Nanoplastics in environmental biota: analytical challenges, tissue translocation, and biomarkers for biomonitoring.

Nanoplastics are increasingly recognised as relevant contaminants in environmental biota, yet their integration into biomonitoring remains limited by analytical and interpretative uncertainties. This review critically examines nanoplastic detection in biological matrices, evidence of uptake and tissue distribution, and biomarkers of early biological effects. Although experimental studies suggest that model nanoplastics may reach internal tissues, quantitative confirmation of intact-particle translocation remains limited, and fluorescence-based findings may be affected by dye leaching, tissue autofluorescence, external particle association, and insufficient chemical confirmation. Oxidative stress, immune and inflammatory responses, genotoxicity, and metabolic disturbances are frequently reported across taxa, but their low specificity limits their use as stand-alone indicators. We therefore outline a tiered conceptual approach for future biomonitoring, integrating the following: (i) polymer-specific particle confirmation, (ii) assessment of internal burden using complementary mass-, number-, and size-based metrics, and (iii) interpretation through mechanistically linked multi-biomarker panels. This approach distinguishes environmental occurrence from internal exposure and biological effect and highlights the need for contamination control, complementary analytical methods, environmentally relevant exposure conditions, and transparent uncertainty reporting. Nanoplastics are not yet ready for routine biomonitoring, but coordinated analytical validation and mechanism-based interpretation may support their future inclusion in environmental monitoring and risk assessment.