Plastic has been one of the most useful inventions of the twentieth century. It is light, durable, inexpensive to produce, and can be shaped into nearly any form. Modern life would be almost impossible without it. Medical equipment, packaging, electronics, construction materials, and countless household items depend on plastic in ways that previous generations could scarcely have imagined. Yet this remarkable material has also created one of the most troubling environmental problems of our time, particularly in the world's oceans.

Each year, an estimated eight million tons of plastic enter the oceans. Some comes from ships and fishing operations, but most arrives from land—washed down rivers, blown by wind from poorly managed waste sites, or deliberately dumped. Once in the sea, plastic does not decompose in the way that organic materials do. Instead, sunlight and waves gradually break it into smaller pieces, eventually producing microscopic particles that spread throughout the marine environment. Plastic that entered the ocean decades ago still persists, and continues to be broken down into ever smaller fragments.

The consequences for marine life are substantial. Sea turtles mistake floating plastic bags for jellyfish and swallow them, sometimes with fatal results. Seabirds feed plastic fragments to their young, mistaking them for food. Large mammals, including whales, have been found dead with stomachs full of plastic debris. Microscopic plastic particles are now consumed by fish and other creatures throughout the food chain. The full effects on marine ecosystems are still being identified, but the early evidence is alarming.

Concern is also growing about effects on human health. Plastic particles have been detected in seafood that humans consume, in drinking water, and even in the air we breathe. Studies have begun to find these particles in human blood and tissue. Whether they cause measurable harm is not yet fully understood, but researchers anticipate that the long-term consequences could be significant. The chemicals used in plastic production, some of which interfere with hormonal systems, raise additional concerns when these particles enter our bodies.

The accumulated plastic in the oceans has formed enormous concentrations in certain regions. The largest of these, sometimes called the Great Pacific Garbage Patch, covers an area roughly three times the size of France. Despite the name, it is not a solid floating island but rather a vast expanse of water containing plastic fragments distributed at varying densities. Cleaning such accumulations is extraordinarily difficult. Most of the plastic is too small to collect efficiently, and what remains continues to fragment.

Several responses have emerged. Many countries have banned or restricted single-use plastic items such as bags, straws, and packaging. Some have established systems to collect plastic before it reaches the ocean. Innovative technologies have been developed to capture floating plastic, though the cost is high and the impact, so far, modest. The most effective interventions appear to be those that reduce the production of unnecessary plastic in the first place. Once plastic enters the environment, removing it is enormously expensive and only partially successful.

Yet the problem cannot be solved by individual nations alone. Plastic flows across borders with the currents, and waste produced in one country can contaminate the coastlines of another. International cooperation has been developing, though progress has been slow. Companies that produce plastic and the products that contain it have substantial responsibility for the problem, and there is increasing pressure on them to design materials that can be recycled or that decompose more readily. Some progress has been achieved, but the volume of plastic produced continues to grow.

Perhaps the most important change is psychological. For decades, plastic was treated as essentially free—an inexpensive material that could be discarded without consequence. The recognition that this assumption was mistaken, and that plastic carries significant hidden costs, is gradually altering how individuals, companies, and governments think about the material. The plastic in the oceans cannot easily be removed; what may be possible is to prevent further damage by changing the patterns of production and consumption that produced it. Whether humanity can make these changes quickly enough to preserve healthy marine ecosystems remains genuinely uncertain.