Naphtha (Fischer-Tropsch), light, C4-10-branched and linear

Repeated dose toxicity: inhalation

Administrative data

Endpoint:

sub-chronic toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

1998

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

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

Deviations:

not specified

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Naphtha (petroleum), light alkylate

EC Number:

265-068-8

EC Name:

Naphtha (petroleum), light alkylate

Cas Number:

64741-66-8

IUPAC Name:

Naphtha (petroleum), light alkylate

Details on test material:

- Name of test material (as cited in study report): Naphtha (petroleum), light alkylate [CAS 64741-66-8]
- Test substance is closely related to Naphtha (Fischer-Tropsch), light, C4-10 - branched and linear; it is defined as : 'A complex combination of hydrocarbons produced by the distillation of the reaction products of isobutane with monoolefinic hydrocarbons usually ranging in carbon numbers from C3 through C5. It consists of predominantly branched chain saturated hydrocarbons having carbon numbers predominantly in the range of C7-C10 and boiling in the range 90-160°C (194-320°F).'

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Administration / exposure

Route of administration:

inhalation

Type of inhalation exposure:

whole body

Vehicle:

other: 99.98% nitrogen

Details on inhalation exposure:

Exposure levels were determined three times daily by gas chromatography.

Analytical verification of doses or concentrations:

yes

Duration of treatment / exposure:

6h/d and 5d/week for 13 weeks (at least 65 exposures)

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

719 ppm (nominal)

Doses / concentrations 2

Dose / conc.:

2 073 ppm (nominal)

Doses / concentrations 3

Dose / conc.:

7 127 ppm (nominal)

Doses / concentrations 4

Dose / conc.:

668 ppm (analytical)

Doses / concentrations 5

Dose / conc.:

2 220 ppm (analytical)

Doses / concentrations 6

Dose / conc.:

6 669 ppm (analytical)

No. of animals per sex per dose:

12 animals/sex/group

Control animals:

yes

yes, sham-exposed

Examinations

Observations and examinations performed and frequency:

Exposure Chamber Monitoring (three times during exposure); Clinical Observations (twice daily); 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), Hematology and Clinical Chemistry (wk 14), Neurobehavioral Studies during wk 5, 9, 14 and 18 (recovery groups) (Motor Activity, Functional Operational Battery)

Sacrifice and pathology:

During week 14 (recovery groups (control and high dose only): week 18)

Statistics:

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 summea 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 or Jonckheere's test for monotonie trend in nonparametric cases.

Results and discussion

Results of examinations

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

Increased incidence of red facial staining in both male and female rats

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:

no effects observed

Ophthalmological findings:

no effects observed

Haematological findings:

effects observed, non-treatment-related

Description (incidence and severity):

Decrease in hemoglobin (5%), hematocrit (5%) and erythrocytes (7%) in blood of high dose males. These differences are within the historical range for control animals in this laboratory and therefore are not considered toxicologically relevant.

Urinalysis findings:

not examined

Effect levels

1

Dose descriptor:

NOEL

Effect level:

2 220 ppm (analytical)

Sex:

male/female

Basis for effect level:

organ weights and organ / body weight ratios

2

Dose descriptor:

NOEL

Effect level:

>= 6 646 ppm (analytical)

Sex:

male/female

Basis for effect level:

behaviour (functional findings)

neuropathology

3

Dose descriptor:

LOEL

Effect level:

>= 6 646 ppm (analytical)

Sex:

male/female

Basis for effect level:

clinical signs

organ weights and organ / body weight ratios

Target system / organ toxicity

Critical effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

Systemic LOEL = 6646 ppm (24.3 g/m3) based on increased liver weight and red facial staining; NOEL = 2220 ppm (8.2 g/m3).
The Neurotoxicity NOEL = 6646 ppm (24.3 g/m3).

Executive summary:

Light alkylate naphtha (LAN, CAS #64741-66-8; approx 100% paraffinic) has been tested as a vapor distillate fraction (approx. 100% paraffinic) by inhalation in the rat for systemic toxicity and neurotoxicity, and in the rabbit by dermal exposure.

Sprague Dawley rats (12/sex/group) were exposed to a LAN light end distillate at concentrations of 0, 668, 2220, and 6646 ppm (2.44, 8.1 and 24.3 g/m3), 6 hours/day, 5 days/wk for 13 weeks, according to OECD guideline 413. The test material (LAN-D) was prepared to be representative of the fraction of light alkylate naphtha to which man would be exposed during normal handling and use. It was obtained by the distillation of light alkylate naphtha (LAN) and collection of that fraction that boiled over the temperature range 78 to 145°F. The maximum exposure level was 75% of the lower explosive limit for LAN distillate. Extra groups of 12 rats of each sex exposed to the high dose level and a recovery control group were maintained untreated for 28 days following cessation of the 13 weeks exposure. Neurobehavioral evaluations of motor activity and functional activity [FOB] were performed pretest and during weeks 5, 9, 14 and week 18 for recovery groups. Animals were not exposed to LAN-D during these tests. Ophthalmoscopic evaluations were performed pretest and just prior to the scheduled sacrifices at 14 weeks and 18 weeks (recovery groups). Body weights and food consumption were measured throughout the study. Blood samples were taken from 12 fasted rats/sex/group at 14 and 18 weeks for hematological and clinical chemical measurements. At termination (after 13 weeks exposure for the main study and after 18 weeks for the recovery animals) all animals were killed and subjected to a complete macroscopic examination. The following organs were weighed: adrenals, brain, heart, kidneys, liver, lung, ovaries, prostate, spleen, testes (with epididymides), thymus and uterus. Brain lengths and widths were measured for each rat. Thirty nine tissues removed from the control and high dose animals, were fixed, stained with hemotoxylin-eosin and examined histopathologically. Additionally, kidneys from selected animals were stained with Mallory-Heidenhain and examined. Tissues were collected from the nervous system (central and peripheral) of all animals and nervous system tissues were selected randomly from 6 rats per sex/group in the high dose and controls at the end of 13 weeks for microscopic examination. Specific brain regions examined were forebrain, cerebral cortex, hippocampus, basal ganglia, midbrain cerebellum and pons and medulla.

Neurobehavioral studies included motor activity, monitored as the number of beam breaks in an activity box, at pretest, and during weeks 5, 9, 14, and at the end of the 4- week recovery period. The Functional Operational Battery (FOB) was comprised of home cage evaluations, handling and open field behaviors and reflex assessment. Animals were also evaluated for fore limb and hind limb grip strength, landing foot splay and air righting ability.

There were no mortalities during the study and there were no treatment related signs of toxicity with the possible exception of an increased incidence of red facial staining in rats of both sexes in the high dose group. Mean body weights, body weight gains and food consumption were unaffected by treatment. Hematologic changes were a 5% decrease in hemoglobin and a 7% decrease in erythrocyte counts. Hemoglobin was still decreased 4% after the 4 week recovery period. However all these decreases were small and within historical control range for the laboratory. Decreases in AST and ALT in high dose females were not considered toxicologically significant because several control females had AST and ALT levels that were elevated relative to the other control females and relative to the historical control range. Comparison of values from high dose females with these elevated control values indicates that some were different by statistical criteria, but these differences were not toxicologically important. Organ weight changes were few. Statistically significant increases in kidney weights in high dose males correlated with microscopically observed hyaline droplet formation and degeneration of proximal renal tubules were observed, indicative of alpha 2-microglobulin mediated nephropathy, also identified as light hydrocarbon nephropathy, a species and sex specific syndrome not relevant to humans (US EPA, 1991). Increased liver weights in high dose rats of both sexes had no microscopic correlate and appeared reversible after 4 weeks of recovery. Absolute and relative liver weights were observed in the high dose males and females at 13 weeks but the differences had disappeared after the recovery period. There were no pathological findings associated with this increase. In the neurobehavioral studies no treatment-related effects were observed in the functional operational battery. In the study of motor activity there were some statistically significant differences, but overall they did not occur in a dose related manner and furthermore were smaller than some of the differences seen during the pre-dosing period. The systemic LOAEL = 6646 ppm (24.3 g/m3) based on increased liver weight and red facial staining and the NOAEL = 2220ppm (8.2 g/m3). The Neurotoxicity NOAEL = 6646 ppm (24.3 g/m3).