The seasonality of the concentration of endocrine phenolic compounds in the matter attached to the surface of microplastics

Rapid biofilm formation on microplastic (MP) surfaces in marine environments and the tendency of hydrophobic pollutants to bioaccumulate may increase the exposure of organisms to ingested plastics and transport pollutants far from their sources. The role of the matter attached to MPs (MaM) in the interactions between MPs and other pollutants in marine environments is poorly understood. This paper studies pollutant sorption in MaM for three phenolic endocrine-disrupting chemicals (EDCs): bisphenol A (BPA), 4-tert-octylphenol (4-t-OP), and 4-nonylphenol (4-NP). Polypropylene (PP), expanded polystyrene (EPS), and polylactide (PLA) MPs were exposed to an environment conducive to biofouling (Vistula Lagoon, Baltic Sea) for four weeks in summer, spring, and winter. The concentrations of EDCs in MaM and the suspended particulate matter (SPM) were similar and were 2–3 orders of magnitude higher than those in water and sediment. The type and morphology of the polymers were less significant for determining the concentrations of EDCs in MaM than the season. The concentrations were higher in the growing season than in winter. EDCs increased linearly with the increase in particulate organic carbon. The relationships between organic carbon partition coefficients and octanol/water partition coefficients indicate that hydrophobic partitioning into organic matter was the dominant mechanism of 4-t-OP and 4-NP binding in MaM and in SPM. For BPA, additional sorption mechanisms seem to be significant. In addition to the direct sorption from ambient water, the binding of phytoplankton-derived particles, most probably via attachment to extracellular polymeric substances, appears to be a source of EDCs in MPs. Rough estimates showed that the largest load of particulate matter and EDCs was attached to expanded polystyrene. This study suggests that the potential negative impacts of MPs on the environment are seasonal and that low-density porous plastics can be particularly effective carriers of large EDC loads.