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Common Organic Pollutants Linked to Neural Tube Defects

Researchers at Beijing University investigating the relationship between environmental chemicals and fetal development have established a causal link between exposure to organic pollutants by pregnant women and the incidence of neural tube defects.

coal fire stove_Yunan China_Leighsa Haze
Coal fire stove_Yunan China (credit: Leighsa Haze)

A team of Chinese medical researchers have confirmed the relationship between exposure to high levels of organic pollutants (primarily polycyclic aromatic hydrocarbons, or PAHs) by pregnant women and the occurrence of neural tube defects. Organic pollutants result from the burning of natural substances such as coal, wood, and other plant matter. A similar link was found with DDT residue exposure, even thought the pesticide has been banned in China since 1982.

Neural tube defects  (NTDs) develop early on in pregnancy and affect over 300,000 infants world-wide, each year. Such defects lead to diseases such as spina bifida (in which the spinal covering does not seal the cord completely) and anencephaly (a cranial abnormality which can produce still births).

Earlier studies — based upon anecdotal evidence or blood analysis alone — had linked certain pollutants (especially PAHs) to neural tube defects, but this recent research investigated placental exposure to the pollutants through biomarker analysis — indicating that the toxins were actually reaching the fetus and not simply circulating in the mother’s bloodstream.

In this controlled study, the researchers were able to identify a dose-response relationship which indicates that a “true link” (causal relationship) is most likely at work.

“A dose–response relationship was observed between PAH levels and the risk of NTDs” — Researchers Aiguo Ren et al

Over a three year period (2005 – 2007), reproductive health scientist Aiguo Ren of the Institute of Reproductive and Child Health at Peking University in Beijing, and environmental scientist Tong Zhu, also at Peking University (and colleagues*), studied placental PAH levels in 80 fetuses or newborns that had been previously identified as having neural tube defects. These samples were matched against 50 healthy placenta samples (the control group) taken from newborns from the same geographic area.

Fig. S1. Concentration (ng g-1 lipid) of typical pollutants in 80 placentas of neural tube defects (NTDs) cases and in 50 control placentas. Black horizontal line represents the median, box represents the 25th–75th percentiles, and whiskers represent 10th and 90th percentiles.

Their results showed that the risk of a defect was 4 to 5 times greater with PAH levels above the average of 597 ng (nanograms) per gram of lipid; the more the PAH level rises, the more the risk of NTDs rises — up to 11 times the risk at the highest measured levels.

The most common source of PAHs in this study region comes from coal-burning stoves (which are often located inside homes in many developing nations), with additional sources being tobacco smoke, and car exhaust. Many dwellings in the developing world are far from air-tight, and so, externally produced pollutants, like car exhaust, become indoor pollutants along with coal stove and tobacco smoke.

Coal for domestic use being transported by use of a bike
Coal for domestic use being transported by use of a bike

The team also examined the possibility that other environmental or nutritional factors were  contributing to the results;  researchers took into account other influencing factors such as whether the mother was taking folic acid supplements  (which decrease the incidence) or were smokers (which increases the incidence). Additionally, the team looked at exposures to other chemicals such as the pesticide DDT, polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (used as flame retardants in clothing).

Surprisingly– despite the fact that DDT was banned in China in 1982 — the team detected DDT or its metabolic end-products in many of the placenta samples and found a  similar relationship between high levels of DDT and fetal defects as they found with PAHs. Their findings make clear that toxic chemical residues can persist in the environment and accumulate in the body long after they are officially banned from commercial use.

The team found no dose-response relationship amongst the last two listed pollutants

Ren and Zhu plan on conducting follow up genetic analyses of both mothers and fetuses to see if genetic risk factors influence the impact of these environmental pollutants.

Results of the research were published in the Proceedings of the National Academy of Sciences (July 18, 2011) under the title: Association of selected persistent organic pollutants in the placenta with the risk of neural tube defects

Some source matieral for this post came from the Nature News article Pollutants’ role in birth defects becomes clearer by Katherine Sanderson

   * Other research team members include: Xinghua Qiu, Lei Jin, Jin Ma Zhiwen Li, Le Zhang, Huiping Zhu, and Richard H. Finnellc,d

Bottom photo: Brian Kelley ; CC – By – SA 2.0




One comment
  1. Neural Tube Defects

    Great article nice to see some light being shed on this defect. The neural tube is an early embryonic structure which forms 18 to 30 days after conceptions, so any exposure to enviromental pollutants can cause the neural tube to fold up and fuse, forming cylinder or tube. This neural tube forms the brain and spinal cord.

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