June 23, 2010

By Tyson Bottenus

I was in the lab Saturday performing a "100 count" when I ran into something bizarre. A "100 count" is a test we perform after every neuston tow where we quantify a random sample of one hundred zooplankton to get an idea about the biodiversity in the area we're sailing through. For a geologist like me, it's a great way to bulk up on my marine biology. I've become adept at identifying copepods, ostracods, phroenemid amphipods (the organism the Alien films are based on), and shrimp larvae.

But last night I found something I wasn't expecting. It was microscopic, angular, and translucent. When I prodded it, it broke into even smaller pieces. I asked Skye Moret, the scientist on watch, to help me identify what was under my microscope. She told me that it was no doubt a piece of plastic.

I took my eye off the microscope and looked down at the Petri dish. I couldn't pick out the piece of plastic I had just seen. It was that infinitesimal. Micrometers in size – smaller than a pencil dot – it had gone undiscovered by the crew who had painstakingly extracted dozens of plastic bits from the filtered remains of the neuston tow. I asked Skye if we should include this piece of plastic in our tow data. She said no, it was just too small.

So this is what happens, I thought, when plastic breaks down. I continued counting zooplankton, hoping I wouldn't see any more plastic.

I remember the first field trips with my university's geology department where we learned about how our state's granite bedrock made up the surrounding beaches. Source rock broke down into cobble, which reduced to coarse-grain sand, which further reduced to the fine-to-medium grain sand we typically find on the shoreline. That sand, if subjected to enough mechanical force, would eventually break down to clay and silt particles, too tiny to really see.

Plastic, as we've seen along our cruise track, never really biodegrades but it does photodegrade – breaks down from the damaging rays of the sun – when it floats along in the North Atlantic subtropical gyre. The physical force of water assists sunlight in fracturing plastic into smaller pieces. While the plastic breaks down, the synthetic polymer never unwinds. Other researchers have found that filter feeders like quahogs and mussel clams are prone to digesting these Lilliputian bits of plastic.

So just how much plastic is there really in the ocean? As scientists, we can only count what we see with our naked eye and our instruments, but the microscopic world suggests the problem is far worse than we can measure.