Soot pollution particles ‘cross the placenta’

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Pregnant woman

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Particles of black carbon – or soot – can cross the placenta, a study has found.

The Nature Communications research is the first direct evidence the particles can get into the part of the placenta that feeds the developing foetus.

It could be the first step to explaining why high pollution is linked to an increased risk of miscarriage, premature birth and low birth weights.

Experts said women could take measures like avoiding busy roads.

But they warned tackling air pollution could only be achieved at a “policy level”.

How the placenta works

The placenta is made up of two parts. The foetal placenta, made from the same tissue that forms the foetus, and the maternal placenta which is made from tissue from the mother’s uterus.

Oxygen and nutrients are able to cross from the maternal placenta to the foetal placenta, and are then carried to the foetus via the umbilical cord.

Waste products from the foetus, such as carbon dioxide pass back the other way.

In-between is a semi-permeable membrane, made up of placental tissues

Substances such as alcohol, nicotine and other drugs are known to be able to cross the placenta, which is why women are advised to cut those habits out during pregnancy.

The scientists in this study looked at placentas from five pre-term and 23 full-term births.

Using high-resolution imaging, they found black carbon particles on the foetal side in each of the placentas studied.

The 10 mothers who lived closest to busy roads, and who had been exposed to highest levels of pollution during pregnancy had the highest levels of particles in the placenta, compared to the 10 who had been exposed to the lowest – and who lived at least 500m away from a busy road.

The researchers suggest the particles travel from the mother’s lungs to the placenta.

‘Plausible mechanism’

Writing in the journal, the scientists from Hasselt University in Belgium led by Prof Tim Narwat, said: “Our results demonstrate that the human placental barrier is not impenetrable for particles.

“Further research will have to show whether the particles cross the placenta and reach the foetus,” and if that “represents a potential mechanism explaining the detrimental health effects of pollution, from early life onwards.”

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Prof Jonathan Grigg, a leading expert in the effects of air pollution on children, from Queen Mary University of London said: “There’s very strong epidemiological evidence that maternal exposure to air pollution particles is associated with adverse outcomes such as miscarriage.

“This is the beginning of showing that this is a “plausible mechanism” that could be causing these effects.”

Andrew Shennan, professor of obstetrics at King’s College London said: “Small particles, such as through smoking, can cause considerable disease related to the placenta, and these findings of particles in the placenta are a concern.

“Their possible effects on the baby and mother warrant further investigation.”

What can pregnant women do?

Both experts accept pregnant women cannot change the environment where they live.

Prof Grigg said: “Women shouldn’t be too paranoid about walking down the street. but they could be thinking about how they could reduce their exposure.”

Prof Narwat said there were small measures that could help.

“For an individual it’s very difficult to escape from it – people have to breathe.”

He advised: “Don’t ventilate houses at the front where the traffic is. It’s better at the back. And if possible if you cycle or walk, choose a road with less traffic.

“But in general this needs to be addressed at policy levels.”



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