Every plastic bottle, synthetic shirt, and food wrapper eventually becomes something smaller. Not through disappearance, but through fragmentation—breaking into pieces so tiny they become invisible to the naked eye while remaining stubbornly present in the environment.

These microplastics, defined as particles smaller than five millimetres, have now been detected in every environmental compartment scientists have examined. They're in Arctic sea ice, deep ocean sediments, mountain air, and agricultural soils. More troublingly, they're in the fish we eat, the water we drink, and the air we breathe.

Tracing how plastic moves from your washing machine or the local landfill into your bloodstream reveals a contamination pathway that modern toxicology is only beginning to understand. The journey is complex, involving environmental chemistry, food web dynamics, and cellular biology—but the endpoints are becoming clearer with each new study.

Plastic doesn't biodegrade in any meaningful timeframe. Instead, it photodegrades—breaking apart when ultraviolet radiation from sunlight attacks the polymer chains that give plastic its structure. This process creates progressively smaller particles without actually destroying the material.

UV exposure causes oxidation, which makes plastic brittle and prone to mechanical fragmentation. Wind, waves, and physical abrasion then shatter these weakened materials into microplastics, and eventually into nanoplastics smaller than one micrometre. The fragmentation is essentially irreversible under environmental conditions.

Synthetic textiles represent a particularly efficient fragmentation source. A single wash cycle can release hundreds of thousands of microfibers from polyester, nylon, and acrylic clothing. These fibres are too small for many wastewater treatment plants to capture, passing directly into rivers and oceans. Studies estimate that textile washing contributes roughly 35% of primary microplastics entering marine environments.

Tire wear particles constitute another major source, often overlooked. As vehicles brake and accelerate, tires shed microscopic rubber fragments containing synthetic polymers and chemical additives. These particles wash into storm drains during rainfall, eventually reaching waterways. Urban areas can contribute thousands of tonnes of tire microplastics annually to nearby aquatic systems.

Takeaway

Plastic doesn't disappear—it disperses. Fragmentation multiplies the number of particles while expanding their reach into environments the original product never touched.

Microplastics enter food webs at their base. Zooplankton and filter-feeding organisms consume particles that resemble their natural food sources. Mussels, oysters, and other bivalves are particularly effective at concentrating microplastics because they process enormous volumes of water to extract nutrients.

Bioaccumulation occurs as these particles move up trophic levels. Small fish eat contaminated zooplankton; larger predatory fish eat the small fish. By the time a tuna or swordfish reaches your plate, it may carry microplastics from hundreds of prey organisms. Studies have found microplastics in over 800 marine species, including many consumed by humans.

Terrestrial food chains face similar contamination. Agricultural soils receive microplastics through sewage sludge application, plastic mulch degradation, and atmospheric deposition. Earthworms and soil organisms ingest these particles, potentially transferring them to crops. Research has detected microplastics in vegetables, with root vegetables showing particularly high concentrations.

Drinking water provides another direct exposure route. Bottled water consistently shows higher microplastic counts than tap water—likely from packaging degradation. A 2018 study found an average of 325 plastic particles per litre in bottled water across major brands. Even tap water contains detectable levels, with concentrations varying by source and treatment method.

Takeaway

Microplastics don't stay in one place—they ride food webs like escalators, concentrating as they climb from plankton to apex predators, including us.

The toxicological picture is emerging but incomplete. Microplastics have been detected in human blood, lung tissue, placental tissue, and stool samples. A 2022 study found plastic particles in 80% of blood samples tested, with PET and polystyrene appearing most frequently. The question is no longer whether we're exposed, but what that exposure means.

Particle size matters enormously for biological effects. Nanoplastics can cross cellular membranes that exclude larger particles, potentially entering organs and even individual cells. Animal studies show that nano-sized particles accumulate in liver, kidney, and brain tissue, triggering inflammatory responses and oxidative stress.

Chemical additives complicate the toxicity assessment. Plastics contain plasticizers, flame retardants, UV stabilizers, and other compounds that can leach into surrounding tissues. Bisphenol A and phthalates—both endocrine disruptors—are common plastic additives. When microplastics enter the body, they may deliver concentrated doses of these chemicals directly to tissues.

The scientific uncertainty shouldn't be mistaken for safety. Current evidence suggests potential links between microplastic exposure and inflammatory bowel conditions, cardiovascular effects, and reproductive impacts. Research is constrained by detection limits for smaller particles and the difficulty of establishing causation in human populations with universal exposure.

Takeaway

We've moved past the question of whether microplastics reach human tissues—we're now investigating what they do once they arrive.

The pathway from consumer product to cellular exposure follows a logic that environmental toxicology is designed to trace. Fragmentation creates the particles, environmental transport distributes them, food webs concentrate them, and biological uptake delivers them to tissues.

What makes microplastic contamination particularly challenging is its diffuse nature. There's no single source to regulate, no single exposure route to block. The contamination is systemic—woven into how we produce, use, and discard materials.

Understanding these pathways doesn't immediately solve the problem, but it clarifies where interventions might work. Reducing plastic production at source, improving textile design, capturing particles at wastewater plants, and limiting food chain entry all become visible as leverage points once the contamination pathway is mapped.