Changes in the sense of balance correlate with concentrations of m-xylene in venous blood

Nine healthy male volunteers were exposed to m-xylene for four hours a day, three hours in the morning and one hour in the afternoon, with a 40 minute break in between, at six day intervals during six succeeding weeks to explore the effects of m-xylene on the sense of balance. The atmospheric m-xylene concentrations were either fixed at 8.2 mumol/l (200 ppm) or they fluctuated (5.2-16.4 mumol/l; 135-400 ppm) with peaks of 16.4 mumol/l and duration of 10 minutes at the beginning of each exposure session. The subjects were sedentary or exercised at 100 W for 10 minutes at the time of the peaks. The two control days, with and without exercise, were similar to the exposure days but without exposure. Body sway was measured with the subjects' eyes open and closed before they entered the chamber and in the chamber immediately after the cessation of the peak exposure when blood samples for gas chromatographic analysis were also drawn. Changes in the eyes closed/open ratio of the average and maximal body sway along the sagittal and lateral axes were calculated using the morning value as a reference. Changes in the eyes closed/open ratios of both average and maximal body sway correlated positively with blood m-xylene concentrations during fixed (8.2 mumol/l) exposure at rest and during fluctuating exposure combined with exercise as analysed with linear regression analysis. The results suggest that m-xylene has a dose related effect on the sense of balance at moderate atmospheric levels.     

Changes induced by short-term xylene exposure in human evoked potentials

Summary Nine healthy male volunteers were exposed to m-xylene for 3 h in the morning and 40 min in the afternoon with a 40-min break in between. The atmospheric m-xylene concentrations were either stable at 8.2 mol/l (200 ppm) or they fluctuated (5.2–16.4 mol/1; 135–400 ppm) with peaks of 16.4 mol/1 and duration of 20 min at the beginning of each exposure session. The subjects were either sedentary or exercised at 100 W for 10 min at the beginning of each session during both exposure types. The two control days, with and without exercise, were similar to the exposure days but without exposure. Evoked potentials were recorded in the morning before the exposure and immediately after the morning and afternoon sessions. Visual evoked potentials were studied to a pattern reversal stimulus (pattern VEP) and to a light flash (flash VEP). For pattern VEPs the latencies of P50, N70, P100, N135 and P170 as well as the peak-to-peak amplitude of N70 to P100 were measured. For flash VEPs the latencies of P50, N70, P100, N150 and P200 as well as the peak-to-peak amplitude of P100 to N150 were measured. Short-latency auditory evoked potentials arising in the brainstem (BAEP) were recorded for a click stimulus. The peaks 1, II, III, IV and V were identified from the grand averages. The effect of various exposure paradigms was evaluated by comparing the individual changes on an exposure day to those during the control days. The latency N135 of the pattern VEP decreased in exposure at 400 ppm with exercise, and the latency P210 in the flash VEP decreased both at the stable and fluctuating exposure with exercise. The results might suggest some activation of the arousal level of the subjects after the most intensive exposure situations.     

Distribution of m-xylene to subcutaneous adipose tissue in short-term experimental human exposure.

When volunteers were exposed in three different patterns of exposure to approximately 3.7--8.2 mumol/l (90--200 ppm, constant or time-weighted average concentration) of m-xylene for five consecutive days plus one day after the weekend, approximately 3.7--8.0% of the total body uptake was estimated to be distributed to the adipose tissue on the basis of m-xylene determinations made from subcutaneous fat. Distribution seemed to be affected by the exposure pattern; a proportionately greater distribution to subcutaneous fat occurred when the volunteers performed physical exercise part of the time, particularly when the peak xylene concentrations in the air coincided with the exercise. The median elimination half-time of m-xylene from subcutaneous fat was 58 h (range 25--128 h). A positive correlation was found between the individual elimination half-times of m-xylene in subcutaneous fat and the relative fat mass of the individuals in two exposure groups, but not in one.     

Electroencephalographic findings during experimental human exposure to m-xylene

Aromatic hydrocarbon solvents, used widely in industry, cause central nervous system symptoms in exposed workers. Acute effects of m-xylene were studied in nine voluntary subjects exposed experimentally to stable or varying concentrations of m-xylene at rest or while exercising. Each subject participated in four exposure and two control sessions in a single-blind fashion. The time-weighted average (TWA) m-xylene concentration was always 200 parts per million (ppm) (8.2 mumol/l) during the 4-h exposure period, complying to a TWA of 4.1 mumol/l.8 h, which is equivalent to the hygienic limit allowed in work situations. The short-term peak concentrations were 400 ppm or less. Electroencephalography was recorded at the beginning of exposure, during exposure, and after exposure was stopped. Eighteen 60-s EEG samples for each subject on each experimental day were analyzed automatically. Exercise increased theta percentage and delta power and percentage; these changes were more prominent in the control session without exposure. Exposure increased the dominant alpha frequency and alpha percentage during the early phase of exposure and also counteracted the effects of exercise. The effects of short-term m-xylene exposure on EEG were minor, and no deleterious effects were noted. Perhaps alpha activation is indicative of stimulating and excitatory effects induced by m-xylene exposure, which has been noted heretofore in the absorption phase of alcohol intake.     

Effects of short-term xylene exposure on psychophysiological functions in Man

Summary Six male students were exposed to m-xylene at concentrations of 4.1–8.2 mol/1 (100–200 ppm) in an exposure chamber for several successive days, 6 h a day during two subsequent weeks to assess the effects of xylene on psychophysiological functions such as equilibrium, reaction time and critical flicker fusion. The influence on these functions by different exposure patterns constituting stable (4.1-8.2 mol/1) and periodically varying m-xylene concentrations (4.1–16.4 mol/l; 100–400 ppm) in inhaled air was also studied. During the study the subjects acted as their own controls. An inhalation exposure to m-xylene already at a concentration of 4.1 mo1/1 was observed to have a deleterious acute effect on the equilibrium and the reaction time performance of nonadapted human subjects. Adaptation to the test situation or tolerance seemed to develop against these effects over five subsequent exposure days, but the effects were again discernible in the following week, and were most pronounced when the exposure constituted peak concentrations which exceeded twofold any previous ones. In this study the effect of xylene seemed to be related to the level of xylene in the blood.     

Effects of short-term m-xylene exposure and physical exercise on the central nervous system

Summary Eight male volunteers were exposed on 5 consecutive days and 1 day after the weekend to m-xylene vapour at either a constant (Study I) or a periodically varying (Study Il) concentration of 3.7–8.2 mol/1(90–200 ppm, time-weighted average). The effects of the exposure on psychophysiological functions, such as reaction time, manual coordination and body balance, and EEG were studied. The same tests were completed on 2 non-exposure days for control purposes in both studies, in which physical exercise of 10O W was included.An inhalation exposure to m-xylene already at a concentration of 3.7 mol/1 (90 ppm) had acute deleterious effects on the above mentioned psychophysiological functions of non-adapted subjects. EEG indicated lowered vigilance during exposure to varying concentrations with peak exposures of 8.2 mol/l. Slight exercise, especially at the beginning of the exposure, seemed to antagonize the effects of xylene, particularly when the concentration fluctuated. Tolerance against the observed effects developed over one working week, but some effects were again discernible in the following week. A dose-response relationship between blood m-xylene concentrations and the effects of m-xylene was not found. This was probably due to tolerance.     

Changes in postural sway during a period of sustained wakefulness in male adults.

Nocturnal variations in postural sway during a period of sustained wakefulness were studied in seven healthy male adults. Postural sways with the subject's eyes open and with them closed were measured every hour from 22:00 to 04:00 h the following day. Parameters of postural sway [rectangle area (RA), root mean square of length in the anterior-posterior direction (RMSL-y), and medium-frequency-band (0.2-1.0 Hz) power of postural sway in the lateral (MF-x) and anterior-posterior (MF-y) directions] showed significant nocturnal variations. RA, RMSL-y, MF-x and MF-y increased after midnight and reached peaks at 04:00 h. Moreover, changes in RA and MF-y depended on visual conditions. The increases in RA and MF-y were larger with the eyes closed than with them open. These postural sway parameters showed positive correlations with subjectively rated sleepiness and negative correlations with electroencephalographic alpha activity. The results suggest that changes in postural sway during the night are influenced by the increase in sleepiness.     

Effects of mixed organic solvents on neuromotor functions among workers in Buddhist altar manufacturing factories

To clarify the neuromotor effects of long-term exposure to mixed organic solvents, postural sway and tremor were measured in 62 solvent workers of four Buddhist altar manufacturing factories who had worked for 1-46 (mean 12) yr. By using the passive gas sampler, 8-h time-weighted average concentrations in the workers were estimated to be 0.02-8.7 ppm for toluene, 0.02-7.7 ppm for xylene, 0.02-5.5 ppm for styrene and 0.02-40.5 ppm for n-hexane. Sagittal sway and sway area of the posturography with eyes closed were significantly larger in the solvent workers than in 35 age-matched controls (p<0.05), and there was a significant difference in Romberg quotient of sagittal sway between the two groups (p<0.05). Also, tremor intensities at 1.0-5.9 Hz, 6.0-9.9 Hz and 10.0-13.9 Hz with the right hand, and at 6.0-9.9 Hz with the left hand were significantly stronger in the solvent workers than in the controls. Among the solvent workers, transversal and sagittal sways with eyes open and tremor intensity at 10.0-13.9 Hz were significantly related to toluene exposure (p<0.05), which may have been due to the acute effects of such solvents. These findings suggest that long-term exposure to mixed organic solvents may impair neuromotor functions as measured by postural sway and tremor.     

Acute effects of m-xylene inhalation on body sway,reaction times,and sleep in man

Summary Nine male volunteers were exposed to either a constant or a fluctuating exposure pattern of m-xylene with a time-weighted average exposure concentration of 200 ppm in both cases. The subjects remained sedentary throughout the exposure, or the exercised at 100W for 10 min at the beginning of the morning and the afternoon sessions. In another experiment, 12 sedentary male volunteers were exposed to a fixed 200 ppm of m-xylene. The effects of m-xylene on body sway, reaction time performance, and overnight sleep were measured. Body balance was stabilized after exposure to the peaks of 400 ppm of m-xylene in both sedentary and exercising subjects. Simple visual reaction times were prolonged after the peak exposures at rest whereas auditive choise reaction times were prolonged after peaks combined with exercise. Exposure to m-xylene at a constant level of 200 ppm did not affect the ratio of active to quite sleep in the volunteers as measured with the static charge sensitive bed recording, but decreased slightly the number of body movements in bed. On the next morning no changes were found in body sway and reaction time performance as compared to the morning before exposure.     

Critical dose of lead affecting postural balance in workers

BACKGROUND: The threshold blood lead (BPb) level for nervous system dysfunction in adults has been estimated to be 30-40 microg/dl. This study was carried out to estimate the critical dose of lead affecting the neuromotor function in workers by introducing the benchmark dose (BMD) approach, as well as to identify the specific postural sway to lead exposure. METHODS: Postural sway parameters with spectral analysis were compared between 121 lead workers with BPb levels of 6-89 (mean 40) microg/dl and 60 unexposed controls. RESULTS: All sway parameters, except for sagittal sways with eyes open, were significantly larger in the lead workers than in the controls; also, the Romberg quotient for sagittal sway was significantly higher in the lead workers. The BPb level in the lead workers was significantly related to sagittal sways at 1-2 Hz and 2-4 Hz with eyes open, and sagittal and transversal sways at 1-2 Hz and 2-4 Hz with eyes closed. The BMD levels of BPb (i.e., lower 95% confidence limits of BMD) were estimated to be 12.1-17.3 (mean 14.4) microg/dl for postural sway. CONCLUSIONS: Neuromotor dysfunction in lead workers may be initiated at BPbs below the level previously accepted as effectless, and be characterized mainly by an increased sway of high frequency (1-4 Hz) in the sagittal direction with eyes closed (high Romberg quotient).     

Acute effects of 1,1,1-trichloroethane inhalation on the human central nervous system

 The object of this study was to examine the immediate nervous effects of variable 1,1,1-trichloroethane (TCE) exposure combined with physical exercise. The effects on the quantitative electroencephalography (EEG), visual evoked potentials (VEP) and body sway were analyzed. Nine male volunteers were exposed to either a stable or a fluctuating exposure pattern with the same time-weighted average concentration of 200 ppm (8.1 μmol/l). In both cases, the subjects engaged in physical exercise during the exposures. Exercise alone induced an increase in the dominant alpha frequency in the EEG and, after an initial drop, an increase in the alpha percentage with a concomitant decrease in theta, whereas delta and beta bands remained unaffected. By contrast, exposure to TCE and exercise did not affect the alpha, theta or delta activities but induced changes in beta during the morning recordings at peak exposure to TCE. The body sway tended to decrease slightly during the fluctuating TCE exposure, and the later peaks in VEPs showed slight prolongations. Overall, no deleterious effects of exposure were noted. Received: 27 July 1995/Accepted: 8 March 1996     

Subclinical cerebellar anterior lobe,vestibulocerebellar and spinocerebellar afferent effects in young female lead workers in China: computerized posturography with sway frequency analysis and brainstem auditory evoked potentials

By computerized static posturography with sway frequency analysis, subclinical effects of lead on postural balance was examined in 29 female workers (lead workers) employed at a glass factory for 3-17 (mean 7.9) years in Beijing, China, in relation to brainstem function assessed by brainstem auditory evoked potential (BAEP). Their blood lead concentrations ranged from 26 to 79 (mean 55.7) microg/dl; ages were 21-30 (mean 28) years. Control subjects, aged 22-29 (mean 27.0) years, were 14 healthy female workers at a textile factory located in the same district. With eyes closed, power of the sway of high (2-4 Hz) and low (1 Hz or less) frequencies in lead workers was significantly larger than that in controls; with eyes open, their power of the sway of low frequency was significantly larger (p<0.05). The multiple regression analysis showed that the power of high frequency sway with eyes closed and of low and high frequencies with eyes open were significantly related to blood lead concentrations in lead workers (p<0.05). On the other hand, no significant differences in BAEP latencies between lead workers and controls were observed. The low frequency sway with eyes open was significantly correlated with the high frequency sway with eyes closed in the lead workers. The pattern of changes in postural balance suggested that the anterior cerebellar lobe, vestibulo-cerebellar and spinocerebellar afferent systems were affected asymptomatically in female lead workers; the sway of vestibulo-cerebellar and anterior cerebellar lobe types were simultaneously affected by lead. It appears that a computerized static posturography with sway frequency analysis is useful technique for assessment of subclinical lead neurotoxicity.     

Are hearing loss and balance dysfunction linked in construction iron workers?

The objective was to determine whether an association existed between hearing loss and balance dysfunction in construction workers exposed to noise. Screening pure tone audiometry and balance testing were performed using a sound emitter and dual microphone system to evaluate 78 iron workers who were compared with 128 histology technicians. Most iron workers showed hearing loss at frequencies below 3000 Hz. Their sway speeds were significantly faster both with the eyes open (1.05 (SD 0.39) v 0.91 (SD 0.22) cm/s) and with eyes closed (1.66 (SD 0.82) v 1.31 (SD 0.51) cm/s) than those of histology technicians. Coefficients for sway speed with the eyes closed and hearing loss in the left ear were significantly correlated at 500 to 8000 Hz. They were also correlated with the sway speed, eyes open, at low and high Hz. It is concluded that the use of air impact power tools in an inordinately noisy work environment makes iron workers prematurely deaf and impairs their balance. Falls may be related to balance dysfunction and impaired equilibrium. Falls from height injure and kill iron workers. Further investigations will determine whether injuries from falls are linked to these impairments.     

Are hearing loss and balance dysfunction linked in construction iron workers?

The objective was to determine whether an association existed between hearing loss and balance dysfunction in construction workers exposed to noise. Screening pure tone audiometry and balance testing were performed using a sound emitter and dual microphone system to evaluate 78 iron workers who were compared with 128 histology technicians. Most iron workers showed hearing loss at frequencies below 3000 Hz. Their sway speeds were significantly faster both with the eyes open (1.05 (SD 0.39) v 0.91 (SD 0.22) cm/s) and with eyes closed (1.66 (SD 0.82) v 1.31 (SD 0.51) cm/s) than those of histology technicians. Coefficients for sway speed with the eyes closed and hearing loss in the left ear were significantly correlated at 500 to 8000 Hz. They were also correlated with the sway speed, eyes open, at low and high Hz. It is concluded that the use of air impact power tools in an inordinately noisy work environment makes iron workers prematurely deaf and impairs their balance. Falls may be related to balance dysfunction and impaired equilibrium. Falls from height injure and kill iron workers. Further investigations will determine whether injuries from falls are linked to these impairments.     

Cumulative concentrations of blood lead and postural stability.

OBJECTIVE: To study the association in a group of battery manufacturing workers between computerised postural sway parameters and present concentrations of blood lead (PPb), index of cumulative blood lead years (CBI), and cumulative blood lead at different years of exposure (CPbYs). METHODS: Postural stability was investigated with a computerised postural sway measurement system in 60 workers exposed to lead with exposure duration of 84 (range 3-366) months and in 60 control subjects. An index of CBIs in 55 workers (previous blood lead results of five workers were not available) and CPbYs were computed for each worker by calculating the area under the curve of concentrations of blood lead against time. RESULTS: The mean (SD) PPb was 36.0 (11.7) (range 6.4 to 64.5) micrograms/dl for the exposed workers and 6.3 (2.4) (range 3.1-10.9) micrograms/dl for the 14 randomly selected control subjects. Significant differences between groups for the postural sway parameters obtained when the eyes were closed were found for length of sway path (L); mean velocity of the centre of pressure along its path (Vel); area included within the path of the centre of pressure (Ao); 95% confidence elliptical area (Ae). The Romberg ratio (the relation between eyes closed and open) for the Vel, L, Ao, and Ae of the exposed group were also significantly different from those of the controls. The postural sway parameters (eyes closed) were not significantly correlated with PPb or CBI. However, the cumulative blood lead for the past two years before the postural sway assessment, CPbY2, was significantly correlated with all the postural sway parameters. CONCLUSION: The study showed that workers exposed to lead had significantly poorer postural stability than a control group. Lead may affect certain parts of the somatosensory system resulting in postural instability when the visual input is cut off. The CPbY2 was significantly positively correlated with most of the postural sway parameters. Effects of lead on postural stability may be related to recent increases in blood lead concentration among the exposed workers rather than to cumulative body burden.     

Toxicokinetics of inhaled 2-butoxyethanol (ethylene glycol monobutyl ether) in man

Seven male volunteers were exposed to 2-butoxyethanol at the Swedish occupational exposure limit (20 ppm or 0.85 mmol/m3) during light physical exercise (50 W) on a bicycle ergometer. The exposure took place in an exposure chamber and lasted 2 h. Expired air was collected at regular time intervals for estimation of the respiratory uptake of the solvent. Arterialized capillary blood and urine were sampled during and after the exposure period and analyzed for 2-butoxyethanol and its metabolite butoxyacetic acid. A new sensitive method for analyzing 2-butoxyethanol in biological specimens is described. 2-Butoxyethanol was derivatized with pentafluorobenzoyl chloride and analyzed by gas chromatography with electron capture detection. The respiratory uptake of 2-butoxyethanol averaged 10.1 mumol/min or 57% of the inspired amount. The concentration in blood reached a plateau level of 7.4 mumol/l. The apparent values of elimination half-time, mean residence time, total blood clearance, and steady-state volume of distribution were 40 min, 42 min, 1.2 1/min and 54 l, respectively. The amount of 2-butoxyethanol excreted in urine was less than 0.03% of the total uptake, while that of butoxyacetic acid ranged from 17 to 55%.     

Ethanol induced modification of m-xylene toxicokinetics in humans.

This study was undertaken to determine whether previous subacute treatment with ethanol could modify the kinetics of m-xylene in humans. A group of six volunteers was exposed twice to either 100 or 400 ppm of m-xylene during two hours (between 0800 and 1000). Ethanol was given orally in the early evening on each of two consecutive days before exposures (total ethanol intake of 137 g). Such ethanol pretreatment affected the kinetics of m-xylene but only at the high exposure (400 ppm). The modifications were: (1) decreased concentration of m-xylene in blood and alveolar air during and after exposure; (2) increased urinary excretion of m-methylhippuric acid at the end of exposure. Ethanol treatment also enhanced the elimination of antipyrine in saliva. Overall, this study showed that the effect of enzyme induction on the metabolism of m-xylene, after ethanol ingestion, depends on the exposure concentration and is not likely to occur as long as the exposure concentrations remain under the current maximum allowable concentration (100 ppm) in the workplace.     

Combined effects of ethanol and hyperbaric air on body sway and heart rate in man.

Eight amateur divers took part in crossover experiments to study the combined effects of ethanol (0.72 g/kg b.wt.) and hyperbaric air (4 and 6 ATA) on heart rate and body-sway movements. Body sway with open and closed eyes was measured in lateral and sagittal directions by a statometer device. In the alcohol condition, there was an initial increase in body sway corresponding to the acute phase of ethanol intoxication. At a mean blood alcohol concentration of 0.77 mg/ml, this increase in body sway was statistically significant (P less than 0.01) compared with the alcohol-free condition. At 90 min from start of drinking, body sway scores at 1 ATA were not significantly different from alcohol-free measurements. On raising the pressure to 4 and 6 ATA, increased body sway occurred in both alcohol and alcohol-free conditions and, moreover, the rate of increase was more extreme in the alcohol condition. Significant pressure-alcohol interactions were established, suggesting a potentiating action of alcohol on the increase in body sway induced by acute exposure to high pressures of air. Heart-rate measurements with and without alcohol were not significantly different, although increases in ambient pressure caused a drop in heart rate in both conditions.     

Balance measured by head (and trunk) tracking and a force platform in chemically (PCB and TCE) exposed and referent subjects.

To determine comparability of methods, postural sway was measured simultaneously with a force platform and a device that registers head (and trunk) movements (head tracking). The effects of age, sex, height, weight, shoe area, and grip strength on both measurements were examined in 162 subjects. To determine whether either method had advantages in detecting abnormal balance 46 reference subjects were compared with 116 people randomly selected from 500 residents whose well water was contaminated with polychlorinated biphenyls (PCBs) and trichloroethylene (TCE) from a metal casting plant. Speed, mean radius, and distance of sway were equally reproducible with both methods. Correlation coefficients were 0.672 with the eyes closed and 0.588 with the eyes open. The balance of those exposed to PCBs and TCE was significantly worse than that of unexposed subjects by both head tracking (1.50 + 71 cm/s v 1.27 + 0.36 cm/s; p < 0.034) and the force platform (4.93 + 1.56 N (kg force) v 4.29 + 1.14 N; p < 0.013) with the eyes closed and differences were also significant with the eyes open. Head tracking and the force platform produced equivalent results. Measurement by head tracking is recommended for field studies because the device is more portable and is less influenced by weight and height. Both methods showed impaired balance associated with years of exposure to PCBs and TCE.     

Effects of covered solid sorbent tube sample holders on organic vapor measurements

A study was conducted to examine whether there are significant differences between organic vapor concentrations measured using charcoal tubes with three different configurations: uncovered sample holder (open tube), SKC, and Buck brand covered sample holders. A fractional factorial experimental design was used with the following factors and levels: vapor (n-hexane vs. m-xylene), pump type (pulsating vs. continuous), exposure profile (variable vs. constant), flow rate (30?mL/min vs. 200?mL/min), duration (30?min vs. 80?min), and sample placement (mannequin vs. free hanging). Two of each sampler configuration (six total) were placed in an exposure chamber, and a dynamic test-atmosphere generation system was used to prepare atmospheres containing approximately 12-15?ppm n-hexane or m-xylene with exposure profiles and sampling conducted according to a run sheet generated for the experimental design. A total of 24 runs were completed with six samplers per run, yielding 144 samples that were analyzed by gas chromatography/flame ionization detector. Concentration results for each pair of SKC and Buck covered sample holders were averaged and normalized by dividing by the average result for the open tube sampler from the same run to eliminate the effect of daily variation in chamber concentrations. The resulting ratio of covered sample tube holder and open tube concentrations was used as the response variable. Results of analysis of variance using the general linear model (MINITAB 16) identified statistically significant main effects and/or interactions for pump type, exposure profile, flow rate, and sample holder. However, the magnitude of the effects was generally less than 10%, and overall mean concentration ratios were 0.989 and 1.02 for the Buck and SKC sample holders, respectively. These results show good agreement between covered sample holder results and open tube measurements and demonstrate that exposure assessment errors resulting from the use of covered sorbent tube sample holders for organic vapor monitoring are relatively small (<10%) and not likely to be of practical importance.