The deep sea is a major sink for microplastic debris

Abstract

Marine debris, mostly consisting of plastic, is a global problem, negatively impacting wildlife, tourism and shipping. However, despite the durability of plastic, and the exponential increase in its production, monitoring data show limited evidence of concomitant increasing concentrations in marine habitats. There appears to be a considerable proportion of the manufactured plastic that is unaccounted for in surveys tracking the fate of environmental plastics. Even the discovery of widespread accumulation of microscopic fragments (microplastics) in oceanic gyres and shallow water sediments is unable to explain the missing fraction. Here, we show that deep-sea sediments are a likely sink for microplastics. Microplastic, in the form of fibres, was up to four orders of magnitude more abundant (per unit volume) in deep-sea sediments from the Atlantic Ocean, Mediterranean Sea and Indian Ocean than in contaminated sea-surface waters. Our results show evidence for a large and hitherto unknown repository of microplastics. The dominance of microfibres points to a previously underreported and unsampled plastic fraction. Given the vastness of the deep sea and the prevalence of microplastics at all sites we investigated, the deep-sea floor appears to provide an answer to the question-where is all the plastic?

Keywords: fibres; litter; marine; microplastic; plastic; seabed.

Figure 1.

Locations of sampling sites of bottom sediment and deep-water coral where content of microplastics was investigated. Sample depth ranged down to 3500 m, for details see table 1. Sediment was collected by the University of Barcelona (circles) and the Natural History Museum (filled squares), and deep-water corals were collected by the Natural History Museum (open squares). Bathymetry corresponds to ETOPO1 Global Relief Model.

Figure 2.

The quantity and type of plastic fibres found in 50 ml of sediment sampled from the North Atlantic Ocean, Mediterranean Sea and SW Indian Ocean.