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Repeated dose toxicity: inhalation

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Administrative data

sub-chronic toxicity: inhalation
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP-guideline study
Reason / purpose for cross-reference:
reference to same study

Data source

Reference Type:

Materials and methods

Test guideline
equivalent or similar to guideline
OECD Guideline 413 (Subchronic Inhalation Toxicity: 90-Day Study)
GLP compliance:
Limit test:

Test material

Constituent 1
Reference substance name:
Naphtha (petroleum), light alkylate
EC Number:
EC Name:
Naphtha (petroleum), light alkylate
Cas Number:
Details on test material:
- Name of test material (as cited in study report): Light alkylate naphtha distillate (LAND-2, C4-C10, CAS 64741-66-8)
- Analytical purity: no data
- Molecular weight (if other than submission substance): Average molecular weight 89.2.
- Composition of test material, percentage of components: Comprised of components with carbon numbers predominantly in the C5-C8 range with a boiling range of 90-160°C (194-320°F). Light alkylate naphtha was collected from a refinery sulfuric acid alkylation unit. Light alkylate naphtha distillate (LAND-2) was prepared by charging a glass-lined Pfaudler kettle, operated as a closed system, with 1000 gal of the light alkylate naphtha. The sample was slowly heated and stirred as the bottoms temperature was raised from 68 to 202°F and the overhead was raised to 189°F. The vapor leaving the kettle was condensed by passing through a series of two receiving vessels chilled with cold water (200 gal) and dry ice (50 gal), respectively. Additional vapor traps chilled in dry ice/isopropyl alcohol were connected to the chilled dry ice vessel. The distillate collected represented 15.46% of the initial sample weight. The LAND-2 was characterized by gas chromatography using a modified ASTM D5134-92 procedure (ASTM, 1992) on a Hewlett Packard 5890 instrument. The chilled LAND-2 was mixed, transferred to 5-gal containers, and shipped to the testing laboratory, where it was stored at ambient temperature in a solvent storage building until use.

LAND-2 (Vapor) Carbon number (vol. %): C4 - 3.25; C5 - 33.30; C6 - 18.91; C7 - 9.81; C8 - 31.14; C9 - 3.21; C10 - 0.39.; composition (vol %): n-Paraffins: 3.47, total paraffins: 99.97, total olefins: 0.03

Test animals

Details on test animals or test system and environmental conditions:
- Strain: Male and nulliparous, nonpregnant female Sprague-Dawley rats (VAF/ Plus Crl:CD BR)
- Source: Charles River Laboratories, Kingston, NY
- Age at study initiation: approximately 5 wk old when purchased, acclimated for approximately 2 wk prior to the initiation of the study
- Housing: Animals were housed individually in suspended stainless steel wire mesh cages in air-conditioned rooms
- Diet (e.g. ad libitum): Certified rodent diet 5002 (PMI Feeds, Inc., St. Louis, MO) ad libitum
- Water (e.g. ad libitum): water from an automated watering system was available ad libitum
- Acclimation period: 2 weeks. All animals were assigned a temporary identification number at receipt and examined by the staff veterinarian during the acclimation period.

- Temperature (°C): 18-26°C
- Humidity (%): 40-70% relative humidity
- Photoperiod (hrs dark / hrs light): 12/12 during the acclimation and all nonexposure periods

Administration / exposure

Route of administration:
inhalation: vapour
Type of inhalation exposure:
whole body
other: nitrogen
Details on inhalation exposure:
Rats were exposed to wholly vaporized LAND-2 generated in nitrogen, by inhalation in whole-body exposure cages 6 h/d, 5 d/wk for 13 wk at analytical concentrations of 668, 2220, and 6646 ppm (2.4, 8.1, and 24.3 g/m3). Exposure levels were determined three times daily by gas chromatography. The highest concentration was approximately 75% of the lower explosive limit. Animals’ positions in the cages were rotated for each exposure to ensure uniform exposure of every animal.

Chamber Operation: Animals were housed individually in wire mesh, stainless steel cages within a 1000-L glass and stainless steel exposure chamber. Chamber temperature and humidity were monitored every half hour during exposure and maintained, to the extent possible, within the ranges of 20–24°C temperature and 40–60% relative humidity. Animals did not receive food or water during the exposure period. Exposure chambers were operated dynamically at a calibrated airflow rate of 200 L/min (lpm). Recordings of airflow and static pressure were made every half hour. All animals remained in the chamber for a minimum of 30 min at the end of exposure while the chamber was operated using clean air only. Chambers were exhausted through a system of coarse filter, HEPA filter, and charcoal filter.

Atmosphere Generation: LAND-2 was pumped directly from the 5-gal container, housed within a freezer constantly flushed with nitrogen, using a laboratory pump, equipped with a piston, that was insulated within a styrofoam container. An ice bag was placed on top of the piston to keep the piston chamber cold to inhibit volatilization of LAND-2 in the pump and delivery lines. LAND-2 was delivered onto the central glass helix of a countercurrent volatilization chamber (one generator per chamber). The glass helix was heated by an internal nichrome wire inserted in the center of the glass tube that supported the helix (external to the volatilization chamber) and was controlled by a variable autotransformer. House-line nitrogen delivered from a regulator with a backpressure gauge was divided with a stainless steel T into the generation flow system and a purge flow system. Purge nitrogen was delivered to the bottom of the tube containing the nichrome wire to continuously purge the area surrounding the wire, protecting it from oxidation. Nitrogen for the generation system was directed through a flowmeter to the ball-and-socket joint at the bottom of the volatilization chamber, flowed up the chamber, passed over the coil, and volatilized the test material. The LAND-2-laden nitrogen flowed through a T tube at the top of the volatilization chamber into the turret of a 1-m3 glass and stainless steel exposure chamber, where it mixed with room air to appropriate exposure concentrations as it was drawn into the chamber (flow rate of 200 lpm). Control animals were sham-exposed to nitrogen alone introduced into the turret and mixed with air in the chamber.

Exposure Chamber Monitoring: Samples for determination of analytical exposure levels and the major components of LAND-2 vapor 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 pulled through Teflon lines into the multipositional control module and directed to a Hewlett Packard 5890II gas chromatograph, equipped with a flame ionization detector for analysis by ASTM method D5134-92 (ASTM, 1992). Composition and stability of the test material were evaluated by characterizing neat LAND-2 and comparing the major components in the neat and generated atmospheres at the beginning and end of the study. Particle size distribution measurements of any background aerosol were performed once during each exposure for chambers and room air using a TSI Aerodynamic Particle Sizer. Samples were drawn for 20 s at a rate of 5 L/min. Mean mass aerodynamic diameter (MMAD), geometric standard deviation (GSD), and total mass concentration (TMC) were calculated. Nominal concentrations (mg/m3) were calculated from the loss of weight from the generation apparatus divided by the total air flow through the chamber during exposure. This value was converted to parts per million (ppm) using an average molecular weight for this mixture of 89.2.
Analytical verification of doses or concentrations:
Details on analytical verification of doses or concentrations:
Determined three times daily by gas chromatography.
Composition and Uniformity Chamber Gas Chromatographic Results (% Weight): n-Butane: 3.21; iso-Pentane: 34.343; 2,3-Dimethylbutane: 12.977, 2-Methylpentane: 4.096; 2,4-Dimethylpentane: 5.663; 2,3-Dimethylpentane: 2.680; 2,2,4-Trimethylpentane: 16.885; 2,3,4-Trimethylpentane: 3.578; 2,3,3 –Trimethylpentane: 4.505; 2,2,5-Trimethylhexane: 2.499.
Duration of treatment / exposure:
13 weeks
Frequency of treatment:
6 hours/day, 5 days/week
Doses / concentrations
Doses / Concentrations:
0, 668, 2220, and 6646 ppm (0, 2.4, 8.1, and 24.3 g/m3)
analytical conc.
No. of animals per sex per dose:
Control animals:
yes, sham-exposed
Details on study design:
Neurobehavioral evaluations of motor activity (MA) and functional operational battery (FOB) were performed pretest and during wk 5, 9, 14, and 1 8 (recovery groups). Animals were not exposed to LAND-2 on the days of neurobehavioral testing. Exposure days were added to ensure that each animal received at least 65 exposures.

Following 13 wk of exposure, 12 animals/sex/group were necropsied and microscopic examination was performed on selected tissues. Nervous tissue from 6 rats/sex/group was also examined microscopically. At the end of the 4-wk recovery period, 12 animals/sex from the high and control groups were necropsied and selected tissues examined microscopically.


Observations and examinations performed and frequency:
Animals were evaluated twice daily for mortality and gross signs of toxicological or pharmacological effects. During each exposure, rats were observed as a group once for abnormal behavior. Detailed physical examinations were performed twice pretest and weekly during the study. Ophthalmoscopic evaluations were performed pretest and just prior to the scheduled sacrifices at wk 14 (terminal) and 18 (recovery).

Body Weights and Food Consumption. All animals were weighed twice pretest, weekly during the study period, and prior to scheduled sacrifice. Food consumption was measured once during the week prior to treatment initiation and over a 6-d interval each week during the study period.

Animals were transported from the room in which they were housed during non-exposure hours to the neurotoxicity laboratories. Behaviors were evaluated pretest and during wk 5, 9, 14, and 18 (recovery groups). Temperature, humidity, and illumination were measured and recorded to minimize variation in environmental conditions during evaluations. Noise levels were not recorded. Testing was staggered over 8 sessions within a 4-d period, each session consisting of approximately 2 rats/sex/treatment group.

Motor Activity. Locomotor activity was monitored as a function of the number of beam breaks in an activity box, using an automated photo- beam activity system. Sessions were 60 mm in length divided into twelve 5-mm intervals. Rats were evaluated at pretest, at 3 time points during the treatment period (wk 5, 9, and 1 4), and at the end of the recovery period. Treatment groups were counter balanced across test times. Three sets of analyses were performed. The first analysis was conducted using the pre-dose data with animals nested within the interaction effect of sex crossed with treatment group, with a profile measure across the 12 time intervals. The second analysis used data from the 3 treatment time points, and animals were nested within the interaction effect of sex crossed with treatment group, with a profile measure across the 12 time intervals nested within the 3 time periods. The third analysis was similar to the first, using the recovery data. All three analyses tested for treatment effects, sex differences, treatment group by sex interactions, and these effects crossed with periods (second analysis only) and intervals. Analyses were repeated using transformed rank data to achieve a normal distribution of the residuals. Residuals from the models were tested for normality by the Shapiro-Wilk W-test or the Kolomogorov D-test.

Functional Operational Battery. The battery was comprised of home- cage evaluations (posture, vocalizations, and palpebral closure), handling evaluations (reactivity to general stimuli, signs of autonomic function), open-field behavior (arousal level and gait, urination and defecation frequency, convulsions, tremor, abnormal behaviors, piloerection, and exophthalmos), and reflex assessments (response to visual and auditory stimuli, tail pinch, pupillary function). Animals were also evaluated for forelimb and hindlimb grip strength, landing foot splay, and air righting ability. For landing foot splay, a small dot of paint was applied to each hindpaw. The rat was dropped from a height of 2 ft above a flat surface and the distance between the marks left by the hindpaws was measured in centimeters. To evaluate air righting reflex ability, the rat was held upside down, dropped from a height of 2 ft above a container of bedding, and the landing position was observed. Treatment groups were counterbalanced across test times. The observer performing the evaluation did not know the identity of the animal’s dose group.
Sacrifice and pathology:
All animals were sacrificed by intraperitoneal injection of sodium pentobarbital, and tissues were preserved in situ by transcardial perfusion with phosphate-buffered saline (pH 7.4) followed by 4% paraformaldehyde/1 % glutaraldehyde in the same buffer. Animals were killed at termination of 13 wk of exposure (week 13 terminal sacrifices performed during week 14) or at the completion of the 4-wk recovery period (control and high-dose groups only). A complete macroscopic examination was performed on all animals and 12 organs were weighed: adrenals, brain, heart, kidneys, liver, lung, ovaries, prostate, spleen, testes (with epididymides), thymus, and uterus. The length and width of the brain of each rat was measured.

Thirty-nine tissues were preserved from all animals in all dose groups. Tissues from all animals in the control and high-dose groups were processed, embedded in paraffin, mounted on glass slides, and stained with hematoxylin and eosin for histopathological examination. The kidneys of selected animals were also stained with Mallory-Heidenhain stain. In addition, tissues of the nervous system were fixed for all animals. Brain, spinal cord, ganglia, and spinal nerve roots were processed, embedded in paraffin, mounted on glass slides, and stained with hematoxylin-eosin, Luxol fast blue, and Sevier-Munger stains. Peripheral nerve sections (sciatic, tibial, sural, and optic) were embedded in glycol methacrylate and stained with toluidine blue. Slides of nervous system tissues were examined from animals (6/sex/group) designated through random selection for neuropathology, in the control and high-dose groups sacrificed at the end of 13 weeks of exposure. Specific brain regions examined were forebrain, cerebral cortex, hippocampus, basal ganglia, midbrain cerebellum and pons, and medulla.
Statistical evaluations were performed on the following parameters: body weights, body weight change from wk 0, and food consumption; hematology and clinical chemistry; and organ weights, organ/terminal body weight ratio, and organ/brain weight ratio. Barlett’s test at 1 % significance, two-sided risk level, was used to determine if groups had equal variance. All other tests were conducted at 5% and 1 % significance, two- sided risk level. Parametric procedures were standard one-way analysis of variance (ANOVA) using F distribution for significance. If significant differences among means were indicated, Dunnett’s test was used to determine significant differences from controls. The Kruskal-Wallis test was the nonparametric procedure for testing equality of means, and if differences were indicated, Dunn’s summed rank test was used to determine differences from controls.

A statistical test for trend in the dose levels was also performed, using standard regression techniques with a test for trend and lack of fit where variances were equal orJonckheere’s test for monotonic trend in nonparametric cases.

Results and discussion

Results of examinations

Clinical signs:
no effects observed
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
Haematological findings:
no effects observed
Clinical biochemistry findings:
no effects observed
Urinalysis findings:
not examined
Behaviour (functional findings):
no effects observed
Organ weight findings including organ / body weight ratios:
effects observed, treatment-related
Gross pathological findings:
effects observed, treatment-related
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Histopathological findings: neoplastic:
no effects observed
Details on results:
All animals survived the treatment period and were sacrificed according to study design at the end of 13 wk or at 18 wk (recovery groups). No test-related observations were noted in the exposure chambers during any exposure period for any treatment groups or during non-exposure periods. From weekly clinical observations, the only apparent treatment-related finding was an increased incidence of red facial staining in both male and female rats in the high dose group. No LAND-2-related ocular disease was observed. All groups showed similar mean body weights, body weight gains, and food consumption.

At wk 13 terminal sacrifice, there was a statistically significant decrease, relative to control values, in hemoglobin (5%), hematocrit (5%), and erythrocytes (7%) in blood of high dose males (data not shown). The hemoglobin was still decreased (4%) after the 28-d recovery period. However, because these differences were small and within the historical range for control animals in this laboratory, they are not considered toxicologically relevant. Clinical chemistry results showed a statistically significant decrease in aspartate aminotransferase (AST 32%) and alanine aminotransferase (ALT 46%) in females of the high-dose group (data not shown) compared to controls. However, several control female rats had elevated AST and ALT relative to the other nine female rats in the group and historical controls. Comparison of ALT and AST values from high-dose females with these elevated concurrent control values produced a statistical significance that is not toxicologically relevant. These results are not considered LAND-2 related.


Motor Activity. Shapiro-Wilk analysis of data from the predose period indicated that the only statistically significant effects on response pattern occurred in the low-dose group due to inactivity among females for intervals 6—8, and increased activity of males during interval 10 (data not shown). Data from the treatment intervals and the recovery period were analyzed based on the Blom transformed data because the residuals from the model were not normally distributed by the Shapiro—Wilk statistic at the .01 level. There were statistically significant differences in the number (ct < .04) and relative pattern (cx. < .02) of beam breaks among the dose groups over the treatment testing periods. There were expected differences between sexes, and pattern differences across the 1 2 measuring intervals. In the recovery period in which only the room air controls and the high-dose animals were evaluated, there were no dose-group-related differences in response. Overall, dose-group differences did not occur in a dose-related pattern. Although statistically significant, the magnitudes of the differences were not large, and none of the treatment-group differences were larger than differences seen during the pre-dose period.

Functional Operational Battery. No differences were detected in the distance between foot splay for male or female rats in any dose group over any time interval evaluated. Grip strength of both fore- and hindlimbs in general increased from pretest through wk 14 for both sexes in all treatment groups. Values for control and high-dose recovery animals were lower at wk 18 than in previous treatment weeks but similar between the groups. There was no test-material-related effect on any endpoint evaluated within the functional operational battery of tests.

Pathology. At the wk 13 terminal sacrifice there were statistically significant dose-related increases in absolute and relative kidney weights in males of all 3 treatment groups. The kidney weights of high-dose males remained elevated after the recovery period. These increases correlated with microscopic observations of hyaline droplet formation in the proximal convoluted tubules considered to contain an alpha2-microglobulin-hydrocarbon complex, based on positive staining reaction by the Mallory-Heidenhain method, and increase in incidence and severity of nephropathy and dilated tubules at the corticomedullary junction. These microscopic finding are characteristic of ‘light hydrocarbon nephropathy” also known as hyaline droplet nephropathy and are male rat specific and are not considered relevant to humans. Statistically significant increases in absolute and relative liver weights were observed in high-dose male and female rats at wk 13 sacrifice. Differences were not present after the recovery period and had no microscopic correlate. Lung and brain weights were comparable to controls. Lungs were macroscopically and microscopically comparable to controls. Brain length and width measurements showed no test-material-related effects. There were no microscopic findings in the brain, spinal cord, or peripheral nerves that could be attributable to exposure to LAND-2.

Effect levels

Dose descriptor:
Effect level:
24 300 mg/m³ air (analytical)
Basis for effect level:
other: no effects except adaptive response of liver weight to exposure equivalent to 6646 ppm

Target system / organ toxicity

Critical effects observed:
not specified

Applicant's summary and conclusion

The NOAEC of LAND-2 for subchronic toxicity and neurotoxicity is 6646 ppm.
Executive summary:

The NOAEC of LAND-2 for subchronic toxicity and neurotoxicity is 6646 ppm.