Contaminants and the ocean deep - sampling from the seafloor of the Mariana and Kermadec trenches persistent organic pollutant levels of PCBs and PBDEs were fifty times that of the most polluted Chinese rivers. They bioaccumulate into the bodies of large organisms and can fall to the depths when the creatures die where deep dwelling animals consume them and show high pollution levels.
from a paper in Natural Ecology and Evolution
Bioaccumulation of persistent organic pollutants in the deepest ocean fauna
Alan J. Jamieson, Tamas Malkocs, Stuart B. Piertney, Toyonobu Fujii & Zulin Zhang
The legacy and reach of anthropogenic influence is most clearly evidenced by its impact on the most remote and inaccessible habitats on Earth. Here we identify extraordinary levels of persistent organic pollutants in the endemic amphipod fauna from two of the deepest ocean trenches (>10,000 metres). Contaminant levels were considerably higher than documented for nearby regions of heavy industrialization, indicating bioaccumulation of anthropogenic contamination and inferring that these pollutants are pervasive across the world’s oceans and to full ocean depth.
The oceans comprise the largest biome on the planet, with the deep ocean operating as a potential sink for the pollutants and litter that are discarded into the seas 1 . The spatial and bathymetric expanse of the deep sea infers that there are still large areas untouched by anthropogenic activity, although the intrinsic linkages between the deep sea and surface waters 2 would suggest this inference is ill-conceived 3 . The hadal zone (6,000 to 11,000 m deep) is comprised of trenches formed at tectonic subduction zones, and represents the least explored ecosystem on Earth and the last major marine ecological frontier 4 . Trenches have been considered as pristine environments, but also (given their locations and topography) as likely sinks for contaminants that enter the marine environment 2 . Of particular concern are the persistent organic pollutants (POPs) that are highly detrimental to organismal health through their endocrine disrupting properties 5 . POPs possess an inherent hydrophobicity that confers a high binding affinity to organic or inorganic particles present in the water column that, through vertical transport, will collect in the deep ocean. They also have inherent lipophilicity, meaning these compounds readily bioaccumulate in organisms, with cumulative increases at each trophic level 6 .
POPs were released into the environment through industrial accidents and discharges, leakage from landfills, or incomplete incineration 7 . Two key POPs are polychlorinated biphenyls (PCBs, used as dielectric fluid) and polybrominated diphenyl ethers (PBDEs, used as flame retardants). From the 1930s to when PCB production ceased in the 1970s, the total global production was ~1.3 million tonnes 8 . Approximately 65% is thought to be contained in landfills or still within electrical equipment, with the other 35% residing in coastal sediments and open oceans 9 . These pollutants are invulnerable to natural degradation 10 and so persist in the environment for decades. Moreover they can spread great distances, including to seemingly isolated environments, such as polar regions and the open ocean 3 .
Pollutants entering the deep sea are deposited in sediments and can readily accumulate in the food chain 11 . Studies on deep-sea organisms have reported higher concentrations than in nearby surface-water species 11,12 . However, although these studies are described as ‘deep sea’, they rarely extend beyond the continental shelf (<2,000 m), so contamination at greater distances from shore and at extreme depths is hitherto unknown.
We measured the concentrations of key PCBs and PBDEs in multiple endemic and ecologically equivalent Lysianassoid amphipod Crustacea from across two of the deepest hadal trenches — the oligotrophic Mariana Trench in the North Pacific, and the more eutrophic Kermadec in the South Pacific. Two endemic amphipods (Hirondellea dubia and Bathycallisoma schellenbergi) were sampled from the Kermadec between 7,227 and 10,000 m, and one (Hirondellea gigas) from the Mariana between 7,841 and 10,250 m. Samples were obtained using traps deployed on deep-sea landers 13 . The concentrations of seven PCB congeners identified by ICES 14 for marine pollution assessment and seven PBDE congeners were measured both in sample dry weight (dw) and lipid weight (lw).
The salient finding was that PCBs and PBDEs were present in all samples across all species at all depths in both trenches (Figs 1 and 2). The ΣPCB7 concentrations ranged from 147.3–905 ng g−1 dw in the Mariana and 18.03–42.85 ng g−1 dw in the Kermadec, with mean values of 382.28 ng g−1 dw (±281.6 s.d.) and 25.24 ng g−1 dw (±9.1 s.d.), respectively. Across individual PCB congeners, PCB 153 was detected in the highest concentration (mean 64.45, range 5.03–373.63 ng g−1 dw). Congeners PCB 138 and 153 alone accounted for 65% of the total PCB concentration, which suggested that the heavier congeners were more recalcitrant towards degradation.