2,2,4-trimethylpentane

Neurotoxicity

Description of key information

There is no data available for 2,2,4-trimethylpentane. However, data is available for structural analogues light alkyl naphtha distillate and 2,4 -dimethylhexane and presented in the dossier. This data is read across to 2,2,4-trimethylpentane based on analogue read across and a discussion and report on the read across strategy is provided as an attachment in IUCLID Section 13.

Three studies were identified that examined neurotoxicity endpoints. These studies were comprised of sub-chronic and short-term inhalation toxicity studies (light alkyl naphtha distillate) and a test on visual discrimination performance and functional observation battery and motor activity (2,4 -dimethylhexane). The weight of evidence based on an analogue approach indicates that 2,2,4-trimethylpentane is unlikely to present a hazard as neurotoxicant.

Key value for chemical safety assessment

Effect on neurotoxicity: via oral route

Endpoint conclusion

Endpoint conclusion:

no study available

Effect on neurotoxicity: via inhalation route

Link to relevant study records

Reference

Reference 1

Endpoint:

neurotoxicity: inhalation

Remarks:

other: acute and subacute

Type of information:

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

Adequacy of study:

key study

Study period:

20 Jan 1999 - 12 Feb 1999

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study

Justification for type of information:

The justification for read across is provided as an attachment in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across: supporting information

Principles of method if other than guideline:

Neurobehavioral functioning was evaluated using selected measures from a standardized functional observational battery (FOB) and motor activity assessment protocol similar to that used in the WHO/IPCS Collaborative Study on Neurotoxicity Assessment (Moser and MacPhail, 1992; Moser et al., 1997a; Moser et al., 1997b).

GLP compliance:

yes (incl. QA statement)

Remarks:

Inspectorate for Health Protection, Commodities and Veterinary Public Health, Ministry of Health, Welfare and Sport

Limit test:

no

Species:

rat

Strain:

other: WAG/RijCrlBR

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Deutschland, Sulzfeld, Germany
- Age at study initiation: 14 weeks
- Weight at study initiation: approximately 250 g at randomization

- Housing: Prior to randomization, the animals were housed individually in macrolon Type III cages (Tecniplast Type 2154F) with wood-shavings on the floor. After randomization animals were housed individually in wire-mesh cages.
- Diet (ad libitum): commercial rodent diet (Rat & Mouse No. 3 Breeding Diet, RM3)
- Water (ad libitum): Tap water suitable for human consumption (quality guidelines according to Dutch legislation based on EEC Council Directive 80/778/EEC, see Annex 3) was supplied by N.V. Waterleidingbedrijf Midden-Nederland (WMN).
- Acclimation period: 9 days


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20-24 and in exposure chambers: 19-24 (lowest 18.5)
- Humidity (%): 31-70 (exposure chamber: 30-55)
- Air changes (per hr): 10
- Photoperiod (hrs dark / hrs light): artificially illuminated for 12 hours between 7.30 a.m. and 7.30 p.m until 1999-01-13. From 1999-01-13 onwards lights were on from 07:00 a.m. to 07:00 p.m.


IN-LIFE DATES: From: 1999-01-20 To: 1999-02-12

Route of administration:

inhalation: vapour

Vehicle:

other: air

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: Test atmosphere was generated by pumping liquid n-octane into stainless steel tubing using peristaltic pumps. The tubing was led through a water bath at 60 °C and the resulting vapour was transported with an airstream from a compressed air source and added to the main airflow system.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

During exposure a total carbon analyzer was operated with 4 ports for control and 3 test concentrations. In addition, the test atmosphere of the low concentration port was continuously analysed during exposure by a separate total carbon analyzer which was used to stabilize the level of the concentration. Shortly after the experiment, a stability check of the concentrations was performed.

Duration of treatment / exposure:

8 hours

Frequency of treatment:

single exposure and once daily for 3 consecutive days

Remarks:

Doses / Concentrations:
0 g/m3; 1.4 g/m3 corresponding to 300 ppm; 4.2 g/m3 corresponding to 900 ppm; 14 g/m3 corresponding to 3000 ppm
Basis:
nominal conc.

No. of animals per sex per dose:

8

Control animals:

yes, concurrent vehicle

Details on study design:

- Rationale for animal assignment: The rat was selected because this species is considered suitable for this type of study and was the species specified in the TNO EZ Collective project proposal. The strain of rats used in these experiments has been used extensively in behavioral studies within TNO.

Observations and clinical examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: at least once daily
- Cage side observations checked: no details given

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: prior to randomization (no details given)


BODY WEIGHT: Yes
- Time schedule for examinations: body weight was recorded during randomization and on days of testing

Neurobehavioural examinations performed and frequency:

FUNCTIONAL OBSERVATIONAL BATTERY: Yes
- Parameters checked:
Neuromuscular: gait, forelimb and hindlimb gripstrength, landing foot splay
Sensorimotor: response to tail pinch, click, touch, approach of a visual object
Convulsive: clonic and tonic movements
Excitability: arousal
Activity: motor activity

- Minimization of bias: Technicians were blind to treatment status of animals: Yes
- Site of testing: open arena (77x55x7 cm)
- Time schedule for examinations: FOBs were carried out 6 days prior to the start of exposure and immediately following the first and third exposure period.
- Duration of observation period for open field observations: 1 minute


LOCOMOTOR ACTIVITY: Yes
- Type of equipment used: automated quantitative microprocessor-based video image analysis system (Ethovision, Noldus Information Technology b.v., The Netherlands)
- Length of session, number and length of subsessions: 30 minutes
- Parameters measured: The position of the rat was continuously monitored throughout the test session concerning total distance run, number of movements and mean velocity. Spontaneous motor activity was expressed as the total distance run in a test period. In addition, quantitative measures of locomotor speed and patterns of locomotor activity were also recorded.

Statistics:

All data were analyzed using the SAS® statistical software package (release 6.12). For each test measure, probability values of p≤0.05 were consideredsignificant.
Continuous variables from the FOB were analyzed using ANOVA. Treatment effects were analyzed using repeated measures analysis of variance. Group comparisons were made using Dunnett´s multiple comparison tests. Rank data were analyzed by Kruskal-Wallis one-way analysis of variance.

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Behaviour (functional findings):

no effects observed

Details on results:

Exposure levels (single exposure and once daily for 3 consecutive days) used in these studies were sufficiently high to induce signs of general intoxication. Signs of intoxication, however, were very mild.

CLINICAL SIGNS AND MORTALITY
No remarkable clinical signs were observed.

BODY WEIGHT AND WEIGHT GAIN
During the 3-day exposure period, mean body weights decreased in the 14 g iso-octane/m3 group. Analysis of covariance at each test time point revealed a significant effect of exposure after the first and the third 8-hour exposure period. Post-hoc group comparisons showed that mean body weight in the 14 g iso-octane/m3 group was significantly decreased when compared to the control group at both test time points.


NEUROBEHAVIOUR
FOB: Following exposure, no changes in functional observational measures were observed that could be related to exposure to iso-octane.
Motor activity: Statistical analysis of motor activity data at each test time point did not indicate any of the exposure groups to be significantly differentfrom the control group.

Key result

Dose descriptor:

NOAEC

Effect level:

> 14 000 mg/m³ air (nominal)

Sex:

male

Basis for effect level:

other: overall effects (no effects) highest dose tested

Remarks on result:

other:

Conclusions:

In conclusion, short-term high-level exposure to iso-octane did not induce any toxicologically significant effects on functional observations and measures of motor activity.

Executive summary:

In conclusion, short-term high-level exposure to iso-octane did not induce any toxicologically significant effects on functional observations and measures of motor activity.

Reference 2

Endpoint:

neurotoxicity: short-term inhalation

Type of information:

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

Adequacy of study:

key study

Study period:

16 Dec 1998 - 12 Feb 1999

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study

Justification for type of information:

The justification for read across is provided as an attachment in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across: supporting information

Principles of method if other than guideline:

Effects of the test compound on cognitive performance were evaluated using a discrete-trial two-choice visual discrimination task.

GLP compliance:

yes (incl. QA statement)

Remarks:

Inspectorate for Health Protection, Commodities and Veterinary Public Health, Ministry of Health, Welfare and Sport

Limit test:

no

Species:

rat

Strain:

other: WAG/RijCrlBR

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Deutschland, Sulzfeld, Germany
- Age at study initiation: 14 weeks
- Weight at study initiation: approximately 200 g at randomization


- Housing: From the acclimatization period onwards, the animals were housed in groups of 4 in macrolon Type III cages (Tecniplast Type 2154F) with wood shavings on the floor. From 5 weeks prior to the pre-exposure test week until the end of the experiment the animals were housed in groups of 4 in wire-mesh cages.
- Diet (ad libitum): commercial rodent diet (Rat & Mouse No. 3 Breeding Diet, RM3)
- Water (ad libitum): Tap water suitable for human consumption (quality guidelines according to Dutch legislation based on EEC Council Directive 80/778/EEC, see Annex 3) was supplied by N.V. Waterleidingbedrijf Midden-Nederland (WMN).
- Acclimation period: 12 days


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20-24 and in exposure chambers: 19-24 (lowest 18.5)
- Humidity (%): 31-70 (exposure chamber: 30-55)
- Air changes (per hr): 10
- Photoperiod (hrs dark / hrs light): artificially illuminated for 12 hours between 7.30 a.m. and 7.30 p.m until 1999-01-13. From 1999-01-13 onwards lights were on from 07:00 a.m. to 07:00 p.m.


IN-LIFE DATES: From: 1998-12-16 To: 1999-02-12

Route of administration:

inhalation: vapour

Vehicle:

other: air

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: Test atmosphere was generated by pumping liquid n-octane into stainless steel tubing using peristaltic pumps. The tubing was led through a water bath at 60 °C and the resulting vapour was transported with an airstream from a compressed air source and added to the main airflow system.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

During exposure a total carbon analyzer was operated with 4 ports for control and 3 test concentrations. In addition, the test atmosphere of the low concentration port was continuously analyzed during exposure by a separate total carbon analyzer which was used to stabilize the level of the concentration. Shortly after the experiment, a stability check of the concentrations was performed.

Duration of treatment / exposure:

8 hours

Frequency of treatment:

once daily for 3 consecutive days

Remarks:

Doses / Concentrations:
0 g/m3; 1.4 g/m3 corresponding to 300 ppm; 4.2 g/m3 corresponding to 900 ppm; 14 g/m3 corresponding to 3000 ppm
Basis:
nominal conc.

No. of animals per sex per dose:

8

Control animals:

yes, concurrent vehicle

Details on study design:

- Rationale for animal assignment: The rat was selected because this species is considered suitable for this type of study and was the species specified in the TNO EZ Collective project proposal. The strain of rats used in these experiments has been used extensively in behavioral studies within TNO.

Observations and clinical examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: at least once daily
- Cage side observations checked: no details given

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: clinical signs of ill health recorded prior to randomization and on Mondays during operant training: no details given

BODY WEIGHT: Yes
- Time schedule for examinations: body weight was recorded during randomization and on a weekly basis until the end of the study, and further after testing was completed on each day of exposure.

Neurobehavioural examinations performed and frequency:

LEARNING AND MEMORY TESTING: Yes
(1) Overall testing design
Visual discrimination performance: Effects of the test compound on cognitive performance were evaluated using a discrete-trial two-choice visual discrimination task.
Parameters evaluated:
General measures: trials responded to, % reinforcements obtained
Stimulus control: discrimination ratio, % ITI periods responded to
Disinhibition: repetitive errors, repetitive ITI responses
Psychomotor slowing: two choice S+ latency, short latency responses, long-latency responses, within-subject variability and single-choice SR+ latency, within-subject variability
(2) Equipment used
- Type of equipment: The apparatus consisted of 16 operant chambers and programming and recording equipment programmed with the MedState® notation system (Med Associates, Inc., Georgia, VT). Each of the operant chambers (32x30x28 lxwxh) was equipped with two levers, two stimulus lights and a water dipper for delivering water reinforcement. A photocell assembly was mounted in the water trough in order to detect the entry of the rat´s head when obtaining the reinforcement. Each operant chamber was located in a ventilated sound-attenuated cubicle.
Although 32 rats were randomly assigned to the test groups before the start of the study, a total of 36 animals were trained.
(3) Testing and training procedures
Prior to treatment, water-deprived rats were first trained to obtain water reinforcements and to lever press using autoshaping techniques. The rats subsequently received four weeks of training on a discrete-trial light-dark visual discrimination task in order to stabilize baseline responding. Animals were trained 5 days/week, from Monday to Friday.
Test sessions consisted of 100 trials or 60 minutes whichever came first and were conducted at approximately the same time each day. On days of exposure, rats were tested immediately following the end of the exposure period. A post-exposure test was performed the day after the last exposure period in order to evaluate the persistence of effects.
Trials were signaled by the illumination of either the left or right stimulus light (S+) and the rat´s task was to depress the lever under the illuminated light in order to obtain water reward. Illumination of right and left stimulus lights was counterbalanced and occured in a predetermined semi-random order. If the rat pressed the correct lever (S+ response), the stimulus light was extinguished and a water reward (SR+) was delivered. If the initial response during a trial was on the incorrect lever (S- response), the rat was allowed to correct its mistake by pressing the lever under the illuminated stimulus light. A given trial remained in effect until the correct lever had been pressed. Trials were separated by an intertrial interval (ITI) of 10 seconds. A response during the ITI reset the ITI timer and the rat was required to wait a further 10 seconds before the initiation of the following trial.
(4) Control procedures
The correctness of the initial response on each trial was recorded.
Examination of baseline performance averaged across 5 days in the week preceding exposure (pre-day) for each rat indicated that all animals were well-trained prior to exposure.
(5) Performance measures
If the initial trial response was correct (S+ response), the latency of the lever press was also recorded (S+ response latency). If the initial response was incorrect (S- response), the number of incorrect lever responses made by the rat switching to the correct lever was recorded. During the intertrial period, lever responses were measured to determine the number of ITI periods on which 1 or more lever presses occured and the number of repetitive ITI lever responses.
From these measures, a number of dependent variables were defined to describe effects on general levels of responding, stimulus control and disinhibition, and response speed.

Statistics:

All data were analyzed using the SAS® statistical software package (release 6.12). For each test measure, probability values of p≤0.05 were consideredsignificant.
Body weights were analyzed using one-way ANOVA followed by Dunnett´s multiple comparison tests.
One-way ANOVA was conducted to examine baseline performance prior to exposure.
Treatment effects were analyzed using repeated measures analysis of variance of the data recorded after the first and the third exposure period. When a significant treatment effect was demonstrated, pairwise group comparisons were performed in order to determine which solvent-treated group significantly differed from the control group. When a significant treatment-by-time interaction was demonstrated, one-way analysis of variance was performed at each test time point followed by Dunnett´s multiple comparison tests. Persistence of effects was evaluated by analysis of variance of post-exposure data.

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Behaviour (functional findings):

no effects observed

Details on results:

Exposure levels used in these studies did not induce clear signs of general intoxication. No significant effects of exposure were observed on body weight.

CLINICAL SIGNS AND MORTALITY
No remarkable clinical signs were observed.

BODY WEIGHT AND WEIGHT GAIN
Body weights were not decreased more in iso-octane-exposed animals compared to controls.


NEUROBEHAVIOUR (Visual discrimination performance)
Visual discrimination performance was also not significantly changed after exposure to iso-octane. A number of statistically significant effects were observed during testing prior to exposure and during the exposure period, but no significant differences between iso-octane-exposed groups and the control group were observed for general measures of responding, measures of stimulus control, measures of disinhibition or measures of psychomotor speed.

Key result

Dose descriptor:

NOAEC

Effect level:

> 14 000 mg/m³ air (nominal)

Sex:

male

Basis for effect level:

other: overall effects (no effects) highest dose tested

Remarks on result:

other:

Conclusions:

In conclusion, short-term high-level exposure to n-octane did not induce any toxicologically significant effects on measures of learned performance.

Executive summary:

In conclusion, short-term high-level exposure to n-octane did not induce any toxicologically significant effects on measures of learned performance.

Reference 3

Endpoint:

neurotoxicity: sub-chronic inhalation

Type of information:

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

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: This study is classified as reliable without restriction because it was conducted according to OECD guideline 413 and was GLP compliant.

Justification for type of information:

A discussion and report on the read across strategy is given as an attachment in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across: supporting information

Qualifier:

according to guideline

Guideline:

other: OECD Guideline 413 (Subchronic Inhalation Toxicity: 90-Day)

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Kingston, NY
- Age at study initiation: 7 weeks
- Weight at study initiation: Not reported
- Housing: Individual
- Diet (e.g. ad libitum): Ad libitum
- Water (e.g. ad libitum): Ad libitum
- Acclimation period: 2 weeks


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 18 to 26 °C
- Humidity (%): 40 to 70%
- Photoperiod (hrs dark / hrs light): 12 hrs dark / 12 hrs light

Route of administration:

inhalation: vapour

Vehicle:

other: nitrogen

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: 1000 litre exposure chamber
- Method of holding animals in test chamber: Cages
- Source and rate of air: 5-gallon container, flushed with nitrogen using laboratory pump
- Method of conditioning air: System of coarse filter, HEPA filter, charcoal filter
- System of generating particulates/aerosols: Volatilization chamber
- Temperature, humidity, pressure in air chamber: Monitored every half hour during exposure; 20 to 24 degrees C, 40 to 60% relative humidity
- Air flow rate: 200 litres per minute
- Method of particle size determination: TSI Aerodynamic Particle Sizer, once each exposure

TEST ATMOSPHERE
- Brief description of analytical method used: Gas chromatography
- Samples taken from breathing zone: yes

VEHICLE (if applicable)
- Composition of vehicle: Nitrogen
- Purity of vehicle: 99.98%

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Samples for determination of analytical exposure levels were withdrawn by vacuum pump from the breathing zone in the exposure chambers three times per exposure for treated groups, and once per exposure for controls. Samples were analyzed using gas chromatography using a flame ionization detector.

Duration of treatment / exposure:

13 weeks

Frequency of treatment:

6 hours per day, 5 days per week

Remarks:

Doses / Concentrations:
6646 ppm (24.3 mg/m3)
Basis:
analytical conc.

Remarks:

Doses / Concentrations:
2220 ppm (8.1 mg/m3)
Basis:
analytical conc.

Remarks:

Doses / Concentrations:
668 ppm (2.4 mg/m3)
Basis:
analytical conc.

No. of animals per sex per dose:

12

Control animals:

yes, concurrent no treatment

Details on study design:

- Dose selection rationale: Highest concentration approximately 75% of the lower explosive limit
- Post-exposure recovery period in satellite groups: 28 days

An extra 12 rats per sex for the high dose and control recovery groups were maintained untreated for 28 days after termination of exposure, to assess reversibility of effects.

Observations and clinical examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Twice daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Twice pretest, weekly during the study period

BODY WEIGHT: Yes
- Time schedule for examinations: Twice pretest, weekly during the study period, prior to sacrifice

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

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: Pretest and prior to sacrifice
- Dose groups that were examined: All

HAEMATOLOGY: Yes
- Time schedule for collection of blood: Prior to sacrifice
- Anaesthetic used for blood collection: Yes (carbon dioxide/oxygen)
- Animals fasted: Yes
- How many animals: 12 per sex per group
- Parameters checked in table 1 were examined.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: Prior to sacrifice
- Animals fasted: Yes
- How many animals: 12 per sex per group
- Parameters checked in table 2 were examined.

URINALYSIS: No

Specific biochemical examinations:

No data reported.

Neurobehavioural examinations performed and frequency:

NEUROBEHAVIOURAL EXAMINATION: Yes
- Time schedule for examinations: Pretest, weeks 5, 9, 14, and 18 (recovery groups)
- Dose groups that were examined: All
- Battery of functions tested: sensory activity / grip strength / motor activity / handling / open-field behaviour / reflexes

Sacrifice and (histo)pathology:

GROSS PATHOLOGY: Yes
HISTOPATHOLOGY: Yes
Organs weighed: adrenals, brain, heart, kidneys, liver, lung, ovaries, prostate, spleen, testes (with epididymides), thymus, and uterus
Tissues histopathologically examined: 39, preserved, not reported

Other examinations:

No data reported.

Positive control:

No

Statistics:

Statistical evaluations to determine variance and significance were performed on the following parameters: body weights, body weight change from week 0, food consumption, haematology, clinical chemistry, organ weights, organ/terminal body weight ratio, and organ/brain weight ratio.

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

no effects observed

Clinical biochemistry findings:

effects observed, treatment-related

Behaviour (functional findings):

effects observed, treatment-related

Gross pathological findings:

no effects observed

Neuropathological findings:

not examined

Other effects:

not examined

Description (incidence and severity):

Migrated information from 'Further observations for developmental neurotoxicity study'

Details on results (for developmental neurotoxicity): Not examined.

Details on results:

CLINICAL SIGNS AND MORTALITY: No treatment-related effects were observed.

BODY WEIGHT AND WEIGHT GAIN: No treatment-related effects were observed.

FOOD CONSUMPTION: No treatment-related effects were observed.

OPHTHALMOSCOPIC EXAMINATION: No treatment-related effects were observed.

HAEMATOLOGY: Statistically significant decreases in haemoglobin, hematocrit, and erythrocytes in blood of high-dose males when compared to controls were not found to be toxicologically relevant, as the values were within the historical range for control animals.

CLINICAL CHEMISTRY: Statistically significant decreases in aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels in blood of high-dose females when compared to controls were not found to be toxicologically relevant, as several control female rats had elevated AST and ALT as well.

NEUROBEHAVIOUR -Motor Activity: There were statistically significant differences in the number and relative pattern of motor activity among the dose groups over the treatment testing periods, but overall, these differences did not occur in a dose-related pattern. The magnitudes of the differences were not large, and none of the treatment-group differences were larger than differences seen during the predose period.
-Functional Operational Battery: No treatment-related effects were observed.

ORGAN WEIGHTS: At terminal sacrifice, there were statistically significant dose-related increases in absolute and relative kidney weights in males of all three treatment groups. High-dose male kidney weights remained elevated after the recovery period. This correlated with microscopic observations indicating light hydrocarbon nephropathy. At terminal sacrifice, there were also statistically significant increases in absolute and relative liver weights in high-dose male and female rats. Liver weights did not remain elevated after the recovery period. There was no microscopic correlation for this condition, so this was considered a functional adaptation to treatment. There were no differences in lung and brain weights when compared to controls.

GROSS PATHOLOGY: No treatment-related effects were observed.

HISTOPATHOLOGY: NON-NEOPLASTIC: Microscopic observations included hyaline droplet formation in the proximal convoluted tubules, considered to contain an alpha2-microglobulin-hydrocarbon complex, and increase in incidence and severity of nephropathy and dilated tubules at the cortico-medullary junction.

Key result

Dose descriptor:

NOEC

Remarks:

(Subchronic toxicity)

Effect level:

> 2 220 ppm

Sex:

male/female

Basis for effect level:

other: Organ weights

Remarks on result:

other:

Key result

Dose descriptor:

NOEC

Remarks:

(Neurotoxicity)

Effect level:

>= 6 646 ppm

Sex:

male/female

Basis for effect level:

other: Organ weights

Remarks on result:

other:

Conclusions:

The NOEC of the test substance was found to be > 2220 ppm for subchronic toxicity, and >= 6646 ppm for neurotoxicity. The test substance did not cause neurobehavioral or neuropathologic effects in rats after 13 weeks of inhalation exposure at a maximum concentration of 6646 ppm (24.3 mg/m^3). The test substance did induce "light hydrocarbon nephropathy", characterized by increased organ weight and microscopic effects of the kidney (increased incidence of hyaline droplets) in male rats, but since this syndrome is species and sex specific, it is not considered relevant to humans for risk assessment purposes.

Executive summary:

In a 90-day inhalation toxicity study, light alkylate naphtha distillate-2 was administered to 12 Sprague-Dawley rats/sex/concentration by dynamic whole body exposure at concentrations of 0, 668, 2220, or 6646 ppm (0, 2.4, 8.1, and 24.3 mg/m^3) for 6 hours per day, 5 days/week for a total of 13 weeks.

 

There were no treatment-related effects inmortality, clinical signs, neurotoxicity, body weight, or food consumption. Significant effects noted in haematology and clinical chemistry were not determined to betoxicologically relevant, and kidney weight increases found in high-dose males were not determined to be relevant to human toxicity risk assessments. The LOEC for subchronic toxicity is >= 6646 ppm, based on haematology, clinical chemistry and organ weights. The NOEC is > 2220 ppm for subchronic toxicity and >= 6646 ppm for neurotoxicity.

 

This study received a Klimisch score of 1 and is classified asreliable without restriction because it was conducted according to OECD guideline 413 and was GLP compliant.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

24 300 mg/m³

Study duration:

subchronic

Species:

rat

Quality of whole database:

1 key and 2 short-term sub-chronic studies from structural analogues available for assessment.

Effect on neurotoxicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

There is no data available for 2,2,4-trimethylpentane. However, data is available for structural analogues, 2,4-dimethylhexane and light alkyl naphtha distillate and presented in the dossier. This data is read across to 2,2,4-trimethylpentane based on analogue read across and a discussion and report on the read across strategy is provided as an attachment in IUCLID Section 13.

2,4 -dimethylhexane

Groups of male rats (8/dose level) were exposed by inhalation to 0, 1400, 4200 or 14000 mg/m³ (corresponding to ca. 300, 900 and 3000 ppm) of iso-octane (Alkanes, C7-10-iso-, CAS No. 90622-56-3), 8 h per day, for 3 consecutive days. Animals were tested daily for effects on motor activity, functional observation measures and learned performance of a visual discrimination task. The exposure levels used were sufficiently high to induce very mild signs of general toxicity (slightly decreased body weights). No significant neurobehavioural effects were observed up to the highest dose, therefore the NOAEC was considered to be greater than 14000 mg/m³ (CEFIC, 2001).

Light Alkyl Naphtha Distillate

In a 90-day inhalation toxicity study (Schreiner, 1998), light alkylate naphtha distillate-2 was administered to 12 Sprague-Dawley rats/sex/concentration by dynamic whole body exposure at concentrations of 0, 668, 2220, or 6646 ppm (0, 2.4, 8.1, and 24.3 mg/m^3) for 6 hours per day, 5 days/week for a total of 13 weeks. There were no treatment-related effects inmortality, clinical signs, neurotoxicity, body weight, or food consumption. Significant effects noted in haematology and clinical chemistry were not determined to betoxicologically relevant, and kidney weight increases found in high-dose males were not determined to be relevant to human toxicity risk assessments. The LOEC for subchronic toxicity is >= 6646 ppm, based on haematology, clinical chemistry and organ weights. The NOEC is > 2220 ppm for subchronic toxicity and >= 6646 ppm for neurotoxicity.

Justification for classification or non-classification

2,2,4-trimethylpentane is classified as as STOT Single Exp. 3 (H336: May cause drowsiness or dizziness) in accordance with Annex VI of the CLP EU Regulation 1272/2008.