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Acute Toxicity: inhalation

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Administrative data

Endpoint:
acute toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Study period:
7 January 1994 to 7 May 1996
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
Although conducted according to accepted guidelines and with GLP compliance, the study was not designed specifically as an acute inhalation toxicity study. However, exposure concentrations were sufficiently high to provide information essentially equivalent to an acute inhalation toxicity study. This study is also summarized in Section 7.9.1 (Neurotoxicity) of this dataset.
Cross-reference
Reason / purpose:
reference to same study

Data source

Referenceopen allclose all

Reference Type:
publication
Title:
Acute and subchronic neurotoxicology evaluation of tetrahydrofuran by inhalation in rats
Author:
Malley, L.A., Christoph G.R., Stadler, J.C., Hansen, J.F., Biesemeir, J.A. and Jasti, S.
Year:
2001
Bibliographic source:
Drug Chem. Toxicol., 24(3): 201-219
Reference Type:
study report
Title:
Unnamed
Year:
1996
Report Date:
1995

Materials and methods

Test guideline
Qualifier:
equivalent or similar to
Guideline:
other: U. S. EPA, Toxic substances Control Act Health Effects Testing guideline, 40 CFR Part 798 Subpart G, Neurotoxicity (1985) and USEPA/FIFRA Neurotoxicity Pesticide Assessment Guidelines F, PB 91-154617 (1991)
Deviations:
yes
Remarks:
US EPA (Letter to Chemical Manufacturers Association, October 18, 1983); reflects advances as specified in [U.S.EPA/FIFRA Neurotoxicity Pesticide Assessment Guidelines F: Hazard Evaluation: Human and Domestic Animals Addendum 10. PB 91-154617 (1991)].
Principles of method if other than guideline:
The experimental design incorporated certain modifications to the standard test guidelines as approved by authorized representatives of the US EPA. The modifications reflect advances in the methodology as specified by the EPA.
GLP compliance:
yes
Test type:
other: Acute Inhalation Neurotoxicity Evaluation
Limit test:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Name of test material: tetrahydrofuran- Physical state: colorless liquid- Analytical purity: >99.9%- Impurities (identity and concentrations): not identified, none considered to be of toxicological importance- Purity test date: Samples submitted on 1/4/94, 1/7/94 and 1/24/94 (prior to study start and after last exposure)- Lot/batch No.: H-20378 (Haskell No.)- Expiration date of the lot/batch: not given- Stability under test conditions: stable based on purity sample analyses- Storage condition of test material: not given

Test animals

Species:
rat
Strain:
other: Cr1:CD(IM)BR
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS- Source: Charles River Breeding Laboratories, Inc., Kingston, New York (USA)- Age at arrival: approximately 54 days- Weights on day after arrival: males, 235.1 +/- 8.8 (sd); females, 192.2 +/- 6.4 (sd)- Fasting period before study: none- Housing: individually housed, wire-mesh, stainless steel cages (except during neurotoxicity evaluations)- Diet (ad libitum): Purina(TM) Certified Rodent Chow #5002 (meal)- Water (ad libitum): United Water of Delaware (tap water)- Acclimation period: minimum of 6 daysENVIRONMENTAL CONDITIONS- Temperature (°C): 23 +/- 2- Humidity (%): 50 +/- 10- Air changes (per hr): not stated- Photoperiod (hrs dark / hrs light): 12/12IN-LIFE DATES: From: 17 January 1994 To: 4 February 1994

Administration / exposure

Route of administration:
inhalation
Type of inhalation exposure:
whole body
Vehicle:
other: conditioned air
Details on inhalation exposure:
GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION- Exposure apparatus: stainless steel chambers (1 control, 3 test)- Exposure chamber volume: approximately 150 liter- Method of holding animals in test chamber: stainless steel, wire-mesh baskets- Source and rate of air: compressed high-pressure air, flow rates of 32 to 34 L/min (mean)- Method of conditioning air: not given- Treatment of exhaust air: directed through vapor scrubber and discharged to fume hood- Temperature and humidity in air chamber: temperature, 23 +/- 2 deg C; humidity, 50 +/- 10%- Uniform distribution of test atmosphere: stainless steel baffle, positioned directly inside chamber inletTEST ATMOSPHERE ANALYSIS- Brief description of analytical method used: gas chromatography with flame ionization detection; atmospheric concentrations determined approximately at 30-minute intervals during each 6 hour exposure- Samples taken from areas of chambers where rats were exposed.
Analytical verification of test atmosphere concentrations:
yes
Duration of exposure:
6 h
Concentrations:
0, 500, 2500, or 5000 ppm
No. of animals per sex per dose:
12
Control animals:
yes
Details on study design:
BODY WEIGHTS:Body weights were determined on the day after arrival and two additional times during the quarantine period. Body weights were also recorded on the day of baseline neurobehavioral assessments and on test days 1, 2, 8 and 15.FOOD CONSUMPTION:Food consumption was determined for the intervals between test days 1-2, 2-8, and 8-15.CLINICAL SIGNS:Animals were examined daily to detect moribund or dead rats. Clinical signs were recorded on the day after arrival and two additional times during the quarantine period. Beginning on test day 1, clinical signs were recorded daily through test day 14, except for days of neurobehavioral testing.NEUROTOXICITY EVALUATIONS:A neurobehavioral test battery consisting of motor activity and functional observational battery (FOB) assessments was conducted prior to compound administration (baseline) and again after removal of animals from inhalation chambers on day 1. Care was taken to minimize the time from termination of exposure to the start of motor activity testing. Approximately 19 hours after termination of the exposure (test day 2), a motor activity test was followed by an abbreviated FOB. The motor activity and FOB tests (complete) were conducted again on test days 8 and 15.Motor Activity:Each rat was evaluated for motor activity during a 60-minute period in a 30-station automated motor activity monitoring device (Coulbourn(TM) Infrared Motor Activity System). These evaluations were initiated on test day 1 no more than 40 minutes after removal of the animals from the exposure chambers.Motor activity was quantified as both duration and number of movements. A continuous movement, regardless of duration, was counted as one movement by the system. Duration of movement and number of movements were evaluated in six consecutive blocks of 10 minutes each as well as for the total 60 minute session.Functional Observational Battery (FOB):FOB assessments were conducted after the motor activity test and consisted of a series of quantified behavioral observations conducted in a sequence that proceeded from the least interactive to the most interactive. The order of the testing of the rats and the order of assessments in the FOB was the same on all days of testing.During FOB assessments, each rat was evaluated in three environments: 1) inside a home cage; 2) upon removal from the home cage and while being handled; and 3) in a standard “open field” arena (approximately 85 x 59 x 20 cm). For the purposes of these measurements, the home cage was the cage on the transport rack for delivering the rats to the assessment area. The FOB home cage assessments began after 15 minutes of acclimation to the transport cages.The following parameters were assessed during the FOB in the order listed. Those used in the abbreviated FOB are indicated:In Motor Activity Room:defecation, urination, pupillary responseParameters assessed in home cages:- posture (abbrev. FOB)- palpebral closure (abbrev. FOB)- writhing- circling- bitingParameters assessed in removal and handling:- ease of removal- ease of handling- muscle tone- vocalization- piloerection- bite marks on tail and/or paws- palpebral closure- fur appearance- lacrimation- salivationParameters assessed in the open field evaluation:- righting reflex (abbrev. FOB)- labored breathing (abbrev. FOB)- convulsions (abbrev. FOB)- coordination (abbrev. FOB)- grooming- gait characteristics (abbrev. FOB)- ability to locomote- arousal (abbrev. FOB)- vocalization (abbrev. FOB)- palpebral closure (abbrev. FOB)- defecation- urinationManipulations assessed in open field evaluations:- approach and touch response (abbrev. FOB)- auditory response (clicker) (abbrev. FOB)- tail pinch response (abbrev. FOB)- forelimb grip strength- hindlimb grip strength- foot splayFore- and hindlimb grip strength were measured by a strain gauge device (Chatillon(TM) Dial Push-Pull Gauge). Landing foot splay was assessed by measuring fresh ink impressions made by the hindpaws when the rat was released from a height of approximately 30 cm.The presence or absence of pupillary constriction was assessed after a beam of light was directed into each eye.
Statistics:
Clinical observation incidence data, as well as descriptive FOB parameters were evaluated by the Cochran-Armitage test, for trend and a test to determine lack of fit to a monotonic concentration-response relationship. When a significant trend was found, the highest dose group was dropped and the analysis repeated. This process was repeated until no significant effects were found. If a significant trend was not found but the lack of fit was significant, a Fishers test with Bonferroni correction compared each concentration level to control within each gender.Body weights, body weight gains, food consumption, and continuous data from the FOB (fore and hindlimb grip strength, landing foot splay), were analyzed as parametric data. Statistical procedures employed included Bartlett’s Test for Homogeneity of Variance and, when this did not show significance, data were analyzed by univariate Analysis of Variance (ANOVA), with Dunnett’s Test used to identify significant treatment group. Significance was judged at the p < 0.05 level, with the exception of Bartlett’s Test which was judged at alpha = 0.005. Separate analyses were performed on male and female animals.Statistical analysis of motor activity data was initially performed with Shapiro-Wilk’s and Levene’s tests followed by a Bonferroni correction. Motor activity data failed to satisfy the assumption of normality, so non-parametric statistical analyses were performed. These consisted of the Kruskal-Wallis test and a modified Dunn’s multiple comparison procedure to compare each treatment group to control. Separate analyses were performed on each gender and statistical significance was judged as p

Results and discussion

Preliminary study:
A pilot study was conducted at exposure concentrations of 0, 500, 4000 and 5000 ppm of tetrahydrofuran. Four male and female rats were exposed at each concentration, whole-body for 6 hours. Body weights were measured before exposures and on test day 1 and daily through test day 4. Three rats in each control group and 4 rats from each exposed group underwent a motor activity evaluation (40-minute session) after the single exposure. The motor activity test was conducted again on test day 2. An abbreviated FOB was conducted following the motor activity test on days 1 and 2.The results from the pilot study suggested that exposure to 5000 ppm for 6 hours resulted in detectable adverse effects including reduced body weight gains (days 1 to 2), reduced responsiveness to an alerting stimulus, lethargy, reduced motor activity, slowed righting reflex, and possibly palpebral closure. Males were slightly more sensitive than females as indicated by some signs of sedation (slowed righting reflex) and effects on body weight change at 4000 ppm male, but not 4000 ppm females.Suggestive evidence of similar effects at 4000 versus 5000 ppm were not sufficiently compelling to select the 4000 ppm as the high exposure concentration in the definitive study.
Effect levelsopen allclose all
Sex:
male/female
Dose descriptor:
other: NOEC
Effect level:
500 ppm
Exp. duration:
6 h
Remarks on result:
other: On the basis of these data, the principal effect of acute inhalation exposure of THF is a transient sedation with exposure concentrations of 2500 ppm and 5000 ppm. The degree of sedation appears to be concentration dependent.
Sex:
male/female
Dose descriptor:
LC50
Effect level:
> 5 000 ppm
Remarks on result:
other: No mortality recorded in this study
Sex:
male/female
Dose descriptor:
LC50
Effect level:
> 14.7 mg/L air (nominal)
Exp. duration:
6 h
Remarks on result:
other: Based on 1 mg/l = 340 ppm conversion factor
Mortality:
All rats survived to scheduled euthanasia.
Clinical signs:
other: Signs of sedation were detected in the 2500 ppm and 5000 ppm groups during the inhalation exposure in a time- and concentration-dependent manner. Prior to exposures, all exposed rats were judged normal in response to an alerting response. After 2 hours
Body weight:
Mean body weights of male and female rats were unaffected by test compound administration throughout the study. Mean body weight gains of the 5000 ppm male rats were significantly less than control values on the interval between test days 1 and 2, however, these rats displayed increased body weight gains on test days 2 to 8, when compared to controls.Summary of mean body weight gains (g) for control and dosed groups, male rats:Test Day 1-2: -10.5 +/- 5.2 (control); -8.9 +/- 5.6 (500); -13.6 +/- 5.0 (2500); -20.5 +/- 5.5* (5000)Test Day 2-8: 38.6 +/- 5.3 (control); 37.0 +/- 6.4 (500); 39.1 +/- 13.0 (2500); 46.4 +/- 7.5 (5000)Test Day 8-15: 30.9 +/- 8.0 (control); 33.4 +/- 5.2 (500); 30.1 +/- 5.5 (2500); 31.9 +/- 6.7 (5000)* stat. sig p < 0.05Female rats were similarly affected, however, the changes were not statistically significant.Summary of mean body weight gains (g) for control and dosed groups, female rats:Test Day 1-2: -7.2 +/- 5.9 (control); -7.4 +/- 6.5 (500); -8.2 +/- 8.3 (2500); -12.1 +/- 9.6 (5000)Test Day 2-8: 13.4 +/- 7.9 (control); 13.6 +/- 7.6 (500); 15.2 +/- 9.3 (2500); 18.7 +/- 11.2 (5000)Test Day 8-15: 10.6 +/- 9.3 (control); 7.7 +/- 9.4 (500); 14.9 +/- 7.8 (2500); 12.3 +/- 6.5 (5000)
Gross pathology:
None obtained.
Other findings:
Motor ActivityThere were no statistically significant effects of the test substance on the total duration of movement or the total number of movements for male rats. The 5000 ppm female rats exhibited a tendency toward reduced number and duration of total movements during the motor activity session on day 1, but results were not statistically significant. Analysis of successive 10-minute blocks within the session with high-dose female rats on test day 1 indicated reduced number and duration of movements in the second block. This was regarded as compound-related as there was other evidence from clinical signs of lethargy and behavioral sedation.Motor activity data from day 1 provides evidence of the sedative effect of tetrahydrofuran immediately following acute inhalation exposure. The subsequent motor activity measurements revealed only minor decreases in the number and duration of movements during the early portion of the session for the 5000 ppm female rats. The lack of effects in the 2500 ppm groups suggests that rapid and complete recovery from sedation had occurred in the 2500 ppm groups within one hour. The minor motor activity effects in the 5000 ppm females and the lack of effects in the 5000 ppm males suggest that recovery from sedation was occurring rapidly upon termination of exposure.On test day 2, motor activity results were generally unremarkable. In male rats at 5000 ppm, the duration of movement was significantly increased (18%) over control for the first 10-minute block of the sessions and 35% for the second. The total duration of movement for this group was increased 26% over control but was not statistically significant. The data indicate a rebound hyperactivity on the day following exposure, however, the meaning of this observation is not completely clear. The interpretation is further confounded by differences between 5000 ppm males and controls during baseline assessments prior to exposure. These baseline measurements indicated increased duration of movement for this same group over controls (not significant).There were no compound-related effects noted for the remainder of the study for either gender of rat.Functional Observational Battery (FOB)Of the 36 parameters evaluated during the FOB, only righting reflex, palpebral closure, and ease of handling were adversely affected by the test substance in the 5000 ppm groups.A notable slowing of righting reflex was observed in 33% (4/12) 5000 ppm males and 17% (2/12) 5000 ppm females on test day 1. Both groups had a single animal for which the righting reflex was absent. Although none of these observations were statistically significant, they were judged as toxicologically relevant as compound-induced sedation.The 5000 ppm female group displayed an increased incidence (17%, 2/12) of palpebral closure despite the appearance of wakefulness. Two rats in this group were judged “too easy” to handle and did not display a normal amount of resistance.Fewer home-cage 5000 ppm male rats (8%, 1/12) were found asleep versus control (50%, 6/12). This finding may indicate a recovery from sedation at the 5000 ppm level but a definitive interpretation is not known.On test day 1, a significantly decreased arousal level for 500 ppm female rats was considered spurious and not compound-related.Several parameters of defecation and urination during the FOB were statistically significantly different among control and treated groups. On test day 1 in females, the concentration-response did not appear to be compound-related. In males, the incidence scores decreased in a concentration-related fashion. The importance of this is not clear.No statistically significant nor biologically remarkable effects of the test substance were found on test day 15.

Applicant's summary and conclusion

Interpretation of results:
other: R67 (Vapours may cause drowsiness and dizziness)
Remarks:
Criteria used for interpretation of results: other: EU DSD classification criteria (EU Directive 67/548/EEC)
Conclusions:
Exposure to 2500 and 5000 ppm tetrahydrofuran by inhalation produced sedative effects in adult male and female rats. The effects were not apparent during and immediately after exposure. The sedative effects were relatively mild in the 2500 ppm group but were more prominent and of longer duration in the 5000 ppm exposures. These neurobehavioral effects were completely absent a few hours after exposure to 2500 ppm and within 19 hours after exposure to 5000 ppm. The 5000 ppm males and females exhibited reduced body weight gains on test days 1-2, and the 5000 pm males exhibited reduced food consumption during this interval. None of the body weight and food consumption effects persisted during the remainder of the study. The no-observed-adverse-effect level was determined to be 500 ppm by the inhalation route.Based on the clear presence of CNS depression in animal studies, tetrahydrofuran is classified as R67 (Vapours may cause drowsiness and dizziness) under the EU DSD classification criteria.Tetrahydrofuran would be rated STOT SE 3, based on CNS depression according to the EU CLP classification criteria (EU Regulation 1272/2008).
Executive summary:

Young adult male and nulliparous female Cr1:CD(TM)BR rats (12 rats/gender/concentration) were exposed for a single six-hour session by inhalation to tetrahydrofuran via whole body at concentrations of 0, 500, 2500 or 5000 ppm. Neurobehavioral tests consisted of observations of the rats during exposure as well as motor activity (MA) and functional observational (FOB) battery assessments conducted prior to compound administration and again on test day 1 as soon as practical following exposure. A MA and an abbreviated FOB were conducted on day 2. A MA and full FOB were conducted again on days 8 and 15. Body weights were recorded before exposure and on test days 1, 2, 8 and 15. Food consumption was recorded for the intervals between test days 1-2, 2-8 and 8-15. Clinical signs were recorded immediately upon removal from the test chambers and daily thereafter except on days of neurbehavioral testing. Following the final neurobehavioral tests, all rats were euthanized and discarded without pathological evaluation.

All rats survived to scheduled euthanasia. Signs of sedation were present in a time- and concentration manner in the 2500 and 5000 ppm groups during inhalation exposures. After 2 hours of exposure, 25% of the 2500 ppm rats and 50% of the 5000 ppm rats exhibited a diminished alerting response. After 4 hours, all 2500 ppm rats displayed a diminished response; 50% of the 5000 ppm rats displayed a diminished response and 50% no observable alerting response. The control and 500 ppm rats were judged normal.

Clinical signs recorded immediately upon removal from the exposure chambers revealed additional signs of sedation. Lethargy was present in almost all 5000 ppm rats and in two 2500 ppm female rats. Other signs included splayed rear legs (2500 and 5000 ppm groups) and abnormal gait (5000 ppm). The clinical signs observed the 5000 ppm rats (lethargy, abnormal gait or mobility, and splayed rear legs) were absent a few hours later during the FOB assessment.

Motor activity tests began within 40 minutes of removal from exposure chambers revealed only minor decreases in number and duration of movements during early portions of the analysis for the 5000 ppm female rats. The lack of effects at 2500 ppm suggests a rapid and complete recovery from sedation. Complete recovery from sedation for the 2500 ppm group was confirmed by the absence of compound-related effects in the FOB assessment that was conducted after the MA analysis. Of the 36 parameters evaluated in the FOB assessment, only righting reflex, palpebral closure and ease of handling were adversely affected in the 5000 ppm group.

With the exception of possible rebound hyperactivity during portions of the MA test on 5000 ppm male rats on test day 2, no toxicologically important neurobehavioral effects were detected after test day 1. Body weight gains were significantly decreased in the 5000 ppm males between test days 1 and 2. The 5000 ppm females showed a similar weight gain pattern, although the effects were not significant. Similarly, mean food consumption was significantly decreased in the 5000 ppm male rats between test days 1 and 2; as for weight gain decreases, decreased food consumption in female rats was not significant. Body weight gains increased (not significantly) over control values between test days 2 and 8, suggesting a compensatory increase. No other compound-related effects were observed during the remainder of the study.

The principal effect of acute inhalation exposure of tetrahydrofuran in rats is transient sedation with exposure concentrations of 2500 ppm and 5000 ppm. The degree of sedation appears to be concentration dependent. The no-observable-adverse-effect-level for acute exposure in male and female rats was determined to be 500 ppm by the inhalation route.