Coupled interactions between particulate microplastics and leached plastic-derived additives during magnetite-assisted water treatment

The coupled interactions between particulate microplastics and dissolved plastic-derived additives were investigated using magnetite (Fe₃O₄). The investigated materials included tire wear particles (TWP), poly(vinyl chloride) (PVC) pipe particles, and reference polymers. Magnetite rapidly induced heteroaggregation and enabled efficient magnetic separation of the investigated MPs. Simultaneously, dissolved plastic-associated organic compounds were scavenged from model solutions, with removal depending on their physicochemical properties. SEM, FTIR, and magnetic analyses confirmed attachment of Fe₃O₄ particles to microplastic surfaces, the formation of Fe₃O₄–MP aggregates, and the absence of detectable chemical modification of the investigated polymers. Magnetic measurements further demonstrated that the magnetic response of the heteroaggregates depended on polymer type, pH, and aggregate organization. Statistical analysis and exploratory Random Forest modelling were used to examine relationships among the investigated variables and to identify their relative contributions within the experimental dataset. Phthalate release from TWP continued after rapid magnetite-induced aggregation and separation of the microplastic particles, indicating that removal of the particulate fraction did not immediately terminate additive release from the polymer matrix. The simultaneous presence of MPs and magnetite therefore involved coupled processes associated with particulate aggregation, additive release, and scavenging of dissolved compounds. These findings demonstrate that physical removal of microplastic particles alone does not necessarily eliminate the dissolved fraction of plastic-derived contamination. The study provides an experimental assessment of these coupled processes under controlled conditions and highlights the importance of considering both particulate and dissolved plastic-related contaminants when evaluating magnetite-assisted treatment strategies.