Concern in the 1970s over the widespread health problems among Great Lakes wildlife led to a human epidemiologic study that examined the health effects in infants whose mothers ate two to three meals a month of Lake Michigan fish for at least 6 or more years before their pregnancies (Jacobson and Jacobson 1996
). Only healthy mothers and infants were selected for this study. Within 24 hr of birth, significant delays in neuromuscular and neurologic development were detected in the children whose mothers ate the most fish contaminated with PCBs. At 4 years of age some children showed an association between short-term memory problems and the amount of PCBs in the mothers’ blood at delivery. The same children at 11 years of age displayed significantly reduced academic skills accompanied by a mean 6.2-point IQ reduction. This again was associated with their prenatal exposure to PCBs, not the concentration of PCBs in their blood at the time of testing. Although there is no way to prove that PCBs interfered with the development of the cochlea in these children, the affected children had difficulty with audiovisual discrimination and information processing. Some children were as much as 2 years behind their peers in school, were hyperactive, and had attention problems (Jacobson and Jacobson 1996
Another healthy mother–infant study commenced 12 years later in Oswego, New York, on Lake Ontario to replicate and expand the design of the Lake Michigan study (Darvill et al. 2000
). As in the Lake Michigan study, the high fish eaters consumed about the same amount of Lake Ontario fish before their pregnancies (Stewart et al. 1999
). Again, prenatal exposure to PCBs was associated with neurodevelopmental changes in their children at approximately 4 years of age. Using another battery of tests, Stewart et al. (2000b)
found that the temperaments of the affected children were altered compared with those of lesser-exposed children. They smiled less, were more fearful, and had difficulty adapting to changes in their environment.
Stewart et al. (2000b)
also compared the content of the highly chlorinated PCB homologs or isomers with 7, 8, or 9 chlorines (septa-, octa-, and nonyl-chlorinated biphenyls) in the mothers’ blood at the end of the first trimester with their fish diet. The mothers who never ate fish from the lakes had the lowest concentrations of the highly chlorinated PCBs in their blood. In 1984 when the first fish advisories were issued warning pregnant women not to eat the fish from Lake Ontario, the mothers who stopped eating fish had less of the isomers than the mothers who only stopped eating Lake Ontario fish when they found they were pregnant. The mothers who did not stop eating fish throughout their pregnancies had the highest PCB isomer concentrations (Stewart et al. 1999
). Stewart et al. (2000a)
found a dose–response relationship between the prenatal exposure of the children to the highly chlorinated PCBs and increases in their reflexive and autonomic deviations from the norm and their reduced ability to habituate under various conditions. MRI examination of the most highly exposed children in this study revealed an inverse dose–response association between their PCB cord blood and the volume/size of the splenium of the corpus callosum at 7.8 years of age, and their response inhibition at 4.5 years of age, a behavioral characteristic seen in ADHD children where they do not adapt well to their environment and have trouble settling down (Stewart et al. 2003
). The splenium is the bridge between the right and left sides of the corpus callosum.
Another set of studies with healthy mothers and infants performed in the Netherlands examined a cross-section of the population, not just fish eaters (Koopman-Esseboom et al. 1996
). This team found neuromuscular delays in the children at 3 months of age in association with in utero
exposure to PCBs and dioxins measured as dioxin toxicity equivalents (TEQs) (Brouwer et al. 1995
). Additionally, an inverse dose–response association was observed between increased TEQs with thyroid levels in the children and a positive association with unusual changes in their immune system (Weisglas-Kuperus et al. 1995
). Further comparisons are difficult because the same battery of tests as those used in the United States was not employed in this series of studies.
The Netherlands research team divided the mothers into two groups, low TEQ (< 30.74 pg/g fat) and high TEQ (> 30.75 pg/g fat), on the basis of the equivalents in the plasma of the mother during the last month of pregnancy (Koopman-Esseboom et al. 1994
). The differences between the two cohorts in total T4
(177.5–159.9 nmol/L) and thyroid-stimulating hormone (TSH) (1.9–2.6 μIU/mL) were significant at 2 weeks of age. However, the TSH levels of the mothers were within the normal range (3.0 IU/mL is the cutoff).
All the effects reported in the children in the studies described above were linked to the children’s prenatal experience. In each study mentioned, even though the decrements among the children were statistically significant at the population level, the parents or doctors of the infants would not have known they were compromised. It took skilled psychologists and technicians to quantify the changes in the children.
In the Lake Michigan study trained psychologists were able to measure developmental delays in infants shortly after birth if the blood fat of the mother held 1.00 parts per million (ppm) PCBs (Jacobson and Jacobson 1996
). At 1.25 ppm PCBs, the change was statistically significant (p
< 0.001) because there was so little variance. The intelligence and behavioral impairments reported in this study are populationwide. They are not rare events such as cancer. In this healthy mother–infant study, at 11 years of age, 11% of the children were affected (Jacobson and Jacobson 1996
). At 4 years of age, 17 children were removed from the study because they were too hyperactive and would not take the tests (Jacobson et al. 1990
). If the outliers had remained in the study, 20% of the children would have been affected. It was later determined that the children who were removed from the study were the children of the mothers with the highest PCB concentrations in the study. Another child was removed from the study at the end because he or she had an IQ below 70 (Jacobson and Jacobson 1996
). These researchers noted that consuming fish is not the only source of PCBs, but these compounds are found in many other foods such as meats, fatty foods, fast foods, cheeses, ice cream, and even in the most rigid vegan diet (Schecter et al. 2001
A Japanese group measured TEQs in breast milk at approximately 3 months postpartum and compared those with T3
in blood of the infants at 1 year of age (Nagayama et al. 1998
). Only healthy mothers and full-term infants from southern Japan were selected for this study. There was a significant inverse relationship between total TEQs and T3
of the infants (n
= 40). In this study, TSH had no association with the contaminants, suggesting that TSH may not be as sensitive an end point as previously considered without accompanying T3
measurements. No behavioral results accompanied these data. This study confirms, however, the transfer of contaminants, measured as TEQs, from the mother to the child and a change in the circulating thyroid hormones of the child distinguishable at the population level.