1 | INTRODUCTION
Nanoparticles (NP) (usually understood as in the range 1-100nm) are, in principle, capable of intercellular barrier penetration as well as ingestion by cells, particularly phagocytes and transporting epithelia. Here we focus on particulate black carbon (BC) and nanoplastics.
BC arises as a sooty paracrystalline insoluble product during combustion of wood, other plant material (including tobacco combustion products inhaled by smokers) or petroleum products in spaces with limited oxygen. It is used as a stabiliser in tyre manufacture, paints and pigments and as a food colourant. Particulate material from vehicle emissions is classified by size, for example PM2.5 are NP<2.5nm. Carbon NP are produced by design too, for example as nanofibres or nanotubes. Routes of exposure are most likely to be via inhalation or ingestion. High exposures may occur as a result of vehicle emissions from nearby roads. Epidemiological studies have suggested associations between particulate air pollution (including PM2.5) and hypertensive disorders of pregnancy, growth restriction and preterm birth but are often confounded by the presence of other pollutants.
Microplastics (around 1-100mm) in the environment generally arise from pellets, packaging, personal protective equipment, textiles, tyres or fishing nets, either directly as a by-product of manufacturing or by mechanical, light-mediated or biological fragmentation and degradation. They are already very widespread in soil and aquatic environments, and concentrations are rising. Microplastics break down into nanoplastic particles which are more difficult to detect and quantify, and more likely to become incorporated from air, water, soil or food into biological systems. In addition, primary nanoplastics are directly made for use in cosmetics, facial cleansing products, and air blasting technologies. There are currently no data showing a direct association between microplastics and abnormal pregnancy outcomes.
Research is required to inform the updating of legislation to protect women as early as possible in their pregnancies, or ideally those planning a pregnancy. Within this context, epidemiology data supported by laboratory investigations are essential in understanding the placental transfer of NP and their impact on placental biological function and fetal development.