Microplastics and antibiotic toxicity in aquatic organisms: Exposure, interactions and mechanisms.

Micro- and nanoplastics co-occur with antibiotic residues in aquatic environments, but whether particles increase antibiotic hazard remains unresolved. We conducted a structured qualitative synthesis of original aquatic co-exposure studies identified through Europe PMC searches to 25 September 2026, a complementary OpenAlex search and citation chasing. Experiments were compared by organism, particle properties, both contaminant concentrations, exposure route, comparator design and endpoint. Reported outcomes include amplification, attenuation and dose- or endpoint-dependent reversals. Marine bivalve and other invertebrate studies extend this evidence to low antibiotic concentrations, but low antibiotic exposure does not by itself establish realistic particle exposure. Microbiome shifts were distinguished from host injury and fitness impairment. A mixture response exceeding either single treatment does not establish synergy, and increased tissue accumulation does not alone establish particle-mediated delivery. Our study-level appraisal separates conditional co-exposure findings from designs capable of identifying an interaction and from evidence supporting a specific mechanism. The five-level hierarchy is proposed as a framework for evaluating current claims and designing future research; its highest levels are evidentiary targets, not a claim that the existing literature has already established causal pathways at environmentally realistic exposures.