5 Gyres - Understanding Plastic Pollution Through Exploration, Education, and Action

The funny thing about knots is that they make plastic last longer at sea. It’s not uncommon to find only the knot from a degraded fishing net, or a knotted plastic bag shredded on all ends, but the knot stays intact. Our first sample from the 2011 expedition produced a handful of multi-colored confetti of plastic fragments and a knot. With the naked eye we did not see foamed plastic of thin films, just thick rounded fragments.

 Plastic fragments have a much lower surface area to volume ratio than foams or films. This is why we do not find Styrofoam cups or plastic bags in the middle of the gyres very often. Consumer items that stand out are toothbrushes, bottle caps, and soles of shoes. These are the products that by design happen to behave in the ocean like giant fragments. They are similar to the other large items we find from the fishing industry, like buoys with 1cm thick plastic walls, or hard plastic floats. These are the things designed to last whole in the ocean for a long time, and they do. When thin films or netting gets knotted, it reduces the surface area exposed to UV light, so it behaves like a fragment and degradation is slowed.

When we trawl we use a 300-micron mesh net, with holes smaller than your t-shirt, to skim the sea surface and capture micro-plastics. That’s where the thin films of polyethylene are, like what plastic grocery bags are made of. When we analyze our samples in the lab for plastic type, weight and count, we find that the numbers of plastic films are second only to the number of plastic fragments.

What’s important to note here is that although you may not here reports of your common everyday, single-use, plastic products floating in the ocean, it is likely still here as micro-plastic particles or chemically diffuse throughout the sea, unless it’s tied in a knot.

(Marcus Eriksen reports from the North Pacific Gyre, currently aboard the Sea Dragon with the Algalita Marine Research Foundation)