Microplastic contamination in deep-sea sediments and polymetallic nodules: Insights from the Clarion-Clipperton Zone, Pacific Ocean

Abstract

This study investigates MPs in sediments and polymetallic nodules collected from the Clarion Clipperton Zone (CCZ) in the Pacific Ocean, using samples collected during a deep-sea mining exploration. MPs were detected in over half of the sediment samples and a third of the nodule samples, with an abundance ranging from 0 to 480 items/kg dry weight (d.w.) and 0 to 80 items/kg d.w. for sediments and nodules, respectively, with no significant difference between the two matrices. In terms of size, the smallest particle found was 0.165 mm in sediments and the largest 10 mm in nodules, being >40 % of the particles counted <1 mm, with fibers being the predominant morphology for both matrices. Transparent and blue particles presented the highest percentages, whereas nodules displayed a more balanced percentage distribution among the observed colors. Raman spectroscopy analysis identified polyacrylonitrile (PAN) and polyethylene terephthalate (PET) as the most abundant polymers, along with pigments like indigo blue (IB), acetoacetic arylide (PY), and phthalocyanine blue (PB) commonly associated with synthetic textiles and industrial sources. A global review of deep-sea MPs (>1000 m) reveals considerable variability in reported concentrations, underscoring the challenge of assessing MP pollution in remote marine environments. The findings highlight the need for standardized methodologies to improve comparability across studies and enhance understanding of MP distribution in deep-sea ecosystems. Given the CCZ's ecological and economic significance, further research is crucial to assess the potential risks posed by MPs in this region.

Keywords: Deep-sea; Microfibers; Pollution; Polymetallic nodules; Seafloor; Sediment.