Organic matter degradation causes enrichment of organic pollutants in hadal sediments

Anna Sobek; Sebastian Abel; Hamed Sanei; Stefano Bonaglia; Zhe Li; Gisela Horlitz; Arka Rudra; Kazumasa Oguri; Ronnie N Glud

doi:10.1038/s41467-023-37718-z

Organic matter degradation causes enrichment of organic pollutants in hadal sediments

Nat Commun. 2023 Apr 10;14(1):2012. doi: 10.1038/s41467-023-37718-z.

Authors

Anna Sobek¹, Sebastian Abel², Hamed Sanei³, Stefano Bonaglia⁴, Zhe Li², Gisela Horlitz², Arka Rudra³, Kazumasa Oguri^{5

6}, Ronnie N Glud^{5

7

8}

Affiliations

¹ Department of Environmental Science, Stockholm University, Stockholm, Sweden. anna.sobek@aces.su.se.
² Department of Environmental Science, Stockholm University, Stockholm, Sweden.
³ Lithospheric Organic Carbon (LOC) Group, Department of Geoscience, Aarhus University, Aarhus, Denmark.
⁴ Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden.
⁵ HADAL and Nordcee, Department of Biology, University of Southern Denmark, Odense, Denmark.
⁶ Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan.
⁷ Danish Institute for Advanced Study (DIAS), University of Southern Denmark, Odense, Denmark.
⁸ Department of Ocean and Environmental Sciences, Tokyo University of Marine Science and Technology, Tokyo, Japan.

Abstract

Burial of persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs) in deep-sea sediments contributes to 60% of their historical emissions. Yet, empirical data on their occurrence in the deep-ocean is scarce. Estimates of the deep-ocean POP sink are therefore uncertain. Hadal trenches, representing the deepest part of the ocean, are hotspots for organic carbon burial and decomposition. POPs favorably partition to organic carbon, making trenches likely significant sinks for contaminants. Here we show that PCBs occur in both hadal (7720-8085 m) and non-hadal (2560-4050 m) sediment in the Atacama Trench. PCB concentrations normalized to sediment dry weight were similar across sites while those normalized to sediment organic carbon increased exponentially as the inert organic carbon fraction of the sediment increased in degraded hadal sediments. We suggest that the unique deposition dynamics and elevated turnover of organic carbon in hadal trenches increase POP concentrations in the deepest places on Earth.