Two of the pesticides found in high concentrations in the placentas of affected newborns and stillborn fetuses were endosulfan and lindane. Endosulfan is only now being phased out in the United States for treatment of cotton, potatoes, tomatoes and apples. Lindane was only recently banned in the United States for treatment of barley, corn, oats, rye, sorghum and wheat seeds.
Strong associations were also found between spina bifida and anencephaly and high concentrations of polycyclic aromatic hydrocarbons (PAHs), which are byproducts of burning fossil fuels such as oil and coal. Spina bifida is a defect in which the backbone and spinal canal do not close before birth. Anencephaly is the absence of a large part of the brain and skull.
PNAS - Association of selected persistent organic pollutants in the placenta with the risk of neural tube defects
Wikipedia on Spina Bidida
Spina bifida is one of the most common birth defects, with an average worldwide incidence of 1–2 cases per 1000 births, but certain populations have a significantly greater risk. Spina bifida can be surgically closed after birth, but this does not restore normal function to the affected part of the spinal cord.
In the United States, the average incidence is 0.7 per 1000 live births. The incidence is higher on the East Coast than on the West Coast, and higher in whites (1 case per 1000 live births) than in blacks (0.1–0.4 case per 1000 live births). Immigrants from Ireland have a higher incidence of spina bifida than do nonimmigrants.
The highest incidence rates worldwide were found in Ireland and Wales, where 3–4 cases of myelomeningocele per 1000 population have been reported during the 1970s, along with more than six cases of anencephaly (both live births and stillbirths) per 1000 population. The reported overall incidence of myelomeningocele in the British Isles was 2–3.5 cases per 1000 births. Since then, the rate has fallen dramatically with 0.15 per 1000 live births reported in 1998, though this decline is partially accounted for by the fact that some fetuses are aborted when tests show signs of spina bifida (see Pregnancy screening above).
"We've suspected for a while that some of these pollutants are related to an increase in birth defects, but we haven't always had the evidence to show it. Here we quite clearly showed that the concentration of compounds from pesticides and coal-burning are much higher in the placentas of cases with neural tube defects than in controls."
The study, which was published in August in the Proceedings of the National Academy of Sciences, is the result of a more than decadelong collaboration between Finnell and a team of researchers in Shanxi, a province in northern China.
Working with public health officials in four rural counties in Shanxi, researchers collected placentas from 80 newborn or stillborn fetuses that suffered from spina bifida or anencephaly. Once a fetus or a newborn with such defects was identified as a case, the placenta of a healthy newborn with no congenital malformations born in the same hospital was selected as a control.
Finnell and his colleagues screened these placentas for the presence of a class of substances known as persistent organic pollutants (POPs). Common POPs include agricultural pesticides, industrial solvents and the byproducts of burning fuels such as oil and coal.
They found strong associations between the birth defects and high levels of a number of compounds present in commonly used pesticides. They also found elevated placental concentrations of PAHs.
"This is a region where they mine and burn a lot of coal," says Finnell. "Many people cook with coal in their homes. The air is often black. You don't need to be a rocket scientist to say that maybe there's something in there that isn't good for babies."
Finnell says although the environmental conditions in Shanxi are dramatically worse than they are in most areas of the United States, they are comparable to what the United States was like a century ago, and the neural tube defects are not solely a Chinese problem.
Every year approximately 3,000 pregnancies in the United States are complicated by neural tube defects. Many other congenital conditions, including autism, may one day prove to be related to environmental pollutants.
"Ultimately you need enough cells to make a proper, healthy baby," says Finnell, "and these are the types of compounds that cause cell death. At the most basic level, we're learning that environmental things kill cells, and if that occurs in a critical progenitor population at a crucial time, you're going to have problems."
Persistent organic pollutants (POPs) have been associated with a wide range of adverse health effects. Our case–control study was performed to explore the association between placental levels of selected POPs and risks for neural tube defects (NTDs) in a Chinese population with a high prevalence of NTDs. Cases included 80 fetuses or newborns with NTDs, whereas the controls were 50 healthy, nonmalformed newborn infants. Placental concentrations of polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides, polychlorinated biphenyls, and polybrominated diphenyl ethers were analyzed by gas chromatography–mass spectrometry. The medians of PAHs, o,p′-isomers of dichlorodiphenyltrichloroethane (DDT) and metabolites, α- and γ-hexachlorocyclohexane (HCH), and α-endosulfan were significantly higher in case placentas than in controls. PAH concentrations above the median were associated with a 4.52-fold [95% confidence interval (CI), 2.10–9.74) increased risk for any NTDs, and 5.84- (95% CI, 2.28–14.96) and 3.71-fold (95% CI, 1.57–8.79) increased risks for anencephaly and spina bifida, respectively. A dose–response relationship was observed between PAH levels and the risk of NTDs, with odds ratios for the second, third, and fourth quartiles, compared with the first, of 1.77- (95% CI, 0.66–4.76), 3.83- (95% CI, 1.37–10.75), and 11.67-fold (95% CI, 3.28–41.49), respectively. A dose–response relationship was observed for anencephaly and spina bifida subtypes. Similar results were observed for o,p′-DDT and metabolites, α-HCH, γ-HCH, and α-endosulfan, whereas no dose–response relationship was observed for the last two pollutants. Elevated placental concentrations of PAHs, o,p′-DDT and metabolites, and α-HCH were associated with increased risks of NTDs in this population.
3 pages of supplemental information
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