SinS 2025: Microplastic exposure during pregnancy may disrupt foetal development: study

Pregnancy may represent a previously underappreciated window of heightened vulnerability to environmental pollutants, according to research presented by Professor Cathy Thornton of Swansea University at the 2025 Solutions in Science conference, held in Brighton, United Kingdom. Thornton, a researcher in maternal and child immunology, outlined mounting evidence that exposure to micro- and nanoplastics during pregnancy may adversely affect placental function and foetal development, with potentially long-lasting consequences for child health.

In a wide-ranging talk, Thornton framed pregnancy’s particular physiological and immunological state, during which substantial changes in the respiratory, cardiovascular, metabolic and immune systems influence how the body interacts with environmental contaminants. Increased ventilation and altered gut permeability, for example, may elevate the absorption of airborne or ingested pollutants.

While the impact of fine particulate matter in air pollution has been well documented, Thornton’s research has focused on less widely studied pollutants, particularly microplastics – 1 µm to 5 mm – and nanoplastics – less than 1 µm. These synthetic particles result from the degradation of plastic materials and can enter the human body via ingestion, inhalation or dermal contact. Common sources include packaged foods, urban air and personal care products.

A particular concern, Thornton said, is the ability of plastic particles to cross the placental barrier. The placenta is a complex, selectively permeable organ of foetal origin that facilitates nutrient and gas exchange while also serving an important immunological role for the foetus. Thornton presented data suggesting that its ability to block environmental particles is limited. Studies from Italian and US groups, supported by her own findings, have detected microplastics embedded in placental tissue and even in foetal-facing blood vessels, indicating a potential route to the developing foetus.

One longitudinal study from Hawaii, United States, conducted between 2006 and 2021, demonstrated a marked increase in microplastic contamination in placental tissue over time. By 2021, every placenta which was sampled contained detectable particles. Commonly identified polymers included polystyrene, polyethylene, polypropylene, and polyethylene terephthalate, which is often found in packaging and textiles. These particles appeared as fibres, fragments and spheres.

Thornton explained that the surface properties of microplastics – including size, shape, charge and chemical composition – influence their ability to traverse biological membranes. Her team has shown that plastic particles can accumulate not only in the general tissue matrix of the placenta but also in specific microvascular structures, raising the possibility of direct foetal exposure via umbilical blood flow.

The potential implications of such exposure are concerning. Thornton presented findings from observational studies indicating a correlation between elevated placental microplastic burden and poor pregnancy outcomes, including intrauterine growth restriction, low birth weight and reduced head circumference. Babies in these cases also recorded lower Apgar scores at birth. While causality has not been definitively established, the consistency of these findings across multiple cohorts lends weight to concerns about plastic exposure as a contributing risk factor.

In laboratory studies, Thornton’s group used fluorescent-labelled nanoplastics to investigate immune responses in monocytes, a type of white blood cell integral to innate immunity. Using flow cytometry, they have observed that monocytes preferentially internalise particles of 40–100 nm diameter. Strikingly, monocytes from pregnant individuals exhibited significantly higher rates of uptake than those from non-pregnant control subjects. This enhanced responsiveness may reflect the finely balanced immunological state of pregnancy – which must simultaneously tolerate the semi-allogeneic foetus and maintain surveillance against infection.

Further experiments showed that exposure to nanoplastics triggered inflammatory responses in monocytes, characterised by elevated cytokine release and markers of oxidative stress. These reactions suggest that even chemically inert plastics may act as physical stressors, with the potential to disrupt immune regulation at a critical developmental stage.

Thornton acknowledged the limitations of conventional toxicological studies that rely on idealised plastic particles. Most experimental work to date has used uniform, spherical particles composed of a single polymer. In reality, environmental microplastics are chemically complex, often bearing surface residues such as absorbed pollutants or microbial biofilms. Her group has collaborated with materials scientists to develop more representative test particles, which are irregular in shape and aged to simulate real-world degradation. Preliminary studies in zebrafish models indicate that these more realistic plastics elicit stronger biological effects than their pristine counterparts.

Turning to postnatal impacts, Thornton emphasised that children are particularly vulnerable to environmental toxins due to their still-developing physiological systems and immature immune defences. Yet, she noted, relatively little research has investigated how children interact with microplastics or how early-life exposures may influence lifelong health trajectories.

To illustrate the plausibility of lasting effects, she cited an animal study in which pregnant mice were exposed to polyethylene particles. Their offspring exhibited behavioural traits analogous with autism spectrum disorders, including reduced social interaction and increased repetitive behaviours. While acknowledging the limitations of animal models, Thornton said such findings offer valuable mechanistic insights into how environmental pollutants could negatively affect neurodevelopment.

Thornton concluded by placing microplastic exposure within the wider context of climate change and cumulative environmental risk. She noted that rising global temperatures, extreme weather events and increased pollutant exposure disproportionately affect those in pregnancy and young children. According to global health estimates, 90% of the disease burden attributable to climate change occurs in children under five years of age.

Microplastics, Thornton argued, should not be viewed in isolation but rather as one component of a complex and interrelated network of environmental threats. Her presentation underscored the need for more holistic public health research and enhanced regulatory frameworks.