Evaluation of teratogenicity and neurotoxicity with maternal inhalation exposure to methyl chloroform

Binge toluene exposure in pregnancy and pre-weaning developmental consequences in rats

Binge Toluene Exposure in Pregnancy and Pre-weaning Developmental Consequences in Rats. Bowen, S.E. and Hannigan, J.H. The persistent rate of abuse of inhaled organic solvents, especially among women of child-bearing age, raises the risk for teratogenic effects of maternal toluene abuse. In this study, timed-pregnant Sprague Dawley rats were exposed from Gestation Day (GD) 8 to GD20 to 12,000 or 8000 parts per million (ppm) toluene, or 0ppm (controls) for 30min twice daily, 60min total daily exposure. Pups were assessed from postnatal day (PN) 4 to PN21 using a developmental battery measuring growth (i.e., body weight), maturational milestones (e.g., eye opening & incisor eruption), and biobehavioral development (e.g., negative geotaxis & surface righting). Pups exposed in utero to 12,000ppm or 8000ppm toluene weighed significantly less than the non-exposed control pups beginning at PN4 and PN12 (respectively) until PN21. Toluene resulted in significant increases in an index of poor perinatal outcome, specifically a composite of malformations, defined "runting" and neonatal death. No significant delays were observed in reaching maturational milestones. The results reveal that brief, repeated, prenatal exposure to high concentrations of toluene can cause growth retardation and malformations in rats. A comparison of the present, conservative results with findings in previous studies implies that binge patterns of toluene exposure in pregnant rats modeling human solvent abuse can result in developmental and morphological deficits in offspring. These results do not exclude the possibility that maternal toxicity as well as teratogenic effects of toluene may contribute to outcomes. The results suggest that abuse of inhaled organic solvents like toluene may result in similar early developmental outcomes in humans.

Alterations in rat fetal morphology following abuse patterns of toluene exposure

Toluene is a commonly abused organic solvent. Inhalant abusers are increasingly women in their prime childbearing years. Children born to mothers who abused solvents during pregnancy may exhibit characteristics of a "fetal solvent syndrome" which may include dysmorphic features. This study examined the teratological effects of an abuse pattern of binge toluene exposure during gestation on skeletal and soft tissue abnormalities, body weight, and body size in fetal rats. Pregnant Sprague-Dawley rats were exposed for 30 min, twice daily, from gestational day (GD) 8 through GD20 to either air (0 ppm), 8000 ppm, 12,000 ppm, or 16,000 ppm toluene. Two-thirds of each litter was prepared for skeletal examination using Alizarin Red S staining while the remaining third of each litter was fixed in Bouin's solution for Wilson's soft tissue evaluation. Exposure to toluene at all levels significantly reduced growth, including decreases in placental weight, fetal weight, and crown-rump length. In addition, numerous gross morphological anomalies were observed such as short or missing digits and missing limbs. Skeletal examination revealed that ossification of the extremities was significantly reduced as a result of toluene exposure at all levels. Specific skeletal defects included misshapen scapula, missing and supernumerary vertebrae and ribs, and fused digits. Soft tissue anomalies were also observed at all toluene levels and there was a dose-dependent increase in the number of anomalies which included cryptorchidism, displaced abdominal organs, gastromegaly, distended/hypoplastic bladder, and delayed cardiac development, among others. These results indicate that animals exposed prenatally to levels and patterns of toluene typical of inhalant abuse are at increased risk for skeletal and soft tissue abnormalities.

Final Report on the Safety Assessment of Trichloroethane

Trichloroethane functions in cosmetics as a solvent. Although Trichloroethane has been reported to the Food and Drug Administration (FDA) to be used in cosmetic products, an industry survey found that it is not in current use in the cosmetic industry. Trichloroethane is considered a Class I ozone-depleting substance by the Environmental Protection Agency (EPA) and its use is prohibited in the United States, unless considered essential. The FDA has stated that Trichloroethane's use in cosmetics is considered nonessential. Trichloroethane is detected by gas chromatography, gas chromatography-mass spectrometry, and gas-liquid chromatography. In rats, Trichloroethane, whether inhaled or injected, is mostly expelled intact from the body through exhalation. A very small percentage is excreted in the urine. In humans, Trichloroethane is rapidly absorbed through the skin and eliminated in exhaled air and a very small percentage is excreted in urine. Inhaled Trichloroethane is eliminated in exhaled air. Acute oral LD50 values have been reported as follows: 12.3 g/kg in male rats; 10.3 g/kg in female rats; 11.24 g/kg in female mice; 5.66 g/kg in female rabbits; and 9.47 g/kg in male guinea pigs. Acute toxicity studies using other routes of exposure, including subcutaneous injection and inhalation, produced no evidence of significant toxicity, except at very high exposure levels. Continuous inhalation exposure of rabbits to 750 mg/m3 for 90 days did not produce any signs of toxicity. Continuous exposure of rats, guinea pigs, rabbits, and monkeys to 500 ppm Trichloroethane for 6 months did not produce any signs of toxicity. Other short-term and subchronic inhalation exposures confirmed acute and short-term exposure findings that the toxic effects of inhalation were a function of both concentration and time. Rats receiving 750 or 1500 mg/kg day–1 Trichloroethane in corn oil by oral gavage 5 days per week for 78 weeks had reduced body weights and early mortality. Reduced body weights, decreased survival rates, and early mortality (in females) were found in mice dosed with 3000 or 6000 mg/kg day–1 (over the last 58 weeks; lower doses were administered for the first 20 weeks). Mice exposed to prolonged periods of Trichloroethane in an inhalation chamber had increased motor activity at levels up to 5000 ppm. Further increase of concentration of exposure resulted in less of an increase of motor activity until motor activity began to fall below normal at 10,000 ppm. Adverse effects on motor activity in rats were seen at exposures as low as 3000 ppm for 4 h. Rabbits had slight reddening and scaling after 10 24-h applications to abdominal skin of Trichloroethane mixed with 2.4% to 3.0% dioxane, and slight to moderate erythema, slight edema, and slight exfoliation was observed when 75% Trichloroethane and 25% tetrachloroethylene were applied to rabbit ears for 11 days. Undiluted Trichloroethane applied to the clipped backs of guinea pigs produced histopathologic damage in the epidermis. A primary irritation index of 5.22 (out of 8) was reported in rabbits. Trichloroethane applied to the eyes of rabbits resulted in transient irritation and apparent pain, but no corneal damage. There was no effect on gestation, pup survival, or growth in mice given Trichloroethane in drinking water at up to 5.83 mg/ml during mating and/or gestation. Rats exhibited no or minimal effects of ingestion of Trichloroethane up to 30 ppm in drinking water during mating and/or gestation. There was no effect on gestation, pup survival, or growth in mice or rats inhaling 875 ppm Trichloroethane. However, prenatal exposure of rodents to Trichloroethane can produce developmental toxicity in the form of delayed development in the offspring. Trichloroethane has been found to be mutagenic in the Ames assay in some studies and not mutagenic in others. Trichloroethane induced transformations in Fischer rat embryo cell system at 99 μM, was not mutagenic using the mouse lymphoma assay at up to 0.51 μg/ml, was equivocal in that assay when tested with S9, and was also equivocal in a sister-chromatid exchange assay using Chinese hamster ovarian (CHO) cells with and without S9. Mice ingesting 80,000 ppm Trichloroethane in their drinking water had an increase in the frequency of micronucleated normochromatic erythrocytes. A peripheral blood micronucleus test in female mice was negative. Trichloroethane was not carcinogenic to rats when administered 1500 mg/kg by oral gavage 5 days/week for 78 weeks or in mice administered 6000 mg/kg. Exposure to 1500 ppm Trichloroethane vapor for 6 h/day, 5 days/week for 2 years likewise gave no indications of oncogenic effects in rats or mice. People who have been exposed to Trichloroethane have reported dizziness, lassitude, unconsciousness, respiratory depression, peripheral vascular collapse, impaired postural control, mild encephalopathy, perioral tingling, burning on the tongue and discomfort in the hands and feet. The Cosmetic Ingredient Review (CIR) Expert Panel recognizes that Trichloroethane (1,1,1-Trichloroethane) has been declared a Class I ozone-depleting substance by the EPA and its use is limited to essential products. The FDA has determined that use of Trichloroethane in aerosol cosmetic products is considered nonessential. At issue for this assessment is the safety of direct exposure to individuals as a result of exposure to cosmetic products that may contain Trichloroethane. The Expert Panel found the available data to be sufficient to support the safety of Trichloroethane as a solvent in cosmetic products.

Developmental toxicity of prenatal exposure to toluene

Organic solvents have become ubiquitous in our environment and are essential for industry. Many women of reproductive age are increasingly exposed to solvents such as toluene in occupational settings (ie, long-term, low-concentration exposures) or through inhalant abuse (eg, episodic, binge exposures to high concentrations). The risk for teratogenic outcome is much less with low to moderate occupational solvent exposure compared with the greater potential for adverse pregnancy outcomes, developmental delays, and neurobehavioral problems in children born to women exposed to high concentrations of abused organic solvents such as toluene, 1,1,1-trichloroethane, xylenes, and nitrous oxide. Yet the teratogenic effects of abuse patterns of exposure to toluene and other inhalants remain understudied. We briefly review how animal models can aid substantially in clarifying the developmental risk of exposure to solvents for adverse biobehavioral outcomes following abuse patterns of use and in the absence of associated health problems and co-drug abuse (eg, alcohol). Our studies also begin to establish the importance of dose (concentration) and critical perinatal periods of exposure to specific outcomes. The present results with our clinically relevant animal model of repeated, brief, high-concentration binge prenatal toluene exposure demonstrate the dose-dependent effect of toluene on prenatal development, early postnatal maturation, spontaneous exploration, and amphetamine-induced locomotor activity. The results imply that abuse patterns of toluene exposure may be more deleterious than typical occupational exposure on fetal development and suggest that animal models are effective in studying the mechanisms and risk factors of organic solvent teratogenicity.

Abuse pattern of gestational toluene exposure and early postnatal development in rats

Inhalant abuse in the United States trails only alcohol, marijuana and nicotine abuse. Toluene, found in glues and cleaners, is among the most commonly abused inhalants. While teratogenicity due to occupational exposure to organic solvents (i.e., relatively long-term exposure to lower concentrations) has been studied, the teratogenic potential of organic solvent abuse (i.e., brief inhalation exposures to very high concentrations) has not been thoroughly examined. In a preclinical model of abuse patterns of fetal solvent exposure, timed-pregnant rats were exposed to 8000 parts per million (ppm) or 12,000 ppm of toluene, or to air (0 ppm), for 15 min twice daily from gestation day 8 (GD8) through GD20. After parturition, pups were tested from postnatal day 4 (PN4) to PN21 in a developmental test battery including measures of growth (i.e., body weight), maturational milestones (i.e., pinnae unfolding, incisor eruption and eye opening) and biobehavioral development (e.g., negative geotaxis, surface righting and grip strength). Pups exposed in utero to 12,000 ppm toluene weighed significantly less than the control pups at all ages before PN16. There were significant toluene-induced increases in an index of poor perinatal outcome (i.e., a combination of malformations, "runting" and neonatal death) and deficits in negative geotaxis. There were no significant delays in reaching maturational milestones. The results demonstrate that brief, repeated, prenatal exposure to high concentrations of toluene can cause growth restriction, malformation and impairments of biobehavioral development in rats. A comparison of the present outcomes to previous studies of occupational exposure patterns suggests that for a given daily "dose" of toluene, a binge pattern of exposure may pose a greater risk for fetal development. Since the pattern of exposure in this experiment models binge exposure in human solvent abuse, the results imply that abuse of inhaled organic solvents, such as toluene, can cause similar teratogenic outcomes in humans.

Inhalant abuse in pregnancy

Information from a variety of sources suggests the possibility of adverse effects of maternal inhalant abuse, although a well-controlled, prospective study in this area has not been conducted. One source of this concern is the data from occupational exposure to some of the abused solvents, specifically toluene and TCE, with numerous reports suggesting increased spontaneous abortion and fetal malformations. There are also data suggesting decreased fertility and an increased risk for spontaneous abortion in health care workers exposed to nitrous oxide. The relevance of these studies to problems of inhalant abuse is not clear. Although the chemicals involved are the same, there are many differences in the exposure parameters, the populations exposed, and the types of associated risk factors. Nonetheless, there are more than 100 cases reported in the literature of children born to solvent-abusing mothers. Many of these children were small at birth, and some have craniofacial abnormalities not unlike that seen in children with FAS. In the few studies reporting the findings of follow-up in these children, some evidence has been obtained for retardation in growth and development and for residual deficits in cognitive, speech, and motor skills. Clearly, more research is needed to rule out the concomitant risk factors and to identify specific chemicals and patterns of use associated with adverse effects. Animal studies provide more direct evidence that prenatal exposure to toluene or TCE can produce reduced birth weights, occasional skeletal abnormalities, and delayed neurobehavioral development, even under conditions designed to mimic inhalant abuse patterns. Additional research is needed to identify other chemicals with adverse effects, critical periods of exposure, effects of combinations of inhalants, or interactions with drugs of abuse. The research literature seems sufficient to alert clinicians to possible problems in patients who abuse inhalants while pregnant. Diagnosis and good prenatal care for these women are important. The evidence for neonatal withdrawal is limited at this time; however, infants born to women who have recently used inhalants should be observed carefully for an alcohol-like withdrawal syndrome. Although it is not possible to link a specific birth defect or developmental problem in the child of an inhalant abuser to prenatal exposure to a specific chemical, it is clear that inhalant abuse and its associated lifestyle place children at increased risk. A wider appreciation of this is needed among health care professionals and the general public.

Developmental consequences of intermittent and continuous prenatal exposure to 1,1,1-trichloroethane in mice

The effects of 1,1,1-trichloroethane (TCE) on physical and behavioral development were examined in CD-1 mice prenatally exposed under two regimens. In the first study, pregnant mice were exposed to either 2,000 ppm TCE or filtered air for 17 hrs. during gestational days (GD) 12-17. A third group remained untreated. The results revealed no differences on pregnancy outcome. TCE-exposed pups gained less weight, exhibited delays in developmental landmarks and acquisition of the righting reflex, had poorer performance on tests of motor coordination and exhibited delays in negative geotaxis relative to sham or untreated pups. A second experiment was designed to more closely parallel the intermittent, acute, high-concentration pattern of solvent abuse. Pregnant mice were exposed for 60 min. to 8,000 ppm TCE or sham placement in exposure chambers three times/day during GD's 12-17. The results were very similar to what were obtained in the more continuous exposure study. TCE-exposed pups gained less weight, had delays in developmental landmarks and acquisition of the righting reflex and exhibited weaker grip strength, poorer negative geotaxis and less rooting intensity in comparison to sham pups. These data provide evidence for the behavioral and developmental teratogenicity of prenatal TCE exposure late in gestation.

Neurotoxicologic examination of rats exposed to 1,1,1-trichloroethane vapor for 13 weeks

Large evoked potential and EEG changes occurred in a pilot study in Fisher 344 rats during exposure to 2000 ppm of 1,1,1-trichloroethane (1,1,1-T; a cleaning solvent with anesthetic properties). In the main study, rats were evaluated for persistent nervous system effects the week following exposure to 0, 200, 630, or 2000 ppm 1,1,1-T for 6 h/day, 5 days/week, for 13 weeks. Rats were clinically examined regularly and were given a functional observational battery monthly (FOB, including forelimb and hindlimb grip performance testing). After 13 weeks of exposure, the rats were evaluated by FOB and by visual, auditory, somatosensory, and caudal nerve-evoked potentials. After functional testing, a subgroup of rats had histopathologic examination of brain, spinal cord, peripheral nerves, and limb muscles. There were no post-exposure treatment-related findings in any parameter (FOB observations plus 39 dependent variables) except for a slightly smaller forelimb grip performance in the 2000-ppm exposure group. There was no recognized toxicologic significance for the difference in forelimb grip performance; a lack of findings in any other clinical, evoked potential or morphologic parameter did not support a diagnosis of neurotoxicity.

Health risk assessment of environmental exposure to 1,1,1-trichloroethane

In 1986 a survey was published by CEFIC on the occurrence of chlorinated solvents in ambient air, in surface water, and in ground water. The present article concentrates on 1,1,1-trichloroethane (1,1,1-T), and puts into perspective the environmental occurrence and the toxicity. Critical toxicological data are briefly discussed. As no evidence of a carcinogenic effect of 1,1,1-T is apparent, the no-adverse-effect levels in chronic inhalation exposure in rats (875 ppm) and mice (1500 ppm) form the basis for the estimation of potential risk to human health. Environmental exposure to 1,1,1-T is mainly via the atmosphere (120 micrograms/day); the contributions of drinking water (2 micrograms/day) and food (3 micrograms/kg) are negligible. Safety margins are calculated by comparing the no-adverse-effect levels in rat and mouse studies with the total body burden. Safety margins are also calculated after converting no-adverse-effect levels into estimated internal dose levels by physiologically based pharmacokinetic modeling. Safety margins vary with the starting point, but are of the order of 10(5) for the general population and more than 10(4) for the population close to industrial activities. It may be concluded that the risk of a potential health effect resulting from environmental exposure to 1,1,1-trichloroethane is negligible.