Comparison of mangroves and other coastal vegetation in effectively trapping microplastics

Abstract

Mangrove areas have been recognized as the most retentive zone for microplastics (MPs) originating from both terrestrial and marine sources. In this study, the level of MPs in the different parts of the mangrove species Avicennia marina, like leaves and roots as well as the sediment associated with its roots, was evaluated in the coastal mangroves of Tuticorin, Southeast Coast of India. The MPs were characterized by optical microscopy and ATR-FTIR. The mean abundance of MPs ranged from 0.6 to 1.2 items/cm2 (0.9 ± 0.3 items/cm2) in leaves, 1 ± 0.3 to 11 ± 6.3 items/kg (4.2 ± 3.8 items/kg) in roots, and 28 ± 5.2 to 53 ± 7.67 items/kg (30.33 ± 13.67 items/kg) in the root-associated sediment. The denser pneumatophore promotes entrapment and accumulation of MPs in sediment, which also enhances the absorption of MPs in pneumatophores due to direct environmental contact. The retention capacity of mangrove leaves for atmospheric MPs was compared with that of the leaves of terrestrial plants in the surrounding terrestrial environment. The specific leaf morphology of each species distinctly influenced the capacity for capture and retention. MP retention on the leaves of A. marina was greater due to the presence of waxy cuticles, small hairs, and salt crystals. In sediment, unlike leaves, the presence of diverse polymers was noted, while fiber-shaped MPs with polyethylene polymer were commonly found in leaves, roots, and sediment. This study concluded that mangrove plants have the potential to act as bioindicators of MPs. Based on this information, plant species with most MP-retaining abilities can be selected to build urban green infrastructure that lessens MP pollution.