4 | CONCLUSION
Exposure to high levels of air pollution and microplastics can have an
adverse effect on the fetus14 possibly due to
deterioration in placental endocrine, metabolic and immunological
functions, while a range of effects have been shown in animal models
including altered growth and protein expression. There is also evidence
that nanoparticulate material may bind viruses and facilitate their
entry into cells. Well-controlled epidemiological and experimental
studies distinguishing direct and indirect effects of NP are now
required as well as determining the timing (early or late) of exposures
in pregnancy. More sophisticated 3D models of the human placental
barrier are also required. Appropriate use of animal species will enable
the possible longer-term impacts on offspring to be evaluated. In human,
effects may alter after 11 weeks of gestation with the onset of maternal
blood flow to the placenta. Most work to date on transplacental transfer
has focussed on solutes, and so methods for the quantification and
accurate tracing of particles into and across the placental barrier need
improving, including monitoring of location, accumulation and
persistence in placental tissue, and metabolic and inflammatory
adaptation.