February, 2017 - A polluted abyss

Bruno Danis, Marine Biology Lab

Bruno Danis, should we be surprised to find man-made pollutants at the Earth's most extreme points, such as the Mariana Trench?

No, this is not surprising. PCBs are pollutants that persist in the environment and degrade over a long time. This means they are more likely to spread across the environment, including over long distances. For instance, PCBs were found in the Arctic. What is preoccupying is that we do not know what effects these pollutants -PCBs and others- have on ecosystems, because this subject is not well studied. Contaminants generally have effects at the sub-cellular level (e.g. by destabilising DNA), disrupt hormonal systems, and impact reproduction. At such great depths, however, biological processes occur slowly, and we believe toxicity does not affect deep-ocean organisms in the same way as in other habitats. Without knowing more about this environment, we cannot predict what the impact on its ecosystems will be.

How do pollutants reach such inaccessible places?

First, there are ocean currents, which can carry particles over large distances. Then, it can depend on the pollutant itself: for instance, different types of plastic degrade in different ways. Certain float, others sink, others break up into tiny particles. Finally, there is a constant flow of organic matter towards the bottom of the ocean: marine animals die and sink, and any pollutants their bodies may contain end up on the ocean floor.

You mentioned plastic, which is another problem: it seems like we are seeing more and more headlines about the ‘plastic patch’, or animals eating plastic.

The presence of plastic in the environment and its impact are widely publicised topics, and people tend to pay attention. Yet the actual effects of plastics on ocean ecosystems is another dark area in our scientific knowledge. We do know that plastic attracts all sorts of other hydrophobic pollutants; but are organisms affected by the plastic, by the other contaminants, or by both? This is an area of research that is unfortunately not well studied. During our next mission in Antarctica, we will begin an inventory of marine biodiversity, which will include a study of plastic in this environment that should be relatively untouched by human activity.

How can we limit this pollution?

There is no single solution: what we really need to do is reconsider our lifestyle, our consumption, and our relationship with nature. Why are we still producing and consuming so much plastic? Why not be more cautious, instead of creating pollution without knowing the consequences? Why is there no political agreement on this topic, like there was on climate or the ozone layer? If no policies are implemented, I fear this type of pollution will simply continue. As researchers, our duty is to document and identify problems as objectively as possible, and hopefully people will react. Still, I regret that there is no coordination of research on the environmental impact of plastic and other pollutants. And this is an important question, because while ecosystems can survive without humans, humans need ecosystems to survive.

The number of endangered species keeps growing: see graphics on the left.