Maternal age, parity, body weight, and weight gain during the 15 pregnancies are shown in Table . The three exposure-based groups differed only slightly from one another in regard to background information. Whereas maternal serum and milk were analyzed for the complete set of 87 environmental chemicals, the 20 PCDDs, PCDFs, and coplanar PCBs were not determined in cord blood, cord tissue, and placenta due to insufficient sample sizes combined with low lipid contents. The perfluorinated compounds (PFCs) were analyzed in 12 sets of maternal serum, cord serum, and milk. Of the 58 organohalogen compounds determined in fetal samples, only 2,2,5,5,8,9,9,10,10-nonachlorobornane (Parlar-62), BDE-85, and PCB-18 were below the detection limit for all samples. Parlar-62 was detected in maternal serum, although in only three samples. In general, environmental chemical concentrations for Group 1, who did not eat traditional food during pregnancy, tended to be lower than the results for the two other groups, and the results for Group 3 with the high milk-PCB concentrations were among the highest also for most of the chemicals analyzed. Thus, the sampling strategy ensured a wide range of results.
Characteristics of Births from Which Sample Sets Were Collected for Analysis for Environmental Chemicalsa
Concentrations in umbilical cord serum and milk, and to a lesser extent those from cord tissue and placenta, correlated well with the maternal serum concentrations. In cord serum, only pentachlorobenzene (PCBz) and γ-HCH seemed to diverge from this pattern. In placenta and cord tissue, the highly chlorinated PCBs correlated the best with the maternal serum concentration, whereas PCB congeners 28, 44, 49, 52, 66, 101, 105, 128, and 149 showed much scattering. Greater variability in the apparent partition occurred at concentrations close to the detection limit. The a priori requirement of at least five sample pairs with detectable concentrations reduced the numbers of sample pairs to 43, 45, 50, and 59 for cord serum, cord tissue, placenta, and milk, respectively. A correlation coefficient of at least 0.7 resulted in further reduction to 39, 34, 29, and 56 sample pairs. Based on the required agreement with an overall ratio in regard to maternal serum, the partition ratios for the four specimens were based on 33, 22, 21, and 38 sample pairs.
Based on the overall mean ratios, cord serum, cord tissue, and placenta had lower lipid-based concentrations of organohalogen substances than maternal serum, while the relative lipid-based concentrations in milk were higher (Table ). Support for these overall results was also obtained from several median ratios calculated for sample pairs with correlation coefficients below 0.7 (Tables S1−S3). Among the brominated substances, BDE-47 and, less clearly, BDE-100 tended to show increased concentrations in tissue and milk compared to maternal serum (Table S1). The chlorinated pesticides PCBz and γ-HCH showed a relative excess in fetal samples (Table S2). When compared to the β-HCH concentrations, the results for the gamma isomer were generally almost 2 orders of magnitude lower in maternal serum and milk, but of similar magnitude in the fetal samples. p,p-DDE concentrations showed averages about 50-fold higher than those of the DDT isomers, which had less stable ratios. Several pesticides showed concentrations in milk that were higher than anticipated from the overall average ratio.
Overall Average Ratio of Organohalogen Concentrations in Fetal Samples and Human Milk in Comparison with the Concentration in Maternal Serum, with and without Lipid Adjustment
For the sum of polychlorinated biphenyls (Figure ), the lipid-based cord serum concentration correlated very well with that of the maternal serum (r = 0.99) and showed a concentration ratio of 0.56. For milk, the correlation was not as close (r = 0.87), and the average ratio was 1.35. Cord tissue PCB concentrations correlated as well as milk (r = 0.88), although with an average ratio of 0.64, while placenta concentrations showed a poorer correlation of 0.53.
Lipid-based concentration (ng/g) of the sum of all quantified polychlorinated biphenyl congeners in milk and fetal tissues (identified by different symbols), as compared to the concentration in maternal serum in fifteen sets of samples.
Some PCB congeners showed higher lipid-based concentrations in fetal samples than in maternal serum and milk (Table S3), but some of these ratios may be imprecise due to concentrations close to the detection limit and poor correlations between paired samples. When the PCBs were grouped according to chlorination, the partition between maternal serum and milk decreased at higher number of chlorine substitutions (Figure ). For the other paired samples, correlations between partitions and the degree of chlorination were less clear and more variable.
Average partition ratio between lipid-based concentrations of polychlorinated biphenyl congeners in milk and maternal serum from 15 sample pairs in regard to the number of chlorine substitutions of each congener measured.
Concentrations of the dioxin-like compounds varied somewhat less than other halogenated substances. Still, several PCDDs and PCDFs, and PCB congeners 126 and 169, showed high correlations between paired maternal serum and milk samples, and they were in agreement with regard to the relative distribution in the two matrices. Overall, the partitioning between the lipid phases agreed with the ratio of approximately 1.5 for milk versus maternal serum for 1,2,3,7,8-pentachlorodibenzo-p-dioxin (12378D), 123478D, 123678D, 2,3,4,7,8-pentachlorodibenzofuran (23478F), 123478F, 123678F, and PCB congeners 126 and 169. Although sufficient numbers of detectable concentrations were not available for several dioxin-like substances, increased chlorination tended to show a lower ratio between milk and maternal serum concentrations.
All five PFCs were detected in the samples analyzed. Perfluorooctanic acid (PFOA), perfluorooctane sulfonic acid (PFOS), perfluorononanoic acid (PFNA), and perfluorodecanoic acid (PFDA) revealed excellent correlation between maternal and cord serum concentrations, with ratios of 0.72, 0.34, 0.50, and 0.29, respectively (Table ). Perfluorohexane sulfonic acid (PFHxS) showed a poor correlation, but the median ratio of 0.74 confirmed that transplacental passage occurred. In the milk samples, only PFOA was detected, and then only in 7 of 11 samples analyzed. Assuming a PFOA concentration of 0 in the milk samples below the detection limit, the correlation with the maternal serum PFOA concentration was 0.80 and with cord blood was 0.72.
Average (Median) Concentrations (in ng/mL) of Perfluorinated Compounds in 12 Sets of Maternal Serum, Cord Serum, and Milk Samples, with the Ratio and Correlation Coefficient for Maternal v. Cord Serum
In regard to the trace elements (Table ), lead was below the detection limit in all cord tissue samples. Although poorly correlated, the average lead concentrations were quite similar in cord blood and milk, but higher in the placenta. Cadmium showed a 100-fold excess in placenta in comparison to that in cord blood, but blood concentrations close to the detection limit made partition calculations unstable. Mercury and selenium showed similar partition ratios, although the average ratio for cord tissue versus cord blood was much higher for mercury than for selenium. Mercury showed excellent correlations among concentrations in different matrices (Figure ), while selenium showed much scattering. In the matrices analyzed, the two elements correlated only poorly (e.g., r = 0.27 for cord blood), and the average molar concentration of selenium in cord blood, placenta, and milk exceeded that of mercury by approximately 20-fold.
Average (Median) Concentrations of Trace Elements in 15 Sets of Cord Blood, Cord Tissue, and Placenta, with the Ratio and Correlation Coefficient for Each of the Other Matrices with the Cord Blood Concentration
Total mercury concentrations in cord tissue and placenta (left vertical scale), and maternal hair (right vertical scale) in relation to those in cord blood (horizontal scale) from 15 sets of samples.