Human response to controlled levels of toluene in six-hour exposures.

Human response to controlled levels of toluene in six-hour exposures. Scand j work environ health 9 (1983) 405-418. The nasal mucus flow, lung function, subjective response, and psychometric performance of 16 young healthy subjects was studied during 6-h exposures to clean air and to 10, 40 or 100 ppm of toluene under controlled conditions. The toluene exposures did not affect nasal mucus flow or lung function. At 100 ppm irritation was experienced in the eyes and in the nose. There was a significant deterioration in the perceived air quality and a significant increased odor level during all exposures to toluene. The test battery investigated visual percep- tion, vigilance, psychomotor functions, and higher cortical functions and comprised five-choice, rotary pursuit, screw-plate, Landolt's rings, Bourdon Wiersma, multiplication, sentence comprehension, and word memom tests. In these eight tests measuring 20 parameters, no statistically significant effects of the toluene exposure occurred. For three tests (multiplication errors, Landolt's rings, and the screw plate test) there was a borderline significance (0.05 % < p < 0.10 %). The subjects felt that the tests were more, difficult and strenuous during the 100-ppm exposure, for which headache, dizziness, and feeling of intoxication were significantly more often reported. The exposures to 10 and 40 ppm did not result in any adverse effects.

The biological effects of toluene are well documented (12,20,27). The narcotic and neurotoxic properties of this substance represent the main health hazards, but in very few studies have human subjects been exposed to toluene under controlled conditions and during periods comparable to a workday. Changes in behavior are normally considered the earliest manifestations of neurotoxicity. Only two studies, one Swedish and one Japanese, of toluene's behavioral effects have been performed under controlled exposure conditions. Gamberale & Hultengren (15) investigated reaction time and two tests of perceptual speed with 12 male students. They found no effects from 20-min exposure to 100 ppm, but performance was impaired at higher concentrations. Ogata et a1 (23), in a 7-h exposure of 23 male students to 100 ppm, found no effect on reaction time.
The purpose of the present investigation was to study, during 6-h exposures, the effects of different concentrations of toluene on airway function in young healthy subjects with no former regular exposure to solvents, the discomfort created, and the ability to perform a range of manual and mental tasks simulating various aspects of industrial work. This project was carried out in order to establish dose-effect curves for these functions at the level of the hygienic standard and lower. The present hygienic standard for toluene is 100 ppm (375 mg . m-3) both in the United States (3) and in Denmark (8).
The chamber had a floor area of 29 m2 and a volume of 83 m3. The design of the chamber is shown in fig 1. During the experiment the average air and globe temperature + one standard deviation (SD) were 22.0 (SD 0.3YC and 22.6 (SD O.l)"C, respectively; the relative humidity was 46 (SD 6) %, the air velocity was 10-20 cm . s-1; and fresh air was supplied at a rate of 420 m3. h-'. This level gave an air change rate of five per hour. The air change rate was measured by the dilution of a tracer gas -Krypton (Kr-78) -and checked continuously by measurement of the volume of intake air (fig 1, number 6). The fresh air supplied to the chamber was filtered through absolute dust filters removing 99.99 % of the particles and through charcoal filters removing organic gases and vapors. By means of a pressure pump (Milton Roy, Riviera Beach, FL, United States) toluene was injected through a heated nozzle in the air supply system (fig 1, number 15) to obtain concentrations of either 10,40, or 100 ppm during one exposure day. The toluene used was spectroscopy grade and from the same production batch (Toluol, Merck, number 8331, 99.7 % pure).
The toluene concentration was monitored continuously by a photoionization detector (HNU 201, HNU System Inc, Newton, MA, United States). The detector was calibrated every second hour against a pressurized standard mixture of 106 ppm of toluene in dry air (150 bars or 15. lo5 Pa) (Linde, Hollriegelskreuth, Federal Republic of Germany), and by 6-h sampling on charcoal tubes subsequently analyzed by gas chromatography (HP 5700, Hewlett-Packard, Avondale, PA, United States). Mixing of the air in the chamber was achieved by a recirculation loop with a flow rate of 1,400 m3. h-1. No vertical or horizontal concentration gradients were found in the chamber. The variations in toluene concentrations with time were always within 8 % of the planned value. No other components than toluene were found in the air by the gas chromatographic-mass spectrometry method, which has a detection limit of 0.1 mg . m-3. The dust concentration was measured during the exposure period by gravirnetric methods. The filters were Sartorius 11107 x 0.2 pm weighed on a microbalance Mettler ME22. The average dry dust concentration was 9.5 (SD 4.6) pg . m-3.

Subjects
The subjects exposed were 16 healthy Danish students. Their average age was 24 years, and the range from 21 to 32 years of age. All were males without any symptoms or signs of diseases. Three were smokers with a consumption of one to nine cigarettes per day. All were "nose breathers" and without any previous regular exposure to organic solvents.

Procedure
The subjects were in the chamber in groups of four for 8 h a day on four consecutive days. They were dressed in allcotton work suits with an insulation value of 0.7 clo. Before the study each subject was trained in all procedures at a 2-h session. During the study the procedures were identical each day, the only variable being the concentration of toluene, which was either 0, 10,40, or 100 ppm on the 4 d.
No agents were used to mask the different odor levels each day. For the exposure of the four groups a balanced Latin-square design was used (see table 1). The subjects knew that they would be exposed to different concentrations of toluene at or below the level of the hygienic standard, but they were not told when, for how long, or how much. vital capacity measurements, and body plethysmography. These measurements served as controls each day (run 0). The 25 target words of a word memory test and a first questionnaire on discomfort were also presented then. After 1 h of clean air exposure in the chamber the concentration of toluene was steadily increased during 30 min to the concentration intended for the day. When the equilibrium concentration was reached, a second questionnaire on discomfort was presented. After 1 h of exposure all subjects went through all physiological, discomfort, and performance measurements for the next 1.5 h (run 1). After a 1-h lunch period in the chamber a similar second series of measurements was made during the fifth and sixth hours of exposure (run 2). Then the subjects left the chamber.
Physiological measurerne1Lt.s We measured the nasal removal of toluene from the inhaled air during 100-ppm exposure periods by drawing air through the The daily procedures are shown in fig 2. nose by means of a pharyngeal sampling tube placed in the oropharynx and connected to the photoionization detector. The subject performed a Valsalva maneuver while a vacuum pump drew air through the subject's nose at a rate of 20 1. min-l. The toluene concentration in the end expiration air was measured by the collection of the air in a 50-ml gas-pipette and subsequent analyses by gas chromatography. Nasal mucociliary flow was measured by external detection of a technetium 9gmlabeled resin particle (diameter 0.6 mm) placed on the superior surface of the inferior turbinate and by the passage time of a saccharin-dye particle from this position to the oropharynx. Nasal flow resistance was measured through an oronasal mask with a pneumotachometer (Mercury, Glasgow, United Kingdom) attached. were measured with a single breath instrument (Vitalographa, Buckingham, United Kingdom). These techniques have been described in detail earlier (5,6,7). Functional residual capacity and airway resistance were measured in a whole-body plethysmograph (Mercury) (13,14).

Subjective discomfort
Subjective estimates of discomfort were obtained with the following procedure: The subjects were asked to place a mark on a continuous scale with end points defined by a verbal description. The votes were read by us as the percentage of the full scale. The subjects were asked to estimate air temperature, humidity, air movements, light intensity, noise level, air quality, odor level, fatigue, sleepiness, work strain, difficulty of work, effort, and speed of reaction. In the same way they were asked about irritation of the eyes, nose, throat, and lower airways and about coughs, headache, feeling of intoxication, dizziness, and nausea.

Pe~ormance tests
Eight different performance assessment tests were used to cover different skills.
All tests were performed twice each day, once in each of the two runs (runs 1 & 2) during the exposure period. For the "pencil and paper tests" eight different parallel versions of each test were available.
The five-choice serial reaction test has been described by Poulton (24) and has been used extensively to measure the effects of heat, noise, alcohol, etc, upon perseverance and concentration. The subject uses a metal probe to touch five small targets in a continuous random sequence given by a five-lamp display. Two further aspects were added in our test to measure aiming and vigilanceresponses initially missing the targets were recorded (aiming) and the subject had to press a hand-held button to report brief, barely visible delays automatically introduced at random in 5 % of the events (vigilance). Data for each response were recorded on a paper-tape punch during the 35-min test period. The test was self-paced. In the analysis we looked at eight different measures (as listed in table 4 of the Results section).
In the rotary pursuit test the subject tries to maintain a hand-held probe on a small target near the periphery of a rapidly rotating Gramophone type of turntable. Time on target was recorded on a counter during five 20-s periods with 10-s rest periods in between. The task demands coordination between vision and arm movements; it is sensitive to heat and cold (26).
In the screw-plate test the subject transfers small nuts and bolts between holes in an aluminum plate. Thirty-two nuts and bolts were transferred during each test, and the time was measured. Half of the nuts were on one side and half on the other to equalize the advantage for left-and righthanded subjects. Coordination between vision and finger movements is important in this test. A test along similar lines has been used to test the manual dexterity of divers under water (10) and in the cold (18). The present version, in which the screwplate stands on a transverse flange, leaving both hands free, was developed by Wyon et al (29).
In Landolt's ring test a card is presented with 100 small circles, of which 50 % have a gap oriented in random directions. The subjects should mark the broken rings with a pencil. The time used and the number of errors were recorded. The present test, using the classic Landolt rings not to determine threshold acuity but to construct a visually demanding repetitive performance task, was first used by Lofberg et a1 (19). All our subjects performed a vision test before the study, and some had to use glasses to obtain normal vision. The light intensity at table level was 300 lx, and the subject's head was fixed at reading distance during this and the following test, which too simulates the performance of a repetitive task placing some demands on visual acuity and perception.
The Bourdon Wiersma test is of a similar design. In it a paper with 175 three-, four-, and five-dot figures at random is presented. The subjects mark the four-dot figures with a pencil. The time used and the number of errors were recorded (17).
Finally the higher cortical functions were examined with three tests. In the multiplication test two three-digit random numbers were to be multiplied. All six digits were different, and no zeros occurred. There were 25 of these units in each test. The time used to complete one sheet and the number of errors were recorded.
In the sentence comprehension test the subjects worked through a typed list of 75 statements, marking them as true or false. The statements were a Danish translation of the reasoning test first used by Baddeley (9), and were of the following kind: The answers to these two statements are true and false, respectively. The statements were selected in a random sequence from 96 possible choices using four sentence constructions that could also be negated, the two letters used being a combination of two of the following three: A, B, C. The passive voice, being uncommon in Danish, was not used. The time taken to complete the test and the errors were recorded.
In the word memory test a list of 25 common words was presented visually and simultaneously to all the subjects, who read each word aloud in unison with the experimenter. The list was removed, and 6 h later the subjects were presented with a list containing 50 common words, including the 25 "target words." The number of target words correctly identified was re-corded together with omissions and incorrect identifications, allowing a signal detection analysis as described earlier (28). The results are expressed as word memory area and word memory beta.

Statistical methods
The data from each test were examined by analysis of variance techniques (ll), using the GENSTAT system (2). To ensure that the assumptions of the statistical method (normal error distribution, homogeneity of variances) were correct, untransformed measurements and two transformations of the data (log and square root) were considered in an initial analysis of each set of test results. The appropriate transformed measurements were used in the subsequent statistical analysis.
In the statistical model a measurement was described as a sum of a systematic component and a random component. The systematic component represented the part of the measurement which could be explained by the design; it contained the following factors: exposure, day (representing a possible effect of learning), group (see table 1) and run, the last factor referring to the measurement period within a day (fig 2). The random component consisted of three terms representing, respectively, the intersubject random variation (U), the intrasubject random variation between days (V), and the intrasubject and intraday random variation between runs (XI. A few of the analyses required an additional random term describing the intrasubject random variation between runs (W). The random terms were assumed to be statistically independent with means of zero and variances of aU2, oV2, ow2 and ax2.
In the statistical analysis the influence of each of the factors in the design was tested against an appropriate error term by a standard F-test. For each test the results of the analysis of variance were summarized in an analysis-of-variance table of the form shown in tables 2 and 3. Table 2 was used for the measurements obtained twice a day during the period of exposure (the performance tests, the word memory test, and the subjective evaluation of work conditions). For the mean squares the sum of and the difference between the two daily measurements from each subject were computed, and analyses of variance were  applied to these sums and differences. The mean squares thus obtained were exactly twice the corresponding mean-square values given in table 2. The analysis of the sums gave the mean-square values in strata 1 and 2, while the corresponding values in stratum 3 were obtained from the analysis of the differences. The analysis-of-variance table contains the main effects and interactions considered in the statistical analysis. The inter-actions are indicated by a dot between the factors involved. The sum of squares ascribed to the exposure factor was further subdivided into a sum of squares for linear trend in dosage and a sum of squares for deviation from linearity. The interaction between run and exposure was treated in a similar manner. The additional random term W was introduced in the statistical model if the variance ratio s~~~/ s~~ differed significantly from 1. In this case the third stratum split up into two strata, and the appropriate variance ratio tests were those given in parentheses.
The experimental design did not allow an estimation of all potentially interesting interaction terms; especially the exposureday interaction and the exposure-group interaction were confounded with the group-day interaction and hence could not be estimated with the present design.
The statistical analysis of the lung function measurements, for which daily control measurements (run 0) were available, were summarized in an analysis of variance table almost identical to table 2. In this case the degrees of freedom in stratum 3 were doubled and 2ov2 was replaced by 3ov2 in the expression for the expected values of the residual variation. In this case the mean-square values in strata 1 and 2 were obtained as three times the corresponding mean squares in an analysis of variance of the average daily measurement. To derive the remaining meansquare values, the differences run 1 -run 0, run 2 -run 0, and run 2 -run 1 between measurements from the same subject on the same day were calculated, and analyses of variance were applied to these differences. The mean-square values in stratum 3 were then obtained as the average of the corresponding mean squares in these three analyses. The presence of a daily control measurement implied that the effect of exposure could be tested against the intrasubject random variation on the same day (stratum 3). This aspect was further explored by an analysis of variance, shown in table 3, of the simple exposure contrast given as the difference between the average measurement during exposure and the control measurement.
The statistical analyses of the subjective discomfort evaluation obtained four times a day (see fig 2) were summarized with the analysis of variances in table 3. The analvsis was based on the differences between the average score during exposure and the control score. However, the discomfort evaluations relating to irritation of the eyes, nose, throat, and lower airways, as well as cough, headache, feeling of intoxication, dizziness, and nausea, were not suitable for an analysis of variance. Instead the four differences between the average score during exposure and the control score were ranked for each subject, and nonparametric statistical methods (Friedman's test and van Elteren's test) were applied to evaluate the effect of exposure.
The reliability of the tests used in this experiment was evaluated through correlation coefficients between measurements obtained in runs 1 and 2. Two correlations, reflecting different aspects of the correlation structure, were calculated, namely, r, = ( s~,~ + svL)I(sUL + sVL + sXL) and where the estimates sU2, sV2 and sx2 were derived from the set of equations obtained from setting the expected values of the error terms equal to the corresponding mean squares. If the additional random term was needed in the model, the formulas above should be modified by the addition of sW2 in the denominators. The correlation coefficient r, gives the correlation between runs 1 and 2 (corrected for the influence of the systematic factors) from different subjects, while r2 gives the correlation between run 1 and run 2 measurements (corrected as above) from the same subject on different days.
Our level of significance was 5 %.

Test reliability
The reliability of the tests was evaluated through correlation coefficients between measurements obtained in run 1 and run 2. The two correlation coefficients r, and r2 for each test reflect the group and individual reproducibility of the test, respectively. The group reproducibility was excellent for the vitalograph measurements (r, = 0.981, whereas less acceptable group reproducibilities (r, < 0.78) were found for the five-choice test (choice error rate and false button press rate), the number of errors in Bourdon-Wiersma, and word memory beta. An even less acceptable group reproducibility (r, < 0.70) was found for the body plethysmographic measurements and for subjective voting on work difficulty and impression of reaction time.
The individual reproducibility r, was in general small, indicating a pronounced daily personal variability for most tests. The only tests with an r, bigger than 0.50 were the rhinomanometric measurements and memory area.

Physiological measurements
The concentration of toluene in the pharyngeal air during 100-ppm exposure was not different from the concentration in the room air. The detection limit of the method was 5 ppm, corresponding to 5 % of the values measured, and we conclude that only little, if any, absorption took place in the nose. The average concentration (+ one standard deviation) of toluene in the end expiratory air measured by a gas bag method after 6 h of exposure was 29 (SD 4.0) % of the room air concentration.

80
START TOLUENE EXPOSURE NO ODOR Nasal mucus flow was measured with the tagged particle technique and with the saccharinldye transit time measurement. With the first technique we found the average flow in the anterior and posterior third of the nose to be 0.6 cm.min-l, whereas flow in the middle third was 0.9 cm. min-1. There was no significant change from control values during any of the three exposures to toluene. This result applies to all five measuring points in the nose. The transit times for the dyed saccharin particles were from 6 to 18 min for 15 of the subjects, the average being 10 min. One subject had a transit time of 25 min. The toluene exposure did not affect the transit time. There were no differences between smokers and nonsmokers. Subjective discomfort All the subjects found the temperature, humidity, air velocity, light, and noise levels comfortable under all conditions. No statistically significant effects of toluene concentration on the subjective judgements of these factors could be shown. Air quality and odor level were the only climate descriptors that significantly correlated with the air concentrations of toluene. When the toluene concentration increased, the subjects felt that the air quality deteriorated and the odor level increased.
The subjects' average impression of the odor level during the day is shown in fig 3. It appears that the air is almost odorless under control conditions (0 ppm) and on the first evaluation each day (0 ppm). After an initial high odor estimation an adaptation phenomenon is seen during all the exposures; it is more pronounced in the first part than during the second part of the exposure period. The odor adaptation is more pronounced than the air quality adaptation. At all toluene concentrations the odor impression was significantly different from that of the control condition. At the 100-ppm exposure level three subjects found the odor unacceptable, whereas all the subjects found the odor acceptable at the other exposure levels.
The voting of the subjects on irritation of the eyes, the nose, the throat, and the lower airways showed that during the 100ppm exposure a statistically significant irritation was experienced in the eyes and in the nose, but not in the throat or in the lower airways. On the average, irritation never exceeded 13 on a scale with a maximum value called strong irritation (= 100); the highest individual estimation was 64. Six subjects did not report any irritation during the 100-ppm exposure. In general the irritation therefore may be described as slight. The irritation was felt just after the exposure began and was constant throughout the exposure day.
The subjects did not experience nausea nor did they cough. There was a statistically significant increase in the occurrence of headache, dizziness, and feeling of intoxication during the 100-ppm exposure, but not during exposure to the other concentrations. This phenomenon was experienced by about half of the subjects, and the intensity was slight to moderate.
The subjects' impression of the quality of the air is given in fig 4. They felt that the air quality was significantly lower during all toluene exposures than in clean air. The a.ir quaIity deterioration was more pronounced at the higher toluene concentrations. Some adaptation occurred, but it was less than the odor adaptation. During the 100-ppm exposure three subjects found the air quality unacceptable. At the lower exposures all subjects considered the air quality acceptable.
The subjects felt that the work was more strenuous during the 100-ppm exposure than during the other exposures. The subjects also had the impression that their reaction time was prolonged during the toluene exposures. These effects were statistically significant. There was no effect of toluene concentration on the subjects' expressed interest in the work or on their mood, fatigue, and sleepiness.
Symptoms or complaints other than those already mentioned were never reported even though space was available for such reports in the questionnaire.

Peqormance tests
In table 4 the arithmetic means and the standard errors of the means after 5 h of exposure to clean air are given for the different parameters measured in the fivechoice test, and the results of an analysis of variance are given in table 5. From this table it can be seen that no effects of the toluene exposures were found for any of the five-choice test parameters. There was a significant interaction between exposure and time on day (run).
The average results of the other perforrnance tests after 5 h of exposure to clean air are shown in table 6, and the results of an analysis of variance are given in table results of the screw-plate test, Landolt's 7. There was a borderline correlation ring test, and the number of errors in (0.05 < p < 0.10) between toluene and the multiplication.
No effects of toluene concentration on Table 4. The arithmetic means of the five-choice test parameters after 2and 5-h exposure to clean air. For the latter exposure the standard error of the mean is also given.
other tests could be shown. All tests were significantly affected by learning.

Discussion
Test parameters Arithmetic Standard error mean of the mean Despite the wide use of toluene in industry only a few experimental exposures have been performed at or below the present hygienic standard of 100 ppm (1,15,21,23,25). Only very few subjects have participated in these studies, and the impurities in the toluene used have not been measured. In our shtdy with 16 subjects we intended to imitate the conditions in the workplace with 6-h exposure periods and with subjects constantly participating in tests or physiological measurements. We exposed the subjects to toluene under  well-controlled conditions and without any simultaneously occurring gaseous and particulate pollutants. Spectroscopy grade toluene was used to enable the exclusion of additive or synergistic effects due to impurities. The exposure in the workplace to technical grade toluene containing more impurities than spectroscopy grade toluene, to peak concentrations, to simultaneously occurring other gaseous and particulate pollutants, to high local temperatures, noise, etc, however, makes it probable that less adverse effects are caused by the present exposure than by exposure to a similar average concentration of toluene in the workplace. We were not able to detect any absorption of toluene during the passage of inspiration air througl; the nose, which is in accordance with the low solubility of toluene in water and with its low reactivity.
Only slight irritation was reported for the mucous membranes of the eyes and the airways, and even at 100 ppm six subjects did not report any irritation. The highest average irritation and the highest individual irritation experienced were 13 and 64, respectively, on a scale with 100 (strong irritation) as the end point. Interindividual variation in irritation was thus  The sensitivity of the eyes and the nose were identical and constant during the exposure day. There was no adaptation in the irritation response. There was less irritation of the throat and lower airways than of the eyes and the nose, and the dose effect at the two first-mentioned positions was not statistically significant. The mucociliary flow in the nose was not influenced, and there was no change in nasal resistance to breathing or in the resistance of the lower airways. This finding indicates that no engorgement of the mucous membranes or increase in mucus production took place. These effects are prominent when irritating substances such as sulfur dioxide are inhaled (6).
In reviews of toluene toxicity (12,20,27) several studies are listed concerning the irritative effects of toluene. The evidence is ambiguous, however. From the present study it appears that, in concentrations up to the present hygienic standard of 100 ppm, pure toluene is only slightly irritating for the mucous membranes. On the other hand the odor sensation was strong and was felt to be unacceptable by 20 % of the subjects exposed to 100 ppm. This result is in accordance with the odor thresholds stated in the literature. During the last decade the range reported has been from 0.2 to 16 pprn (16).
At the end of the exposure period about 29 % of the inhaled toluene was present in the end expiratory air, indicating an absorption of about 71 %. This finding is also in accordance with other observations. Astrand (1) thus found that the alveolar concentration reached the steady state in 15 subjects exposed under controlled conditions to 100 pprn of toluene for 30 min. During rest the alveolar concentration was 20 %, and during work (50 W) it was 35 %, of the inhaled value. In an investigation of toluene exposure in a photogravure printing plant the toluene content in alveolar air was about 20-50 % of the mean concentration in the inspiratory air at the same time (22).
Our performance test battery was composed to cover visual perception, motor performance, the coordination between visual perception and motor performance, vigilance, and intellectual capacity. These functions are all very important for most workers exposed to toluene, eg, painters and workers in the printing industry. There were no significant changes in any tests due to the toluene exposure, but we saw some minor, nonsignificant changes in performance due to the day-long toluene exposures. These changes might indicate a slight neurotoxic effect.
Although the objective behavioral changes were small, the subjects felt the work to be more strenuous and their reaction time prolonged during the 100-ppm exposure in comparison with the other exposures. In fact the measured reaction times showed no effect of the 6-h toluene exposure, a finding also reported by Ogata et a1 (23). This result indicates that an increased effort was necessary at this exposure condition to obtain an unaltered test result.
Another indication of a slight neurotoxic effect of toluene exposure is the significant increase that occurred for headaches, dizziness, and feeling of intoxication only during the 100-ppm exposure. In the literature (21) moderate fatigue and slight headache have been reported by one of three volunteers exposed to 100 pprn of toluene during 8 h, and drowsiness and very mild headache occurred in one of two volunteers exposed to 50 pprn during the same period of time. The present hygienic standard in the United States and in Denmark is 100 pprn (3,8), but in Denmark a change to 50 pprn has been proposed. From this study of the acute exposure of young healthy males it is apparent that workday-long exposure to 100 pprn causes no change in airway physiology and only minor changes in performance, but it causes discomfort for more than "the small percentage of workers" which is the basis for the setting of hygienic standards (3,8). During exposures to 10 or 40 pprn this discomfort was not experienced; therefore a hygienic standard of 40 pprn of toluene would be adequate to fulfill the previously mentioned goal. A hygienic standard of that magnitude would also protect the workers against the greater irritation caused by the excursions to concentrations of up to 1.5 of the hygienic standard which are allowed for 15-min periods provided the daily average is not above the hygienic standard (8). The final setting of a health-based hygienic standard for toluene should also include experiences from short-term exposures at different work loads for workers with daily exposure to toluene and from long-term exposures in the workplace.
The introduction of energy efficient procedures due to the high cost of energy has caused a decrease in the supply of ventilating air and a n increase i n the use of recirculation air. It has been suggested that the concentration of any contaminant in supply air should never exceed 10 % of the hygienic standard (4). From the present study it appears that toluene reduces the perceived quality of the air (fig 4) and that it is moderately odorous. A supply of air with 10 p p m of toluene would cause an initial impression of a decrease in air quality and a slight perception of odor, but both effects would disappear after 1 to 2 h of continuous exposure.