Levels of non-ortho-substituted (coplanar), mono- and di-ortho-substituted polychlorinated biphenyls, dibenzo-p-dioxins, and dibenzofurans in human serum and adipose tissue.

We have measured non-ortho-substituted (coplanar) polychlorinated biphenyl (PCB) levels as well as polychlorinated dibenzo-p-dioxin (PCDD) and polychlorinated dibenzofuran (PCDF) levels in human adipose tissue and serum collected in Atlanta, Georgia. The results show that the concentrations of the coplanar PCBs can be more than an order of magnitude higher than the concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin. Our measurements in pooled serum collected in 1982, 1988, and 1989 show a decrease in coplanar PCB levels from 1982 to 1989. We found that the pattern of relative amounts of coplanar PCBs in adipose tissue varied greatly from person to person unlike the PCDD and PCDF patterns, which were more nearly the same. Age was significantly correlated with the concentrations of 2,3,7,8-TCDD,3,3'4,4'-PCB, 3,3',4,4',5-PCB, and 3,3'4,4',5,5'-PCB in adipose tissue. We also measured levels of the mono- and di-ortho chlorine-substituted PCBs in human serum. The levels for some of these PCB congeners were three orders of magnitude higher than the coplanar PCBs, PCDDs, and PCDFs. We used the international toxicity equivalency factors (TEFs) for PCDDs and PCDFs and the TEFs proposed by Safe for PCBs to calculate the 2,3,7,8-TCDD equivalents. Four PCBs (3,3',4,4',5-; 2,3',4,4',5-;2,3,3',4,4'-;2,3,3',4,4',5-) make a larger contribution than 2,3,7,8-TCDD, while four other PCBs (3,3',4,4'5,5'-; 2,2',3,4,4',5'-;2,2',4,4',5,5'-;2,2',3,4,4',5,5'-) make nearly the same contribution as 2,3,7,8-TCDD. The mono-ortho-chlorine-substituted 2,3',4,4',5-PCB, however, is the major contributor to the total 2,3,7,8-TCDD equivalents in general population samples from the United States, Sweden, and Japan.(ABSTRACT TRUNCATED AT 250 WORDS)

Tanabe et al. (10) have found clear positive correlations between concentrations oftotal PCBs and each ofthe three coplanar PCBs in all mammal samples analyzed (r=0.81-0.96 over a concentration range offive orders ofmagnitude). These authors concluded that the sources of coplanar PCB contamination to the environment are principally from commercial PCB preparations. Tanabe et al. (10) also reported that in fish samples, 95 % ofthe coplanar PCBs were PCB-77, 5% were PCB-126, and less than 1% were PCB-169 (this pattern is the same as in commercial PCB mixtures). Marine and terrestrial mammals, on the other hand, had a lower percentage of PCB-77, and the bioconcentration ofPCBs-126 and 169 was obvious. The authors suggested that the concentrations of coplanar PCBs in humans and animals suggest that the order of biodegradability is PCB-77 > PCB-126 > PCB-169 (10). This order of metabolic stability is consistent with findings in studies ofanimals (20,21) and humans (22).

Sample Cleanup and Quantification
We spiked the adipose tissue (32,33,36) or serum (29,34,35,37) samples with carbon-13-labeled PCDDs, PCDFs, and coplanar PCBs and in a separate analysis with carbon-13-labeled nonplanar PCBs. The separate analysis eliminated a previous problem with high recoveries of carbon-13-labeled PCB-77 (29). The samples were then extracted with organic solvents, and the solvent extracts were processed through a five-column cleanup procedure developed by Smith et al. (38) and modified and semiautomated (33,39) by us for PCDD, PCDF, and PCB analyses. The final extracts were quantified by high-resolution gas chromatography/isotopedilution high-resolution mass spectrometry for the PCDDs and PCDFs and by high-resolution gas chromatography/isotopedilution high-and low-resolution mass spectrometry for the PCBs.

Sample Procurement
Pooled Human Serum. Serum collected by the Centers for Disease Control (CDC) blood bank in Atlanta, Georgia, was pooled and aliquotted into 100-g samples and stored at -600C until analysis.
Collection ofAdipose llssues. We collected adipose tissue samples at autopsy from the abdominal wall ofmen and women who died suddenly in Atlanta, Georgia, in 1984 or 1986. The samples were taken according to a specific protocol designed to ensure that the samples were not cross-contaminated or laboratory contaminated. The dead persons were from the general population in Atlanta, Georgia.

Results and Discussion
The levels that we measured for coplanar PCB-77, PCB-126, PCB-169, 3,4,4 '5,-PCB (PCB-81), mono-and di-ortho-PCBs, PCDDs, and PCDFs in pooled human serum and in adipose tissues collected in Atlanta, Georgia, are given in Tables 3-5. We measured 2,3,7,8-TCDD and coplanar PCB levels in 28 adipose tissue samples collected either in 1984 or 1986. The results given in Table 3 indicate that the concentrations ofthe coplanar PCBs aLevels are in parts-per-trillion on a lipid-adjusted bases. bExcluding person 5, whose levels were obviously above normal U.S. background levels (40) c Including person 5.
can be more than an order of magnitude higher than the concentrations of 2,3,7,8-TCDD in human adipose tissue samples from the general population. In addition to measuring the coplanar PCBs, we measured the levels of all the PCDDs and PCDFs (Table 4) in the tissue of 5 of the 15 persons whose data are in Table 3. The mean levels of the PCDDs, PCDFs, and coplanar PCBs for these five are in Table 4. Data on subject 5 were excluded from the calculation of the means since her levels were obviously elevated above normal U.S. background levels (40). We also measured PCB levels in pooled serum that was collected in Atlanta, Georgia, ( Table 5). The coplanar PCB levels were similar in the 1988 and 1989 pooled samples, whereas the level of PCB-77 was three to six times higher in the 1982 pooled sample. The levels of PCB-126 and 169 were about twice as high in bThese persons are the sane as those descibed in Table 3. cThis mean concentration excludes person 5, whose levels were above normal U.S. background levels (40).
the 1982 pooled sample. These data are consistent with a decrease in human exposure to PCBs and a shorter half-life in humans for PCB-77 than for PCBs-126 and 169.
The only data reported in the scientific literature on levels of PCDDs, PCDFs, and PCBs with which we can compare our results are given in Table 6. These data should be compared with caution, however, because the U.S. (29), Japanese (10,(25)(26)(27), and Swedish (28,41) samples represent people with different background exposures and were not collected to represent a certain population group. In addition, individual PCB congeners (42,43) as well as total PCBs (44)(45)(46) have been shown to be positively associatedwithage; differencesbetweenthe sexeshave also been noted (43,46). The studies in Table 6 representcohorts with different mean ages and varying male-to-female ratios.
Toxic equivalency factors (TEFs) have been developed for the various congeners of PCDDs, PCDFs, and PCBs (4,47). The TEF scheme compares the in vivo and in vitro responses ofsome species of animals to various congeners relative to that of 2,3,7,8-TCDD (Table 7). In deriving the TEFs (44), data from the following effects were used in descending order of priority: results oflong-term carcinogenicity studies; data from reproductive studies; results of subchronic experiments thatmeasure Ah receptor-mediated responses such as thymic atrophy, body weight loss, and immunotoxicity; acute toxicity studies; and in vivo or in vitm biochemical responses such as enzyme induction or receptor binding (4). A complete set of data that included long-term carcinogenicity studies was available only for 2,3,7,8-TCDD, and therefore the TEFs assigned to other congeners were subjective assessments made by using the above priorities as a guide (4). The 2,3,7,8-KDD equivalents have been calculated for data in all studies available for comparison and are given in Table 6 along with the percentage of the total 2,3,7,8-TCDD equivalents for PCDDs, PCDFs, and coplanar PCBs. Figure 1 is a comparison of studies that measured all three compound classes in each ¶hble 5. Measured levels of 2Z3,7,8TCDD, non-ortho, mono-orlo, and di-orihoPCBs in pooled human serum.  bPooled human serum (total lipid = 475.3 mg/dL) collected in 1988 from more than 240 donors. This pool has been spiked to a higher level with 2,3,7,8-TCDD (see Table 6 for levels on a lipid-adjusted basis).
CThe number of repeat analyses on the same pool.
dThis pool is of unspiked, normal human serum collected in 1989 from more than 200 donors. eThis pool is of unspiked, normal human serum collected in 1982 from more than 200 donors. gPooled serum collected in 1988 from Atlanta, Georgia (see Table 5).
hData from the present study. Tissues collected in 1986 from four perons who died suddenly in Atlanta, Georgia (data from Table 4).
'Tissues collected in 1984 and 1986 in 28 persons who died suddenly in Atlanta, Georgia (data from Table 3).
CRecommended as a preliminary value until more data can be acquired for these PCBs (4).
sample for each person. The reported levels in adipose tissue collected in 1985 and 1986 from Japan show that most of the 2,3,7,8-TCDD equivalents are due to the coplanar PCBs. Pooled mothers' milk collected by Noren (28)  equivalents due to PCDDs, PCDFs, and coplanar PCBs. The majority ofthe 2,3,7,8-TCDD equivalents in adipose tissue collected in 1986 from Atlanta, Georgia, are due to the PCDDs (67%), whereas the coplanar PCBs account for the second highest percentage (24%). Measurements in pooled mother's milk by Thornburg (21) collected in 1988 from Sweden indicate that 63 % ofthe 2,3,7,8-TCDD equivalents are due to the coplanar PCBs. The differences between our results in adipose tissue (Figure 1) and the results from the studies in Sweden and Japan could be due to several factors: a) different matrixes; b) different mean ages; c) different sample collection years from different countries [the data ofPatterson et al. (48) and Stanley et al. (49) indicate that PCDD and PCDF levels may be decreasing in U.S. serum and adipose tissue, and the data ofNoren et al. (28) show that levels of PCDDs, PCDFs, and coplanar PCBs decreased from 1972 to 1985 in pooled mothers' milk in Sweden]; d) our adipose tissue levels were measured in men and women, but the mothers' milk levels were measured in women who may have been breastfreding infants when the samples were collected [breastfeeding may have altered the normal PCDD, PCDF, and PCB patterns]; and e) different background exposures to PCDDs, PCDFs, and PCBs in the United States, Japan, and Sweden.
The levels and 2,3,7,8-TCDD equivalents of2,3,7,8-TCDD and coplanar PCBs that we found in the adipose tissue of men and women from Atlanta, Georgia, are compared in Table 8 to those reported by Tanabe (24) and Kanman (25). In the U.S. samples, women had higher levels of each analyte, whereas men had higher levels in the Japanese samples. The number of samples in both ofthese studies is, however, too small to make statistically significant statements concerning the observed differences.
The patterns ofcoplanar PCB levels in adipose tissue also appear to be different for men and women in the Atlanta samples  ( Table 3). The level of PCB-126 is the highest of the three coplanar PCBs in 12 ofthe 14 women and PCB-169 is the highest in 8 of the 14 men (the number of individual samples is too small to establish a definite pattern difference). Within a group ofnormal population samples, the reported pattern of PCDDs and PCDFs is ususally the same. The absolute levels may vary from person to person, but the relative amounts of the various congeners are generally the same (for example, see Table 4). This similarity of pattern is not true for the coplanar PCBs. The various patterns of the coplanar PCBs that have been reported are shown in Figure 2. Tanabe and Kannan (10,25) found patterns A and B (Fig. 2) in adipose tissue from Matsuyama, Japan, but Miyata et al. (26) found patterns C and D (Fig. 2) in adipose tissue from Osaka City, Japan. We also found patterns C and D (Fig. 2) in adipose tissue and pattern B (Fig. 2) in serum from Atlanta, Georgia. We measured coplaner PCB levels in a pooled plasma sample that was collected from Sweden as part of a World Health Organization (WHO)-sponsored laboratory round-robin study of PCDDs, PCDFs, and PCBs (50). We observed pattern C (Fig. 2) in this pooled plasma sample. Pooled mothers' milk collected in Sweden (28,41) exhibited pattern D (Fig. 2). These variable patterns may be caused by different dietary habits (N. Kannan, personal communication), by different metabolic elimination rates, or by different routes of exposure.
We have calculated Pearson correlation coefficients and probability values (Table 9) for the coplaner PCB and 2378-TCDD data from Table 3. There are statistically significant correlations  (Table 5) for 1982 and 1988/1989 suggest a shorter half-life for PCB-77 relative to PCB-126 and 169 and is consistent with a study in mice that showed that PCB-126 was more slowly metabolized than PCB-77 (52). The bioconcentration ofPCB-126 and 169 is also clearly seen by comparing the relative levels in the human exposure sources (Aroclors and Kanechlors, Table 1) to the relative amounts found in human tissues (Table 6). In Figure 3, we compare the levels of mono-and di-orthosubstituted PCBs in pooled serum samples taken in Atlanta in 1988 (29) with the levels in serum samples taken in 1986 from 200 Wisconsin consumers of sport fish (53); serum samples taken in 1988 from 19 Columbia, Missouri, residents (54); pooled serum taken in 1990 from Finland (55); and pooled serum taken in 1990 from Quebec, Canada (56). The relative amounts of the various PCB congeners were similar in our pooled serum and the Columbia, Missouri, residents(54), as well as in pooled serum from Canada (56). The mean levels for the three major diortho-substituted PCBs [2,2 ',3,4,4 ',5 '-(PCB-138); 2,21'4,4 '5,5 '-(PCB-153); 2,2'3,4,4 '5,5 '-(PCB-180)J and the major mono-ortho-substituted PCB-118 were higher by a factor of about two in the Wisconsin samples than in the Atlanta pooled serum. The differences in PCB levels may be due to the high fish consumption among persons who provided the Wisconsin samples (53). Fiore et al. (57) have found statistically significant positive Spearman correlations between sport-caught fish meals and PCB serum levels. Humphrey (58) has reported that, among Michigan residents, increased fish consumption correlated positively with increased PCB concentrations in serum. Figure 4 shows the results of six studies with data on mothers' milk, adipose tissue, and lipid-adjusted serum levels of monoand di-ortho-substituted PCBs. Although the absolute amounts ofthe individual PCB congeners vary among studies, the relative distribution patterns ofthe PCB congeners within each study are similar. In addition, the di-ortho-substituted PCB levels are higher than the mono-ortho-substituted levels, which are in turn higher than the coplanar PCB levels (Fig. 4 (28), and adipose tissue (10,25) are compared in Figure 5. Clearly, each ofthe coplanar PCBs, and mono-and diortho-substituted PCBs makes a major contribution to the total 2,3,7,8-TCDD equivalents in these general population samples. In fact, PCBs-126, 118, 105, and 156 all make a larger contribution than 2,3,7,8-TCDD, while PCBs-169, 138, 153, and 180 make nearly the same contribution as 2,3,7,8-TCDD. The major contributors, however, to the total 2,3,7,8-TCDD equivalents in samples from the United States, Sweden, and Japan (Table 10) are the mono-ortho-chlorine-substituted PCBs 105, 118, and 156 (within this group, the PCB 118 was by far the major contributor: see Fig. 5). The coplanar PCBs were the second most important contributor in the Swedish and Japanese samples, whereas the PCDDs were the second most important in the U.S. samples.
Undoubtedly, more and more measurements of PCBs in environmental and biological specimens will be done by congenerspecific methods. In the United States, however, regulatory agencies such as the Food and Drug Adminisration, Environmental Protection Agency, and Department of Agriculture have established guidelines and analytical methods (based on packed-column gas chromatography) for total PCBs, not for individual congeners (60,61). In Europe, PCB levels are frequently regulated on the basis of the concentration of five or six PCBs that are normally found at the highest relative levels. Certainly, more comparisons, such as those performed by Burse et al. (62), need to be made between results ofpacked-column and capillarycolumn methods. More specifically, however, future work will be based on methods that involve capillary-column gas chromatography/mass spectrometry and allow identification and quantification ofcoplanar PCBs and other PCBs that, although minor in concentration, greatly contribute to the 2,3,7,8-TCDD equivalents. For human studies, we need more work on exposure assessment, half-lives, partitioning within the body's compartments, and assessments of any adverse health effects that these coplanar PCBs alone or in combination with other environmental contaminants may cause.
Use oftrade names is for identification only and does not constitute endorsement by the Public Health Service or the U.S. Department ofHealth and Human Services.