Cheap to make, durable, and handy to use, plastic, polymers are ubiquitous throughout our world. In the past half-century, they have become the optimal material for packaging and preserving and have been molded into millions of different products. Their very permanence, however, also is their biggest drawback. Relatively speaking, plastics are forever. Since the oceans are "downhill" from virtually all mankind's activities, the sea is the final resting place for tens of millions of tons of lost and dumped plastics.
Most research on the effects and fate of marine plastic wastes has been done in the North Pacific Gyre, the immense clockwise current that characterizes this region. This work is in its earliest stages, but published reports paint a troublesome picture. And what has been found here gives an indication of conditions in the rest of the World Ocean.
Manufactured items are the greatest source of debris. There also are preproduction plastic resin beads and pellets found in the sea and along coastlines. The raw materials from which products are made, they get into the oceans through at-sea loss of shipping containers or by being flushed from land by runoff from manufacturing plants. Particle count varies by location, but studies have found that between 6% and 20% of waste is from this source.
Plastic polymers in the ocean are both inert and long-lived. They do not biodegrade like most other marine wastes. They do, however, photodegrade when exposed to solar radiation. This and the movements of the seas result in most plastic items being reduced to very tiny particles. The smaller particles are found throughout the water column, though most are concentrated in the upper 100 feet. Since about half of all manufactured plastics are heavier than water, they sink to the bottom, where they enter the sea and are not affected by photodegradation. Their presence has a negative effect on the seafloor biota.
There are three major problems caused by marine plastic debris. First is entanglement of birds, mammals, and fish. This is primarily a problem caused by fishing nets and lines that have been dumped or lost in the sea. Many keep on fishing. It is estimated that entanglement claims the lives of hundreds of thousands of marine mammals and seabirds each year.
A second problem is indigestion, that is, these materials have no nutritional value and cannot be readily eliminated by living organisms that mistake them for food. Filter feeders such as jellyfish, clams, and oysters concentrate these materials in their bodies, reducing their ability to take in nutrients from the waters around them. This also is the case with some fish, seabirds, and turtles. Many of these animals gulp down the plastics and, feeling full, reduce their feeding activities. This can lead to eventual starvation with a full stomach.
The third problem has the most serious consequences for life in the oceans: smaller plastic materials in the sea act as an ideal substrate to concentrate toxic materials such as PCB and DDT compounds. Scientists have estimated that plastics have the ability to hold a million times more of these toxic substances than an equivalent volume of seawater. When these bits are ingested by animals, they get a massive dose of these toxins. Researchers have found this can result in biological damage that affects reproduction and the health of offspring and may even cause mutations. If these animals are in the food chain leading to eventual consumption by humans, even more concentration occurs. This seafood is far from healthful.
These materials are everywhere and increasing in volume. They are essentially man-made plankton. Some research has shown that in the North Pacific Gyre the weight of this "plankton" is six times greater than the natural biomass of Zooplankton. Recent studies have estimated that the amount of plastics going into the World Ocean has tripled in the past ten years. And the rate of increase is accelerating.
What can be done? Stopping deliberate dumping is a good place to begin. Human nature, however, suggests that a 100% reduction is unlikely. Concurrent with international education and regulatory efforts, there should be global agreements to require most plastics to be biodegradable in the marine environment.
This is not an impossible dream. Some manufacturers now make plastics that are serviceable for intended use and then break down in a natural environment on land, with many requiring the heat of a compost pile to begin degradation. Japanese researchers, for instance, have developed biodegradable CDs and DVDs using polymers from com. Cooler ocean temperatures, however, significantly retard the degradation process in most compostable plastics produced today—so more work is needed to develop marine-degradable plastics.
The plastic ocean should not be a permanent feature of our planet.