Biological monitoring of occupational exposure to tetrachloroethene.

MONSTER A, REGOUIN-PEETERS W, VAN SCHIJNDEL A, VAN DER TUIN J. Biological monitoring of occupational exposure to tetrachloroethene. Scand j work environ health 9 (1983) 273-281. In the breathing zone of 32 workers concentrations of tetrachloroethene were measured during five consecutive workdays. The feasibility of biological monitoring was tested by the measurement of the concentrations of tetrachloroethene in blood and exhaled air and the urinary excretion of trichloroacetic acid and trichloroethanol. The best parameter to estimate the time-weighted average exposure to tetrachloroethene over the whole workweek appears to be the concentration of both tetrachloroethene and trichloroacetic acid in blood 15-30 min after the end of the workday at the end of the workweek. Among the noninvasive methods the best parameter is the tetrachloroethene concentration in exhaled air 15-30 min after work at the end of the workweek, followed by the measurement of trichloroacetic acid in urine at the end of the workweek. In exposure to 2,050 iimol of tetrachloroethene/m3 (340 mg/m3, 50 ppm) the estimated values for the biological parameters are 13.2 ?xmol of tetrachloroethene/1 of blood, 33 iimol of trichloroacetic acid/1 of blood, 920 ^imol of tetrachloroethene/m3 of exhaled air and 6.1 iimol of trichloroacetic acid/mmol of creatinine in urine, respectively. With 95 % confidence it may be stated that an individual with a value for a biological parameter not exceeding 8.3 iimol of tetrachloroethene/1 of blood, 20 (irnol of trichloroacetic acid/1 of blood, 515 iimol of tetrachloroethene/m3 of exhaled air and 3.0 iimol of trichloroacetic acid/mmol of creatinine, respectively, had an exposure not exceeding 2,050 ^imol of tetrachloroethene/m3. The measurement of trichloroethanol in urine may be used for the estimation of the time-weighted average exposure over the previous 2 d. The concentration of tetrachloroethene in exhaled air 1530 min after exposure had little value for the estimation of the time-weighted average exposure over the last 4 h. On Monday morning the concentration of tetrachloroethene in exhaled air is still about 15 % of the time-weighted average exposure concentration during the whole preceding workweek. The half-time of trichloroacetic acid in urine and blood during the weekend is about 65-90 h.

a m o u n t absorbed is metabolized into trichloroacetic acid (2, 8) a n d probably even a smaller p a r t into trichloroethanol (5). T h e concentration of tetrachloroethene i n exhaled air or i n blood a n d of trichloroacetic acid in u r i n e or blood c a n b e used as a n indicator of occupational exposure.
In the present s t u d y w e measured, by m e a n s of personal sampling, t h e tetrachloroethene concentration i n inhaled air of workers d u r i n g workhours over a normal workweek. I n t h e same period biological monitoring was carried out b y measuring t h e concentration of tetrachloroethene in blood a n d exhaled air, the concentration of trichloroacetic acid in blood, and the concentration of tri-ionization detector. The temperatures chloroacetic acid and trichloroethanol in were as follows: oven llO"C, injector urine. The objective of the study was to 125"C, detector 140°C. Nitrogen (30 ml/ establish relationships between external min) was used as the carrier gas. exposure and the aforementioned bio-The time-weighted average concentralogical parameters.
tion was calculated for each subject from the individual 4-to 6-h samples. The total

Material and methods
weekly work time varied from 37 to 54 h. Lunch and coffee breaks were included, Subjects except when the subject left the contaminated area. The calculated time-Thirty-two subjects (3 females and 29 weighted average exposure was adjusted males), 16 to 59 years of age, who worked to a 40-h week in table 1. in four different workshops [three textile drycleaning shops (A, B, C) and one metal cleaning shop (D)], were studied. Body height ranged from 1.56 to 1.90 m and body weight from 48 to 100 kg. The deviation from the "ideal" body weight (height in cm -100) varied between -20 and 22 kg with a mean of 0 (SD 10) kg (table 1).

Air sampling and analysis
Measurement of the concentrations of tetrachloroethene in air were performed during a 5-d workweek. Workroom air was collected from the breathing zone of the worker through charcoal sampling tubes with personal sampling pumps (Cassella) for two periods of about 4-6 h each day. Under these conditions the risk of tetrachloroethene passing through the charcoal tubes was very small. The level of risk was proved in the laboratory. Tetrachloroethene adsorbed on the charcoal was desorbed with dimethylformamide and analyzed by gas chromatography. A stainless steel column (length 2 m, internal diameter 3.2 mm) was used; the column was packed with 15 % tricresylphosphate on Chromosorb W AW, 80-100 mesh. The detector was a flame Blood sample collection and analysis Venous blood samples were obtained in a well-ventilated room on Monday morning before the subjects started work, on Wednesday and Friday at about 15-30 min after the end of the workday, and again Monday morning before work. The concentrations of tetrachloroethene and trichloroacetic acid (after methylation) in blood were determined with a headspace technique and by gas chromatography with a 3H electron capture detector according to the method described for trichloroethylene by Monster & Boersma (6).

Exhaled a i r sample collection and analysis
Exhaled air samples were collected in duplicate about 1 min before the collection of the blood samples (Monday morning, Wednesday and Friday after the end of the workday, and again Monday morning before the start of work). The exhaled air was collected in a glass tube (length 20 cm, volume 65 cm3) each end of which (8 mm internal diameter) could be closed by means of caps. The caps had a predrilled hole for gas sampling; both caps had

Ambient a i r concentrations
The individual time-weighted average concentration of tetrachloroethene in the air varied from 65 to 6,600 pmol/m3 over the whole workweek (table 1). For fifteen subjects, all working in workshops B and C, the level exceeded the present Dutch maximal acceptable concentration of 1,450 pmol/m3 (240 mgIm3). About one-third of the 311 4-h samples exceeded 1,450 pmol/m3, and 10 % exceeded 2,900 pmol/m3 (480 mg/m3). the "ideal" body weight (height in cm -100) and the other with body weights above this level. The decrease in concentration in blood and exhaled air during the weekend was more pronounced in the slim subjects (N = 17) than in the obese ones (N = 12). In the slim subjects the decrease was a factor of 4.1 (1.5) for exhaled air (the geometrical standard deviation in parentheses) and 3.7 (1.4) for blood, and for the obese subjects the factors were 3.3 (1.5) and 3.0 (1.41, respectively.

Trichloroacetic acid concentrations in blood and urine
The concentrations of the metabolite trichloroacetic acid increased during the workweek in blood, as well as in urine. The relative concentrations on Wednesday and Friday after work were higher by about a factor of two than on Monday morning. The increase of the concentration in urine was more pronounced than that in blood. At the start of the following week the relative concentrations had returned to about 100 70.

Trichloroethanol concentration in urine
Small amounts of trichloroethanol (< 4 pmol/mmol of creatinine) were detectable in the urine collected on Wednesday and Friday after work from subjects with a relatively high exposure Estimation of the f individual) timeweighted average exposure from biological parameters The data of a few workers had to be partly discarded because some workers did not work on Friday (N = 2) or had been already in contact with tetrachloroethene early on Monday morning before the measurements took place (N = 3). Among the measurements from workshop D only the concentration of tetrachloroethene in blood and exhaled air could be used because in that workshop the metabolites trichloroacetic acid and trichloroethanol in blood and urine were for a greater part derived from exposure to l,l,l-trichloroethane (see table 1). The metabolism of tetrachloroethene is so small that an increase or decrease in metabolism, possibly caused by the presence of 1,1,1trichloroethane, will hardly have any influence on the concentration of tetrachloroethene.
The various biological parameters on Friday after work and on the second Monday morning before work correlated better with the time-weighted average exposure over the whole workweek than with the time-weighted average exposure over the preceding day. Table 2 shows various simple and multiple regression equations for the estimation of the individual time-weighted average exposure from biological parameters.
With one parameter the smallest residual error for estimating time-weighted average exposure over the whole workweek was obtained for the tetrachloroethene concentration in blood on Friday (A = 1.22, see fig 4) followed by trichloroacetic acid in blood on Friday (A = 1.27) and tetrachloroethene in exhaled air on Friday (A = 1.28). A combination of the two parameters measured at the same time in blood or in excreta (tetrachloroethene in exhaled air and trichloroacetic acid in urine) with multiple regression analysis resulted in a somewhat smaller residual error in estimating the time-weighted average exposure than obtained from the single parameters (table 2). In the multiple regression the tetrachloroethene and trichloroacetic acid concentrations contributed about equally to the estimation of the time-weighted average exposure. The urinary excretion of trichloroethanol (in micromoles per millimole of creatinine) on Wednesday and Friday correlated better to the time-weighted average exposure of the two preceding days (R2 = 0.61, A = 1.38) than to the time-weighted average exposure of the preceding day (R2 = 0.32, A = 1.91) or preceding week. Table 3 presents the estimated value of the biological parameters in the case of tetrachloroethene exposure of 2,050 pmol/m3     (340 mg/m3, 50 ppm, present threshold contains the value of the biological paralimit value, United States, and Maxi-meters for which (with 95 % confidence) male Arbeitsplatzkonzentration, Federal it may be stated that an individual having Republic of Germany). Furthermore it such a value (or lower) did not exceed a tetrachloroethene exposure level of . developed from sedentary exposures for 2,050 pmol/m3. For two parameters these 7.5 hid, 5 diweek, 4-6 % (4, 11). However, values are also indicated in fig 1 and 4. they did not take into account the higher uptake during occupational exposure caused by physical activity and presumably a higher degree of saturation of the Discussion and conclusions body with tetrachloroethene due to The concentration of tetrachloroethene in blood and exhaled air and of trichloroacetic acid in blood and urine were only slightly higher on the second Monday than on the first Monday morning. This finding implies that the exposure in the week of measurement was of the same magnitude or somewhat higher than in the preceding workweek@). Tetrachloroethene is metabolized only to a minor extent. The most important form of excretion is through exhalation. The quotient between the concentration of tetrachloroethene in blood and in alveolar air is rather constant [15.2 (SD 2.6)]. This finding corresponds well with the blood/gas partition coefficient of 13.1 measured by Sato & Nakajima (10). The olive oillgas partition coefficient for tetrachloroethene is about 2,000 (1, 10). Correspondingly the solubility of tetrachloroethene in blood and body tissues is high, and consequently the rate of elimination is slow. The concentration of tetrachloroethene in exhaled air after the weekend was still about 15 ' 70 of the mean inhaled concentration in the previous workweek (table 3). This high percentage is caused by the lack of metabolism and the slow rate of elimination through the lungs. This percentage is higher than that predicted from the breath decay curves repeated occupational exposure for months. The percentage is also higher than the level predicted from a mathematic model for the simulation of repeated exposure at rest (alveolar ventilation 7 limin) for four weeks, 8 hid, 5 dlweek, about 5 % (3); the authors used a smaller partition coefficient, 9, for bloodlgas and for oillgas, 960. Therefore the rate of excretion of tetrachloroethene in this model will be faster than in a model with a higher partition coefficient and than in occupational exposure with a heavier work load.
The increase in concentrations in biological media (from Monday morning to Wednesday evening) and the decrease (from Friday evening to Monday morning) was more pronounced for the trichloroacetic acid concentration in urine than for the trichloroacetic acid concentration in blood. Monster et a1 (7) showed that during exposure to trichloroethylene (2,900 pmol/m3, 4 h, 5 d) the amounts of trichloroacetic acid excreted in urine produced during the night were always lower than those excreted during the previous and following periods, whereas the trichloroacetic acid concentration in blood increased steadily. Therefore the concentrations of trichloroacetic acid measured in urine on the Monday mornings are relatively low and give rise to the Table 3. Estimated concentrations in blood, alveolar air, and urine at the end of the workweek in subjects exposed to 2,050 pmol of tetrachloroethene (PERC)/m3 (340 mg/m3, 50 ppm) 8 h a day, 5 d a week, and the value for which it may be stated (with 95% confidence) that a new subject having such a value (or lower) did not exceed an exposure of 2,050 pmol PERClm3. (TCA = trichloroacetic acid, TCE = trichloroethanol). In occupational exposure to tetrachloroethene Ikeda et a1 (5) measured urinary metabolites in 2-h samples at the end of the workday. From their curves the average excretion in exposure to 2,050 ymol/m3 (340 mg/m3) can be estimated to be about 285 ymol of trichloroacetic acid11 and about 200 ymol of trichloroethanol/l. These values are much higher than those measured in the present study (table 3). This difference may at least partly be explained by the difference in analysis. Ikeda et a1 (5) used a nonspecific spectrophotometric method (a modified Fujiwara-reaction), and in the present study a specific gas chromatographic method was used.
With a gas chromatographic method Weichard & Lindner (13) measured small concentrations of trichloroacetic acid and trichloroethanol in urine of workers exposed to tetrachloroethene. The time of sampling was not specified however. Extrapolation of the mean concentrations to exposure to 2,050 ymol/m3 (340 mglm3) resulted in trichloroacetic acid and trichloroethanol concentrations of about 20 ymol/l and about 5 ymolll, respectively. In experimental exposure to pure tetrachloroethene no trichloroethanol was detected in urine (2, 4, 8).
On the basis of this study the best parameter to estimate the time-weighted average exposure to tetrachloroethene over the whole workweek appears to be measurement of the concentration of both tetrachloroethene and trichloroacetic acid in blood at the end of the workday on Friday (the smallest geometrical standard deviation). The second best parameter is measurement of only the concentration of tetrachloroethene in blood on Friday, followed by measurement of tetrachloroethene in exhaled air combined with trichloroacetic acid in urine on Friday. After single 4-h exposure to tetrachloroethene the best results in estimating exposure were also obtained from the concentrations in blood (9).

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Among the single noninvasive methods the best method is tetrachloroethene in exhaled air on Friday after work, followed by trichloroacetic acid in urine on Monday morning.
For estimating the time-weighted average exposure over a shorter period than a week, trichloroethanol in urine may be used. With a biological half-time for trichloroethanol of 10-12 h (7) the exposure magnitude on the day before the last exposure will have influenced the trichloroethanol concentration in urine, especially when the magnitude of exposure on the day before the last exposure was high compared to exposure on the day on which trichloroethanol in urine was measured. Therefore, the best result was obtained by estimating time-weighted average exposure over the previous 2 d.
As expected, there was a high correlation (R" 0.93) between the exposure concentration during the last 4 h and the concentration of tetrachloroethene in exhaled air 15-30 min after the end of exposure. However the confidence interval was rather large, an occurrence which makes estimation of the time-weighted average exposure of little value. The exhaled alveolar air concentration was high compared to the exposure concentration during the last 4 h of exposure. This high concentration can partly be explained by 1.5 (SD 0.8) ( N = 46) times higher exposure concentrations during the morning than during the afternoon. Estimation of individual time-weighted average exposure from the biological parameters can probably be improved when the following points can also be taken into account: 1. Physical activity during and after work. Moderate exercise during exposure increases the uptake and the postexposure tetrachloroethene concentrations in blood and exhaled air (4,8). Because in the present study physical acitivity (respiratory minute volume) was not measured, this factor could not be taken into account in the estimation of the time-weighted average exposure from the biological parameters.
2. Influence of adipose tissue on uptake and, especially, excretion. This influence was shown in the present study in the faster decrease of t h e tetrachloroethene concentrations in blood and exhaled air from Friday to Monday i n slim subjects if compared to m o r e obese subjects.
3. S k i n absorption. F r e q u e n t immersion of t h e h a n d s in liquid tetrachloroe t h e n e will result in substantial u p t a k e through the skin (12). This aspect was not taken into account in t h e present study. 4. P e a k exposure. When taking 4-h workroom samples t h e r e is insufficient insight into t h e variation of t h e exposure concentration a n d also into t h e influence of t h e variation o n biological parameters.
5. I n this study we did not measure t h e biological parameters o n t h e next morning after exposure (before t h e n e x t exposure). Probably such measurements may also b e a reference point for estimating t h e time-weighted average exposure.