Dermal Uptake and Elimination of Europium-Labeled Nanoplastics in Earthworms

ObjectiveThe accumulation of nanoplastics (NPs) in soils poses potential threats to earthworm health. As key indicator species in soil ecosystems, earthworms play a crucial role in assessing the ecological risks associated with soilborne NPs. However, the quantification of NPs in complex biological and environmental matrices has remained a major challenge, limiting progress in this research field. Therefore, a comprehensive understanding of the absorption and excretion process of NPs by earthworms is essential for accurate exposure risk assessment.MethodIn this study, europium-labeled polystyrene nanoparticles were utilized as model NPs to quantitatively investigate the absorption, distribution, and excretion kinetics of NPs in earthworms. The organisms were exposed to the nanoparticles via three distinct administration routes: topical application onto the epidermis, direct injection into the body cavity, or introduction into the soil medium with or without oral exposure restriction (mouth sealing).ResultSkin exposure experiments demonstrated that NPs were capable of penetrating the earthworm epidermal barrier, with absorption kinetics exhibiting a biphasic pattern: an initial rapid phase (0-3 h), primarily driven by concentration gradient–mediated passive diffusion, followed by a slower phase (3-24 h), significantly impeded by the resistance of the epidermal mucus layer and NP aggregation. Body cavity exposure studies revealed that NPs excretion via the skin also followed a biphasic pattern, characterized by rapid clearance (28.7% ± 1.4% within 3 h) and subsequent slow attenuation. The skin exudation rate was markedly lower than the penetration rate, indicating that the skin predominantly functions as an absorptive interface during NPs metabolism. Integrated sealing experiments further clarified the time-dependent shift in NPs uptake pathways: cutaneous absorption dominated during the early exposure phase (ConclusionThis study highlights dermal penetration as a critical yet previously underestimated route for the uptake of NPs in earthworms, thereby providing a robust scientific basis for refining ecological risk assessment models of soilborne nanoparticles. It also contributes valuable theoretical insights into the biogeochemical cycling of NPs within soil ecosystems.