Microplastics show up in Kruger Park river creatures

Purvance Shikwambana and Dumisani Khosa were not really surprised to find significant volumes of microplastic floating in the water or buried in the mud banks of two big rivers in South Africa’s most famous national park.

After all, air- and water-borne pollution know no boundaries, with big and small pieces of plastic now found almost everywhere in the world. This is the legacy of several decades of pollution by the petrochemical-plastics industry that manufactures one of the most versatile and convenient consumer products ever invented.

More surprisingly, however, local researchers have now detected microplastics in the bodies of a wide variety of very small aquatic creatures in the Crocodile and Sabie rivers in Kruger National Park.

Made up of fragmented plastic and tiny synthetic beads, microplastics are tiny (varying in sizes comparable to grains of rice or specks of dust).

Shikwambana, a researcher at the University of Mpumalanga, and Khosa, a freshwater ecologist at South African National Parks, are among several local scientists who have chosen to zoom in on the potential threats posed by microscopic-size plastic in South Africa’s freshwater aquatic life.

Khosa explains that macro invertebrates (small water animals with no backbones such as nymphs, crustaceans, worms and snails) can ingest or swallow these fragments by mistaking them for natural food.

While Khosa’s and Shikwambana’s recent studies mainly focused on quantifying the presence of local microplastics, studies in other parts of the world have shown that such particles can translocate from the gastrointestinal tract into body tissues.

A study by Dr Anja Ramsperger and colleagues at Germany’s Bayreuth University suggests that once internalised into tissue, the plastic fragments may also cause toxicological effects that have implications for both the environment and human health.

Back in Kruger Park, Shikwambana feels that it is vital to quantify the levels of microplastics in water and sediments by measuring both the volume, type and possible origins of the microplastics.

Where are they coming from? What particular type of plastic waste is involved? And is it harmful to tiny insects, fish and other larger forms of life in the park? And, more critically, how can we arrest or limit this tide of plastic pollution?

“At this stage, we don’t know what the exact impacts are on aquatic life in Kruger,” says Shikwambana, noting that studies from other parts of the world suggest that the impacts can spread through the food chain, affecting reproduction or disrupting animal endocrine systems.

At a local level, this raises concerns that small river insects and fish may be vectors that carry microplastics higher up the food chain into crocodiles, tigerfish, egrets or fish eagles.

Further evidence of tiny plastic pieces moving through the trophic chain (between mosquitoes and midges) was shown in a study involving researchers from the South African Institute for Aquatic Biodiversity and the University of Venda.

Notably, Shikwambana and her colleagues have also detected several “rubbery” polymer fragments in aquatic animals in the Olifants River, indicating that they are swallowing tiny particles of plastic that shear off from car and truck tyres which are then washed off roads into rivers and streams.

In the US and Canada, researchers have linked synthetic plastic additives in vehicle tyres to the death of a variety of fish species. For example, 6PPD-quinone, a chemical breakdown product of certain tyres, starts to kill trout within hours of being washed into rivers and other freshwater bodies.

Elsewhere in South Africa, researchers believe that accumulations of tiny plastic particles in local river sediments can act as “hotspots” for the spread of pathogenic bacteria and antibiotic resistance.

In one of these studies, involving pollution of the Msunduzi River in KwaZulu-Natal and the Swartkops River in the Eastern Cape, researchers Dr Muneer Malla and Nomalihle Malambule found an abundance of antibiotic resistance genes and pathogens in the so-called plastisphere – a term used to describe the unique microbial communities that colonise plastic debris.

“Notably, the plastisphere exhibited an enrichment of mobile genetic elements, increased antibiotic resistance genes and a higher abundance of potentially pathogenic bacteria, suggesting it acts as a hotspot for the acquisition and dissemination of pathogens and antibiotic resistance.”

The research team, from the Institute for Water and Wastewater Technology at the Durban University of Technology and the Institute for Water Research at Rhodes University, note that the pollutants originate from a wide variety of sources – from municipal wastewater treatment works, personal care products, washing machines, industry and even commercial agriculture.

Analysis of this plastisphere niche revealed the presence of several antimicrobial-resistant genes and microbial species including Acinetobacter baumannii and Pseudomonas aeruginosa – both multidrug-resistant bacteria responsible for severe hospital-acquired illnesses such as pneumonia and bloodstream infections.

“Results of this study indicate that different pollution sources significantly influence microplastic abundance and types, as well as the structure of microbial communities, which may ultimately pose a threat to human health.”

Determining the precise impacts of plastic pollution on people from such a wide variety of chemical constituents is still under investigation globally.

In 2022, Dr Heather Leslie and colleagues at the Vrije Universiteit in Amsterdam detected plastic particles in human blood for the first time, with subsequent studies showing similar results in the blood of pigs and cows.

In 2024, the World Health Organization also cited growing scientific evidence that nanoplastics and microplastics accumulate in the human body, potentially causing inflammation, organ damage and immune system disruption.

But sections of the global plastics industry have continued to push back against calls for stricter regulation or global bans on certain plastic products.

Industry lobby groups such as the American Chemistry Council, argue that chemicals and plastics used in healthcare, food packaging and children’s products are already subject to several layers of safety testing and oversight before they enter the market.

The group also notes that the US Food and Drug Administration requires manufacturers of food-contact plastics to provide extensive data on chemical migration and exposure “that reflect the most severe temperature and time conditions of their intended use, such as microwaving, boiling, freezing and refilling”.

Nevertheless, expert bodies such as the Minderoo-Monaco Commission on Plastics and Human Health note that there are thousands of chemicals in plastics, many of which are known human carcinogens, endocrine disruptors, neurotoxicants and persistent organic pollutants.

“These chemicals are responsible for many of plastics’ known harms to human and planetary health. The chemicals leach out of plastics, enter the environment, cause pollution, and result in human exposure and disease.”

As just one example, the commission notes that certain plastic additives have been linked to disruption of endocrine function and an increased risk for premature births, neurodevelopmental disorders, male reproductive birth defects, infertility, obesity, cardiovascular disease, renal disease and cancers.

“Infants in the womb and young children are two populations at particularly high risk of plastic-related health effects. Because of the exquisite sensitivity of early development to hazardous chemicals and children’s unique patterns of exposure, plastic-associated exposures are linked to increased risks of prematurity, stillbirth, low birth weight, birth defects of the reproductive organs, neurodevelopmental impairment, impaired lung growth, and childhood cancer.”

In an expert review published in The Lancet, Professor Philip Landrigan and colleagues characterise plastics as a “grave, growing, and under-recognised danger to human and planetary health”.

“While there remain gaps in knowledge about plastics’ harms and uncertainties about their full magnitude, the evidence available today demonstrates unequivocally that these impacts are great and that they will increase in severity in the absence of urgent and effective intervention at global scale.” DM