How microplastics end up in human blood, semen and brain

Microplastics have been detected in the placenta, nose tissue and at the base of the brain. [iStockphoto]

Dorcas Wacui, a waste picker at Dandora dumpsite in Nairobi, developed an illness that left her incessantly coughing and struggling for breath.

It was the sheer will of a parent who needed to fend for two children in the unforgiving Nairobi economy that kept her going. But silently, the disease was taking hold in her body.

In 2014 her body gave in: she became sick round the clock.

Dandora dumpsite is always smoldering. A thick grey-white, largely undefined, smoke (with the stench of burning litter) is unmistakable.

“From years back one of the ways of reducing this mound of garbage was to burn it. Some of those fires, because they are buried deep in the garbage, never quite die. And thus the smoke,” says Joyce Wambui, who was raised near the dumpsite.

With her mother, Wacui, unable to work, Wambui, dropped out of Success High School in Kasarani in Form Two to become a waste picker and take care of the family.

A big chunk of the waste at the dumpsite, Wambui says, is plastic, “the type that cannot be recycled; therefore, it is left there. It will be burnt. Or just left to keep piling.”

In September 2024, aged 54, Wacui breathed her last.

“Just before she died we had taken her to Mama Lucy Hospital. She was scanned and underwent some tests. The doctor told us that she practically had no lungs,” says Wambui.

Wambui is neither a doctor nor a scientist but she believes the never-ending smoke at the dumpsite played a big role in her mother’s death. And she is probably right.

“When plastic is burnt, the resulting smoke contains millions of micro and nano-plastics as well as toxic chemicals. Inhaling that smoke is breathing in the plastic and its components,” says Griffins Ochieng, an environmental scientist

Environmentalists look at plastic waste in size categories: microplastics (less than 0.5cm in diameter), mesoplastics (0.5 to 5cm), macroplastics (5 to 50cm), and megaplastics (above 50cm).

Of the four, microplastics have been touted as of most concern to human beings. They range in size from less than 0.5 cm to one part of 25,000 equal parts of 2.5cm (1 micrometer).

“Microplastics are very tiny. They are the most dangerous because they are largely invisible and imperceptible. As a result, we eat them in our food and drink them in our water,” says Fredrick Njau, the Renewable Development Program Coordinator at Heinrich Boll Foundation.

A July 2022 study published in the journal Science of the Total Environment, analysed digested human lung tissue samples using spectroscopy technology that could detect diameters of 3 μm (micrometers).

In the study, 39 microplastics were identified in 11 out of 13 lung tissue samples, with an average of 0.69 to 0.84 particles per gram of tissue.

Another study published in the journal Polymer, human breastmilk samples were collected from 34 women and analysed through microspectroscopy.  Microplastic contamination was detected in 26 out of 34 samples.

The detected particles were classified according to their shape, colour, dimensions, and chemical composition: the most abundant microplastics detected in the breastmilk samples were polyethylene (similar to water bottles), polyvinyl chloride (similar to plumbing plastic pipes), and polypropylene (similar to a yoghurt container), with sizes ranging from 2 to 12 µm.

In yet another study, titled ‘Discovery and quantification of plastic particle pollution in human blood’, plastic polymers were identified in human blood.

Published in the journal Environment International, the study established a quantifiable concentration average of 1.6 µg (micrograms) per milliliter of plastic particles in human blood.

And this year, scientists discovered microplastics in human semen and follicular fluid (the liquid that surrounds an egg, in women). The findings were presented on July 1, 2025, in Paris at the 41st Annual Meeting of the European Society of Human Reproduction and Embryology.

In previous studies, microplastics have been detected in the placenta, nose tissue, at the base of the brain, penises and human stool.

The question is, how are these tiny plastics entering the human body?

If you think of plastics as the water bottles, or polythene paper, that ends up in the open dumpsites around us it becomes difficult to imagine it as part of the food we eat, the water we drink, or the air we breathe.

However, imagine that same plastic put through a milling machine that churns out flour-like plastic. If a pinch of the flour were stirred in your stew, would you be able to tell that it’s in there? Chances are you won’t.

Dr Eric Okuku, a marine pollution researcher with Kenya Marine and Fisheries Research Institute (KMFRI), says that plastic litter in the environment – even though they don’t biodegrade – fragment over time into microplastics.

Exposed to the vagaries of nature, such as photodegradation (the effect of sunlight), wind, rain, hailstorm and mechanical abrasion, plastic breaks down.

In 2016, UNEP published findings showing that plastics are the dominant component of marine litter.

Studies show that microplastics are now found everywhere. In a study published in November 2018, in the journal Geochemical Perspectives, researchers reported ‘the abundances of microplastics’ in Mariana Trench (the deepest part on earth) – found in the western Pacific Ocean.

“In the oceans marine animals take up the microplastics; which are tiny enough to move into tissues.

“Microplastics travel up the food chain; human beings are at the apex of that food chain; hence, as we eat sea food we eat the microplastics too.

“In the human body they can enter the bloodstream; which then distributes them throughout to different organs and organ systems,” says Okuku.

Between July and September 2019, Okuku led a team of marine pollution researchers to determine abundance and composition of shoreline meso-litter, in 23 selected beaches along the Kenyan coast.

“We found that plastic was the most abundant litter along the Kenyan shoreline,” he says.

But even away from the marine environment microplastics are found in food and drinks that humans partake on a daily basis.

In a study published in March 2024, researchers at Columbia University, using recent technology, counted between 110,000 and 370,000 microplastics (and nanoplastics: smaller than microplastics), in three popular brands of water sold in the United States.

A study published in volume 187 of the journal Environmental Science and Pollution Research, in August 2020, established presence of microplastics in food meant for human consumption.

The study, done in the city of Catania, Italy, found microplastics in vegetables and fruits: carrots, lettuces, broccoli, potatoes, apples and pears: pointing to the fact that microplastics are small enough to be taken up as ‘nutrients’ by plants.

Here comes the shocker! In a study published in the journal Environmental Science & Technology, researchers at McGill University in Canada, concluded that a single teabag releases, on average, some 11.6 billion microplastics and 3.1 billion nanoplastics.

The point is, in today’s world, ‘eating’ plastic is no longer the exception: it’s norm. Which begs the question: how do microplastics affect human health?

Generally, though, little to nothing is known about the full potential effects of microplastics on health.

Even so, some studies have linked them to respiratory illnesses like lung cancer, asthma, pneumonitis, and neurological challenges like fatigue and dizziness.

A study published in New England Journal of Medicine, in March 2024, found that People with microplastics or nanoplastics in their carotid artery tissues were twice as likely to have a heart attack, stroke or die in three years.

Chemicals used in plastic production — that often leach from plastics — are linked to serious health problems as well.

Ochieng, who is also the Executive Director and Programs Coordinator at Centre for Environment Justice and Development (CEJAD), says: “The chemicals are toxic and have been shown to cause hormonal disruption, respiratory irritation, some cancers, and autoimmune diseases.”

Chemicals in Plastics: A Technical Report published in May 2023 by UNEP, states that there at least 13,000 chemicals that are incorporated in production of different types of plastics. More than 3,200 of these are of major concern due to high toxicity.

These chemicals are typically added during manufacturing to improve mechanical properties such as flexibility, durability, stability, and color.

They include phthalates, bisphenols, biocides, metals and metalloids, flame retardants and polyfluoroalkyl substances (PFASs).

“The human body was not designed to assimilate plastics. In due time scientific research will show direct linkage between bioaccumulation of plastics in the human body and the many diseases people are dying from today,” says Ochieng. 

This story was produced with support from Internews’ Earth Journalism Network