This is the first study in a live mammal to show that the placenta does not block such particles.

The rat foetuses exposed to the particles put on significantly less weight towards the end of gestation. The 20 nanometre beads used were made of polystyrene, which is one of the top five plastics found in the environment.

Twenty four hours after exposure, the weight of the foetuses was an average of 7% lower than in control animals, and placental weights were 8% lower. Weight loss was also seen in other experiments using titanium dioxide particles. The rats were exposed to the plastic nanoparticles on day 19 of gestation, two days ahead of the usual time for birth and when the foetus is gaining the most weight.

The nanoparticles used in the research were a million times smaller than the microplastics found in human placentas, and therefore currently much more challenging to identify in human studies.

A separate experiment showed that the nanoparticles crossed the placenta about 90 minutes after the mothers were exposed. Researchers warn there is an urgent need to assess the issue, particularly for developing foetuses and babies, as plastics can carry chemicals that could cause long-term damage.

“We know nanoparticles have greater toxicity than the microparticles of the same chemical, as smaller particles get deeper into the lungs (…) We found the plastic nanoparticles everywhere we looked – in the maternal tissues, in the placenta and in the foetal tissues. We found them in the foetal heart, brain, lungs, liver and kidney.”
— Prof Phoebe Stapleton, at Rutgers University

See the details of the study: https://particleandfibretoxicology.biomedcentral.com/articles/10.1186/s12989-020-00385-9