2. Background
Plastics are extremely durable synthetic polymers, yet more than 30% are made into disposable items
such as packaging, which are typically discarded within a year of manufacture [1]. The associated throwaway
culture has led to an escalating plastic waste management problem, and widespread accumulation
of plastic debris in the natural environment. Debris is now present on shorelines and at the sea surface
from pole to pole [1,2]. It has major environmental impacts and is recognized as one of the key challenges
of our century [1–3]. However, despite extensive environmental monitoring, there is little evidence of
the expected increasing abundance of plastic debris in natural habitats. Only two studies [4,5] report an
increase over time. Both these papers focused on microplastics, which have not typically been included in
routine monitoring, and are likely to represent a largely undocumented accumulation of plastic debris.
Yet, even for microplastic pollution, temporal trends are unresolved in the majority of datasets [6]. In
addition, a recent study [7] suggested that surface water plastic accumulation was tens of thousands
of tonnes less than expected, and acknowledged that resolving the fate of the missing plastic is a
fundamental issue [8].
Plastics can be denser (e.g. acrylic) or lighter (e.g. polypropylene) than seawater. Those that
are buoyant float when first entering the sea, so historically attention has focused on the
accumulation on shorelines and at the sea surface [9]. However, because of fouling by organisms
and adherence of particles, positively buoyant plastics can, over a timescale of weeks to months,
become negatively buoyant and sink [10]. Some studies have shown the accumulation of large plastic
items in the deep sea [11,12], and one has reported the presence of microplastic fragments at low
densities [13].
Here, we present results from a global analysis of deep-sea sediment collected by two independent
research teams during seven research cruises between September 2001 and August 2012, in the
Mediterranean Sea, SW Indian Ocean and NE Atlantic Ocean (spanning subtropical to subpolar waters).
The purpose of this study was to quantify the abundance and extent of microplastic contamination at a
range of depths and locations in the deep sea.