A research paper published this week identified high levels of anthropogenic pollutants in the tissue of deep-water amphipods living at depths of over 10,000 m in the northwest Pacific, disproving the assumption that deep-water habitats are isolated, pristine environments.
Alan Jamieson and his team, studied the concentration of persistent organic pollutants (POPs) in three species of anthropod crustacea (Hirondellea dubia (pictured above), Bathycallisoma schellenbergi and Hirondellea gigas). The latter of which is found in the Mariana Trench (11, 033 m deep) and the other two species found in the Kermadec Trench (10, 047 m).
POPs included polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) which were produced between the 1930’s and 1970’s. The global content of PCBs is estimated to be split between landfills and within electrical items in landfills (65 %) and in coastal sediment and open oceans (35 %). POPs are hydrophobic particles, meaning they easily bond with organic and in-organic particles in the water column and get transported to depth, through natural sinking of these particles. As POPs are also lipophilic they can easily cross animals membrane barrier (skin) and bioaccumulate within an individual.
Other studies have identified higher concentrations of these contaminants in deeper water species than their shallower water counterparts. Though these studies have never studied species deeper than about 2000 m. To give context to the concentrations of POPs observed within the deep water amphipod, the world baseline levels of PCBs in clean coastal sediments is < 1 ng g-1 dry weight, whilst contaminated sediments in the Pacific range from 314 ng g-1 dry weight in Guam to 160 ng g-1 dry weight in Australia.
Concentrations of PCBs in the amphipod within the Mariana Trench reached concentrations of 905 ng g-1 dry weight. This is 50 x more contamination than crabs found in the paddy fields fed by the Liaohe River, one of the most polluted rivers in China. PCB contamination was consistently higher in the Mariana Trench compared to the Kermadec Trench. Whilst PBDE contamination was lower in both trenches, levels were similar to shallower, coastal areas, indicating contamination was present.
The team discussed several reasons, which may all play a part, in why contamination levels were higher in the Mariana Trench. These included the potential increased input of rubbish and pollutants such as PCBs in the Mariana Trench area due to the North Pacific Subtropical Gyre which is the home to the ‘Great Pacific Garbage Patch’. Variation in the level of contamination observed in carrion falls to the seafloor and variation in physiological uptake of pollutants by the different species of amphipod.
Having now identified anthropogenic pollution has reached the deepest ocean, the challenge for the future is to determine the physiological consequences of contamination and to understand the knock-on effects on ecosystem function.
Jamieson, A. J. et al. Bioaccumulation of persistent organic pollutants in the deepest ocean fauna. Nat. Ecol. Evol.1, 0051 (2017) and the references found within.
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