Microplastic invasion: Electron microscopy analysis of human placenta cells

Over the past century, global plastics production has grown exponentially to over 350 million tons per year produced worldwide, part of which ends up polluting the environment1. Microplastics (MPs) are defined as plastic particles smaller than 5 mm2. They are produced at this size or result from the fragmentation of larger plastic structures. MPs are found in aqueous, terrestrial and airborne environments. In addition, there have been several reports of MPs in food, particularly seafood, sea salt and drinking water. MPs are primarily detected in the gastrointestinal tract of marine animals, while cellular uptake and accumulation of MPs and, especially nanoplastics, in tissues have been demonstrated in experimental settings. Within tissues, plastic particles are seen as foreign bodies and can trigger local immunoreactions18. In addition, MPs can act as a carrier for other chemicals, such as environmental pollutants or plastic additives, which can leak out and cause exposure to hazardous substances. Scientists and public authorities have raised concerns about MPs in food, potential human intake, and health consequences but data are scarce. There are also reports of inhalation of MPs in humans. Recently, our group conducted two studies in which they identified the presence of MPs in placenta. The aim of this thesis was twofold: 1) Locate the MPs within the cellular compartment in placenta; 2) To understand if their position determines structural changes of the neighboring cellular organelles. For this we have analyzed with the Scanning Electron Microscopy (SEM) and with the Transmission Electron Microscopy (TEM) the cellular material, taken with the plastic free technique from ten placentas, coming from normal pregnancies. All preparations contained MPs. Fragments were mostly found in the syncytiotrophoblast, but also in the basement membrane, the cytotrophoblast, and the pericytes surrounding the fetal capillaries. They have been found free in the cytoplasm as well as inside lipid membranes. Sizes of the MPs observed and described by us ranged from 0.1 µm to 18.5 µm. We have precisely located several MPs within the cellular compartment, and we found mitochondrial swelling, ballooning cristae or intracristal swelling, next to mitochondrial pyknosis, several myelin figures arising from endoplasmic reticulum, including whorled membranous bodies, which are likely derived from involuting mitochondria, and autolysosomes containing mitochondrial remnants and other structures. Finally, we have localized MPs in human placental cells, and we have also demonstrated the presence of important morphological and structural alterations of intra cytoplasmic organelles near the MPs.