Are mangrove ecosystems plastic accumulation zones?

Despite documented susceptibility of mangrove ecosystems to marine plastics pollution, comprehensive investigations within these ecosystems are limited. This study simultaneously monitored macroplastics (>1 cm) and microplastics (<0.5 cm) pollution for over a year in nine mangrove sites across Cebu Island, Philippines. In each site, two 10 × 10 m plots were established on both the landward and seaward zones. One plot of each pair served as removal plot where surface macroplastics were removed every 3-6 months over a period of more than a year, while the other plot was set as reference plot. Macroplastics were cleaned, characterized and measured. Microplastics were extracted from mangrove sediment samples through consecutive density separation and digestion followed by visual inspection and polymer identification via FTIR spectroscopy. Macroplastics collected were mostly packaging sachets (28 %), bags (24 %) and fragments (23 %) whereas the microplastics were dominantly PE, PP, PA, and PET polymers. There is a strong correlation between the number of macro- and microplastics across sampling locations (r (34) =0.63, p < 0.001). A total of 94.1 kg (dry weight) or over 12,500 items were removed from the plastic removal plots throughout the study. However, the macro- and microplastic loads in removal and reference plots did not differ significantly, and the initial and final plastic loads were also comparable. These results suggests that macroplastics do not accumulate within mangrove ecosystems, likely due to their redistribution beyond the ecosystem boundaries or fragmentation into microplastics.