Spatial Variation in Microplastic-Associated Hazard-Relevant Chemical Profiles Along an Urban River Corridor

Riverine microplastic (MP) assessments remain dominated by particle abundance, leaving comparatively limited understanding of the chemical profiles associated with recovered MP fractions. We examined spatial variations in MP abundance and chemical occurrence in extracts of recovered MP fractions and water across eight sites representing contrasting land-use settings, spanning 48.8 km of the Yamuna River, Delhi, India. MP abundance was quantified from three independent field replicates per site, whereas field replicates were pooled by site before chemical extraction and screened by non-target Orbitrap LC-MS/MS in positive-ion mode following ethyl acetate and hexane extraction. MP abundance varied nearly fourfold among sites (2,289 particles; mean 3.18 particles L⁻¹; F = 14.74, p = 6.81 × 10⁻⁶), with pellets (26.3%) and blue particles (21.7%) predominant. Chemical screening yielded 268 distinct compound annotations in ethyl acetate and 183 in hexane extracts at Schymansky level 2a, comprising 321 distinct chemical compounds across both solvents. Fifty compounds recurred in extracts of the recovered MP fractions from ≥4 sites, including seven detected at all eight sites. Of these, thirty-six of these compounds matched GHS hazard records, including probable Level 2a annotations of 2-naphthylamine, diuron, 8-hydroxyquinoline and bis(2-ethylhexyl) amine. Other recurrent annotations include benzothiazole-related compounds potentially associated with polymer-related sources and pharmaceutical residues (lidocaine, atomoxetine, domperidone, telmisartan) potentially indicative of wastewater influence. Since the compound identifications relied on accurate-mass and MS/MS spectral-library matching (Schymanski Level 2a), chemical occurrence and peak-area patterns were interpreted descriptively rather than as quantitative measures of partitioning or enrichment. The positive-ion screening used in the study represents a method-defined lower-bound subset of the chemical profile. Overall, the study shows clear spatial differences in MP abundance across river sites and diverse chemical profiles in the recovered MP fractions. Composition and hazard relevance of riverine MPs therefore cannot be inferred from particle abundance alone; spatially resolved characterisation of both fractions better supports assessment of MP-associated hazards in urban rivers.