Researchers are finding an abundance of microplastics in placentas and meconium samples

Researchers are finding an abundance of microplastics in placentas and meconium samples

The embryonic and fetal stages of life are vulnerable to harmful chemicals in the environment. These include microplastics (MPs), which have been found in many living organisms and tissues and come from the environmental breakdown of plastic waste. Using placental tissue and meconium samples, a new study examines the links between exposure to MPs in pregnancy and microbiomes.

Learn: The association between microplastics and microbiota in placentas and meconium: The first evidence in humans. Image credit: SIVStockStudio / Shutterstock

introduction

MPs are plastic particles with a diameter of 5 millimeters (mm) or less. Most MPs are formed through the degradation of plastics by UV radiation, biological agents, heat, oxidation, or light exposure, or are intentionally formed as microspheres that are incorporated into personal care products.

MPs are found throughout the ecosystem, be it on land, in the air, in water or in the food chain. Several previous studies have shown their ingestion and inhalation by humans, potentially posing a significant health risk.

The current study, published in the journal Environmental Science and Technology, attempted to identify them in placenta and meconium samples. Previous research has shown that infants may be more exposed to MPs than adults, which is a concern because polystyrene nanoparticles have been shown to cross the placental barrier to enter fetal tissue as well as placental tissue from the maternal lung in mammals.

Animal experiments demonstrated the ability of ingested MPs to disrupt the normal intestinal epithelial barrier and influence the gut microbiome. However, there is a lack of human evidence on the potential for changes in placental microbiota to influence maternal-fetal unit metabolism, cause gestational diabetes mellitus, or increase the risk of adverse pregnancy outcomes such as low birth weight or preterm birth.

The fetal and preterm microbiome depends on the maternal microbiome in the placenta, amniotic fluid and vagina. This Chinese study was conducted on 18 mother-infant dyads to identify an association between placental and fetal MPs. Samples were collected during pregnancy and examined for MPs using a laser infrared imaging spectrometer (LDIR). Accordingly, microbiota were assessed using 16S rRNA sequencing.

What did the study show?

The mothers in the study had a mean age of 32.5 years and a normal body weight. Only MPs 20–500 μm in size were counted to keep accuracy within LDIR limits.

The researchers found traces of MPs in all samples, mainly polyurethane (PU) and polyamide (PA). More than three quarters of the MPs were between 20 and 50 μm in size. The mean concentration of MPs in the placenta was 18 particles per gram versus 54 particles/g in meconium.

The presence of polypropylene (PP) in the placenta showed a positive correlation with total MPs and with PA and polyethylene (PE) in meconium. Placental polyvinyl chloride (PVC) also showed a positive association with meconium PA.

The microbiome in placenta and meconium samples showed a dominance of Proteobacteria, Bacteroidota and Firmicutes. In placental tissue these accounted for over 40%, one-third and one-fifth of the total, versus one-third each for the first and third and 28% for Bacteroidota in meconium samples. However, beta diversity and composition differed significantly between the two types of samples.

Several bacterial genera were reduced with increasing concentrations of polyethylene (PE). Overall, several genera showed abundant changes associated with total MPs and with PA and PU.

For example, in placental samples, increasing total MP and PA concentrations were positively correlated with the abundance of Porphyromonas. PE increase was associated with decreases in several genera, including Prevotellaceae and Ruminococcus. At higher levels of polytetrafluoroethylene (PTFE) or PVC, there was an increase or decrease in the concentration of Escherichia coli.

Meconium samples showed a positive association between the total MP and some genera such as Streptococcus and Clostridia. In addition, specific associations were also identified, such as a positive correlation between treponema and PA and a negative one with PU.

Again, particle size showed different correlations with the abundance of several genera in the placental microbiota, such as Sediminibacterium with MPs between 100 and 150 μm compared to certain Lachnospiraceae with MPs above 150 μm in the placenta. Several positive associations between certain genera and MPs with a size of 50–100 μm were also identified in meconium

What are the conclusions?

Previous studies indicate that the predominant MPs differ between regions and across studies. This could be due to differences in experimental methods.

PA and PU dominated exposure in this study. Both plastics are used in numerous product areas due to their performance and resistance properties. Household dust and indoor air can therefore contain high concentrations of these MPs, posing a high risk of exposure for pregnant women and infants.

Other sources such as groundwater and reservoir water mainly have PA, PE and polyethylene terephthalate (PET), but PU has been found in raw water and conventionally treated drinking water.

The current study shows that PA, PU, ​​PE and PET are most abundant in placenta and meconium, with positive correlations between specific MPs and total MPs. Furthermore, placental PVC showed a positive association with meconium PA. However, these patterns may be due to similar or identical recording sources.

The increased levels of total MPs and PA in meconium compared to placental samples may indicate that the fetus is exposed to these plastics through other routes as well, although accumulation of these particles during pregnancy may be a simpler explanation.

“MPs may have an important antibacterial effect on key members of the placental microbiota and the meconium microbiota.” This is reflected in the consistent effect of total MPs, PA and PU on multiple meconium microbiota genera.

Not only are MPs widely present in placenta and meconium samples, but their concentrations can also influence the microbiomes in the fetal intestine and placenta.

This is “the first study to address the potential effects of MPs exposure on the human microbiota.”

The extensive exposure levels indicated by this study of pregnant women and fetal meconium are concerning. Furthermore, particle size is related to changes in the fetal meconium microbiome, with a size between 100 and 500 μm showing robust associations with such effects.

Reference:

• Liu, S. et al. (2022). Die Assoziation zwischen Mikroplastik und Mikrobiota in Plazentas und Mekonium: Der erste Beweis beim Menschen. Umweltwissenschaft und -technologie. https://doi.org/10.1021/acs.est.2c04706. https://pubs.acs.org/doi/10.1021/acs.est.2c04706

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