Where on Earth do persistent organic pollutants go? Hadal trenches as global sink for hazardous pollutants (HADAL-POP)

Sediment burial is a major removal pathway for persistent organic pollutants (POPs). It is therefore fundamental to understand mechanisms that govern POP burial in deep ocean sediment. Hadal trenches represent the deepest part of the ocean, stretching 6–11 km of depth.

They offer a unique setting for studying biogeochemical drivers of POP accumulation as they are hotspots for i) organic carbon burial, and ii) decomposition of organic matter.

This makes trenches likely hotspots also for POP burial, as transport of organic matter and POPs goes hand in hand, and as organic matter degradation increases its capacity to store POPs.

Preliminary data from the proposing team demonstrate up to 15 times higher concentrations of polychlorinated biphenyls (PCBs) in hadal compared to shallower sediment, supporting efficient accumulation of POPs in hadal trenches.

In HADAL-POP, we will perform a cruise to the Japan Trench to test hypotheses on how biogeochemistry governs the sediment capacity to accumulate pollutants.

Access to samples from five hadal trenches will allow us to apply our findings from the Japan Trench on other regimes, and thereby generate better understanding of principles that govern pollutant burial also in more polluted systems. HADAL-POP will generate unique data on POPs and chemicals of emerging concern in hadal sediment.

Occurrence of currently-used chemicals on the remote hadal seafloor is a call to decision makers for improving current chemicals management.