microplastics in the ocean clean water and plastic pollution

Environmental

What Happens to Microplastics in the Ocean - and Why It Comes Back to Us

May 2026 7 min read ErasePlastic Team

The ocean covers 71 percent of the Earth's surface and produces half of the oxygen we breathe. It is also now estimated to contain over 170 trillion pieces of microplastic - and that number is growing every year. Understanding what happens to microplastics in the ocean matters not just for marine conservation, but for human health. Because the plastic that enters the ocean does not stay there. It moves through the food chain, enters the seafood on your plate, and cycles back into the water you drink and the air you breathe.

This article follows the journey of a microplastic particle from land to sea and back again - explaining where ocean plastic comes from, how it behaves once it enters the water, what it does to marine ecosystems, and why it is increasingly a human health issue as much as an environmental one.

Where Ocean Microplastics Come From

Around 80 percent of ocean plastic originates on land. It arrives via rivers, stormwater drains, and wind - carried from urban areas, agricultural land, and coastlines into the sea. Synthetic microfibers shed from clothing during washing are a major contributor, with studies suggesting laundry accounts for 35 percent of primary microplastic ocean pollution. Other sources include tyre wear particles washed off roads, microbeads from personal care products, and the fragmentation of larger plastic items that have been discarded in the environment.

Once in the ocean, plastic does not dissolve. It physically breaks down under UV light, wave action, and temperature change into progressively smaller pieces - from visible fragments to microscopic particles to nanoplastics measured in billionths of a metre. This process creates more particles, not fewer, spreading the contamination across an ever-wider area.

Science note: A 2023 analysis published in PLOS ONE estimated the total mass of plastic floating in the world's oceans has increased dramatically in recent decades, with the rate of accumulation accelerating since 2005 despite growing awareness of the problem.

How Microplastics Behave Once They Enter the Water

Plastic particles in the ocean do not simply float on the surface. Their behaviour depends on their density, size, and what attaches to them. Some plastics are denser than seawater and sink to the seafloor, where deep-sea sediment samples have recorded some of the highest concentrations of microplastics anywhere on Earth. Others remain suspended in the water column at various depths, where they are most accessible to filter feeders and small fish.

Microplastics also act as a magnet for persistent organic pollutants - toxic chemicals like PCBs, DDT, and flame retardants that bind to the plastic surface and accumulate at concentrations far higher than in the surrounding water. This means that when a marine animal ingests a microplastic particle, it may be ingesting a concentrated dose of chemical contamination alongside the plastic itself. The particles also colonise with bacteria and microorganisms, creating what researchers call the "plastisphere" - an entirely new ecological niche that can transport invasive species and pathogens across ocean basins.

plastic pollution washed up on beach from the ocean — Plastic that reaches the ocean fragments into microplastics that spread across the entire water column.

The Food Chain: How Ocean Plastic Reaches Your Plate

Marine plastic pollution enters the food chain at its lowest levels. Zooplankton - the tiny organisms that form the base of almost every ocean food web - have been found to ingest nanoplastics at rates that affect their ability to feed and reproduce. Small fish eat the zooplankton. Larger fish eat the small fish. With each step up the food chain, plastic particles and the chemicals bound to them can accumulate in tissues, a process called bioaccumulation.

By the time you eat a portion of shellfish, tuna, or salmon, some level of microplastic contamination is almost certain. Studies have detected microplastics in mussels, oysters, sardines, tuna, cod, and dozens of other species consumed regularly by people. A 2022 study found microplastics in every sample of seafood tested, including fish sold for human consumption in supermarkets. Sea salt, which is produced by evaporating seawater, has also been found to contain microplastics in samples from every country where it has been tested.

Science note: Research published in Environmental Science and Technology estimated that regular shellfish consumers may ingest up to 11,000 microplastic particles per year through seafood alone - not including exposure from other food, water, and air sources.

Microplastics in the Ocean and the Water Cycle

Ocean microplastics do not just re-enter humans through food. They also cycle back through the atmosphere. Research has shown that sea spray - the fine mist generated when waves break - carries microplastic particles into the air, where they can travel thousands of kilometres on wind currents before being deposited by rain. Studies have detected microplastics in rainfall in the French Pyrenees, the Rocky Mountains, and the Arctic - places with no significant local source of plastic pollution.

This means that ocean microplastics become airborne microplastics, which become terrestrial microplastics when they settle on soil and vegetation. The ocean is not just a sink for plastic pollution - it is a distribution mechanism, cycling particles back into every environment on Earth including the food we grow on land.

What Microplastics Do Once They Are in the Ocean Long-Term

The long-term effects of ocean microplastic accumulation are still being studied, but early findings are concerning. Coral reefs, already stressed by warming and acidification, show reduced feeding and increased bleaching when exposed to microplastics. Phytoplankton - which produce roughly half of Earth's oxygen through photosynthesis - have been shown to have impaired reproduction when exposed to plastic leachates in laboratory conditions. If phytoplankton populations are affected at scale, the implications extend far beyond ocean health.

At current rates of plastic production and disposal, researchers project that the concentration of plastic in the ocean will continue to increase for decades even if all plastic pollution stopped today, because of the volume already in the environment fragmenting into ever-smaller pieces. The plastic already in the system is not going away on any timescale meaningful to human life.

The Bottom Line

Ocean microplastic pollution is not a distant environmental problem - it is a cycle that connects the plastic we discard on land to the seafood on our plates, the water in our taps, and the air we breathe. The ocean acts as both a destination and a distribution system for plastic, spreading contamination across every ecosystem on Earth. Reducing what enters the ocean in the first place - through better waste management, fewer single-use plastics, and smarter product choices at home - remains the most effective lever we have. The ocean cannot clean itself of what is already there, but we can stop adding to it.