Judith C. Stadler

Subchronic Toxicity of a Fluoroalkylethanol Mixture in Rats

The objective of this study was to evaluate the subchronic toxicity of a commercial fluoroalkylethanol mixture, which is an intermediate in the production of fluoroorganic compounds that are used as protectants and surfactants. The test substance was administered daily by gavage to Sprague–Dawley rats as a suspension in aqueous methylcellulose. The dosages were 0, 25, 100, or 250 mg kg− 1 day− 1. A 1- and 3-month recovery period was included to evaluate the reversibility of toxic effects. No test substance–related mortality or neurotoxicity occurred. Body weights and/or nutritional parameters were significantly reduced at 100 and 250 mg kg− 1 day− 1, and these effects were reversible. Broken and absent teeth were observed in rats dosed with 250 mg kg− 1 day− 1, and microscopic tooth lesions (ameloblast degeneration/disorganization) occurred at 100 and 250 mg kg− 1 day− 1 and persisted with decreased severity throughout recovery. Decreased red cell mass parameters occurred at 90 days in the 250 mg kg− 1 day− 1 group, but red cell counts were normal thereafter during recovery. A persistent elevation of liver weights was seen in groups given ≥ 100 mg kg− 1 day− 1. The increased weights correlated with microscopic hepatocellular hypertrophy only in males and females administered 250 mg kg− 1 day− 1. Hepatic β-oxidation was increased in a dose-dependent manner and persisted through 1 month of recovery at 250 mg kg− 1 day− 1. Increased kidney weights were observed at 25 (females only), 100, and 250 mg kg− 1 day− 1. These elevated weights persisted in the high dose after recovery and correlated with microscopic tubular hypertrophy (males only). Thyroid follicular hypertrophy was present at 100 and 250 mg kg− 1 day− 1 but was not present after recovery. Total fluorine in whole blood increased with continuous dosing and achieved steady state in approximately 42 days. Both plasma and urine fluoride levels were elevated in adose-dependent manner. Under the conditions of the study, the no-observed adverse effect level for this mixture was 25 mg kg− 1 day− 1 for subchronic toxicity.

Subchronic toxicity of cyclohexane in rats and mice by inhalation exposure

Inhalation studies were conducted to determine the potential toxicity and/or potential neurotoxicity of cyclohexane. Groups of rats and mice were exposed to 0, 500, 2000, or 7000 ppm concentrations of cyclohexane vapor 6 hr/day, 5 days/week for 14 weeks. Subgroups of rats and mice were further observed during a 1-month recovery period. Functional observational battery (FOB) and motor activity (MA) behavioral tests were conducted on rats. These tests were conducted prior to the exposure series and during weeks 4, 8, and 13 on non-exposure days. Clinical pathology evaluations were conducted after approximately 7, 13, and 18 weeks. Approximately 14 and 18 weeks after study initiation, tissues from rats and mice were histologically processed and evaluated by light microscopy. During exposure to 2000 or 7000 ppm, rats and mice had a diminished response or an absent response to delivery of a punctate auditory alerting stimulus. Immediately following removal of rats from the inhalation chambers, 7000 ppm males and females and 2000 ppm females displayed a compound-related increase in the incidence of wet and/or stained fur (which occurred in the areas of the mouth, chin, and/or perineum). These signs were transient, were not observed during exposure or prior to exposure the following day, and were not associated with any behavioral or morphological changes. During exposure sessions, mice exposed to 7000 ppm exhibited clinical signs of toxicity which included hyperactivity, circling, jumping/hopping, excessive grooming, kicking of rear legs, standing on front legs, and occasional flipping behavior. Clinical signs of toxicity observed in 7000 ppm mice immediately after exposure included hyperactivity, hyperreactivity, ruffled fur (females only), gait abnormalities, spasms in both rear legs, and excessive grooming (males only). The clinical signs observed in mice during and immediately after exposure were transient, and were not present prior to the subsequent exposure. A few mice exposed to 2000 ppm appeared hyperactive during exposure in the latter portion of the study. There were no compound-related changes in mean body weights, body weight gains, food consumption, food efficiency, or mortality; and there were no ophthalmological abnormalities in rats or mice. In addition, there were no compound-related effects on 37 different behavioral parameters assessed during the FOB or during motor activity tests in rats. Male and female mice exposed to 7000 ppm had slight increases in measures of circulating erythrocyte mass (red blood cells, hemoglobin, hematocrit) and plasma protein concentration (males only). Male rats and male and female mice exposed to 7000 ppm had significantly increased relative liver weights, and 7000 ppm male mice also had significantly increased absolute liver weights at the end of the exposure period. At the end of the 1-month recovery period, absolute and relative liver weights of male and female mice were similar to control. However, relative liver weights of 7000 ppm male rats continued to be significantly higher at the end of the recovery period. Male and female rats exposed to 7000 ppm had a significantly increased incidence of hepatic centrilobular hypertrophy at the end of the exposure period, which was not observed at the conclusion of the 1-month recovery period. No microscopic changes were observed in mice. In rats, the no-observed-effect level (NOEL) for acute, transient effects was 500 ppm based on a diminished/absent response to an auditory alerting stimulus at 2000 ppm and above. The NOEL for subchronic toxicity in rats was 7000 ppm based on the lack of adverse effects on body weight, clinical chemistry, tissue morphology, and neurobehavioral parameters. In mice, the NOEL for acute, transient effects was 500 ppm based on behavioral changes during exposure at 2000 ppm and above. The NOEL for subchronic toxicity in mice is 2000 ppm based on hematological changes at 7000 ppm.

Evaluation of the Reproductive and Developmental Toxicity of a Fluoroalkylethanol Mixture

The objective of these studies was to evaluate the reproductive and developmental toxicity of a commercial fluoroalkylethanol mixture, which is an intermediate in the production of fluorotelomers. The test substance was administered daily by gavage to Sprague–Dawley rats as a suspension in 0.5% aqueous methylcellulose. In a one-generation reproductive toxicity study, rats (20 per sex per group) were given dosages of 0, 25, 100, or 250 mg kg− 1 day− 1 for a period of 74 days prior to cohabitation, and during mating, gestation, and lactation. Body weights, feed consumption, clinical signs, gross pathology, sperm parameters, estrous cyclicity, and reproductive performance were evaluated for the P1 generation. The F1 offspring were evaluated during the lactation period for growth and survival and given a gross pathology examination at weaning. A subset of the offspring were retained; body weights, feed consumption, clinical signs, and age at onset of vaginal opening and preputial separation were evaluated, and gross pathology was performed on postnatal day 60. In the developmental toxicity study, groups of time-mated Sprague–Dawley female rats were given the test substance as a suspension in 0.5% aqueous methylcellulose at daily dosages of 0, 50, 200, or 500 mg kg− 1 day− 1 by gavage on gestation days 6–20. During the in-life portion of the study, growth parameters and clinical observations were made. On gestation day 21, dams were euthanized, and the thoracic and abdominal viscera were examined. The uterine contents were removed and examined, and fetuses were evaluated for any alterations. In the reproduction study, litter size at birth, number of live pups per litter on day 0 and 4 of lactation, and pup weights during lactation were reduced in groups administered ≥ 100 mg kg− 1 day− 1. No other reproductive parameters were affected. There were no adverse reproductive effects observed at 25 mg kg− 1 day− 1. In the developmental toxicity study, reduced maternal body weight parameters, increased perineal fur staining, and increased fetal skeletal alterations were observed at 500 mg kg− 1 day− 1. There was no maternal or developmental toxicity at 50 or 200 mg kg− 1 day− 1. Under the conditions of the studies, the no-observed adverse effect levels for this mixture were 25 mg kg− 1 day− 1 for subchronic toxicity and reproductive parameters and 200 mg kg− 1 day− 1 for developmental toxicity end points. No functional reproductive or developmental effects were observed at dose levels that did not adversely affect adult animals.

ACUTE AND SUBCHRONIC NEUROTOXICOLOGICAL EVALUATION OF TETRAHYDROFURAN BY INHALATION IN RATS

Groups of adult male and female rats received exposure to tetrahydrofuran (THF) vapor by inhalation in acute or subchronic exposure scenarios. Acute exposure concentrations were 0, 500, 2500, or 5000 ppm for 6 hr. Evaluations conducted immediately after exposure included clinical observations, motor activity assessments (MA), and a battery of functional tests (FOB) designed to reveal nervous system dysfunction. During exposure to 2500 and 5000 ppm, rats had a diminished or absent startle response to a punctate auditory alerting stimulus. Following exposure to 5000 ppm, male and female rats were lethargic, exhibited abnormal gait or mobility, and splayed rear feet. Lethargy and splayed rear feet were also observed in females esposed to 2500 ppm. During the subsequent FOB, males exposed to 5000 ppm had a lower incidence of palpebral closure, higher incidences of slow or absent righting reflex, and a biphasic pattern of reduced motor activity followed by increased motor activity. Females exposed to 5000 ppm had increased incidences of palpebral closure in the open field, increased incidences of slow or absent righting reflex, and decreased motor activity. During the 14-week subchronic exposure series, daily THF exposure concentrations were 0, 500, 1500, or 3000 ppm, and neurobehavioral evaluations occurred on non-exposure days at approximately monthly intervals. Diminished startle responses to an auditory alerting stimulus were observed during exposure to 1500 or 3000 ppm; however, repeated exposures did not cause additional neurobehavioral or pathological effects. This pattern of effects is suggestive of transient sedation. Despite daily reinstatement of acute sedative effects during repeated exposure with up to 3000 ppm, THF did not produce any persistent or cumulative effects on nervous system structure or function. The demonstrated no-observed-effect level of THF for both acute and subchronic exposure was 500 ppm.

Subchronic, Reproductive, and Developmental Toxicity of a Fluorotelomer-Based Urethane Polymeric Product

A commercial fluorotelomer-based urethane polymeric dispersion, consisting of polymer, surfactant, and water, was evaluated in subchronic, reproduction, and developmental toxicity studies. The dispersion was administered daily by gavage to rats at dosages of 0, 50, 250, or 1000 mg polymer/kg/day or with 70 mg/kg/day of the sulfonate surfactant. Dose levels of 0, 50, 250, or 1000 mg polymer/kg/day were also used for the reproductive and developmental studies. Nasal olfactory epithelial degeneration and necrosis occurred in all dose groups in the 90-day study. Nasal adhesions were observed only in rats administered surfactant alone. Liver-enzyme alterations at 250 and 1000 mg/kg were considered to be potentially adverse effects. The subchronic no-observed-adverse-effects level (NOAEL) was 50 mg/kg. For the reproduction study, rats were dosed for 10 weeks prior to cohabitation and throughout mating, gestation, and lactation. There were no effects on reproductive function in males or females at any dosage. Thyroid weight was decreased in the 250 and 1000 mg/kg day F1 groups unaccompanied by microscopic effects. In the developmental toxicity study, female rats were dosed from gestation days 6–20; there was no test-substance-related embryolethality, nor was there any dose-related increase in either fetal malformations. Fetal weight was minimally decreased at 1000 mg/kg/day in the presence of slight maternal toxicity; the NOAEL for developmental parameters was 250 mg/kg/day. The polymeric product was not a specific developmental or reproductive toxin.

Repeated exposure inhalation study of pentane in rats

Pentane (CAS No. 109-66-0) is a chemical being used as a co-solvent in a polymer production facility with potential for inhalation exposure in humans. To assess the toxicity of pentane, groups of 10 male rats each were exposed by inhalation, 6 hr/day, 5 days/week for 2 weeks to either 0 (control), 1,000, 3,000 or 10,000 ppm. Five rats per group were killed following the 10th exposure; the remaining 5/group were killed after a 14-day post-exposure recovery period. Parameters investigated were clinical signs of toxicity, functional behavior, body weights, clinical pathology, and gross and microscopic pathology including organ weights. No unusual clinical observations were seen in the pentane-treated rats, and body weights were not altered. Test rats generally exhibited normal behavioral responses in the functional observational battery. Increases in serum calcium and phosphorus concentrations were seen in rats exposed to either 3,000 or 10,000 ppm. These were reversible during the 2-week recovery period. No other clinical pathology changes were observed and no pentane-related tissue pathology was seen in any of the groups. The no-observed-adverse-effect level was 1,000 ppm with reversible clinical pathology changes produced at 3,000 and 10,000 ppm.

Evaluation of a method used to test for potential toxicity of carpet emissions.

After a private testing laboratory had reported mortality, neurotoxicity, and respiratory irritation in mice exposed to emissions from heated carpet in a modified application of the sensory irritation test (ASTM E981-84), the studies reported in this paper were conducted to evaluate the method used in testing for carpet toxicity and to see if the reported findings were reproducible. Mice were exposed head-only to offgasses generated by heating carpet (AT #3) to temperatures that ranged from 37 to 70 degrees C. Control mice were simultaneously exposed to heated air. The animals were evaluated for mortality, clinical signs and respiratory irritation. Neurotoxicity was evaluated using functional observational battery and motor activity monitoring. Pathological evaluations of organs and tissues, including the nervous system, were also conducted. The carpet samples heated to higher temperatures produced greater concentrations of total volatile organic compounds than those heated to 37 degrees C. Both carpet-exposed and control mice displayed some effects, such as body weight loss, mortality and pathological lesions, that were due to the exposure system. There was no mortality or neurotoxicity, nor were there clinical signs or pathological lesions as a result of carpet exposures. Mice exposed to carpet heated to 70 degrees C had slightly decreased respiratory rates and an increased incidence of breathing patterns indicative of sensory irritation. Therefore, none of the results reported by the private testing laboratory could be reproduced when this carpet was heated to temperatures below 70 degrees C, and slight sensory irritation was the only effect observed at the 70 degrees C test conditions. Effects from the exposure system itself made interpretation of results difficult, and concurrent controls were considered essential for interpretation of data.

SUBCHRONIC INHALATION EXPOSURE TO ACETONE VAPOR AND SCHEDULED CONTROLLED OPERANT PERFORMANCE IN MALE RATS

Groups of adult male rats (10/group) were used to assess whether subchronic inhalation exposure to 0, 1000, 2000, or 4000 ppm of acetone vapor altered schedule-controlled operant performance. Rats were exposed to acetone vapor for 6 h/day, 5 days/wk, for a 13-wk period. Extensive training prior to the exposure series established a stable baseline of lever-pressing on a multiple fixed-ratio-fixed-interval (FR 20-FI 120 s) schedule of food presentation. Operant sessions occurred prior to each daily exposure to avoid confounding the detection of enduring behavioral effects with transient acute effects. FI response rate, FI index of curvature, and FR running rate of response were not affected during or after the 13-wk exposure series. FR post-reinforcement pause duration for the control group increased during the course of the study more than that of the 2000 ppm and 4000 ppm groups, which changed only slightly relative to pretreatment baseline. Based on the performance of historical controls that had FR pause durations similar to those of acetone-treated groups, the differences in FR pause duration were probably due to drift of the concurrent control group and were not related to acetone treatment. Prolonged exposure to up to 4000 ppm acetone vapor does not appear to have enduring effects on nervous system functions that mediate the performance of a complex, learned task.