Emerging investigator series: perspectives on toxicokinetics of nanoscale plastic debris in organisms

Fragmentation of plastic waste in the environment can lead to the formation of nanoscale plastic debris (NPD) of size < 1 μm. Although it is reported that NPD can be taken up by organisms, the current lack of knowledge regarding its toxicokinetics is a problem. It is currently unknown whether/how NPD passes through physiological barriers, and subsequently is biodistributed, biotransformed and/or excreted from organisms. New methods and techniques are being developed at a rapid pace that facilitates gaining insights into the uptake and toxicokinetics of NPD even in complex biotic samples. However, the required knowledge is generated slowly, which hinders environmental risk assessment. In this perspective, we outline the current understanding of the toxicokinetics of NPD in organisms by transferring the acquired knowledge on the toxicokinetics of engineered polymeric NMs to NPD. We briefly discuss the absorption, distribution, metabolism (e.g., biotransformation), and excretion (ADME) of NPD and highlight the knowledge gaps and research required to address them. Building on this, a perspective on toxicokinetics modeling of NPD using physiologically based pharmacokinetic (PBPK) models is presented, discussing the factors that might influence the modeling data and providing recommendations on the factors that need to be considered for developing PBPK models for NPD.