Fate of microplastics in deep-sea sediments and its influencing factors: Evidence from the Eastern Indian Ocean

Although microplastics (MPs) are known to be found in global oceans, their influencing factors and abundance in the deep sea remain largely unknown. Twenty-six surface sediment samples were collected in the deep basin of the Eastern Indian Ocean (EIO). This study showed that MPs abundance ranged from 30.30 particles/kg to 701.7 particles/kg, with an average of 170.5 +/- 140.2 particles/kg. The MPs found in the sediment of the EIO mainly contain fragments and fibers, which account for 47.5% and 45.6%. The MPs were measured in a size range of 44-5000 mu m, and the most frequently detected MPs in size of 200-500 mu m. MPs were in various compositions, but most of them were found in rayon (62.2%) and polyester (25.7%). The spatial distribution of MPs in the sediments shows a decreasing trend from nearshore to the open sea. In the Bay of Bengal (BOB) and the coast of Sri Lanka (COSL), the abundance of MPs was relatively high, indicating that the spatial distribution of MPs is affected by land source input, river input, and anthropogenic activities. Principal component analysis indicated daily commodities and packaging applications/fishing accounted for 36.9% and 12.9% of the MPs occurrence in the EIO, respectively. Average MPs diversity indices for the BOB (0.87 +/- 0.38), the COSL (0.64 +/- 0.56), and the Eastern Indian Ocean Basin (EIOB) (0.60 +/- 0.24) revealed the BOB had the most complicated MPs sources. In addition, we found that the abundance of MPs has no significant effect on organic carbon and sediment grain size. This study is the first report of MPs detection in the deep-sea sediment in the EIO and can provide a baseline of MPs pollution in this area.

Automated summary

This study explores the abundance, composition, and sources of microplastics (MPs) in the deep-sea sediments of the Eastern Indian Ocean (EIO). MPs were found in various compositions, with rayon and polyester being the most common. The spatial distribution of MPs decreases from nearshore to open sea. Anthropogenic activities, land and river sources, and fishing are the major contributors to MPs accumulation. The study provides important baseline data for understanding MPs pollution in the EIO.