inc.) was available ad libitum except during exposure periods and changed weekly.
- Water (e.g. ad libitum): tap water was available ad libitum via an automatic watering system.
- Acclimation period: approximately 2 weeks


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 23 ± 3°C
- Humidity (%): 55 ±15%
- Air changes (per hr): 15±2
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Vehicle:

clean air

Details on inhalation exposure:

Inhalation exposures were conducted at BattelleToxicology Northwest Operations (Richland, WA). MIBK was pumped onto the heated surface of the study laboratory-designed wick generator, where it was vaporized.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The MIBK concentrations in the exposure chambers were monitored by an on-line gas chromatograph approximately every 28 min. Buildup and decay rates for chamber vapor concentrations were determined with animals present in the chambers and the time to achieve 90% of the target concentration after the beginning of vapor generation (T90) was 12 min. Evaluations of chamber uniformity and persistence and monitoring for MIBK degradation impurities were conducted periodically throughout the studies by gas chromatography. Chamber uniformity was maintained and no degradation was detected.

Duration of treatment / exposure:

2 years

Frequency of treatment:

6h/day, 5 days per week

Remarks:

Doses / Concentrations:
0, 450, 900, or 1800 ppm
Basis:
analytical conc.

No. of animals per sex per dose:

50/sex/dose

Control animals:

yes

Details on study design:

- Rationale for animal assignment (if not random): random

Positive control:

Not applicable

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Twice daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Weekly for the first 13 weeks, monthly until the last four months of the studies, every 2 weeks thereafter, and at the end of the studies.

BODY WEIGHT: Yes
- Time schedule for examinations: Body weights were recorded initially and then weekly for the first 13 weeks, monthly until the last four months of the studies, every 2 weeks thereafter, and at the end of the studies.

FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: No

FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: No

WATER CONSUMPTION: No

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: No

CLINICAL CHEMISTRY: No

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
HISTOPATHOLOGY: Yes.

Statistics:

The probability of survival was estimated by the product limit procedure of Kaplan and Meier (1958). Statistical analyses for possible dose-related effects on survival used Cox (1972) method for testing two groups for equality and Tarone (1975) life table test to identify dose-related trends. All reported P values for the survival analyses are two sided. Average severity values were analyzed for significance with the Mann–Whitney U test. The poly-k test was used to assess neoplasm and non-neoplastic lesion prevalence. This test is a survival-adjusted quantal-response procedure that modifies the Cochran–Armitage linear trend test to take survival differences into account. Unless otherwise specified, a value of k = 3 was used in the analysis of site-specific lesions. Tests of significance included pairwise comparisons of each exposed group with controls and a test for an overall exposure related trend. Continuity-corrected poly-3 tests were used in the analysis of lesion incidence, and reported P values are one sided.

Clinical signs:

effects observed, treatment-related

Mortality:

mortality observed, treatment-related

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

not specified

Gross pathological findings:

not specified

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

effects observed, treatment-related

Details on results:

Survival of the 1800 ppm males was significantly less than that of the controls (0 ppm, 32/50; 450 ppm, 28/49; 900 ppm, 25/50; 1800 ppm, 19/50). Mean body weights of 900 ppm male rats were 6–8% less after week 97 and 1800 ppm males were 5–8% less after week 89, than those of the chamber control group. Mean body weights and survival (0 ppm, 35/50; 450 ppm, 34/50; 900 ppm, 26/50; 1800 ppm, 32/50) of all exposed groups of females were similar to those of the controls.

Chronic progressive nephropathy (CPN) similar to that which occurs in aged rats was observed in males and females in all groups, including controls (Tables 1 and 2). In males, significant increases in incidence were observed at 1800 ppm and in severity at all exposure concentrations. The incidence of mineralization was also significantly increased at all exposure concentrations in males; severity was generally increased in exposed groups (Table 1). In female rats, increased incidences of CPN were significant in all exposed groups. The average severity of CPN ranged from minimal to mild and was increased in exposed females at 1800 ppm. In both sexes, changes consisted of a spectrum of lesions that included varying degrees of renal tubule dilatation with and without hyaline (proteinaceous) casts, multifocal degeneration, regeneration, and hypertrophy of the tubular epithelium; thickening of the tubular and glomerular basement membranes; glomerulosclerosis; interstitial fibrosis; and variable infiltrates of mononuclear inflammatory cells within the interstitium. Minimal CPN affected less than 10% of the renal parenchyma, and consisted of focal to multifocal regenerative renal tubules surrounded by a thickened basement membrane. These regenerative tubules were small and lined by cuboidal basophilic epithelial cells. Mild CPN affected approximately 10–39% of the renal parenchyma and consisted of multifocal clusters of regenerative renal tubules, tubules that contained protein, glomeruli with thickened basement membranes, and scattered infiltrates of predominantly lymphocytes and macrophages. Moderate CPN had similar but more severe and widespread changes including glomerular atrophy and variable interstitial fibrosis. Marked CPN was diffuse and of greater severity. Mineralization was generally of minimal to mild severity and consisted of linear deposits of lamellated mineral within the lumen or epithelial cells of the collecting tubules of the renal papilla. There were exposure concentration-related increases in minimal to mild transitional epithelial hyperplasia in the renal pelvis of male rats, which were significant at 900 and 1800 ppm (Table 1). Transitional epithelial hyperplasia consisted of focal proliferation of the transitional epithelium lining the renal pelvis; the affected epithelium appeared thickened and often formed papillary projections into the urinary space. In the single section analysis (standard evaluation) of the kidney in males (Table 1), increases in renal tubule hyperplasia were significantat 450 and 1800 ppm, and the severities in these groups were elevated. There were also slight increases in renal tubule adenoma, carcinoma, and adenoma or carcinoma (combined). There were significant positive trends for adenomas and adenomas or carcinomas (combined). Although not statistically significant, the incidences of renal tubule adenoma and renal tubule adenoma or carcinoma (combined) in the 900 and 1800 ppm groups and renal tubule carcinoma in the 1800 ppm group exceeded the historical ranges for chamber controls from inhalation studies fed NTP-2000 diet. In the extended evaluation of the kidneys (Table 1), additional renal tubule hyperplasias were observed in all exposed groups such that in the combined single and step section analysis, the incidences of hyperplasia in exposed groups were significantly greater than in the controls. Additional renal tubule adenomas were observed in all groups including the controls. No additional renal tubule carcinomas were observed. In the combined single and step section analysis of renal neoplasms, there were significant positive trends for renal adenoma and adenoma or carcinoma (combined) and the incidences of these lesions were significantly increased at 1800 ppm. Hyperplasia occurred as single or multiple expanded cortical tubules composed of increased numbers of tubular epithelial cells arranged in multiple layers that partially or completely filled the tubule. Renal tubule adenomas were discrete, highly cellular, proliferative lesions that were larger than focal hyperplasias (generally greater than the combined diameter of five normal-sized renal tubules). Adenomas tended to have a more complex structure than hyperplasias and were characterized by closely packed tubules and solid nests composed of cells with large vesicular nuclei and abundant pale eosinophilic cytoplasm which sometime contained clear vacuoles. Renal tubule carcinomas were highly cellular, expansive and invasive masses composed of large basophilic to amphophilic cells that formed large multilayered tubular structures, solid nests, and sheets. Renal mesenchymal tumors occurred in two female rats in the 1800 ppm group (Table 2). Both neoplasms observed in this study were single, small to medium sized masses with poorly defined margins and were composed of sheets of mature mesenchymal (spindle) cells that infiltrated the inner cortex, medulla, and renal pelvis encircling and sequestering glomeruli, tubules, and collecting ducts. Lesions at sites other than the kidney were also observed in males. Mononuclear cell leukemia (0 ppm, 25/50; 450 ppm, 26/50; 900 ppm, 32/50; 1800 ppm, 35/50) increasedwith a significant positive trend and at 1800 ppm, the increase was significant and exceeded the historical ranges for chamber controls from inhalation studies fed NTP-2000 diet (188/399, 47±10%; range 32–66%). Adrenal medulla hyperplasia was also significantly increased at 1800 ppm (0 ppm, 13/50; 450 ppm, 18/48; 900 ppm, 18/50; 1800 ppm, 24/50). There were also exposure-related increases in benign or malignant pheochromocytoma (combined) of the adrenal gland in male rats (0 ppm, 8/50; 450 ppm, 9/48; 900 ppm, 11/50; 1800 ppm, 14/50). However, these increases were not significant and were within the historical ranges for chamber controls from inhalation studies fed NTP-2000 diet (69/398, 17±7%; range 10–28%), although the incidence in the 1800 ppm group was the upper limit of the historical range.

Dose descriptor:

NOAEC

Effect level:

450 ppm (analytical)

Sex:

male/female

Basis for effect level:

histopathology: non-neoplastic

Critical effects observed:

not specified

Conclusions:

A NOAEC was not reported by the study authors. Review of the study data suggests that a NOAEC of 450 ppm can be derived for neoplastic and non-neoplastic lesions, based on the non-neoplastic lesions observed in the kidneys at higher dose levels and the irrelevance to humans of the tumour types observed in the kidneys of male rats.

Executive summary:

In a whole body 2-year inhalation study in Fischer 344 rats, animals (50/sex/group) were administered the read-across substance, MIBK, at concentrations of 0 (control), 450, 900 or 1800 ppm for 6 hours per day, 5 days per week for 2 years. This GLP study was equivalent to OECD Test Guideline 451. Mortality was observed in all groups administered test article. However, survival was significantly decreased in males administered MIBK at 1800 ppm as compared to controls. Mean body weights also were decreased in males administered 900 ppm and 1800 ppm as compared to controls. The mean body weights and survival in treated females were similar to controls. The primary target of MIBK toxicity was the kidney in rats. Briefly, chronic progressive nephropathy (CPN) similar to that which occurs in aged rats also was observed in all rats (including controls). There were treatment related significant increases in both the incidence (1800 ppm) and severity in all exposed groups. Kidney lesions that typically accompany CPN also were reported in males exposed to 900 ppm and 1800 ppm MIBK. The kidney lesions observed were suggestive of α2μ-globulin nephropathy (specific to male rat), a mechanism of xenobiotic-induced renal carcinogenesis for which there is no human counterpart. A NOAEC was not identified by the authors. Review of the study data suggests that a NOAEC of 450 ppm (1840 mg/m3) can be derived for neoplastic and non-neoplastic lesions, based on the non-neoplastic lesions observed in the kidneys at higher dose levels and the irrelevance to humans of the tumour types observed in the kidneys of male rats. 

Cross-reference 2

Reason / purpose for cross-reference:

read-across: supporting information

Materials and methods

Test material

Test material information

Constituent 1

Reference substance name:

Reaction mass of 2,6-dimethylheptan-4-ol and 4,6-dimethylheptan-2-ol

EC Number:

939-420-2

Molecular formula:

C9H20O

IUPAC Name:

Reaction mass of 2,6-dimethylheptan-4-ol and 4,6-dimethylheptan-2-ol

Details on test material:

Substance identified by name.

Specific details on test material used for the study:

Values predicted from read-across source substances

Results and discussion

Effect levels

Dose descriptor:

NOAEC

Effect level:

2 650 mg/m³ air

Based on:

test mat.

Sex:

male/female

Basis for effect level:

histopathology: non-neoplastic

Remarks on result:

other: The Key study taken for the DNEL derivation will be the 2 year inhalation study using MIBK. The NOAEC from this study is 1840 mg/m3, this is 18.4mmol/m3. 18.4 mmol/m3 DIBC = 2650 mg/m3

Target system / organ toxicity

Critical effects observed:

not specified

Applicant's summary and conclusion

Executive summary:

The overall data base supports the conclusion that in animal studies, liver and kidney are target organs for this set of chemicals. In the assessment of much of the data, effects on these organs have been considered adaptive given the absence of corroborating histopathological and clinical chemistry findings to indicate damage to organs. The exception is the effects on the male rat kidney. This is considered to be due to alpha 2u-globulin associated nephropathy, although the quality of the evidence supporting that conclusion is limited, and currently subject to additional research. Although there are often reports of kidney enlargement in the females and in mice (to varying degrees) it is again felt that these findings are more adaptive in the absence of any other significant pathological findings. As such, in most cases, effects on the liver and kidney have been considered as non-adverse and not taken into consideration in the determination of the NOAEL.

 

There is no clear trend in toxicity across the group with all substances having effects on the liver and kidneys within a similar range of doses. Given the consistency in the findings and the similarity in dose response it is proposed to use the long term studies on MIBK to derive the DNELs for DIBC. Additional assessment factor of 2 is proposed to address any residual uncertainty associated with the use of a read across/weight of evidence approach for this endpoint.

 

With respect to the conversion of the NOAEC for MIBK into a NOAEC for DIBC, a molar conversion will be used.

 

With respect to the route to route extrapolation, the toxicokinetics information and physical chemical properties indicate that all of the surrogate substances are bioavailable via oral, inhalation and dermal routes. Comparing oral and inhalation studies (where they exist for the same substance) demonstrates a similar pattern of toxicity with the same target organs. As such it is not expected that extrapolating from an inhalation NOAEC to a dermal NOEL would result in misrepresentation of the hazards of that route of exposure. In fact, extrapolating from inhalation to dermal route is likely to represent a conservative assessment due to the slower rate of uptake via the dermal route compared to the inhalation route. i.e. the toxicokinetic differences between these routes would typically lead to a conclusion that dermal exposure would have a lower hazard potential relative to the oral and inhalation routes.

 

The Key study taken for the DNEL derivation will therefore be the 2 year inhalation study using MIBK.

 

The NOAEC from this study is 1840 mg/m3, this is 18.4mmol/m3.

 

18.4 mmol/m3 DIBC = 2650 mg/m3

 

In doing this conversion it is recognized that the converted NOAEC is greater than the highest attainable vapour concentration for DIBC (approx 1000mg/m3 based on a vapour pressure of 17 Pa). However this is not an issue for the derivation of the DNEL since the resulting DNEL would be expected to fall within a possible vapor concentration of DIBC.