Additives in microplastics shape biofilm composition during aging and favour antibiotic-resistant microorganisms.
Plastic additives are emerging as active agents that shape the environmental impacts of microplastics. In this study, we investigated how a polyethylene microplastic formulation containing the commonly used UV filter benzophenone-3 (BP-3) and a calcium carbonate filler affects aging and biofilm colonization in freshwater. The additive-containing formulation altered the density and crystallinity of polyethylene particles and predisposed the material for faster surface transformation and formation of pits and cracks during aging. At the same time, it suppressed biofilm formation, reduced the development of extracellular polymeric substances by microorganisms, and specifically affected phototrophic microorganisms. Microbial community profiling revealed a shift from cyanobacteria-dominated biofilms to heterotrophic, chemically more resilient taxa, accompanied by enrichment of antibiotic resistance genes. Despite comparable genetic potential for polymer degradation, microbial activity was inhibited, indicating a trade-off between abiotic and biotic degradation. These results indicated that the tested additive-containing polyethylene formulation reduces microplastics stability and alters biofilm composition, highlighting the importance of considering additives in assessments of microplastic persistence and environmental effects.