Home, plastic home

We live in an increasingly plastic world. Much of this plastic does not degrade easily. That allows it to pollute the environment. There, a great deal of trashed plastic will break into tinier bits that eventually wash into the ocean. Recently, this debris has begun creating new homes for microbes, research now shows.

Plastic trash in the ocean hosts a diverse world of one-celled organisms, observe Erik Zettler, Tracy Mincer and Linda Amaral-Zettler. The three work at the Woods Hole Oceanographic Institution and Marine Biological Laboratory, both in Woods Hole, Mass. They have given a new name to microbes and their plastic homes: the plastisphere (PLAS ti sfeer).

Microbes in the plastisphere tend to differ from those in the open water, Zettler’s team finds. In fact, the researchers conclude, “that plastic serves as a novel ecological habitat in the open ocean.” They shared their new data July 2 in Environmental Science & Technology.

There’s a lot of trashed plastic to be colonized by germs. People began widely using plastics only a little more than 60 years ago. Since then, the production of plastics has only increased. Each year, manufacturers now make another 245 million tons of plastic. That’s about 35 kilograms (77 pounds) for each man, woman and child on the planet, Zettler’s team observes. It’s also close to the weight of all people alive today.

This plastic isn’t evenly distributed throughout the ocean. Much of it collects at a few distinct sites known as gyres (JI erz). That’s where the Woods Hole researchers sampled for microbes. They netted small pieces of plastic and then analyzed these floating bits of trash for microbes. They focused on bacteria.

The researchers also sampled nearby seawater from outside a gyre.

Some bacteria were rod-shaped. Others were round. And some one-celled predatory microbes were shaped like a stalk with grasping, threadlike arms. Many microbes look pretty similar. So the biologists separated the germs into types by looking at their DNA. This molecule contains the genes that make one species distinct from another.

Many ocean microbes have not yet been formally identified by species (or DNA details). So most germs living in the plastic debris could only be classified as belonging to some basic type. The researchers found that a single tiny bit of plastic might host more than 1,000 different types of one-celled microbes.

Much of the ocean plastic belonged to two common types: polyethylene and polypropylene. The first is lightweight but tough and has a fairly slick surface. The second is stiffer and more scratch resistant. Roughly 30 percent of the microbes collected were found on both types of plastic. The remainder of the collected germs inhabited just one or the other type of plastic, not both. One suspected reason: Some microbes appeared to be eating away at the plastic, and not all may have an appetite for the same entrée.

Another potential reason for the microbes’ pickiness: Some like to hang out with certain other types. Together, they form slimy communities known as biofilms.

Vibrio bacteria were among those germs identified on ocean plastic. Some Vibrio bacteria can cause disease (such as cholera) in animals, including people. This suggests that ocean plastics could help transport harmful germs, the scientists note. And because plastic lasts longer than plant- and animal-based materials, it may ferry harmful germs thousands of kilometers from coasts. Sea turtles, birds and fish in the open ocean may mistake the plastic for food bits and become infected by the germs they carry.

One surprise from the study: Some of the microbes found on the plastic debris are normally only seen floating in the open ocean. Scientists thought these germs would not stick or attach to things like sediment or these plastic bits — until now.

What really makes plastic debris in the ocean dangerous is the poisons it may ferry, says Anthony Andrady. A plastics specialist at North Carolina State University in Raleigh, he did not work on the new study. “In the ocean,” he explains, “plastics act like a sponge.” That means they can absorb and concentrate certain toxic pollutants, including pesticides.

Indeed, several years ago, João Frias collected bits of polystyrene (another type of plastic) and polypropylene from beach sand. Frias works at the Institute of Marine Research at the New University of Lisbon in Caparica, Portugal. “Every sample was contaminated,” he recalls. The plastic bits hosted a range of hard-to-degrade pollutants — many of them harmful. These included the long-banned pesticide DDT and polychlorinated biphenyls (also known as PCBs). Chemical wastes produced by sooty fossil-fuel burning were also found.

Animals, including people, do not naturally produce the chemicals needed to digest plastics. So most plastics should not, on their own, be very toxic to sea life, says Andrady. The problem, he says, will likely come from any pollutants that taint plastics at sea.

Zettler’s team now adds another warning: Harmful germs may pose another major threat to animals that mistake plastic for food.

Power Words

biofilm A gooey community of different types of microbes that essentially glues itself to some solid surface. Living in a biofilm is one way microbes protect themselves from stressful agents (such as poisons) in their environment.

cell The smallest structural and functional unit of an organism.

debris Waste or trash usually having no value and often polluting the environment.

DNA A spiral-shaped molecule inside most living cells that carries genetic instructions. These instructions tell cells which molecules to make.

ecology A branch of biology that deals with the relations of organisms to one another and to their physical surroundings.

gyre (as in the ocean) A ringlike system of ocean currents that rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. Many of the biggest, most persistent gyres have become collection sites for floating long-lived trash, especially plastic.

habitat The natural home or environment of an animal.

marine Having to do with the ocean world or environment.

plastic Any of a series of materials that are easily deformable; or synthetic materials that have been made from polymers (long strings of some building-block molecule) that tend to be lightweight, inexpensive and resistant to degradation.

polyester A synthetic material used chiefly to make fabrics.

species A group of similar organisms capable of producing offspring that can survive and reproduce.