Microplastics in Human Breast Milk and Maternal–Infant Exposure Pathways in Low- and Middle-Income Countries: A Systematic Review

Abstract Background Microplastics (MPs) are a serious concern for public and environmental health because of their ubiquitous distribution and potential adverse biological effects. Recent evidences indicate that maternal–infant exposure to MPs may take place during pregnancy, lactation and early infancy via multiple biological and environmental pathways. However, there are limited and fragmented data from low- and middle-income countries (LMICs). Objective The aim of this systematic review was to consolidate current evidence on the occurrence of microplastics in human breast milk and maternal-infant biological systems, and probable pathways of maternal-infant exposure in LMICs. Methods A thorough search of the literature was performed using PubMed/MEDLINE, Scopus, Web of Science, Embase, CINAHL, ScienceDirect and Google Scholar. We also looked through other sources of gray literature. Included were English-language studies that assessed microplastics in biological samples from mothers and infants or looked at exposure routes in LMICs. PRISMA 2020 guidelines were followed in the selection of the study. Methodological quality was assessed using the Joanna Briggs Institute (JBI) critical appraisal instruments. Due to the considerable methodological variation amongst the research, a narrative synthesis method was used. Results Seven studies were eligible. Microplastics detected in human breast milk, placenta, meconium, infant feces, maternal blood, amniotic fluid, umbilical cord and umbilical vein blood, suggesting pre- and post-natal exposure. Polyethylene (PE), polypropylene (PP), polyamide (PA), polyurethane (PU), polyethylene terephthalate (PET) and polyvinyl chloride (PVC) were the most commonly detected polymers. The particle size distributions were very different between studies due to the different analytical techniques used, such as Fourier-transform infrared spectroscopy (FTIR), Raman micro spectroscopy and laser direct infrared spectroscopy (LDIR). Important exposure pathways identified included feeding bottles, breast milk storage bags, consumption of seafood, bottled water and environmental contamination. Potential health concerns reported in the literature were oxidative stress, inflammation, endocrine disruption and possible neurodevelopmental effects. Conclusion Recent evidence highlights the presence of microplastics in biological systems of mothers and infants and indicates some routes of exposure before and after birth in low- and middle-income countries. However, the lack of standardized analytical protocols, small sample sizes and methodological heterogeneity hinder the comparability of studies. Further large-scale longitudinal studies are needed to gain a more comprehensive understanding of the long-term health effects of maternal and neonatal microplastics exposure.