By Russel Barsh and Madrona Murphy

Annual world production of plastics exceeds 300 million tons and continues to grow. That’s about 100 pounds of new plastics per year for every human on earth.  Of course, plastic use is not evenly distributed.

People in North America, Europe and Japan consume about two-thirds of the world’s plastics. Even in wealthy countries, less than half of the plastic produced is recycled.

The rest is destined for landfills, officially; but a great deal of it ends up in the oceans. No one can say just how much or how it gets there. Illegal dumping almost certainly accounts for more than half of it.

The fate and impact of marine plastic debris depends a great deal on the types of plastics that are involved. To a chemist, we are talking about “thermoplastics,” materials that soften and flow when heated, so they can easily be molded. Most thermoplastics are polymers simply composed of carbon, hydrogen and oxygen, although other compounds or metals are added to them to alter their elasticity, strength, stability or color.

Five polymers account for nearly all thermoplastics in use today. Polyethylene is manufactured from petroleum and is a bit less dense than water, so it floats. Low-density PE is used in food wrapping and plastic bags; high-density PE is used for home insulation (Tyvek) among other things. Sunlight slowly de-polymerizes PE and bacteria metabolize it into carbon dioxide and water.

Polypropylene, used for packaging, textiles and bottles, is manufactured from natural gas. Like PE, PP floats and slowly breaks down into carbon dioxide and water. Both PE and PP are easily recycled.

Polystyrene, used in disposable utensils, jewel cases, Styrofoam cups and packing peanuts; and polycarbonate, used in CDs, electronics and windows; are denser than water and tend to sink unless “puffed up” with air. They are relatively stable and do not degrade in the environment, just abrade into smaller and smaller pieces, producing plastic sand.

In last place is polyvinyl chloride or PVC used extensively for plumbing. It sinks and is very stable chemically, but if burned it releases carcinogenic dioxins. PS, PC, and PVC are not often recycled, and tend to account for a disproportionate amount of micro-plastic debris.

Significant accumulations of plastic debris can be seen on some south-facing San Juan County beaches, deposited by high storm tides and winds. With the help of Marta Branch, her high school class, and Orcas intern Quinn Freedman, we studied the plastic “midden” on the public beach at Eastsound in summer 2012.

Although thousands of pre-consumer plastic pellets (nurdles) were recovered, most of the plastics we sifted from the sand and woody debris were post-consumer: bags, candy wrappers, bottles, housewares, and an astonishing variety of fibers from clothing and other textiles – exactly what would be expected in a landfill. Candy wrappers and bottles enabled us to determine that some of the plastic debris had been thrown away as early as the 1960s.

The impact of marine plastic debris on wildlife remains unclear. Entanglement in fishing lines, netting, and beer

can plastic rings accounts for most documented deaths due to encounters with plastic. Some species of seabirds and sea turtles ingest large quantities and variety of plastic debris, but direct evidence of widespread mortality is limited so far to Skuas, a family of gull-like marine birds that may prey preferentially on some plastics.

Sea turtles ingest a wide range of debris, including plastics, all of which may retard their growth by “diluting” their diet with indigestible gut packing. By contrast, our researchers have found plastics in only a handful of over two thousand juvenile salmon we have gut lavaged since 2008, and only one  of hundreds of otter scat we have examined.

It is fair to say that any species that routinely mistakes plastic debris for food will suffer dietary dilution to some degree, whether or not it is fatal.

Scientists also suspect that plastic debris is rich in toxic chemicals it has “scrubbed” out of seawater.

In our Kwiaht laboratory we use a PP fabric to extract pollution from seawater for testing; the fabric absorbs several times its weight in oil and oily contaminants. Plastic debris may not kill wildlife outright, but condemns animals that ingest it to unhealthy, shorter lifetimes.

Regardless of its toll on wildlife, marine plastic debris is evidence that we make more plastic than we can afford to dispose of. If disposal costs were included in pricing plastics, we would probably use less and recycle more of it.

It would also make the fast-degrading polylactide family of thermoplastics more attractive. Manufactured from sugar or starch rather than petroleum, PLA can be composted safely.

And there is ordinary glass, which is manufactured from sand and when disposed in the environment eventually becomes … sand.