Why is inhalation the most discriminative route of microplastics exposure?

Recent research suggests a definite distinction between indoor and outdoor microplastics (MPs). However, knowledge of different MP kinds and relative exposure via inhalation to humans in outdoor and indoor locations is lacking. Notably, MPs formed from various plastic types could have distinct features, and the relative health risk varies by environment. For example, outdoor polyethylene (PE) goods have recently become more popular. These products are generally of poor structure and recycled material, making them more susceptible to decay. Particularly in the outdoor environment, the constant exposure to an open-air environment increases the risk of fragmentation and atmospheric mixing and thus facilitates MP's availability. Using PE as an example, we aimed to emphasize the importance of explicitly defining exposure intensity and the health risk of each MP type, especially in contrasting situations such as indoor and outdoor. Unchecked and excessive use of these materials can be hazardous, whereas lowering or replacing PE with alternative plastics can significantly reduce potential health hazards.