Exposure to styrene in a polymerization plant. Uptake in the organism and concentration in subcutaneous adipose tissue.

J., ASTRAND, I. and WIGAEUS, E. Exposure to styrene in a polymeri zation plant: Uptake in the organism and concentration in subcutaneous adipose tissue. Scand. j. work environ. & health 4 (1978) 324-329. Three male employees exposed to styrene in the processing of polyester tanks were studied during a work week. From Tuesday to Friday the concentration of styrene in ambient air was measured continuously in the breathing zone. The uptake in the organism was esti mated as the product of the time-weighted average of the concentration in inspir atory air, the time-weighted average of 8-h pulmonary ventilation, and the per centage pulmonary uptake. Pulmonary ventilation was measured with the Wright respirometer. Percentage pulmonary uptake was estimated on the basis of the con centrations in inspiratory and alveolar air. The amount of body fat was estimated by an anthropometric method. The concentration of styrene in subcutaneous adipose tissue was determined by gas chromatography after needle biopsy before and after the workshift on Monday, Wednesday and Friday. The time-weighted average of the concentration of styrene in inspiratory air during the work week was 32-85 mg/ms, Le., below half of the Swedish threshold limit value (210 mg/m 3). The mean daily uptake in the organism was 193-558 mg. On Monday morning the concentration of styrene in adipose tissue was 2.8-8.1 mg/kg and on Friday afternoon 4.7-11.6 mg/kg. The concentrations were higher in the two subjects with a higher exposure of long er duration, as compared to the concentrations in the recently employed subject, who was exposed to lower concentrations in inspiratory air. Both of the two former subjects had a considerable estimated amount of body fat (27 and 41 kg). The calcu lated half-life of the concentration of styrene in adipose tissue after the end of exposure was 5.2 and 2.8 d for these two subjects. Therefore an elimination time of about five weeks is needed by the subject with the slowest elimination before the limit of detection (0.1 mg/kg) is reached.

sorbed styrene is excreted, mainly as mandelic acid in 1!he min'e, there is a certain risk of aocumulation in the body in occupational 'exposure because of the hi1gh solubility of styrene in fait.
Styrene was detectable in adipose tissue for as long as two weeks after 2 h of ex-perimen1Jal exposure to a concentration of 210 mg/m 3 (50 ppm) in mspiratory air, i.e., the present Swedish threshold limit value y = -0.86 x + 79. 3, where Pulmonary ventilation was measured with a Wright respirometer (Medishield HarlQw, Es.sex eM 195 AB, England). A total of 15-23 determinations was made for ea,ch subject during about 5 min on each occasion. Measurements were performed during the various phases of work and during the breaks. The duration of the diffeI'tent per10ds was studied. The time-weighted average (TWA) of the 8-h pulmonary ventilatil()Il over 4 d was calculated.
For the diUerent subjects and the separate wor;kdays the uptake in the organism was calculated as the product of three fa{:tors: TWA styrene concentratic.n in inspi'ra,tory ak, TWA 8-h pulmonary ven:tilation,andthe per,centage of uptake. Since the percentage of uptake did not change significantly in the individual during the different workdays or in the course of the work week, the mean of the measurements w,a,s used. and g,able processing, respectively. The third person :had been employed in the plant for two weeks mounting components for connecting pipes to the tanks.
The amount of body fat of the respective subjects was determined by means of skeletal measurement according to the method described by von Dobeln (3,4).
From Tuesday to Friday aliI' from the breathing zone was continuously sampled during the whole workday with the aw of a personal sampler. During the same pertod alveoJ,ar air samples were collected at hourly interv,als. The quoti,ent between the concentr;ation of styrene in alveolar air ,and in inspira'tory air was used in the oalculation of the amount taken up in the body in proportion to the amount inspired. The per,centage of uptake was calculated on the basis of ea{:h alveolar air sample and the inspiratory air sample collected during the preceding 30-min period. In the calculation of the percentage of uptake (y) th'e following equation, obtained in laboratory experiments (1), was used: (5). The half-life of the styrene concentration in adipose tissue of four subjects was estimated to be 2-4 d (5). Accumulation of styrene in adi,pose tissUie implies indirect exposure of sensi1ii,ve organs, by release of the solvent from adipose ,tissue after exposure. Consequently, determinations of styrene concentrations in adipose tissue can be a tool for the evalUJation of adverse health effects iJn oocupational exposure to this compound.
Wolff et al. (10) performed needle biopsies and gas chromatographic solvent analyses on subcutaneous fat from 25 workers i,n a polymecization plant. Low concentrations of styrene, 0.1-1.2 mg/kg of fat, were noted in 13 out of 17 workers exposed to more than 5 p;pm iIIl inspired air within the previ,ous 3 d. The ooncentmtions in ambient air were not determined iIIl oonnecti,on w~th the study. Exposure was estimated on the basis of a previous survey, whkh had disclosed excursions up to 160 ppm. Styrene was not detectable i'n subjects unexposed for more than 3 d.
The aim of the pI'tesent study was to follow the roncenitrations of styrene in subcutaneous ,adipose tissue of ,employees in a polymeri~atiQln plant during a work week.
The purpose was aloo to rellate these concentr,ations <to the conoentration of styrene in inspiratory air a!Il!d to the amount of solvent taken up~n the org.anism. Finally the results of this field study were compared with those of a previous experimental survey in the laboratory (5).

SUBJECTS, EXPERIMENTAL DESIGN AND METHODS
The study was performed in a plant manufacturing 1JanJks of reinforced polyester plastic. The components of reinforced polyester plastic consist of unsaturated polyester, styrene and f~ber glass. 'I1he unsa'turated polyester compound is dissolved in styrene, which is a reactive monomer. A sol~polymer is formed through reaction between 1Jhe poly;ester compound and styren'e.
DuriJng 'aJ work week :three male employees, .a'~23-48 years, were studied. Two of 'them 'had been employed in the plant for several years 'and their tasks were cylinder x= alveolar air concentration inspiratory air concentration X 100. TabLe 1. Task, duration of employment, anthropometric data, time-weighted average (TWA) concentration of styrene in inspiratory air, estimated mean daily uptake of styrene, and concentration of styrene in subcutaneous adipose tissue at the beginning and end of the work week of three employees in a styrene polymerization plant. The methods employed in the present study in :the ,calculat10n of expolsuve levels and amounts of styrene taken UiP in the body were e~aluated in a study of subj,ects exposed to toluene in a pdnt1ng office (9). The estimated uptake values were in close agreemen't w~th the results obtained wi!th the Dougl,as bag technique. A moredetailed descriJptioiIl of the methods used in the present study for ,the estimation of exposure and uptal~e has been presen1ed in a separate report (7).
Needle b10psy of subcutaneous ad1pose tissue was performed before and after the workshift on Monday, W,ednesday and Friday. 'I1he methods employed i!n sampling and analysis were the same as ,in connection w~th a previous experimental exposure in the laboratory (5).

RESULTS
Anth1"olpometri:c data, the tasks and the durations of ,empLoyment of the three subjects studied ave ,pre:sen'ted in ,ta:ble 1. Subjects 1 and 2, who had been occupi'ed with styrene polymerization for several years, were obese, whereas the recently employed third subject had a normal body weight.

326
During the 4 d of study the 8-h TWA styrene ooncentration in the' breathing zone varied between 22 and 93 mg/m 3 . The TWA ,concentration in the i!nspiratory aliI' over 'the four workdays did not exoeed half of the threshold limit value in any 'of the subjects studied (table 1). DetaHed results of the exposure measurements have been reported in the aforementioned separate report (7).
In the thvee subjects the mean percentage of uptake was 60, 61 and 62, respectively. Within the group and dudng the different phases of the workday, pulmonary ventilation vaded between 17 and 32 lImin. The TWA pulmonary ventilation of the three subjects over the four workdays was 17, 20 and 211/min, respect1vely. The indiv1dually estimated inspired and ret ained 'amounts of styrene during the dif-:Iierent workdays are presented i!n fig. 1. The mean daily uptake in the organism was 193-558 mg.
A successive decrease in the daily uptake was noted in subjects 1 and 3 from Tuesday to Thursday. In all cases the uptake value was higher on Friday than on Thursday. On Friday the capacity of production was fully utilized in the factory. This was not the case earlier in the week.
At the beginning and end of the work vatory study. Moreover, the r,ate of work of the subj'ects in the presen't study w,as lower, i.e., they had a lower pulmonary ventilation and a lower cardiac output. Only in one case was the mean daily uptake in the employees of the plant of the same Qrder (558 mg) 'as during the 2-h exposure i,n the laboratory. However, the concent.l1ations in adipQse tissue of the subjects in the plant were, on an average, higher than in the experimental study. The ,amount of styvene in the total f.at depots of the body can be roughly estimated. In such a calculation it is assumed that the concentratiQ!ll of the solvent in subcutaneous adipose tissue is r,epresentative of that in the :total fat depots. It is also assumed that the total amount of adipose tissue ,can be calcula'ted fmID the estimated week the concentrations of styrene in subcutaneous ,adipose tissue were higher in the two subjects who had been exposed for a longer time and to higher concentrations iJ11 the ambient ak, as oompared to sub}ect 3 (table 1). Subject 2, who had been exposed 1.0 the highest average concentra-t~on of styrene, did not have the highest concentmtion oftlhe solvent in adipooe tissue. This fad could be due to the large volume of distribution.
The concentrations of styrene in adipose tissue at different times during the work week are presented in fig. 2. The changes in exposure and uptake during the week make the evaluation of the adipose tissue concentrations difficult. The pattern of the concentrations in adipose tissue and the relation between this pattern and the uptake measurements could not be analyzed statistically because of the small number of observations. It should also be pointed out that after short-term exposure in the laboratory the error of the method for determining the adipose tissue concentration of styrene was 48 %, including the biological variations in concentration within the specimens. However, it can be stated that all determinations in the two subjects with heavier exposure showed higher values in comparison to those of subject 3. A tendency towards an increase in the concentrations during the week was especially noted in subject 2. In all cases the highest value was noted on Friday afternoon. In a previous laboratory study (5), seven subjects were exposed to 210 mg of styrene per cubic meter of i'llSipir,atory air for 2 h. The subjects were exposed during 30 min at rest aJnd during three 30-min periods of incI'eased work load, from 50 to 150 W.
The mean. uptake in the org,anism during the 2-ih exposure was about 500 mg. The mean ooncentratiJon of styrene 2, 4, and ,about 21 h after exposure was about 3.5 mg/kg. The three subjects in the present study weI'e exposed to a TWA concentration i!ll inspil1atJory air that was below half of fue cOll1centI'ation applied in the labo-amount of body fat (5). According to such an estimation, the iincrelase of styrene in the fat depots durimg the work week was about 120, 190 and 30 mg in subjects 1, 2 and 3, respectively. 'I'hese amounts correspond to 7, 7 and 3 %, respectively, of the amount of styrenetal~en up in the body during the week.
In the c,akulation of the weekly uptake it was assumed ,that the mean daily uptake during the 4 d of study could be applied also Ito the Monday. The smaller retention increase in adipose tissue of subject 300uld Ileasonably be explained by a smaller volume and a higher degree of blood perfusion of adipose tissue.
At the time of the study subj,eds 1 and 2 had both been working for several months without sick leave or vaoatLon. If it is lassumed thalt the ooncentrations of styrene in adLpose tissue followed a steladystate pattern at the time of the study and that the Monday morning concentration obtained was representative also of the following Monday, the half-life can be calculated on the basis of the concentrations on Friday afternoon and Monday morning. Such a calculation results in a halflife of 5.2 d for the concentrations in subject 1 and 2.8 d in subject 2. Therefore about 5 and 2.5 weeks, respectively, are needed after the end of exposure before the concentration of styrene in the adipose tissue of the two subjects reaohes the limit of detection.
Of course such calculations yield only tentative results. However, the calculated half-lives of the styrene concentrations in adipose tissue were of the same magnitude as in the previous laboratory study, where the decline of the concentrations was actually measured (5). In three other subjects in a plastic boat factory the half-lives of the styrene concentration in fatty tissue also varied between 2 and 4 d when determined during the summer vacation (unpublished results of Wigaeus et al.).
Engstrom et al. (6) noted a biph8Jsk urinary leX!cretion ofmandelkaci:d after occupationa,l expOSUIle to styrene. During the first 15-18 h after exposure the mediJan half-time of the concentration was 9.4 and 6.4 h after light (TWA 23 ppm) and heavy (TWA 248 ppm) exposure, respectively. During the second phase (19-64 h 328 after exposure) the median half-time was 16.6 h (range 9.8-56 h for nine subjects exposed to a TWA of 23 ppm). Mandelic acid concentrations in urinary prework samples of 29 subjects indicated that styrene was not completely eliminated in the 16-h period between daily exposure at work. The authors referred to the proposal of Linch (8) that the body burden reaches an equilibrium within 2 d and does not increase thereafter if the half-time is less than 12 h, i.e., providing the daily variation in exposure is not great.
In the studies of mandelic acid of Engstrom et ,al. (6) and in the surveys of styrene in ,adilpose ti'ssue from this lahoratory, the limit proposed by Linch (8) is exoeeded, in some oases to a considerable degree. Lt is evident that conditions exist for accumulation of styrene in the body during occupational exposure. However, the extent of accumulation in long-term occupationa!l exposure to conoentrations higher than in the present study cannot as yet be evaluated.