It seems there is no place on Earth free from pollution. A new study has revealed a very high concentration of chemical pollutants in two of the planet’s deepest oceanic trenches in the Pacific Ocean.
Chemicals banned in the 1970s in the US have been found in the fatty tissue of amphipods (a type of crustacean), retrieved using specially designed “lander” vehicles deployed from a boat over the Mariana and Kermadec trenches, which are over 10km deep and separated from each other by 7,000km.
The finding confirms the fears that the deep ocean can become a “sink” or repository for pollutants. Chemicals accumulate through the food chain so that when they reach the deep ocean, concentrations are many times higher than in surface waters.
The pollutants found in the amphipods included polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs), commonly used as electrical insulators and flame retardants. PCB production was banned by the US in 1979 and by the Stockholm Convention on Persistent Organic Pollutants, a UN treaty signed in 2001.
From the 1930s to when PCBs were banned in the 1970s, the total global production of these chemicals is estimated to be in the region of 1.3mn tonnes. Released into the environment through industrial accidents and discharges from landfills, these pollutants are resistant to being broken down naturally, and so persist in the environment.
In a paper published in the journal Nature Ecology and Evolution, the team led by Dr Alan Jamieson at the University of Newcastle says it can be difficult to place the levels of contamination found below the Pacific into a wider context – in part because previous studies of contamination gathered measurements in different ways.
But they add that in the Mariana trench, the highest levels of PCBs were 50 times greater than in crabs from paddy fields fed by the Liaohe River, one of the most polluted rivers in China.
The researchers suggest that the PCBs and PBDEs made their way to Pacific Ocean trenches through contaminated plastic debris and via dead animals sinking to the sea floor. These are then consumed by amphipods and other deep sea creatures.
The presence of PCBs and PBDEs in two of the deepest points on Earth is evidence of one of the many concerning traits of Persistent Organic Pollutants (POPs), which can travel great distances. These compounds generally do not dissolve well in water, but favour sticking to the surface of materials like plastic – tiny particles of which rain down onto the deepest parts of the ocean. When creatures mistakenly eat this colourful but toxic confetti, the POPs lurk in their fat tissues.
Whales are a common example of such toxicity from accumulation. These massive creatures become heavily polluted with PCBs because the ocean creatures they eat – fish, shrimp, plankton – contain some level of PCBs and PBDEs. And when whales and other sea creatures die, their POP-riddled bodies sink to the ocean floor – where deep sea crustaceans scavenge their remains.
Jamieson and his team are now working to understand the effects that these pollutants and toxins have on deep sea marine life. But the discovery of these pollutants is just one more example that our actions can have wide ranging – and very deep – effects.
