American Journal of Industrial Medicine 13:415-427 (1988)

Studies of Transformer Repair Workers Exposed to PCBs: 1. Study Design, PCB Concentrations, Questionnaire, and Clinical Examination Results

Edward A. Emmett, MB, BS, MS, Marco Maroni, MD, Joanne M. Schmith, RNC, MPH, Barry K. Levin, MD, MPH, and Joan Jefferys, SCM

A cross-sectional study compared 55 transformer repairmen, 38 currently, and 17 previously exposed to polychlorinated biphenyls (PCBs) with 56 non-exposed subjects. PCBs exposures occurred from air and contaminated surfaces, predominantly from Aroclor 1260 with some exposure to Aroclor 1242. Each worker underwent: a question- naire; standardized medical examination; delayed hypersensitivity testing; and determi- nation of serum and adipose tissue lipid total PCB cgncentrations.

Adipose and serum [PCBs] were significantly higher in the currently exposed, but previously exposed workers did not differ significantly from comparison subjects.

No subjects had a classical syndrome of PCB poisoning. A number of neurobehav- ioral and irritant symptoms were significantly more prevalent in the exposed group, but were probably not related to PCBs. Comedones were more frequent in the exposed group, but no evidence of classical chloracne was noted. Cutaneous delayed hypersen- sitivity responses to mumps and to trichophyton antigens did not differ between the groups. The association of PCBs with job functions were explored.

Key words: polychlorinated biphenyls, blood, adipose tissue, symptoms, skin, delayed hypersensitivity, job functions

INTRODUCTION

Transformer maintenance and repair workers represent one of the groups most highly exposed to mixtures of polychlorinated biphenyls (PCBs). The production of PCBs in the United States was suspended in 1977; during the period 1966 to 1974 about 4045% of domestic PCBs sales were to manufacturers of transformers and from 5 to 10% of all U.S. transformers contained an average of 2,000 to 2,500 pounds of PCBs.

Center for Occupational and Environmental Health, The Johns Hopkins University, Baltimore (E.A.E., J.J.). Associate Professor, Instituto di Medicina del Lavoro, University of Milan, Italy (M.M.). Occupational Health Nurse Consultant, U.S. Army, Europe (J.M.S.). Employee Health Services, Warner Lambert Company, (B.K.L.). Address reprint requests to Dr. Edward A. Emmett, National Institute for Occupational Health and Safety, G.P.O. Box 58 , Sydney N.S.W. 2001, Australia. Accepted for publication October, 5 , 1987.

0 1988 Alan R. Liss, Inc.

416 Eniniett el al.

PCBs were produced and used in the United States under the trade name Aroclor. Aroclors are mixtures from among the 209 possible PCB congeners and differ in the chlorination of component congeners. They are identified by a number which, in part, indicates the degree of chlorination; for example, Aroclors 1242 and 1260 are 42% and 60% chlorinated, respectively.

For transformer use, the Aroclors were usually combined with trichlorobenzene in a 60:40 to 70:30 mixture called Askarels [Brinkman and Dekok, 19801. PCBs were typically used in transformers inside buildings where protection against fire was paramount. Although PCBs are gradually being replaced, a number of transformers still contain PCBs. PCB contamination of biota is quite widespread and PCBs are an important component of many hazardous waste disposal sites.

The human health impact of exposures to PCBs is still not completely clear. A distinctive disease, Yusho in Japan and Yu-Cheng in Taiwan, resulted from the ingestion of PCBs-contaminated rice oil used in cooking [Kuratsune, 1980; Chang et al., 19801. These oils contained polychlorinated dibenzofurans and polychlorinated quarterphenyls in addition to PCBs. The mucocutaneous syndrome was particularly characteristic [Kuratsune, 19801. This syndrome has not generally been seen in those occupationally exposed to PCBs, (particularly Aroclors 1248 and 1252), although preclinical and early clinical changes, including altered liver function tests and chloracne, have been seen in these groups [Kimbrough, 19801.

The objectives of this study were to determine whether abnormalities to PCBs were occurring in a population exposed to Aroclor 1260, to compare [PCBs] in past exposed and current transformer workers, and to define [PCBs] in a population without industrial exposure. In this paper we describe the study design, demographic characteristics of the groups, PCBs among current, retired, and comparison workers, and the results of questionnaire, clinical examination, and skin antigen challenge for delayed hypersensitivity.

MATERIALS AND METHODS Study Design

A cross-sectional study utilized present and past switchgear shop employees engaged in transformer repair and a comparison group of presently employed, similarly skilled, operating engineers of the same employer with similar entry educa- tional requirements, never occupationally cxposed to PCBs. The population was balanced for age and race. All participants were male.

Activities of Transformer Repair Workers The exposed groups were responsible for the maintenance and repair of approx-

imately 1,100 high voltage electrical transformers. This shop had been in existence for nine yr; some employees had previously worked at similar tasks. Work activities included: (a) sampling and testing transformer fluids for dielectric properties; (b) adding and topping off transformers when oil levels were low; (c) clean-up of any spills or leaks in transformer vaults using absorbent material and sometimes l , l , l - trichlorethane; (d) repair of transformers by drainage of up to two hundred gallons of transformer oil to replace a secondary bushing; and (e) periodic filtering of the transformer oil to upgrade its diclectric properties. Occupational exposure to leaking transformers was quite common. Other duties, not requiring direct contact with

Transformer Repair Workers and PCB Exposure 417

transformer oils, included working on the high voltage network, and low voltage units within the vault area.

At the time of study in 1980, current employees worked two shifts. The average work time in this shop was 3.75 yr. The majority of workers were skilled electricians by training.

Industrial Hygiene Evaluation of PCB Exposures An industrial hygiene survey has been separately reported [Mosely et al., 19821.

Table I indicates the ranges of PCB concentrations in personal breathing zone samples for various tasks. Ambient air levels were well below the OSHA standard for Aroclor 1254/1260 of 500 pg/m3. The NIOSH recommended level of 1.0 pg/m3 was exceeded in all settings.

Widespread PCB Contamination of workplace surfaces was noted and PCBs were qualitatively detected on the hands of transformer repair workers and on surfaces such as the bannister near the transformer vault and the steering wheel of a truck.

Selected samples of bulk Askarel and of air from transformer vaults were analyzed by GUMS for tetrachlorobenzo-p-dioxin (TCDD) and tetrachloro-diben- zofuran (TCDF). The limit of detection of TCDD was 1 pg/g (lppb) and 2.5 pg/g (2.5 ppb) for TCDF. TCDD was not detected. The TCDF concentration ranged from 13 to 116 ppb by weight. A Varian Mat 212/200P GC/MS/DS was used to further determine whether any TCDF was 2,3,7,8-TCDF. A 50 meter Silar lOcc capillary column was used to separate the various TCDF isomers. At least 10 were present in the samples; the highest concentration of 2,3,7,8-TCDF was 31 ppb. TCDF was found in representative air samples (detection limit 1 nglsample). The pattern and retention times of major peaks in eight bulk samples of Askarel from different transformer locations showed seven to be Aroclor 1260 and one Aroclor 1242.

Selection of Populations All employees who had ever worked in the switchgear shop were identified

from work records. All 72 exposed mem (43 currently exposed and 29 past exposed)

TABLE I. Ranges of PCBs Concentrations* in Personal Breathing Zone Samples for Various Tasks

Sample Sample 8 Hour time weighted Number of duration concentration average concentration

Task samples (hours) (wg/m3) (pg/m3)

Oil drain plug 3 3.1-3.2 43.1-60.0 16.7-24.0 repair and cleanup

oil drain plug repair and cleanup

leak

repair and cleanuD

Sight gauge and 3 3.2 7.9-17.4 3.2-7.0

Cleanup of PCBs 3 1 .o 0.1-3.1 0.0 1-0.4

Secondary oil leak 15 1.5-5.8 2.1-17.1 0.7-12.4

*Predominantly Aroclor 1260. Adapted from Mosely, CL et al. [1982].

418 Emmett et al.

were invited to participate. The 55 participants (38 currently exposed and 17 past exposed) represented 76.4% of the eligiblc workforce; 2% (two) of the eligible men failed to keep appointments, 12.5% (nine) had left the metropolitan area, and the remaining six nonparticipants (8.3%) lived in the area, but declined to participate. The participants represented 87 % of the total currently exposed and 55 % of the total previously exposed workers.

A preliminary questionnaire to assist in the selection of the comparison group, eliciting age, race, smoking habits, alcohol intake, and previous occupational expo- sures to PCBs, was sent to all operating engineers.

Clinical Examinations Participation was voluntary. After informed consent was obtained, each partici-

pant was hospitalized for 24 hr at the USPHS Hospital (now Wyman Park Health System), Baltimore. All medical procedures were performed during this time.

A detailed questionnaire eliciting demographic data, medical history and a review of past and current symptomatology (within the last year) was administered by trained interviewers. Current symptom items included eye and upper respiratory irritation, fertility, sexual desire, changes in the skin, skin abnormalities, and symp- toms rclating to the nervous, hepatic, gastrointestinal, genitourinary, cardiovascular, respiratory and musculo-skeletal systems. Information on occupational history, PCB exposure, and specific work practices was elicited from the exposed group at the conclusion of the questionnaire. With the exception of the interviewers, all physicians and technicians were blinded with respect to the jobs held by participants.

A detailed physical examination was performed. A thorough skin examination was performed by the same dermatologist under the same conditions. For each body region we systematically recorded: the presence and degree or absence of erythema, scaling, hyperpigmentation and elastosis; and the number of closed comedones, open comedones, inflammatory papules, pustules, cysts and milial cysts. In addition, for the facial region, we recorded the presence of hypertrichosis, atrophic scarring, xanthalesma, scleral abnormalities, conjunctival abnormalities including hyperemia, meibomian gland secretion, palpable meibomian glands, lid margin or palpebral changes, superficial corneal pigmentation, oily precorneal film and arcus senilis; and for the oral cavity, pigmentation or other changes. A final dermatologic diagnosis based on clinical findings was made for each subject.

Height, weight, blood pressure, presence or absence of nasal discharge or edema, oral pigmentation, the percentage of occlusion of each ear by cerumen, and skinfold thickness at triceps, suprailiac, and subscapular by the Tanner method 119621 were systematically recorded..

The presence and type or absence of abnormalities on examination of the ocular fundi, thyroid, lymph nodes, chest, cardiovascular system, abdomen and extremities were recorded. Liver size was determined by percussion on each subject. The size and consistency of the testes, presence of hydrocele, varicocele, any epididymal abnormalities were recorded. A rectal examination was performed, prostatic size noted and feces examined for blood using a hemoccult test.

Delayed Hypersensitivity Skin Reactions Delayed hypersensitivity was evaluated by the dermal reaction to 0. lcc intra-

dermal injection of mumps (Eli Lilly, Indianapolis, Indiana) and trichophyton antigen

Transformer Repair Workers and PCB Exposure 419

(1,OOO P units per ml). Induration of 5 mm or more 48 hr later was considered positive.

Determination of PCB Concentrations An early morning fasting blood sample was obtained, serum was separated and

placed in a pesticide free glass vial for PCB analysis. After local anesthesia, adipose tissue was aspirated through a 15 gauge needle from the upper outer quadrant of subcutaneous buttock tissue and washed with normal saline into a pesticide free glass vial. The samples were frozen, prior to analysis at Research Triangle Institute Research Triangle Park, North Carolina (Dr. Edo Pelizarri). They were extracted with hexane, purified on fluorisil column chromatography, analysed by packed col- umn gas chromatography/electron capture detection (GCIECD) using the method of Webb and McCall [1973], and reported as total PCBs. The PCB patterns observed in all groups resembled Aroclor 1260.

Qualitative confirmation of PCBs by packed column GYMS was performed on 18 samples selected to reflect a range of exposure categories and other factors. The presence of contamination due to pesticides, pesticide metabolites, and plasticizers was addressed using visual pattern recognition and worst case calculations. Interfer- ence from dioctylphthalate was circumvented by excluding that peak. DDE and DDT had been detected in the GC/ECD as well as the GUMS analysis and were not included.

For adipose tissue, the PCB content was determined in the hexane extractable fat. In five samples, the mean of percent extractable fat was 49% (range 46% to 65 %).

Data Handling and Analysis Data were coded, keypunched, verified, and validated by range checks. Demo-

graphic and employment characteristics were compared using the chi square test and t-test for discrete and continuous characteristics, respectively. Since the distribution of log transformed PCB levels more closely approximated a normal distribution, PCBs were log transformed after adding 0.01 ppm to adipose concentrations and 0.1 ppb to serum concentations to eliminate zero values

Serum and adipose tissue lipid PCBs in current exposed, past exposed, and comparison groups were analyzed using analysis of variance with Duncans multiple range test. A t-test was used to compare serum and adipose PCBs in all exposed and the comparison group.

Pearson product-moment correlations were calculated for serum and adipose tissue lipid PCBs and continuous variables.

RESULTS Demographic and Employment Characteristics of the Two Groups

The study groups comprised 55 exposed men (45 white, 10 black) and 56 comparison men (47 white, 9 black). Mean (38) and median (36) ages were identical, the age range was 24-60 for the exposed and 24-64 for the comparison group. The groups did not differ significantly in proportion of current smokers (60% vs. 46%) mean cigarettes per day in current smokers, mean pack yr for smokers and ex- smokers, current alcohol drinkers (80% and 71%), mean yr residential in urban

420 Emmett et al.

setting, of employment with current employer, marital status, or level of education. The only significant difference was in the number of employees who currently smoke and drink alcohol (53% exposed, 39% control p < 0.05). No significant differences were found between the two groups for past occupational exposures except to PCBs: all the exposed group and none of the comparison group gave a history of occupational exposure to PCBs.

Serum and Adipose Tissue Lipid PCBs Concentrations Comparisons of serum and adipose tissue lipid PCBs in the total exposed

(currently exposed and past exposed) and comparison group are shown in Tables I1 and 111.

In the comparison group, 48% of serum PCBs were < 5 ppb, 40% from 5-9 ppb. 12% from 10-14 ppb and no values were above 15 ppb. In the exposed group, 24% were < 5 ppb, 31% from 5-9 ppb, 4% from 10-14 ppb, 14% from 15-19 ppb, 10% from 20-29 ppb, 6% from 30-39 ppb, 3% from 40-49 ppb and 8% from 50 to 300 ppb.

For adipose PCBs in the comparison group, 80% of values were c 1 ppm, 13% from 1-1.9 ppm, and 7 % from 2-2.9 ppm. No values were more than 3 ppm. In the exposed group, 30% of values were < 1 ppm, 23% from 1-1.9 ppm, 8% from 2-2.9 ppm, 23% from 3-5.9 ppm, 8% from 6-9.9 ppm, and 8% from 10-30 ppm.

The geometric mean serum PCBs in the exposed group (9.7 ppb) was signifi- cantly higher (p < .01) than that in the comparison group (4.6 ppb). The geometric mean adipose tissue lipid PCBs in the exposed (1.45 ppm) was significantly higher (p < 0.01) than that in the comparison group (0.6 pprn).

The exposed group was subdivided into past and currently exposed as shown in Tables I1 and 111. Differences among the three group were highly significant (p < . O l ) for both serum and adipose tissue lipid [PCBs]. Duncans multiple range test at the .05 level showed that the mean of PCBs in the currently exposed was significantly higher than in both the past exposed and comparison group, which did not differ significantly. Past exposed workers had been away from exposure to PCBs for an average of 4.5 yr. Serum PCBs greater than 15 ppb were seen in 4/17 of past and 161 37 of currently exposed. Adipose PCBs greater than 3 ppm were seen in 1/16 of past and 15/21 currently exposed.

The Pearson correlation coefficient between serum and adipose tissue lipid PCBs was 0.319, statistically significant at p = 0.001.

TABLE 11. Serum PCB Concentrations (ppb) for Total Exposed, Current Exposed, Past Exposed and Comparison Groups

Group comparisons using Geometric log transformed data

Population N Range Median mean Mean S.E. pvalueh

Comparison (54) ND-I5 6 4 .6 1.52 0.14 Current exposed (37) ND-300 12 12.2 2.50 0.22

Comparison (54) ND-15 6 4.6 1.52 0.14

aThe limit of detection was 1 ppb. hF-test or two-tailed t-test.

Total exposed (54) NDa-300 9 9.7 2.27 0.19 .01

Past exposed (17) ND-30 7 5.9 1.78 0.33 .01

Transformer Repair Workers and PCB Exposure 421

TABLE 111. Adipose Tissue Lipid PCB Concentrations (ppm) for Total Exposed, Current Exposed, Past Exposed and Comparison Groups

Group comparisons using log transformed data

Mean S.E. p Valueb Geometric ~ .~

-~ - Population N Range Median mean

Total Exposed (52) ND"-33 I .45 1.56 0.448 0.170 ,ol

Current Exposed (36) ND-33 2.20 2.08 0.731 0.271 Comparison (53) ND-3.0 .60 0.60 -0.505 0.137

Past Exposed (16) 0.3-5.1 .75 0.83 -0.191 0.186 .01 Comparison (53) ND-3.0 .60 0.60 -0.505 0.137

'The limit of detection was 0.2 ppm. bF-lest or two-tailed t-test.

Correlations Between PCB Tissue Concentrations and Work History

Table IV shows Pearson correlation coefficients obtained between the serum and adipose [PCBs] and several historical measures of exposure.

For currently exposed workers, both serum and adipose PCBs were significantly associated with number of years worked in the switchgear shop. The serum, but not the adipose, PCBs was significantly associated with age and the number of years worked with the present employer.

For past exposed workers, neither age nor years worked in the switchgear shop were significantly associated with tissue levels of PCBs. A significant association was seen between the time spent (hr/yr) in the job tasks of repair, storage, and filtering and the adipose PCBs. The absence of correlation with duration of employment may be due to relatively short mean duration of exposure, or to the smaller group size.

For comparison subjects, neither age nor number of years worked with the present employer were significantly associated with [PCBs] .

Questionnaire and Physical Examination

None of the examined individuals presented with a classical syndrome (chlor- acne, jaundice, etc.) clinically recognizable as compatible with PCB toxicity as described in the literature and summarized by Kimbrough [ 19801. Differences in the responses to questions about current symptomatology, past medical history, and in physical findings between exposed and comparison groups are given in Table V. Significant differences were observed for eye irritation and increased tearing, chest pain on walhng, wheezing, loss of appetite, frequent headaches, trouble sleeping, and memory trouble. In each case, the abnormal response was more prevalent in the exposed group.

The only significant difference between the groups in past medical history was in the history of having been tested for fertility problems, reported positively for one subject in the comparison group and eight in the exposed group. A review of the medical history indicated that in five of the eight instances, infertility had been medically investigated and attributed to problems in the wife, or the couple subse- quently had a child. In one instance, there was a preexisting testicular abnormality and in two instances, no further information was available. On examination, three workers, all in the exposed group, were found with unilateral testicular atrophy and three with bilateral atrophy. These differences were not statistically significant. For at least three of the testicular abnormalities, the abnormalities had been long standing

422 Emmett et al.

TABLE IV. Pearson Correlation Coefficients for Tissue Concentrations of PCBs and Work Exposure Status*

Log serum Log adipose PCBs -~ PCBs

Work exposure status R p value R p value

I. Current Exposed (N = 37) (N = 36) Age ,435 .007 ,251 NS Years with

Present Employer ,353 ,030 ,309 NS

.-

Years at

HrsiYr Spent in Maintenance .025 NS a -.I71 NS

HrsiYr Spent in Operations .131 NS - ,009 NS

Hrs/Yr Spent in Repair ,004 NS ,025 NS

Hrs/Yr Spent in Storage & Filtering - .018 NS ,042 NS

XI. Past Exposed (N = 17) (N = 16) Age .390 NS .2Y0 NS Years with

Present Employer ,297 NS ,224 NS Years at

Switchgear shop - ,241 NS ,068 NS Hrs/Yr Spent in

Maintenance ,361 NS ,416 NS HrdYr Spent in

Operations ,303 NS .284 NS Hrs/Yr Spent in

Hrs/Y r Spent in

111. Comparison Group (N = 54) (N = 53) Age ,173 NS ,044 NS Years with Present ,229 NS .052 NS

Switchgear shop ,379 .020 .s IS .001

Repair ,436 NS .646 .007

Storage & Filtering .287 NS ,621 ,010

Employer

*Number of hr per yr at various tasks determined for previous year for currently exposed and for last full year worked for past exposed. "NS, not significant at the 0.05 level.

and had been recognized before the individual's occupational exposure. We concluded that no unequivocal PCB related fertility abnormalities were seen in this group.

Two individuals in the exposed group and none in the comparison group gave a history of rcmoval of a melanoma, although this difference was not statistically significant.

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Cutaneous Delayed Hypersensitivity Response The proportions of positive responses to mumps (92% exposed, 89% control)

and trichophyton (17% exposed, 8% control) did not differ significantly. The mean diameters of the skin reactions to mumps antigen in the two groups were identical (12.6 mm).

DISCUSSION AND CONCLUSIONS

Toxic effects ascribed to PCBs in the published literature have included chlor- acne and other dermatologic disorders [Kuratsune, 1980; Maroni et al., 1981; Fisch- bein et al., 19821, joint inflammation [Kuratsune, 19801, gastrointestinal symptoms [Kuratsune, 19801, abnormalities in liver function [Ouw et al., 1976; Chase et al.. 1982; Maroni et al., 19811, microsomal enzyme induction [Alvares et al., 19771, altered porphyrin metabolism [Maroni et al., 19841, serum lipid abnormalities [Smith et al., 1982; Baker et al., 19801, immunosuppression [Chang et al., 19811, reduced forced vital capacity [Warshaw et al., 19791, neurologic dysfunction [Murai and Kurowa, 197 11, reproductive effects including toxemia of pregnancy [Wasserman et al., 19821 and premature delivery [wasserman et al., 19801. Certain PCB mixtures are carcinogenic to mice [Ito et al., 1973; Kimbrough and Linder, 19741 and rats [Kimbrough et al., 1975; Kimura and Baba, 1973; Morgan et al., 1981; Pereira et al., 19821. Two epidemiologic studies exploring PCB carcinogenity in man have not provided definitive answers [Brown and Jones, 1981; Bertazzi et al., 19811.

A number of symptoms were reported more frequently; in our exposed group. Eye irritation and tearing were significantly more prevalent, however, on examina- tion, abnormal findings of conjunctivitis or tearing were found in only one exposed worker, indicating that these symptoms were mild and/or transient and did not leave permanent sequelae. Reported ocular symptoms suggest that there are irritant sub- stances at the workplace. Eye irritation in PCB-exposed workers has been reported previously [Ouw et al., 1976; Warshaw et al., 19791. PCBs, however, are of low volatility and are relatively non-irritating, leading us to the conclusion that 1,1, l-tri- chloroethane used to clean up spills or trichlorobenzene in Askarcl may be responsible for these complaints.

Although wheezing was reported more frequently in the exposed workers, physical examination of the chest was normal in all the symptomatic workers, and whcczing was not significantly associated with either exposure or smoking when one was adjusted for the other. Thus we did not consider the wheezing to have been associated with PCB exposure.

Although we systematically searched for mucocutaneous symptoms and signs of Yusho including dark brown nail pigmentation, follicular hyperkeratoses, increased palm sweating, and hyperpigmentation of the skin and mucous membranes [Kurat- sune, 1980; Kashimoto et al., 19811, we did not find them. These findings in workers exposed to Aroclor 1260 are generally consistent with occupational studies of other Aroclors and are compatible with the view that Yusho may be associated with dibenzofurans and other impurities rather than PCBs [Kashimoto et al., 19811.

Clinically diagnosable chloracne was not obscrved in this study. Despite a very detailed examination, the only statistically significant difference between exposed and control groups was in the prevalence of closed and open comedones anywhere on the body, which was higher in the exposed group. The significance of the finding is

Transformer Repair Workers and PCB Exposure 425

uncertain, as cutaneous lesions of comedones and cysts from chloracne usually occur first on certain defined regions of the face in a distinctive pattern [Taylor, 19791. Our findings differ from those of Fischbein et al. [1982], who reported a high prevalence of skin findings, including chloracne, in capacitor manufacturing workers exposed to Aroclor of lower chlorination. Some of those workers also had much higher PCB concentrations than those we observed. Chloracne has only rarely been reported at serum PCB concentrations of less than 200 ppb [National Institute for Occupational Health and Safety, 19771.

Two exposed workers reported a history of melanoma, while no cases were recorded in the comparison group, a difference which was not statistically significant. Melanoma is relatively rare in the population, although the incidence is increasing. Bahn et al. [ 19761 reported in a letter to the Editor that three melanomas and two carcinomas of the pancreas were found in a review of charts of 92 petrochemical workers who had been exposed to PCBs among other substances. Our finding is of interest, but the possible association, if any, between PCB exposure and melanoma remains inconclusive. A detailed explanation of this association, perhaps in a case- control study, appears warranted.

Although both adipose and serum [PCBs] were considerably higher in the occupationally exposed group, this difference was due to the levels in currently exposcd workers and neither serum nor adipose [PCBs] were significantly different between past exposed workers and those in the comparison group. As anecdotal information indicated high exposure in the past, the present values appeared to reflect substantial elimination of PCBs. It is interesting, however, that a significant positive correlation could still be found in retired workers with the work activities of trans- former repair and filtering which had been the major sources of PCBs exposure in the past. The recent hygienic control of these exposures probably explains the failure to see this relationship in currently exposed workers. There is no other information in the literature on PCB concentrations after retirement in workers predominantly exposed to Aroclor 1260.

A high correlation between adipose tissue and serum PCB has been reported by Wolff et al. [1982] for capacitor workers, exposed to Aroclor of lower chlorination, we obtained a much lower correlation in transformer repair workers.

The [PCBs] observed in our comparison group which had never had industrial exposure are compatible with those observed in some other studies of background levels [Kutz and Strassman, 19761. Baker et al. [1980] and Kreiss [1981, 19821 reported considerably higher general population concentrations, but both had studied communities where there was substantial PCB contamination. In such communities there is also an association between [PCBs] and age [Kreiss et al., 19821 which we did not find. There is some evidence that general population PCB levels are decreasing [F. Kutz, personal communication], due to decreases in environmental and food PCB exposure; this reduction may also obscure associations with age.

For each of our exposure groups, and for both serum and adipose tissue, PCB concentrations were log-normally distributed. In such circumstances, geometric means or medians should be reported, as we have done, rather than the arithmetic means which have usually been reported in the past. Caution must be taken to ensure that similarly derived means are used in comparisons.

426 Emmett et al.

ACKNOWLEDGMENTS

This project was supported by the U.S. National Institute of Occupational Safety and Health, Environmental Protection Agency, and General Services Administration.

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