Ask a fifth grader how long it takes for a plastic bag to decompose and the likely answer is 1,000 years. Grocery stores tout similar information on recycling bins outside their entrances. Many people mistakenly believe that, given enough time, not just bags but all plastics degrade completely. Plastic decomposes into smaller and ever smaller pieces, but out-of-sight does not mean out-of-existence. With few exceptions, the plastics produced in the last 60-70 years will last for hundreds of thousands of years, and sea turtles and other marine organisms will be facing the consequences.
Light weight, versatility, strength, ease of production, and relatively low cost make plastics such as acrylic, nylon, polyethylene, polypropylene, and styrofoam attractive for many uses. Most plastics are petroleum-based; they consist of simple polymers, molecules of carbon and hydrogen that link together to form chains. In the 1930s Bakelite emerged as the first man-made plastic, but plastic manufacturing did not develop until after World War II. Since then, one billion tons of plastic have been produced, the equivalent of 1,030 commercial airplanes.
Discarded plastics threaten wildlife and ecosystems everywhere, but the dangers are greatest in the oceans. Astoundingly, more than 80% of the enormous quantities of plastics at sea were disposed of on land. Plastics wash up on beaches around the world every day, with even the most remote areas affected. Transported by currents and ocean gyres, plastic debris is often concentrated. Seven major tropical ocean gyres of trash, more than 90% of which is plastic, have been identified in the last several decades, including the 10 million square mile Great Pacific Garbage Patch (North Pacific Subtropical Gyre) between Hawaii and California. Unfortunately, floating debris is literally the tip of the plastic iceberg. In some parts of the Great Pacific Patch, trash is also found many feet below the surface.
Considerable attention has been focused on the threats of marine debris associated with marine wildlife entanglement, injury and death as well as the ingestion of plastic for food, such as albatross chicks and sea turtle hatchlings that die from intestinal blockage or starvation because their bellies are full of plastic. These are compelling dangers, but the worst threats from decomposing plastics in the oceans are less obvious.
The raw materials of plastic manufacturing are called “nurdles,” little plastic cylinders (two millimeters tall) that are melted during manufacturing. At sea, nurdles and degrading plastic fragments attract and strongly concentrate resilient poisons like DDT, PCBs (polychlorinated biphenyls), and other toxins. PCBs, which make plastic more pliable, disrupt hormones and interfere with natural functions like reproduction. When nurdles are eaten by jellyfish and salps, the most abundant filter feeders in the oceans, which in turn are eaten by higher predators, they move up the food chain. For long-lived species like sea turtles, plastics in the food chain can only have adverse consequences.
In recent years, biodegradable plastics have received attention. These products are manufactured from natural plant sugars, like those found in corn, and are broken down by bacteria. Consumers should carefully read labels because some so-called biodegradable plastics do not break down completely. Biodegradable polyester has also been developed from bacteria, and research continues. Using corn to produce biodegradable plastics affects human food production and resource use directly and indirectly.
So what is the future of plastic in the 21st Century? Will we develop and use biodegradable plastics widely? How many thousands of years will it take for bacteria to evolve to consume the plastics made to date? As research continues, let’s hope for a positive change and do our best to use and discard plastics wisely.