Microplastic inventory in sediment profile: A case study of Golden Horn Estuary, Sea of Marmara

Highlights: • Microplastics were identified by Nile red staining in a sediment core. • The Golden Horn estuary has been polluted with microplastics. • Most of the microplastics has buried in deep sediment. • Radiodating of sediment is very useful to interpret temporal trends in MPs pollution. • Small MPs (20–200 μm) were more abundant than large ones (200–4000 μm) in the sediment core. Assessment of microplastics (MPs) in sediment cores is necessary to unveil global plastic pollution since most of the plastic litter might have been stored in sediment columns. In the current study, MPs inventory was determined in a 105 cm sediment core, collected in the Golden Horn Estuary, Sea of Marmara. Radiodating of sediment profile by using naturally occurring ²¹⁰Pb and fission product ¹³⁷Cs allowed us to couple the retrospective of global MP production to sediment MPs inventory. More than 90% of total MPs inventory was found in the deep layer of the sediment column (below 15 cm). Small MPs (20–200 μm) were more abundant than large ones (200–4000 μm). Elevated concentrations of MPs were attributed to industrial and municipal effluent of Istanbul metropolitan. On a local scale, this study suggests that the Golden Horn Estuary was polluted with MPs before the 1950s, and the abundance of MPs reached a maximum in the 1980s. We also propose on a global scale that "the missing" plastics might have been buried in deep sediment and radiodating of sediment is useful to reveal their historical input records.