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Nanoplastics from biodegradable plastics can cross the placenta and accumulate in fetal organs
When the “eco-friendly” bioplastic, polylactic acid (PLA), biodegrades, the resulting nanoplastics can accumulate in the fetuses of pregnant mice and interfere with fetal growth. Yichao Huang and De-Xiang Xu of Anhui Medical University, China, and Mingliang Fang of Fudan University, China, report these findings in a new study published March 26thin the open-access journal PLOS Biology.
PLA, which is made from corn starch and sugarcane, came onto the market as a biodegradable alternative to conventional plastics around two decades ago and has since become one of the most widely used bioplastics. Due to exponential growth in the production of PLA for packaging and medical applications, humans are increasingly exposed to its main breakdown product, oligomeric lactic acid (OLA) nanoplastics, which have recently been shown to have negative health effects.
In the new study, researchers exposed pregnant mice to OLA at doses proportional to what a human typically consumes and looked for impacts on the mouse pups. They demonstrated that OLA crosses the placenta and accumulates in various organs in the fetus. Furthermore, they showed that OLA interferes with a signaling pathway that controls the development of blood vessels in the placenta, which leads to slower growth of the fetus. This is a concern, because in humans, low birth weight is associated with an increased risk of stillbirth, as well as a higher risk of developing multiple other health problems later in life.
This work is the first animal study to evaluate the developmental health effects from the breakdown products of a supposedly eco-friendly plastic in pregnant mammals. The researchers propose that future work should focus on evaluating the exposure levels and health risks associated with eco-friendly plastics in humans, and a rethinking of our approach to plastic alternatives.
The authors add, “One of our co-authors Dr. Mengjing Wang had previously discovered that the widely merchandised PLA microplastics undergo gut enzyme–mediated hydrolysis into oligomeric products that are toxic to the intestinal tract and can trigger enteritis.”
“To follow up on this work, as toxicologists, we went on to ask an additional question: do these oligomeric products, aka OLA, pose developmental threat particularly during the susceptible stage in utero?”
“What we have found was quite astonishing to us. Even under realistic exposure dose scenario during pregnancy, OLA nanoplastics can penetrate the placenta and even reach the fetus, in a mouse model. Such exposure would then cause placental vascular dysplasia and further lead to compromised fetal development.”
“While biodegradable plastics present a viable path to mitigate traditional plastic pollution, their potential health hazards necessitate a recognition in responsibility toward informed consumer intentions and conscientious usage.”
Expert Reaction
These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.
Associate Professor Alex Polyakov is a Clinical Associate Professor in the Faculty of Medicine, Dentistry and Health Sciences at the University of Melbourne and is a Medical Director at Genea Fertility Melbourne
"This is a carefully designed and methodologically rigorous study that should give regulators and the public serious pause. The researchers not only show an association, but they also identified a plausible biological mechanism, which substantially strengthens the findings.
What makes this study stand out is the dose selection. The researchers used amounts of OLA that reflect what humans might realistically be exposed to through everyday contact with PLA products, such as food packaging, disposable cups and medical materials. This is not a high-dose laboratory experiment disconnected from real life.
The finding that these particles crossed the placental barrier and accumulated in fetal brains, livers and kidneys is deeply concerning. The placenta is the baby’s primary shield against environmental contaminants. When that barrier is compromised, the consequences for fetal development can be far-reaching and life-long. The degree of intrauterine growth restriction of the kind observed here is associated with stillbirth, complications in the newborn period, and increased risk of cardiovascular disease, diabetes and kidney disease in adult life.
That said, we must be measured in how we interpret these results. This is an animal study, and mouse placentation is not identical to human placentation simply because humans are not mice! The transport mechanisms by which OLA crosses the placenta remain incompletely understood. The study also focused primarily on placental blood vessel cells, and the role of other critical placental cell types warrants further investigation.
Perhaps most striking is the comparison with conventional microplastics. The dose at which OLA caused fetal growth restriction in this study was dramatically lower than the doses at which traditional plastic particles have shown developmental toxicity. This suggests we may have been significantly underestimating the biological hazard of biodegradable plastic breakdown products.
The global shift toward PLA has accelerated sharply in recent years, driven by plastic reduction policies and consumer demand for sustainable alternatives. This research does not mean that we should stop striving to protect the environment from plastic pollution, but it does mean that ‘biodegradable’ and ‘safe’ are not synonyms, and we cannot continue to assume that they are.
Well-funded human exposure studies, particularly in pregnant women, are urgently required. We owe it to the next generation to ask these questions now, not after decades of widespread exposure. The science must lead policy, not follow it."
Oliver Jones is Professor of Chemistry at RMIT University in Melbourne, Australia
"This paper explores the possible toxicity of plastic oligomers. Firstly, what is an oligomer?
Plastics are polymers. A polymer (from the Greek meaning many parts) is made of repeating subunits called monomers (one part). Polymer chains can be thousands of monomers long, but if you have only a few, usually between two and 40, monomers, the molecule is called an oligomer.
While the study itself sounds scary, I think there are some methodological issues to keep in mind.
Firstly, the authors claim that the amount of plastic they used in the experiment was environmentally relevant. However, they are basing this on only one previous study, which has since been shown to have severely overestimated the amount of plastic we might be exposed to [1, 2]. For example, the dose of 0.1 mg of plastic per kg of body weight per day used here would translate to 8 milligrams of plastic per day for an 80 kg human. A recent independent review suggests that a more realistic dose is only 0.0006 milligrams of plastic per day [3]. Therefore, the dose used in the current study is not realistic.
In addition, the mice were force-fed this dose for 18 consecutive days; it is no surprise they showed some form of effect, but this does not mean the same effect would be seen in people. Even if the dose was correct, mice are not mini humans, and we can’t assume the results would be the same. The plastic used, polylactic acid, is also not very common in the environment.
I know microplastics are an emotive subject, but while the paper raises interesting questions about biodegradable plastics, which are worth exploring, I do not think it is quite the red flag it might at first appear to be."
References
1. Pletz M. Ingested microplastics: Do humans eat one credit card per week? Journal of Hazardous Materials Letters 2022. 3: p.100071.
2. Green H. Are You eating a credit card every week? 2022 Available from: https://youtu.be/2Ntp6BqhSng Accessed 25/03/26.
3. Mohamed Nor N.H. et al. Lifetime accumulation of microplastic in children and adults. Environmental Science & Technology 2021. 55: p.5084-5096.
Professor Ian Rae is an expert on chemicals in the environment from the School of Chemistry at the University of Melbourne. He was also an advisor to the United Nations Environment Programme on chemicals in the environment and is former President of the Royal Australian Chemical Institute
"This paper reports the developmental health effects in mice of synthetic oligomeric lactic acid (OLA). The material being tested is representative of the OLA that can be produced by the biodegradation of the commercial biopolymer polylactic acid (PLA).
PLA is made from lactic acid, the stuff you can taste in sour milk. Industrially, lactic acid can be manufactured from a range of carbohydrate-type materials. Polylactic acid is "eco-friendly' on two grounds, one that it's not made from petroleum hydrocarbons, and two that it is (albeit slowly) biodegradable in the environment. OLA's are among the products of biodegradation of commercial PLA.
At the molecular level, both PLA and OLA consist of chains of lactic acid units. "Oligo" means few, and "poly" means many. The terms are used here to reflect that the number of lactic acid units in an OLA chain is small compared to the great number in commercial PLA. The chain ends of both PLA and OLA are chemically reactive and so both materials can be expected to have biological properties. These are masked in PLA, however, because it is a solid, whereas OLA is (at least to some degree) water-soluble and able to interfere with living organisms in ways that the solid PLA cannot.
To put some numbers on them, commercial PLA weighs in at about 150,000 Dalton, meaning that a typical chain consists of over 1,600 lactic acid units (each 90 Dalton in size). The synthetic OLA chains used in the reported results are about 1,000 Dalton in size, meaning they consist of about 11 lactic acid units. As PLA degrades in the environment, OLAs of various sizes would be produced, so naturally occurring OLA would be a mixture. It's likely that synthetic OLA used in the reported experiments was a mixture, too, albeit one containing a smaller range of chain sizes, with the average size of about 1,000 Dalton."
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