Plastic pollution is usually something we expect to see. A bottle beside a road. Packaging caught in a river. Fragments washed onto a beach.
The smallest pieces are different. Microplastics can move through environments largely unnoticed, travelling through water, soil and, increasingly, the atmosphere.
New South African research has now measured what happens when some of those particles come back down.
Scientists studying an urban area in the Eastern Cape detected atmospheric microplastics falling across urban, peri-urban and more natural environments. Across the three monitoring sites, the researchers recorded an average deposition rate of 86.5 microplastic particles per square metre per day.
But the pollution was far from evenly distributed.
The peri-urban site recorded an average of 178.1 particles per square metre per day, while a semi-natural site roughly 10 kilometres outside the town recorded just 24.7.
The difference provides another clue to an increasingly complicated environmental problem. Plastic does not simply remain where it is discarded. It moves.
Looking for plastic above the ground
The study, published in Scientific Reports, was conducted by researchers affiliated with institutions including the Albany Museum, Rhodes University, the University of the Witwatersrand, Sefako Makgatho Health Sciences University, the South African Institute for Aquatic Biodiversity and the University of Turin.
Researchers collected atmospheric deposits weekly for six weeks at three locations representing different types of land use in a South African town within the Albany thicket biome.
This matters because airborne microplastics remain considerably less studied than plastic pollution in rivers, oceans and other aquatic environments, particularly in Southern Africa.
Atmospheric deposition describes the process through which particles travelling in the air eventually settle onto surfaces.
Some may fall under dry conditions. Others can be carried downward by rain.
Once deposited, those particles do not necessarily stop moving. Material landing on roads, soil or vegetation can eventually enter stormwater systems, rivers and other ecosystems.
The atmosphere may therefore function as another transport route connecting different parts of the plastic pollution cycle.
Most of the particles were fibres
The researchers did not find only small, irregular fragments.
Around 95.5% of the microplastics identified were fibres or filaments. Transparent or clear material was the most common colour, accounting for 46.6% of particles.
Chemical analysis provided another clue. The most commonly identified polymer was polyethylene terephthalate, or PET, representing 42.5% of the analysed material.
PET is a widely used plastic found in products including packaging and synthetic textiles.
The researchers suggest that several local activities could contribute to the particles they observed, including poor waste disposal, sewage seepage, wastewater management and textile-related activity.
The study does not establish exactly how much pollution came from each source.
That distinction is important. Detecting a particular polymer in atmospheric deposits can help researchers investigate where particles may originate, but it does not provide a simple fingerprint identifying a single source.
Urban plastic pollution is rarely that tidy.
Rain may be part of the journey
One of the more interesting observations appeared at the urban monitoring site.
There, microplastic deposition increased alongside rainfall.
The researchers interpret this as evidence that rainfall may influence how airborne particles are deposited locally.
One way to picture the process is to imagine the atmosphere temporarily carrying microscopic debris before rain helps wash some of it towards the surface.
But the relationship was observed at one site, and the monitoring period lasted only six weeks.
It should therefore be treated as an indication of local dynamics rather than proof of a universal relationship between rainfall and microplastic deposition.
Weather can affect airborne particles through several mechanisms, including wind direction, turbulence and rainfall. Local land use can add another layer of variation.
That may help explain why two locations separated by relatively short distances can experience substantially different deposition rates.
Why the peri-urban result matters
Perhaps the study’s most striking result is that the highest deposition was not recorded at the central urban site.
It occurred at the peri-urban location about 4.5 kilometres from the town centre. That finding is useful because environmental pollution does not always follow a simple gradient in which the densest urban centre automatically experiences the highest concentration.
Waste handling, wastewater systems, nearby activities, local air movement and the physical characteristics of an area can all influence where pollutants accumulate.
For environmental monitoring, this creates a practical challenge.
Measuring pollution at a single central location may not adequately represent what is happening across an entire town.
The geography of pollution can be surprisingly local.
South Africa still needs a clearer baseline
Atmospheric microplastics present a particular problem for environmental management because researchers are still establishing basic information about where they occur, how much is present and how conditions affect their movement.
The authors argue that atmospheric microplastics deserve greater attention in environmental monitoring and waste-management policy, particularly in urbanising areas of Southern Africa where baseline information and regulatory frameworks remain limited.
That does not mean this six-week study can tell us how much airborne microplastic exists across South Africa. It cannot.
Three monitoring sites in one area provide a snapshot, not a national map.
The researchers also observed short-term deposition. Longer studies across seasons would be needed to understand how rainfall, wind, temperature and changing human activity affect atmospheric plastic throughout the year.
Different South African cities could also produce very different patterns.
Johannesburg, Cape Town, Durban, Pretoria and smaller towns differ in climate, population density, industrial activity, waste infrastructure and urban form.
This study provides a starting point for asking those questions rather than their final answer.
Pollution rarely respects environmental boundaries
The broader importance of the research lies in how we think about plastic pollution itself.
Water pollution, land pollution and air pollution are convenient categories for environmental management.
Nature is less interested in those categories.
A plastic fibre released in one place may enter the atmosphere, travel, fall with rain, reach soil, wash into a drainage system and eventually enter a river.
The same particle can cross several environmental boundaries during its lifetime.
Understanding microplastic pollution therefore requires researchers to follow the movement of plastic rather than simply examine where it happens to be found.
South African scientists are beginning to fill one of the gaps in that journey.
The plastic beneath our feet and in our waterways may only be part of the story. Some of it has been travelling above us first.
Source Information
Study Title: Spatial patterns and short-term deposition of atmospheric microplastics in an urban environment
Authors: Thendo Mutshekwa, Solethu Mkhencele, Jeffrey Lebepe, Valentina Balestra, Lubabalo Mofu and Samuel N. Motitsoe
Journal: Scientific Reports
Published: 30 June 2026
Accepted: 24 June 2026
DOI: 10.1038/s41598-026-60015-w
Publication note: Springer Nature currently identifies the available article as an early-access, unedited version of the manuscript, which will undergo further editorial production before its final version.
