PCB but not DDE linked to lower birth weight in European studies.
Govarts, E, M Nieuwenhuijsen, G Schoeters, F Ballester, K Bloemen, M de Boer, C Chevrier, M E Patelarou, U Ranft, A Rautio, MS Petersen, R Slama, H Stigum, G Toft, T Trnovec, S Vandentorren, P Weihe, NW Kuperus, M Wilhelm, J Wittsiepe, JP Bonde, on behalf of OBELIX/ENRIECO. Prenatal exposure to polychlorinated biphenyls (PCB) and dichlorodiphenyldichloroethylene (DDE) and birth weight: A metaanalysis within 12 European birth cohorts. Environmental Health Perspectives http://dx.doi.org/10.1289/ehp.1103767.
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The study presents compelling evidence that indicts the industrial chemicals PCBs while finding no link to the pesticide metabolite DDE.
It is known that very high exposures can reduce fetal growth and affect development. The results from this analysis of grouped data suggest the current exposures to PCBs – while generally lower than before the substances were banned four decades ago – are still harmful to the growing fetus.
Persistent organic chemicals like PCBs and DDT were widely used in industrial and agricultural applications prior to the 1970s. PCBs had many uses, including as insulators in industrial equipment like transformers and capacitors. The pesticide DDT controlled insects that damage crops or transmit tropical diseases like malaria.
PCBs and DDT were banned in many countries in the 1970s due to mounting concerns about their toxicity in humans and wildlife. PCB poisonings in Japan and Taiwan resulted in fetal growth restrictions, skin damage and child developmental delays. DDT was linked to egg shell thinning in predatory birds.
Exposures continue even though decades have passed since the bans. The chemical groups persist in the environment, in animals and in people. They generally settle in fatty tissues and can be passed along through the food chain where they accumulate in humans and other top predators.
When stored, PCBs mostly remain in their original chemical form. DDT, though, is mostly changed – or metabolized – into DDE. The DDE then accumulates, mainly in fatty tissues because of their chemical structures. In blood, they stay with the circulating lipids and can be transferred from pregnant women to the growing fetus.
Today, people are exposed to the compounds generally through diet, especially fish, meat and dairy products. Populations with high fish consumption – such as native populations and those living on islands or in lakeside fishing communities – can have relatively higher exposure to the chemicals.
There are still concerns that current levels of PCBs and DDT may be harmful to developing fetuses and children. Compared with decades ago, the current levels are lower, but it is unclear whether the low levels affect fetal development. Previous individual studies yield inconsistent results about their effects on fetal growth.
The researchers collected and analyzed data from human health studies done between 1990 and 2008 in the Netherlands, Faroe Islands, Spain, Germany, Belgium, Greenland, France, Poland, Slovakia, Norway and Greece. The studies examined many health aspects of 12 European birth cohorts with a combined number of almost 8,000 infants.
The researchers examined the association between levels of PCB-153 and p,p’-DDE – a breakdown product of DDT – in cord blood and the birth weight of the infants, as reported in medical records. PCB-153 is usually found in higher concentrations than other PCB forms. It is often used to compare different study findings. p,p'-DDE often has the highest concentration among DDT and DDE compounds. Because PCB-153 and p,p'-DDE remain intact for more than five years, blood levels can represent long-term exposures.
The investigators used cord blood levels of the chemicals as the marker for infant exposure. Levels were either directly measured in the studies or inferred from other biological samples measured in the studies, including mother's blood, cord blood and breast milk.
The researchers statistically adjusted for known factors that may be related to fetal growth, including gestational age, baby's sex, study region, mother's weight and height, smoking, age, number of previous births and ethnicity. The study also considered different findings among the studies and estimated the overall association.
The median levels of PCB-153 ranged from 20 to 480 nanograms per liter (ng/L) in cord serum in these cohorts. The combined data from the 12 cohorts had a median level of 140 ng/L. Faroese population had the highest PCB levels, and Polish populations had the lowest.
The median levels of p,p'-DDE had a range of 50 to 1208 ng/L in cord serum. The combined median was 528 ng/L in the12 cohorts.
The median birth weight of babies ranged from seven pounds (3,210 grams) to 8.3 pounds (3750 g). Most cohorts had cesarean section in less than 25 percent of women. In nine cohorts more than 40 percent of the mothers had no prior birth before the study pregnancy.
For a 1,000 ng/L PCB-153 increase – which is approximately the difference between the minimum to the maximum in these 12 cohorts – the birth weight decreased by about one-third of a pound (150 grams). This reduced weight is on par with the decrease observed in babies born to mothers who smoke 10 cigarettes each day. The association was similar in male and female infants and did not change by study period before or after 2000.
The researchers found no association between p,p'-DDE concentration and infant birth weight.
The association between PCB exposure and birth weight suggests that a mother's PCB exposure may reduce fetal growth and thus the birth weight of her newborn. In contrast, the DDT metabolite DDE was not related to birth weight.
The large-scale analysis shows low-level exposures during development might be harmful. Low birth weight is related to adverse health outcomes, including newborn death, developmental delays and childhood neurological disorders.
The magnitude of the association between PCB exposure and birth weight was not trivial. It was similar to a pregnant women smoking 10 cigarettes per day and was higher than exposure to second-hand smoke.
This study raises some concerns about the reproductive health risks of PCBs, especially in populations with large amounts of fish consumption. PCBs can accumulate in fish and be passed on to people who eat them. Pregnant women can check state advisories to determine what types of fish and how much to consume.
Fish also contain polyunsaturated fatty acids that may be beneficial to fetal growth and neurological development. It is not known whether the fatty acids can counteract the adverse health effects of PCBs and other chemical exposures from fish. Further studies will need to examine whether PCB contamination compromises the benefits of fatty acids.
The association between DDE and birth weight was not significant. Although higher levels of DDE exposure have been associated with low birth weight in the United States, the combined DDE levels in this European study were much lower than those in the U.S. populations in the 1960s before the DDT ban.
Exposures to DDT continue because it is still used for malaria control in sub-Saharan Africa. One recent study reports a three-fold spike of the pesticide in breast milk after just one household spraying. In areas with recent DDT spraying, more research is needed to examine current exposures and understand whether they are linked to fetal growth.
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