Nowadays, a large amount and variety of plastic is being produced and consumed by human beings on an enormous scale. Microplastics and nanoplastics (MNPLs) have become ubiquitous since they can be found in many ecosystem components. Plastic particles can be found in soil, water, and air. The routes of human exposure are numerous, mainly involving ingestion and inhalation. Once ingested, these particles interact with the gastrointestinal tract and digestive fluids. They can adsorb substances such as additives, heavy metals, proteins, or even microorganisms on their surface, which can cause toxicity. During inhalation, they can be inhaled according to their respective sizes. Studies have reported that exposure to MNPLs can cause damage to the respiratory tract, creating problems such as bronchitis, asthma, fibrosis, and pneumothorax. The reports of boards and committees indicate that there is little data published and available on the toxicity of MNPLs as well as the exposure levels in humans. Despite the well-established concept of MNPLs, their characteristics, and presence in the environment, little is known about their real effects on human health and the environment.

Previous work from our group demonstrated that pregnant mice exposed to marijuana smoke presented reduced fetal and neonatal outcomes including reduced birthweight and increased placental weight. To further characterize the possible placental mechanisms underlying these observations, the present study evaluated placental morphology, function and molecular markers in the same experimental model. Female mice were exposed to Cannabis sativa smoke or filtered air daily from gestational day (GD) 0.5 to 18.5 GD. At 18.5 GD, pregnant females were euthanized and placentas were analyzed. Results showed that exposure to Cannabis sativa smoke reduced fetal weight and increased placental weight compared to control animals. Stereological analyses revealed increased volumes of labyrinth and decidua compartments, increased capillary surface area, and decreased thickness of the interhemal membrane. Immunohistochemistry demonstrated increased expression of CB2 receptor and glucose transporter GLUT1. There were no differences between groups in HIF-1a and VEGF expression or in umbilical artery Doppler parameters. These findings suggest that gestational exposure to marijuana smoke alters placental morphology in a manner consistent with compensatory adaptation, possibly in response to reduced oxygen availability.