What Happens When Plastic Reaches the Ocean?

Plastic does not go away when you stop thinking about it.

Most people know that plastic ends up in the ocean. Images of floating debris and entangled wildlife have made that visible enough. What is less understood is what happens next. The piece of plastic that reaches the ocean does not simply stay as it is. What it becomes is harder to see, harder to measure, and significantly harder to address than the original object.

Plastic in the ocean does not go away. It goes smaller.

The Journey Before the Water

Most plastic entering the ocean comes from land-based sources, including inadequately managed waste, urban runoff, stormwater systems, and rivers. During rainfall, plastic litter can be carried through stormwater systems and waterways toward the coast, depending on local conditions.

Once in the ocean, plastic begins a process that is the opposite of disappearing.

Fragmentation: From Visible to Invisible

In the ocean, ultraviolet light from the sun and the mechanical action of waves begin to break plastic down. Large items become smaller items. Smaller fragments can become microplastics, particles of plastic generally defined as smaller than five millimeters. Plastic can also fragment into even smaller particles known as nanoplastics, generally described as particles smaller than one micrometer and too small to be seen with the naked eye.

This process does not eliminate the plastic. It distributes it. Microplastics and nanoplastics have been detected throughout the ocean, from the surface to the deepest seafloor. Research published in 2020 described what scientists at the time called the highest concentration of microplastics ever recorded on the ocean floor, a finding that surprised the research team because the expectation had been that deep-sea environments would be comparatively less affected.

The Great Pacific Garbage Patch is not a solid island of plastic. It is a large area of concentrated marine debris, much of it consisting of small plastic fragments and abandoned fishing gear, distributed across the surface and upper layers of the ocean. Its estimated area is much larger than many people imagine, although its exact extent varies because the debris is dispersed rather than contained.

Into the Food Chain

Marine organisms cannot reliably distinguish microplastics from food. Plankton, which form the base of virtually every marine food chain, have been documented ingesting microplastic particles. Microplastics can move through food webs when organisms ingest them, creating opportunities for exposure across different levels of marine ecosystems. Scientists are still studying how these particles move through organisms and how long they remain in different tissues.

A study published in the journal Proceedings of the Royal Society B found that anchovies are attracted to the smell of plastic debris that has spent time in the ocean, because organic matter colonising the plastic surface creates an odour similar to food. The researchers noted that anchovies are eaten by whales, sea lions, seabirds, and people, making this a pathway of broader ecological concern.

Sea turtles are among the marine animals known to ingest plastic. Some species can mistake floating plastic bags and other debris for prey, while other plastics may be consumed accidentally while feeding.

What Cannot Be Undone

Once microplastics enter the environment, they can persist for extremely long periods and are very difficult to remove. Collection efforts can address visible floating debris at the surface. They cannot effectively remove the particles dispersed through the water column or settled in deep seafloor sediments.

This is not a reason for inaction. It is a reason for understanding that plastic not yet in the ocean is vastly more recoverable than plastic already there.

Reducing plastic at the source is one of the most effective ways to limit the amount of new plastic entering marine environments. Every reusable alternative can reduce demand for another disposable plastic item and, in turn, reduce the amount of plastic entering the waste stream. Stainless steel straws, reusable mesh bags, and beeswax wraps are practical examples of reusable alternatives that can help reduce reliance on disposable plastic.

The ocean is not a destination. It is a consequence.

Sources and Further Reading

• United Nations Environment Programme (UNEP)
• National Oceanic and Atmospheric Administration (NOAA)
• Intergovernmental Panel on Climate Change (IPCC)
• Proceedings of the Royal Society B
• Marine Conservation Society

Want to keep reading?

What Happens to Food Waste After You Throw It Away?

The Case for Cooking Without Plastic Touching Your Food