Short duration exposures to organic solvents: the relationship between neurobehavioral test results and other indicators

Cesium ion-guided detection of trichloroethylene in air

Whereas the close associations of cesium ion with organochlorine compounds have been previously documented, the present report is the first attempt to exploit these interactions to create a trichloroethylene (TCE)-selective sensor. Gold monolayer-protected clusters peripherally functionalized with Cs+ ions were used to prepare a chemiresistance film on MEMS-fabricated interdigitated electrodes. Vapor sensing properties of the cesium-rich chemiresistor were determined using a panel of chlorinated hydrocarbons including TCE as well as polar and non-polar VOCs for comparison. The sensor was selective and highly sensitive toward VOCs containing a 1,2-dichloro group at concentrations as low as 0.1 ppm. The results suggest the key interaction contributing to sensor response is a bidentate, metallocycle-like coordination of the 1,2-dichloro group to the cesium cations at the sensor surface.

An investigation of the acute central nervous system effects of n-decane

Acute central nervous system (CNS) depression is the most sensitive toxicological effect associated with aliphatic hydrocarbon exposure. No observed effect levels for the CNS effects of aliphatic constituents decrease with increasing carbon number to C10 (Lammers et al., 2011; McKee et al., 2011), whereas constituents with carbon numbers > C10 do not produce CNS effects at maximally attainable vapor concentrations (Nilsen et al., 1988). Accordingly, as n-decane appeared to be the "worst case" for acute CNS effects among aliphatic hydrocarbon solvent constituents, experimental studies were conducted to more precisely define the no effect level. Rats were exposed for 8 h to n-decane, either constantly at 3000 mg/m³ or at higher levels using a discontinuous exposure protocol to assess the influence of fluctuating exposures. Neurobehavioral testing methods including visual discrimination performance and motor activity were used to assess performance, and concentrations of n-decane in blood and brain were measured to obtain pharmacokinetic data. No statistically significant differences were observed in the neurobehavioral tests, establishing 3000 mg/m³ as the no effect level for CNS effects in rats. These data support the recommended guidance value of 1050 mg/m³ for C9-C15 aliphatic hydrocarbons for use in calculating occupational exposure levels for complex hydrocarbon solvents and provide empirical evidence that advice from the ACGIH^® that within a working day there should be no more than 3 fluctuations, not longer than 15 min and not exceeding 3 times the Threshold Limit Value (TLV^®), is reasonable for this group of substances.

Organic solvent-induced changes in membrane geometry in human SH-SY5Y neuroblastoma cells - a common narcotic effect?

Exposure to organic solvents may cause narcotic effects. At the cellular level, these narcotic effects have been associated with a reduction in neuronal excitability caused by changes in membrane structure and function. In order to critically test whether changes in membrane geometry contribute to these narcotic effects, cultured human SH-SY5Y neuroblastoma cells have been exposed to selected organic solvents. The solvent-induced changes in cell membrane capacitance were investigated using the whole-cell patch clamp technique for real-time capacitance measurements. Exposure of SH-SY5Y cells to the cyclic hydrocarbons m-xylene, toluene, and cyclohexane caused a rapid and reversible increase of membrane capacitance. The aliphatic, nonpolar n-hexane did not cause a detectable change of whole-cell membrane capacitance, whereas the amphiphiles n-hexanol and n-hexylamine caused an increase of membrane capacitance and a concomitant reduction in membrane resistance. Despite a large difference in dielectric properties, the chlorinated hydrocarbons 1,1,2,2-tetrachoroethane and tetrachloroethylene caused a similar magnitude increase in membrane capacitance. The theory on membrane capacitance has been applied to deduce changes in membrane geometry caused by solvent partitioning. Although classical observations have shown that solvents increase the membrane capacitance per unit area of membrane, i.e., increase membrane thickness, the present results demonstrate that solvent partitioning predominantly leads to an increase in membrane surface area and to a lesser degree to an increase in membrane thickness. Moreover, the present results indicate that the physicochemical properties of each solvent are important determinants for its specific effects on membrane geometry. This implies that the hypothesis that solvent partitioning is associated with a common perturbation of membrane structure needs to be revisited and cannot account for the commonly observed narcotic effects of different organic solvents.

Evaluating suspected work-related neurologic disorders (clinical diagnosis)

The clinical diagnosis of work-related neurologic disorders is essentially one of exclusion because symptoms and signs are often nonspecific. The clinical reasoning requires a three-step approach: (1) establish the characteristics of the presenting disease; (2) ascertain that observed clinical features are consistent with those caused by the suspected agent(s); and (3) assess occupational exposures. A detailed history is of paramount importance in evaluating patients with suspected work-related neurologic disorders as it is in other clinical contexts, especially because in some circumstances it may represent the only criterion to establish causality. Thus, besides characterization of neurologic symptoms, including their location, quality, timecourse, and possible other associated symptoms, the work environment of the patient should be understood in full detail. In this respect, when a neurotoxin is suspected, then the history collection can be guided by the knowledge of the likely syndromes it produces. Similarly, physical examination should be directed to the target of toxicity/entrapment based on information from the work history. Although specific sites and elements of the nervous system may be affected depending on the offending agent, most neurotoxic disorders are characterized by generalized rather than focal neurologic abnormalities. Laboratory toxicologic tests have limited application for the etiologic diagnosis of neurotoxic disorders, except in cases of acute poisoning and in patients exposed to neurotoxic chemicals with prolonged half-life. In most cases examination takes place after the end of exposure, when the offending chemical is no longer detectable in body fluids. Electrophysiologic studies, in particular evoked potentials, electromyography, and conduction velocities, are important to confirm the organic basis of symptoms, particularly to detect subclinical or early neurologic involvement and to reduce the number of disorders to be considered in the differential diagnoses. In general, imaging studies with computed tomography and magnetic resonance are of limited utility in the evaluation of suspected neurotoxic disorders, except for helping to exclude other causes of the patient's clinical state. Improved conditions and safer practices in the workplace have led to a gradual shift in application of neuropsychologic evaluation from the assessment of severe neurotoxic damage to the evaluation of mild subclinical disturbances, and these tests are nowadays extensively used in screening workers exposed to neurotoxicants. Tools used in the screening of large groups of workers exposed to neurotoxicants may differ from those used in the clinic. Whereas some are obviously impractical, such as physical examination, others, such as, for instance, toxicologic tests, are used for biologic monitoring of exposure to ascertain compliance with occupational exposure limits.

Neurobehavioral Effects of Acute Exposure to Aromatic Hydrocarbons

This article reports the results of neurobehavioral tests on representative aromatic constituents, specifically C9 to C11 species. The testing evaluated effects in several domains including clinical effects, motor activity, functional observations, and visual discrimination performance. Exposures ranging from 600 to 5000 mg/m3, depending on the molecular weights of the specific aromatic constituents, produced minor, reversible effects on the central nervous system (CNS), particularly in the domains of gait and visual discrimination. There was little evidence of effects at lower exposure levels. There was some evidence of respiratory effects at 5000 mg/m3 in 1 study, and there were also minor changes in body weight and temperature. The CNS effects became less pronounced with repeated exposures, corresponding to lower concentrations in the brain of 1 representative substance, 1,2,4-trimethyl benzene (TMB). At high exposure levels, the alkyl benzenes apparently induced their own metabolism, increasing elimination rates.

Review of the Toxicology of Mineral Spirits

This review of the toxicology of mineral spirits covers studies of the major classes of mineral spirits and several toxicologically important mineral spirit constituents. This review cites data from numerous previously unpublished animal toxicology studies conducted on mineral spirits during the past 30 years, expanding the existing database on the toxicology of this group of hydrocarbon solvents. The data can be used to better evaluate the potential effects associated with exposure to these materials, including health and environmental reviews such as the U.S. Environmental Protection Agency High Production Volume (HPV) chemical program and the Organization for Economic Cooperation and Development (OECD) HPV Screening Information Data Set (SIDS) program. The majority of animal toxicology studies in the available literature were conducted on mineral spirits categorized as ASTM D235 Type I Class A (149°C to 213°C boiling range; 8% to 22% aromatics) and demonstrate that Type I Class A mineral spirits have a low order of acute toxicity and do not produce significant systemic effects. Some additional studies conducted with ASTM D235 Type II Class C mineral spirits (177°C to 213°C boiling range; <2% aromatics) suggest that Type II Class C mineral spirits have similar toxicity to Type I Class A mineral spirits, though there is some evidence that Type II, Class C mineral spirits have a lesser degree of central nervous system (CNS) effects than the higher aromatic containing Type I Class A materials. In addition, toxicity data on selected chemical constituents of mineral spirits (e.g., n-nonane, n-decane, n-undecane) indicate that these chemicals have similar toxicological properties to mineral spirits. Overall, the data showed that mineral spirits have a low order of acute toxicity and do not appear to produce toxicologically relevant systemic effects. Ongoing studies are evaluating the concerns associated with chronic low-level exposure and central nervous system effects.

Model studies for evaluating the acute neurobehavioral effects of complex hydrocarbon solvents I. Validation of methods with ethanol

As a preliminary step to evaluating the acute neurobehavioral effects of hydrocarbon solvents and to establish a working model for extrapolating animal test data to humans, joint neurobehavioral/toxicokinetic studies were conducted which involved administering ethanol to rats and volunteers. The specific objectives of the present studies were to evaluate the acute central nervous system (CNS) effects of ethanol in rats and humans and to assess relationships between internal levels of exposure and behavioral effects. A more general objective was to validate a battery of neurobehavioral tests that could be used to carry out comparative studies in both species. Accordingly, a range of tests including standardized observational measures, spontaneous motor activity assessments and learned visual discrimination performance was utilized in rat studies to evaluate acute CNS effects. Groups of rats were given ethanol at levels of approximately 0.5, 1.0 or 2.0g/kg, with blood level measurements to verify internal doses. In a volunteer study, 12 healthy male subjects were given 0.65g/kg ethanol, a level approximating the limit for motor vehicle operation in The Netherlands, and neurobehavioral effects were measured prior to and 1 and 3h after ethanol administration, with a computerized neurobehavioral test battery. Blood and air measurements were made to quantify internal doses. Results of the behavioral tests in rats provided evidence of ethanol-induced changes in neuromuscular, sensori-motor, and activity domains. There were also significant changes in visual discrimination, particularly in the areas of general measures of responding and psychomotor speed. In humans there were small but statistically significant effects on learning and memory, psychomotor skills and attention. However, the effects were subtle and not all parameters within given domains were affected. These studies demonstrated a qualitative similarity in response between rats and humans.

A proposed methodology for setting occupational exposure limits for hydrocarbon solvents

Occupational exposure limit (OEL) development for hydrocarbon solvents is complicated because most of these solvents have complex compositions and only a few representative constituents have been studied in detail. A proposed solution to this problem is to group constituents with similar physical, chemical, and toxicological properties and to assign "guidance values" to each group. A unique OEL can then be calculated for each solvent, using a reciprocal calculation procedure (RCP) based on the liquid composition. This procedure follows the American Conference of Governmental Industrial Hygienists' (ACGIH) generic advice for complex mixtures and is recommended by the U.K. Health and Safety Executive for OEL calculations by hydrocarbon solvent manufacturers. The RCP is justified, as the toxicological properties of the constituents are additive and the differences between the vapor and liquid compositions do not substantially affect the calculated exposure limits. The guidance values are based principally on acute central nervous system depression and eye and respiratory tract irritation, effects that are the most sensitive indicators of hydrocarbon solvent exposure. One benefit of this procedure is that it is a relatively simple but practical procedure that requires limited compositional information. Further, it provides OEL recommendations that are consistent with occupational experience and current regulatory advice. Groupings and guidance values are proposed, and sample calculations are provided.

Early spatial memory deficit induced by 2,5-hexanedione in the rat

2,5-Hexanedione (2,5-HD), the major common neurotoxic metabolite of n-hexane and methyl n-butyl ketone, causes a delayed neuropathy with associated sensorimotor impairments. The question arises as to whether specific cognitive deficits occur even prior to changes in sensorimotor ability. The present experiments examined the effects of 2,5-HD on spatial navigation of rats in a water maze at levels/times that did not affect spontaneous exploratory motor activity in an open field holeboard apparatus. Exposure to 1% 2,5-HD in the drinking water for 2 weeks did not significantly affect escape learning, as measured by latency to find a hidden platform. However, 2,5-HD treated animals were impaired in the use of a spatial strategy during a recall test. A similar impairment in spatial memory was observed after i.p. injection of 500 mg/kg/day 2,5-HD for 4 days, in the absence of significant changes in sensorimotor ability or weight loss. Thus 2,5-HD may mediate some of the cognitive effects of hexacarbons and these changes can occur prior to the development of motor symptoms.

The central nervous system and exposure to toluene: a risk characterization

The principal health outcome of exposure to toluene is dysfunction of the central nervous system. Effects range from fatalities and severe neurological disorders in toluene abuse situations to deficits in neurobehavioral function in occupational populations. An Inhalation Reference Concentration (RfC) of 0.4 mg toluene/m3 or 0.1 ppm was developed by the U.S. EPA to protect general populations chronically exposed to toluene. The RfC was derived from results of an occupational study involving Asian workers who developed neurobehavioral deficits at a mean toluene exposure level at the time of the study of 88 ppm. The derivation incorporated several uncertainty factors, one of which was a factor of 10 to account for sensitive subpopulations. Recent evidence indicates that some Japanese and possibly other Asian populations harbor a defective gene for aldehyde dehydrogenase, and thus exhibit a decreased rate of toluene metabolism. Although it is not known if reduced metabolism by aldehyde dehydrogenase also was a factor in the occupational study, preshift blood levels of toluene were considerably higher than preshift levels from non-Asian workers exposed to similar air levels of toluene. The elevated blood levels are consistent with defective metabolism but remain to be confirmed. Inasmuch as air levels of toluene in urban environments are about 10-fold lower than the RfC, an adequate measure of protection is afforded by the RfC with or without an uncertainty factor for sensitive subgroups. However, the uncertainty factor for sensitive subgroups should be retained because there is no information regarding toluene metabolism in children.

Extended workshifts and excessive fatigue

Studies of overtime have pointed to fatigue as a potential factor producing, for example, a three-fold increase in accident rate after 16 h of work, increases in back injuries, hospital outbreaks of bacterial infection, or nuclear-power plant safety compromises. Fatigue has been measured more directly in studies of scheduled long workshifts, where performance decrements in both work-related tasks and laboratory-type behavioural tests have been observed, and significant loss of sleep and increases in subjective sleepiness have been reported. Analyses of accidents or injuries during scheduled extended workshifts, however, have produced equivocal results. Factors which could compound the fatiguing effects of extended workshifts, such as workload, noise, chemical exposure, or duties and responsibilities outside of the workplace, rarely have been studied systematically. It is concluded that extended workshift schedules should be instituted cautiously and evaluated carefully, with appropriate attention given to staffing levels, workload, job rotation, environmental exposures, emergency contingencies, rest breaks, commuting time, and social or domestic responsibilities.

Neuropsychological toxicology of methylene diphenyl diisocyanate: a report of five cases

The neuropsychological functioning of five men suffering alleged physical, cognitive and behavioural changes following exposure to methylene diphenyl diisocyanate (MDI), an industrial chemical, was investigated in the present study. At the time of assessment, four of the five patients remained symptomatic despite having no contact with MDI for periods ranging from 5 to 9 months. All patients reported experiencing subjective symptoms consisting of respiratory distress, headaches, depression, irritability, forgetfulness, decreased calculating ability, word-finding problems and reduced concentration. While the pattern of neuropsychological deficits varied among the patients, common findings for the group included intact psychomotor, psychosensory, visuographic and language functions accompanied by deceased concentration, mental efficiency, rate of information processing, learning ability and abstract reasoning. All five patients also revealed significant emotional distress on an objective personality measure. In general, the neuropsychological test data support the presence of behavioural and cognitive correlates of CNS injury following exposure to MDI.

Adult versus developmental neurotoxicology: an occupational perspective of similarities and differences

Most readers of this journal are involved in neurotoxicology research, whether it is in adult or developing organisms. Although there are a number of similarities between adult and developmental neurotoxicology, there are also a number of differences. The intent of this "perspective" is to highlight some of the similarities and differences between these disciplines in the hopes of enhancing communication among neurotoxicologists.

The neuroepidemiology of styrene: a critical review of representative literature

Because exposure to styrene occurs commonly in some industries and styrene is highly lipid soluble, it is reasonable to be concerned about the possibility that styrene is neurotoxic. Styrene, like many other solvents, volatile anesthetics, and drugs, does, at certain concentrations, produce acute changes in consciousness with consequent alterations of feelings, cognition, and psychomotor functioning. Such acute actions do not imply that styrene also would produce reversible or irreversible damage to the nervous system; the evaluation of long-term exposures to styrene also is necessary to draw conclusions about the full range of neural effects that styrene might produce. To that end, several studies of workers exposed to styrene for up to 30 years have been undertaken in factories in many parts of the world. Epidemiologists have suggested that neuropsychological deficits such as slowing of reaction time, loss of color vision, and vestibulooculomotor dysfunction are reliably induced by styrene at levels near or below current exposure standards, which range from 20 to 50 ppm in most of the world. However, the workers so studied always were described as healthy, and the effects noted were considered to be subclinical. A detailed evaluation of much of the neuroepidemiological literature on styrene (38 papers and related literature), however, indicated that the findings were, almost universally, false positive outcomes due to (1) type I statistical error, (2) the action of some factor other than styrene, and (3) misinterpretation of data. Despite the study of workers exposed for many years, no indications of persisting damage to the nervous system were evident from this review. The conclusions of this review of the neuroepidemiology of styrene are consistent with those based on critical reviews of the solvent literature in general, with specific reference to the probable absence of such an entity as the "painter's syndrome" or "chronic toxic encephalopathy". Because the results on styrene neurotoxicity that provide an inclination to lower the current threshold limit values (TLVs) are false positive findings, there is no scientific basis for a reduction in the current TLV.

Reliability of selected tests from the neurobehavioral evaluation system

NES is a widely used battery of tests designed for use in occupational health studies. Despite its widespread use, information on the reliability of the tests is limited. This article reviews the importance of test reliability and presents the results of analyses which were undertaken to examine the reliability of 11 tests and a mood rating scale contained in the NES. The NES tests were administered to 66 subjects on two testing days separated by a minimum of seven days. Seven tests were administered twice on each test day with a 3-hour interval between testing, and four of the tests were presented only once each test day. Test reliabilities were estimated for various summary measures for each test. Suggestions are made on the appropriate selection of tests and use of these.

Organic solvent encephalopathy: an old hazard revisited

This report describes neurologic and respiratory symptoms among 26 engineers and contract laborers who used organic solvents and detergents to remove polychlorinated biphenyl contamination from a poorly ventilated factory basement. Neurologic symptoms included persistent central nervous system deficits; these developed in one worker after only 3 days. Respiratory symptoms included cough that persisted for more than 2 years. Laborers were more likely to report symptoms than were engineers. Appropriate ventilation or respirator use might have prevented the workers' morbidity. This incident serves as a reminder that organic solvent-related occupational illness continues to occur despite worker-health regulations and knowledge of preventive measures.

Toluene and benzene inhalation influences on ventricular arrhythmias in the rat

We have previously found that toluene did not share the capacity of benzene for increasing the arrhythmogenic action of epinephrine in the rat, but appeared to elicit the opposite effect. The present experiments were carried out to verify this observation in rats subjected to more severe ventricular arrhythmias. In animals previously inhaling either air, toluene or benzene and anesthetized with pentobarbital, arrhythmias were produced by coronary ligation or aconitine. In both models, toluene decreased and benzene increased the number of ectopic ventricular beats in the 30 min following induction of arrhythmia. Gas chromatographic measurement of toluene levels in the heart during and after inhalation revealed essentially constant concentrations at the time of arrhythmia evaluation, equivalent to approximately one-third the peak levels observed at the end of inhalation. Although the mechanism of the effect of toluene on arrhythmia could not be ascertained, nonspecific membrane stabilization or central serotonergic stimulation were considered as possible explanations. Since both mechanisms could be operant also in the case of benzene, the opposite effects of the solvents on arrhythmia could not be readily accounted for.

Acute effects of inhaled dichloromethane on the EEG and sensory-evoked potentials of Fischer-344 rats

Acute effects of inhaled dichloromethane on the spontaneous electroencephalogram (EEG) and sensory-evoked potentials (EPs) were characterized and compared to previously observed effects of toluene; both solvents are common components of abused solvent mixtures. Twelve adult male Fischer-344 rats with chronic epidural electrode implants served as subjects. Each rat was exposed for 60 min to 5,000, 10,000, and 15,000 ppm dichloromethane while held in a plastic restrainer that also served as a head-only exposure chamber. The sequence of exposures was counterbalanced across rats, and the exposures were separated by about one week. To characterize the time course of any changes, somatosensory and flash EPs were recorded every 5 min during the first 45 min of the exposures. As was the case with toluene, electrophysiologic waveforms recorded from different sensory systems, and components of these waveforms, reacted in different ways to dichloromethane. With respect to the FEP and SEP the two solvents produced quite different effects. Toluene increased the amplitudes of early FEP components, eliminated late components, induced oscillations in visual cortex, and had no discernible effects on component latencies. In contrast, dichloromethane eliminated the N1 component, at moderate exposure had little or no effects on amplitudes of the later components (N3 through N4), did not induce oscillations, and had significant effects on latencies. Whereas toluene dramatically increased SEP component amplitudes at moderate concentrations with diminishing effect at higher concentrations and exposure times, dichloromethane rather uniformly decreased SEP amplitude in a simple concentration-related way. Toluene and dichloromethane had similar effects on BAER component latencies. They both caused component (P1 through P5) latencies and the P1-P5 interwave time to increase. However, whereas toluene increased early and late (but not middle) component amplitudes, dichloromethane decreased the amplitudes of early and late components and increased the amplitudes of middle components. These results emphasize the acute pharmacologic specificity of different solvents and suggest that differences in chronic neurotoxicity might also be found; they also suggest that predictable interactions might be found with acute and chronic exposure to mixtures that contain such solvents.