Blood uptake and urine excretion of nano- and micro-plastics after a single exposure

Nano- and micro-plastic (NMP) pollution has emerged as a global issue; however, uptake in the blood is controversial. Also, there is no evidence that NMPs are excreted via urine. This study was designed to clarify the time course of NMPs absorption in blood and the excretion in urine. Male mice received a single administration of fluorescent polystyrene (PS) beads (100-nm and 3-μm) via tail vein injection, gavage, or pulmonary perfusion. Blood and urine samples were measured 0.5, 1, 2, and 4 h after exposure by confocal laser scanning microscope (CLSM). Transmission electron microscopy (TEM) was performed to corroborate the findings. Fluorescence particles were detected in both blood and urine from the 100-nm and 3-μm PS-treated groups after exposure. In the 3-μm PS treated group, particles with corresponding diameters were detected after intravenous injection and pulmonary perfusion, and particles with a diameter <3 μm were detected in blood samples after gavage. The fluorescent signal in urine was particularly weak and the size was <3 μm. Significant time course changes in fluorescence intensity were demonstrated in blood and urine (P < 0.05) after intravenous injection and pulmonary perfusion in the 100-nm PS-treated group. By contrast, significant changes were detected in the urine (P < 0.05), but not the blood, after gavage. TEM confirmed the presence of particles with corresponding diameters in blood samples; however, the excretion in urine was difficult to confirm for nano-plastics (NPs) and micro-plastics (MPs) because all particles with diameters of approximately 100 nm and 3 μm had irregular shapes and no clear boundaries. Our findings revealed that both NPs and MPs enter the blood circulation through digestive and respiratory pathways. Both 100-nm and 3-μm NMPs may be excreted through urine, but further evidence is needed. The physical and chemical properties of MPs may be impacted by digestive processes in vivo.