Pelagic microplastics in surface water of the Eastern Indian Ocean during monsoon transition period: Abundance, distribution, and characteristics

Microplastics (MPs) have been documented in almost all marine environments, including coastal regions, the open ocean, and the deep sea. However, relatively little knowledge was available about MP pollution in the open ocean, especially the Indian Ocean. We conducted field observations at 36 stations in the Eastern Indian Ocean (EIO), using a typical manta trawl with a mesh size of 330 μm for surface water sampling. Ours is the first study to obtained comprehensive and comparable baseline data about MPs in the EIO, including abundance, spatial distribution and characteristics. Abundance of MPs in the EIO varied from 0.01 items m⁻² to 4.53 items m⁻², with an average concentration of 0.34 ± 0.80 item m⁻². The mean concentration of MPs in the Bay of Bengal (BoB) was 2.04 ± 2.26 items m⁻² and 0.16 ± 0.17 items m⁻² in the open ocean of the EIO. These results illustrate the high spatial heterogeneity of MPs distribution. Micro-FTIR analysis of polymer composition showed that the vast majority of MPs consisted of polypropylene (PP, 51.11%) and polyethylene (PE, 20.07%). Our data show that MP pollution in the EIO, whether in the epeiric sea or the open ocean, is among the highest of the world's oceans. The BoB is likely to become a MP hotspot due to the vast input of land-based plastics and the presence of multiscale recirculation gyres. These results are absolutely thought provoking: The EIO needs more attention on MPs.