The Deposition and Accumulation of Microplastics in Marine Sediments and Bottom Water from the Irish Continental Shelf

Abstract

Microplastics are widely dispersed throughout the marine environment. An understanding of the distribution and accumulation of this form of pollution is crucial for gauging environmental risk. Presented here is the first record of plastic contamination, in the 5 mm–250 μm size range, of Irish continental shelf sediments. Sixty-two microplastics were recovered from 10 of 11 stations using box cores. 97% of recovered microplastics were found to reside shallower than 2.5 cm sediment depth, with the area of highest microplastic concentration being the water-sediment interface and top 0.5 cm of sediments (66%). Microplastics were not found deeper than 3.5 ± 0.5 cm. These findings demonstrate that microplastic contamination is ubiquitous within superficial sediments and bottom water along the western Irish continental shelf. Results highlight that cores need to be at least 4–5 cm deep to quantify the standing stock of microplastics within marine sediments. All recovered microplastics were classified as secondary microplastics as they appear to be remnants of larger items; fibres being the principal form of microplastic pollution (85%), followed by broken fragments (15%). The range of polymer types, colours and physical forms recovered suggests a variety of sources. Further research is needed to understand the mechanisms influencing microplastic transport, deposition, resuspension and subsequent interactions with biota.

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Dispersion, Accumulation, and the Ultimate Fate of Microplastics in Deep-Marine Environments: A Review and Future Directions

“…In short, there appears to be no environment on Earth that has escaped microplastic pollution (Taylor et al, 2016). However, our knowledge of the locations of microplastic accumulation in the marine realm is presently incomplete, and in particular the distribution on the seafloor is poorly constrained (Thompson et al, 2004;Barnes et al, 2009;Ballent et al, 2013;Woodall et al, 2014;Martin et al, 2017). This is significant as it is estimated that approximately half of all plastics have a density greater than seawater (United States Environmental Protection Agency [USEPA], 1992;Morét-Ferguson et al, 2010).…”

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“…Especially valuable in the historical framework of plastic waste (Zalasiewicz et al 2016) is the presence of well-defined, datable sediments over the last ca. 150 years that, compared to marine cores (Woodall et al 2014;Martin et al 2017), are more accessible and proximal to terrestrial sources of plastic contamination. Lakes therefore represent catchmentscale sinks for microplastic debris compared with oceans, which are subject to global-scale long-range transport from multiple catchments (Hidalgo-Ruz et al 2012;Hardesty et al 2017).…”