Microplastics have entered the ocean and become a major environmental problem; they are plastic fragments less than five millimeters in size that come from the fragmentation of larger objects or are manufactured at that size for domestic and industrial uses. Its persistence, its tiny size and its ability to travel through water and air explain why they are already present from the coast to the deep ocean.
We are talking about a global problem of enormous complexity that cannot be solved with a simple glance at the surface: Degradation by sun and waves breaks the plastics into increasingly smaller pieces.Invisible to the naked eye, they are capable of entering organisms, binding to pollutants, and traversing entire ecosystems. Although the most notable effects of macroplastics are well known (entanglement, suffocation, injuries), the impact of microplastics requires specialized techniques and a science that is still fine-tuning its measurement tools.
What exactly is the problem?
The rampant production and consumption of plastics, combined with poor waste management, push millions of tons into rivers, sewers, and later, the sea. It is estimated that between a few million and more than ten million tons reach the ocean each year., and various estimates speak of tens of trillions of microplastic particles floating in the planet's waters.
Once in the marine environment, these particles enter the food web. Plankton can ingest them and, by taking up space in their digestive tracts, cause malnutrition and reduce food availability for higher levelsFilter-feeding mollusks, fish, and even large marine mammals mistake microplastics for food or inhale them through the water; the consequences range from physical obstructions to more subtle sublethal effects.
In addition to mechanical damage, microplastics act as taxis for hazardous substances: They can adsorb toxins, heavy metals and petroleum derivatives, transport pathogenic microorganisms, and release the polymer's own additives. This combination of risks complicates the assessment of the impact on organisms and human health, which is still under investigation.
Where they come from and why they reach the sea
Experts distinguish two main sources: primary and secondary microplastics. Primary ones include cosmetic microspheres, exfoliants or industrial abrasives.Secondary wastewater is generated by the degradation of larger products such as packaging, textiles, or tires. Each wash releases synthetic microfibers into wastewater, and urban wear and tear from traffic contributes particles that rain carries into waterways and, ultimately, to the coast.
Current waste management is not up to par. On a global scale, only a fraction of the plastic produced is recycled, another part is incinerated, and Most of it ends up in landfills or dispersed in the environmentEven throwing a bottle into a bin can be scattered by wind or storms; from poorly sealed landfills or sewage systems, waste travels through rivers to the sea. It is estimated that around 80% of marine litter comes from land and 20% from maritime activities, including accidental or deliberate dumping from vessels.
The magnitude of the problem is staggering: international reports have cited figures of around 15–51 trillion fragments in the oceans, while other estimates suggest as many as 50 trillion. These are numbers that far exceed the number of stars in the Milky Way., a metaphor that helps to understand the scale, although not all of that plastic is visible to the naked eye.
Small, ubiquitous and harmful
The most surprising part for anyone who gets on a boat on the high seas is that you won't see compact "islands" of garbage. What there is, above all, is a scattered soup of microfragments, concentrated by currents in the subtropical gyres, but without forming continuous masses. Large objects exist and are problematic, yes, but the tiny fraction is what permeates the water column and maximizes contact with marine life.
Studies with mussels, fish and other organisms show that small particles They can adhere to gills, block filtering organs or lodge in the digestive system.Beyond the physical blockage, behavioral changes, reduced fertility, and effects on offspring development have been observed in association with exposure to chemicals associated with plastic.
In parallel, there are indications that our exposure is habitual: human beings ingests or inhales microplastics through food and airAlthough the evidence on the effects on human health is still growing, it makes sense to reduce the amount of plastic entering the environment and, with it, the potential risk throughout the food chain.
How to measure what cannot be seen
Quantifying microplastics is technically difficult. Traditional nets fail to capture the smallest particles: Below 0,3 mm, they retain virtually no particles, and those around hundredths of a millimeter require very fine filters and laboratory analysis. Between 0,005 mm and 0,3 mm, there is still methodological debate and identification challenges.
To recognize the nature of the polymer, infrared (IR) spectroscopy is key. This technique “reads” the chemical fingerprint of the plastic and allows us to distinguish, for example, whether a fragment comes from polyethylene, polystyrene, or cosmetic microspheres, associating it with specific sources. Optical microscopy helps locate particles, but without IR, identification can be ambiguous.
In the field, low-cost sampling and networks or pumps that filter large volumes of water are used. Recent oceanographic projects have refined sampling down to 0,03 mm., opening a window into a previously overlooked fraction and revealing higher-than-expected concentrations in remote areas of the globe.
What the latest ocean data tells us
During a round-the-world sailing trip, scientific teams aboard racing yachts collected daily samples using a filter system for particles between 0,03 and 5 mm. The result was conclusive: all samples contained microplastics., with averages of thousands of particles per cubic meter and very high peaks near regions such as the South African area or the edge of the English Channel.
Using these more sensitive methods, average values close to 4.800 particles/m³ and point concentrations exceeding 26.000 have been detected. Europe appears with several "hot spots", including the Balearic Sea or the waters of the North Sea, which underlines that pollution is not exclusive to developing regions or specific urban areas.
Beyond how many there are, it matters what type they are: on average, in those campaigns 71% turned out to be microfibers, tiny threads of polyester and other textile polymers that reach the environment through washing machines, dryers, daily use of clothing, abandoned textiles or lost fishing gear.
Distribution: not only surface, but also depth
The idea that plastic "floats" and the problem is primarily superficial is outdated. Sampling at nearly 2.000 stations at different depths has shown that Small microplastics (1–100 μm) dominate in number and are distributed more homogeneously in the water column than large fragments, which tend to accumulate on the surface and bottom.
On continental shelves, closer to emission sources, medians of around 500 particles/m³ have been recorded, about 30 times higher than the high seasToward coastal depths, the concentration decreases rapidly, probably due to sinking facilitated by biogeochemical processes such as diatom adhesion or the precipitation of minerals that weigh down the particles.
In the open sea, the accumulation in oceanic gyres is confirmed, with hundreds of particles per cubic meter of median and stations exceeding 10.000, although This does not imply solid masses visible from the side.The term "islands" can be misleading: what exists is a mosaic of small, scattered, and persistent pieces.
The vertical nature of the problem is even more striking: more than 2.500 microplastics have been measured in the Arctic, and significant concentrations at 6.800 meters at the beginning of the Mariana Trench. Layers of different densities (pycnoclines) act as traps for certain sizes, and below 1.000 meters, in the bathypelagic stratum, the water is barely renewed for centuries, which makes these particles very long-term visitors.
Plastics and the carbon cycle: a disturbing connection
The carbon in plastic is fossilized, and its traces are already being detected in the ocean. Dozens of polymer formulations have been identified and even up to 5% of the carbon measured with plastic signal in some areas, which forces us to rethink flows and balances.
A key component is marine snow, organic aggregates that fall from the surface to the depths, sequestering carbon dioxide from the atmospheric-oceanic system. When that "snow" incorporates microplastics, the descent slows down.The likely result is a reduced flow of carbon to the bottom, and thus a reduction in the ocean's ability to buffer climate change.
There is another side effect: plastic, without radiogenic carbon-14, is altering the isotope ratio that we use as a natural clock to date processes and remains. Deviations equivalent to several centuries have already been observed, an additional headache for geochemists and archaeologists.
Water treatment: Can we “trap” microplastics?
Conventional purification systems retain some, but not all. Pilot trials with membrane bioreactors (MBRs) show that Fine membranes, capable of filtering up to 0,2 μm, retain much more than conventional sedimentationIn field tests, analysis did not detect microplastics in the treated effluent down to 50 μm, while between 1% and 5% escaped and approximately 80% remained in the sludge.
This raises another question: in some countries, more than half of this sludge is used as agricultural fertilizer. If trapped plastic is returned to the soil, it could affect soil organisms and be reintroduced into the hydrological cycle., closing an unwanted circle that goes from the city to the countryside and back to the sea.
Although promising, MBR technology has barriers: it consumes more energy and costs more than sedimentation tanks, so its adoption is often limited to plants with strict requirements or limited space. Some administrations already consider it as a partial solution to microplastics., awaiting agreed measurement standards that will enable solid regulatory objectives to be set.
Governance and standards: the international chessboard moves
Governments have started with supply: Several countries have banned the sale of cosmetics with microspheres, and the United Nations has urged prioritizing policies to prevent the entry of marine litter and microplastics into the sea. In parallel, representatives of Member States are negotiating a specific international instrument on plastic pollution, and there are cleanup projects such as The Ocean Cleanup.
The debate won't be concluded in two newscasts. Science is still working on comparable metrics on a global scale, and Comprehensive regulation of the plastic value chain will take timeStill, every step counts: reducing the production of expendable plastics, improving design for easier recycling, and eliminating leaks in management systems are pillars that can be activated immediately.
Collaborative science: networks, methods and data
In Latin America and the Caribbean, initiatives such as REMARCO work to Diagnose the impact of microplastics on marine ecosystems and translate science into public policy aligned with the Sustainable Development Goals, with a focus on SDG 14 (life below water).
Their approach combines low-cost sampling, microscopy and infrared spectroscopy to identify polymers and sources. Protocols for sampling, analysis, and exchange of results have also been harmonized., taking advantage of existing laboratories in several countries and unifying criteria to compare regions.
Knowledge management is another critical leg: Web data platforms allow authorities to access the information generated and make decisions based on evidence, from specific bans to investments in sanitation or watershed monitoring.
What we can do now (and what to research better)
At home and on the go, there is room to reduce our footprint. Reduce the use of single-use plastics, reuse bags, avoid straws and opt for durable materials. It cuts demand and, with it, the volume that will potentially end up in the sea. These are simple gestures, but multiplied by millions, they take their toll.
On the knowledge front, academic and innovation projects seek more affordable and effective identification and quantification methods, essential for monitoring trends and evaluating policies. Without reliable measurements, it's difficult to set goals and verify their achievement.
The recent context does not help either: the use of plastics skyrocketed with the pandemic for health reasons, with collateral effects on the generation of waste and its leakage into the environmentIn high-consumption countries, the amounts that end up as waste remain considerable, hence the need to strengthen prevention, selective collection, and treatment.
Education and outreach are also important. Explaining processes such as bioaccumulation (the accumulation of substances in organisms) and biomagnification (increasing concentrations along the food chain) helps us understand why plastic we don't see can end up on our platesWhen we understand the journey from clothes to river and from river to fish, choosing better becomes easier.
If the data make anything clear, it's that small plastic has conquered the entire water column and is affecting key components of the ocean-climate system. Stop leaks at source, redesign products, improve purification, standardize measurements, and cooperate internationally It's not a wish list: it's a roadmap to ensure that the sea stops being the invisible dumping ground for our rampant consumption.
