We’ve polluted hadal zones (deep sea trenches) before we could even explore them


aroe Islands postage stamp from 1986 depicting the impacts of marine pollution.
Figure 1: Faroe Islands postage stamp from 1986 depicting the impacts of marine pollution. This stamp documents the fact that we have known marine pollution to be harmful for decades. Unfortunately fitting that it’s a forever stamp. 

Researchers have just found pollutants that were banned since the 1970’s have become concentrated in today’s deep-sea environments (hadal zones).  These pollutants are likely toxic (Figure 1) and seem to be stuck in the food chain.


What pollutants were found and are they bad?

Researchers found high amounts of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in some deep ocean trenches.  According to the EPA, PCBs cause cancer in animals.  They have also been shown to be deleterious to the immune system, reproductive system, nervous system and endocrine system.  That all sucks—I need those systems!

PBDEs are no better.  According to the EPA PBDEs may also cause cancer.  They have also been shown to cause neurodevelopmental toxicity, weight loss, toxicity to the kidney, toxicity to the thyroid, toxicity to the liver and skin disorders in rats.  You may be thinking: okay, but that’s just for rats.

Sure, you’re right; rats aren’t people—but people are!  And PBDEs have been shown to collect in person-fat and to be endocrine system disruptors.  This means that they can mess with your hormones and cause birth defects.

Perhaps the worst fact to keep in mind: these toxins are here to stay (Figure 1).  They have been shown to be “invulnerable to natural degradation” (Jamieson et al., 2017).

How were these pollutants identified and how bad are their concentrations?

A photograph of an amphipod.
Figure 2: A photograph of an amphipod. Credit: Hans Hillewaert. Licence: CC4.0

New research has used amphipods (tiny crustaceans) to identify these pollutants (Jamieson et al., 2017).  The amphipod species Hirondellea dubia and Bathycallisoma schellenbergi were collected using deep-sea landers that can dive deeper than any manned-craft.

Researchers have found that PCBs and PBDEs are lipophilic, which means that they collect in fatty tissue.  When Jamieson et al. examined the concentrations of PCBs and PBDEs in amphipod fatty tissue, the results were shocking.

This new study shows that PCB and PBDE concentrations in the world’s deepest trench (the Marianas Trench) reach 905 ng/g.  How much is 905 ng/g (nanograms per gram)?  Well, the world’s average background level is less than 1 ng/g.  Even more shocking, these levels of contamination are fifty times worse than those found in one of the most contaminated rivers in China (Teng et al., 2013).

Discussion: why care about the ocean?

The deep sea represents the largest ecosystem on the Earth.  However, due to its inaccessibility, it is the least understood (Ramirez-Llodra et al., 2011).  It makes intuitive sense that we should be cautious about how we pollute this resource.  This is especially true given that we aren’t even sure how important it is to our own wellbeing.

Furthermore, research now suggests that human-influence on hadal zone ecology is increasing (Ramirez-Llodra et al., 2011).  Our impact has shifted from using these deep-sea environments as garbage dumps to direct exploitation.  And things may get worse in the future, as our effects will likely include more acidification from global warming (Doney et al., 2009).

Here’s one last thing to consider: we already impact every marine environment!  A review of the Earth’s oceans has found that there is no marine ecosystem that is unaffected by human activity.  Here is a quote from the article (Halpern et al., 2008):

“Our analysis indicates that no area is unaffected by human influence and that a large fraction (41%) is strongly affected by multiple drivers.”


It’s true that some crafty scientists are likely responsible for the original applications of PCBs and PBDEs.  So it’s easy for some to simply want to blame science for this problem and embrace some romantic (wooish) naturalism.  However, it was scientists, not romantics or woo-practitioners, who got these toxins banned in the 1970’s.  And it is scientists who continue to refine what we know about how they interact with the environment today.  One of the things that makes science great is the fact that it corrects itself.

This is a good time to note that today scientists almost unanimously warn us of the dangers of continued fossil fuel reliance.  Maybe it’s time for a new ban—or at least some heavy investments in renewable energy sources.


Doney, S. C., Fabry, V. J., Feely, R. A., & Kleypas, J. A. (2009). Ocean acidification: the other CO2 problem. Annual review of marine science, 1, 169-192. http://annualreviews.org/doi/abs/10.1146/annurev.marine.010908.163834

Halpern, B. S., Walbridge, S., Selkoe, K. A., Kappel, C. V., Micheli, F., D’agrosa, C., … & Fujita, R. (2008). A global map of human impact on marine ecosystems. Science, 319(5865), 948-952. http://science.sciencemag.org/content/319/5865/948

Jamieson, A.J., Malkocs, T., Piertney, S.B., Fujii, T., Zhang, T. (2017). Bioaccumulation of persistent organic pollutants in the deepest ocean fauna. Nature Ecology & Evolution, 1, 0051. http://www.nature.com/articles/s41559-016-0051

Ramirez-Llodra, E., Tyler, P. A., Baker, M. C., Bergstad, O. A., Clark, M. R., Escobar, E., … & Van Dover, C. L. (2011). Man and the last great wilderness: human impact on the deep sea. PLoS One, 6(8), e22588. http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0022588

Teng, M., Zhang, H., Fu, Q., Lu, X., Chen, J., & Wei, F. (2013). Irrigation-induced pollution of organochlorine pesticides and polychlorinated biphenyls in paddy field ecosystem of Liaohe River Plain, China. Chinese Science Bulletin, 58(15), 1751-1759. https://www.researchgate.net/profile/Xb_Lu/publication/257689308_Irrigation-induced_pollution_of_organochlorine_pesticides_and_polychlorinated_biphenyls_in_paddy_field_ecosystem_of_Liaohe_River_Plain_China/links/00b49533cb7a66f1a7000000.pdf

Jared Peters

Jared Peters

Jared Peters, PhD, is a geoscientist who specialises in marine sedimentology, marine palaeoglaciology and climate change.
Jared Peters
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Jared Peters, PhD, is a geoscientist who specialises in marine sedimentology, marine palaeoglaciology and climate change.