We cannot detect or quantify nanoplastics below 100 nm in environmental water samples, which is exactly the size range most likely to cross biological barriers

Current analytical techniques for detecting plastic particles in environmental water hit a hard wall at around 100-200 nm. Optical microscopy is diffraction-limited at roughly 200 nm resolution. FTIR spectroscopy, the workhorse method for microplastic identification, cannot chemically identify particles below about 10-20 micrometers. Raman micro-spectroscopy pushes down to roughly 1 micrometer. Below 100 nm — the nanoplastic range — there is no validated method that can simultaneously detect, count, size, and chemically identify plastic nanoparticles in a complex environmental matrix like river water or seawater. Nanoparticle Tracking Analysis (NTA) can size particles in this range but cannot distinguish plastic from natural organic colloids, clay particles, or other nanoparticulate matter. This is the worst possible blind spot. Particles below 100 nm are precisely the ones that toxicology research indicates can cross the intestinal epithelium, penetrate cell membranes, cross the blood-brain barrier, and enter the placenta. A 2024 study reported the first evidence correlating PFAS accumulation in the central nervous system with Alzheimer's disease symptoms; similar concerns exist for nanoplastics but cannot be investigated because we cannot measure environmental concentrations. Regulatory agencies cannot set environmental quality standards for a contaminant they cannot quantify. Risk assessments are based on microplastic data extrapolated downward, which is scientifically unsound because the number concentration of particles increases dramatically as size decreases. The measurement gap persists because detecting nanoplastics requires solving two problems simultaneously: sizing particles in the sub-100 nm range (achievable with DLS or NTA) AND chemically identifying them as specific polymers (achievable with spectroscopy, but only above the micrometer range). No single instrument does both at the nanoscale in a complex matrix. Emerging approaches like pyrolysis-GC/MS can quantify total polymer mass but destroy size information. Machine learning-assisted spectroscopy and plasmonic nanosensors show promise in laboratory settings but are far from field-deployable.