Cascade Filtration Coupled with Raman Spectroscopy for Size-Resolved Detection of Micro- and Nanoplastics in Drinking Water

Micro- and nanoplastics (MNPs) are increasingly recognized as emerging contaminants in drinking water, yet quantitative data remain limited due to analytical challenges. In this study, the occurrence, morphology, and polymer composition of MNPs were investigated in commercial drinking water from Saxony-Anhalt, Germany, including ultrapure water, tap water, and five bottled mineral waters. A dual-stage cascade filtration system combining silicon filters (5 µm pore size) and aluminum oxide membranes (90 nm pore size) was employed for size-selective particle separation. Retained particles were characterized using optical microscopy, scanning electron microscopy (SEM), and Raman spectroscopy. Tap water exhibited the highest concentration of microparticles, whereas ultrapure water showed minimal microparticle contamination. Nanoparticles were detected in all samples, including ultrapure water, with mean particle sizes below 1 µm, highlighting the pervasive nature of nanoscale plastic contamination. Raman analysis identified polyethylene terephthalate (PET) as the most frequently detected synthetic polymer, together with polypropylene (PP), polystyrene (PS), and poly(methyl methacrylate) (PMMA). The results demonstrate that no drinking water source tested in this study was free of detectable MNPs and underline the need for standardized analytical approaches capable of reliably detecting MNPs in drinking water.