You are what you eat – including plastic

Never mind how trashy it looks. The real focus on plastic pollution should be on how it harms people, animals and the world around us, directly or indirectly.

What is it about plastic pollution that gets some people so hot under the collar?

Is it because plastic is so much more visible than the unseen clouds of poisonous muck that pour from the back end of our vehicles, from power stations or factories? Or is it because plastic trash just looks ugly and is perceived to be a behavioural problem that could be remedied quickly “if lazy people could just learn to pick up their mess”?

Whatever the reasons may be, the scale of global plastic pollution is set to get much worse before lasting solutions emerge and, leaving aside the aesthetic dimensions of plastic trash, local scientists believe we should be paying much more attention to the hidden impact of this pollution in the air, soil and water that surrounds us. 

And in our food.

Plastic in the ocean

In a series of articles in the latest issue of the South African Journal of Science, researchers warn that the country has a long way to go to understand the problem and devise strategies to protect human health and the environment from lasting harm.

Trishan Naidoo, a Durban marine biologist who studies plastic pollution levels in the sea off KwaZulu-Natal, says he is concerned that South Africa is starting to lag behind researchers in other nations because of funding shortages.

Naidoo, whose own research has suggested links between plastic pollution and stunted growth levels in some sea fish, says sublethal effects in people may go unnoticed if local fish populations are not monitored continuously.

He says the World Health Organization currently rates the direct health risk of microplastics to humans as “low”, but believes there is still a need to evaluate the potential effects of microplastics on South Africa’s human population given the country’s reliance on a wide variety of edible marine species.

The problem is not new. Local researchers sounded early alarms decades ago.

Undated: Microplastic pollution is fast becoming hotly debated globally, but Durban marine biologist Trishan Naidoo and other scientists are worried that local research efforts are lagging because of funding shortfalls. (Photograph supplied)
Undated: Microplastic pollution is fast becoming hotly debated globally, but Durban marine biologist Trishan Naidoo and other scientists are worried that local research efforts are lagging because of funding shortfalls. (Photograph supplied)

Back in the 1970s, marine researcher George Hughes found plastic pellets in the stomachs and digestive systems of loggerhead turtle hatchlings stranded on the beaches of Zululand. Later, fellow scientist Peter Ryan reported that plastic debris in the sea could block and rupture the digestive tracts of turtles and possibly kill them.

Since then, a number of fish, turtle, bird and mammal species in South Africa’s oceans have been found to be affected by plastics – but Naidoo and fellow scientist Anusha Rajkaran say that a comprehensive assessment of the variety and degree to which local biota are affected is still lacking. 

“Many of the impacts, particularly in relation to microplastic ingestion, are sublethal, but the consequence of not continuously monitoring these products is that the sublethal impacts may go unnoticed, which could directly impact consumers both locally and abroad.”

Last year, Naidoo and  David Glassom of the University of KwaZulu-Natal published research findings which suggest that glassfish that were fed virgin plastic and microplastic trash collected in Durban harbour showed clear signs of stunted growth and lower survival rates compared to control specimens that were fed a plastic-free diet.

In another study published in 2016, Naidoo and his colleagues reported that 73% of the mullet collected in Durban harbour had plastic particles in their guts, with a mean of 3.8 particles per fish.

Microplastics have also been found in several fish species in KwaZulu-Natal mangrove estuaries, yet there are currently no published estimates of microplastic concentrations in the country’s most commercially important fish species.  

Health hazards of ingesting plastic

Elsewhere, researchers have voiced concern that some plastic compounds are hazardous to health as they contain monomers that can cause cancer, genetic damage or hormonal and endocrine imbalances.

“The fate of consumed microplastics may depend on the size of the particle,” says Naidoo, “Some studies have identified microplastics in the faeces of humans, showing that most particles (90%) are excreted.”

However, studies had shown that much smaller plastic particles may move from the gut to the lymph and circulatory systems, with the tiniest particles likely to penetrate the organs or to move through cell membranes, the blood-brain barrier and the placenta.

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“The body responds to the presence of these particles by triggering a number of responses such as immunosuppression, immune activation and abnormal inflammatory responses. Unfortunately, at the time of this review no published studies had been conducted in South Africa but given the high dietary seafood content of a considerable proportion of the country’s population, future research in this area should be prioritised. 

“Much of the uncertainty around the impacts of marine plastic debris on South African biota stem from the lack of monitoring marine debris in the country’s water bodies, more especially microplastics. Additionally, reports of plastic ingestion in a wide range of biota (sharks, fish, turtles, birds and mammals) in South African waters point to the need to monitor trends in the amount and composition of debris ingested by indicator species, as well as those species that are regularly consumed.”

Naidoo believes the presence of microplastics in shrimp and lobster in Norway and Scotland suggest that South Africa should also be monitoring plastic levels in commercially valuable species such as pilchards and to determine whether there are harmful effects to humans through secondary ingestion.

Overall, Naidoo and his colleagues conclude that the current research infrastructure in South Africa is insufficient to monitor and characterise marine plastic debris and, in many cases, it is not in line with global standards. 

In our drinking water

In separate articles in the latest journal issue, other researchers have drawn attention to the potential for indirect repercussions to human society and the environment.

For example, there is concern that the thick mats of plastic trash on beaches and the seabed can smother marine life, kill filter feeding organisms or alter oxygen levels and the temperature.

Henk Bouwman and Carina Verster of North-West University (Potchefstroom) estimate that somewhere between 15 000 and 40 000 tonnes of plastic is carried into the oceans from South Africa per year – mainly by river.

12 December 2019: Mounds of plastic rubbish litter the beach near the mouth of the Umgeni River in Durban, KwaZulu-Natal. (Photograph by Reuters/ Mike Frew)
12 December 2019: Mounds of plastic rubbish litter the beach near the mouth of the Umgeni River in Durban, KwaZulu-Natal. (Photograph by Reuters/ Mike Frew)

Worryingly, they note that municipal waste water works have deteriorated to such an extent that up to 40% of the country’s waste water is left untreated.

Another major source of river-borne plastic pollution comes from poor municipal refuse collection networks, particularly in shack settlements.

Bouwman and Verster suggest that about 82% of urban households have weekly solid waste removal services, but only 1% of rural households have formal waste collection at least once a week. Roads in shack settlements are often too narrow to be accessed by garbage trucks and, without proper infrastructure, plastic and other waste leak into the environment through wind and water run-off.

They also note that microplastic fibres have been found all over the globe in the remotest of environments, suggesting they were blown there. 

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Bouwman and Verster also worry that plastic particles removed by municipal sewage treatment works will eventually end up in farmers’ fields after being deposited there as sewage sludge or fertiliser.

A third article by Water Research Commission scientist Eunice Ubomba-Jaswa raises additional concerns about the growing level of plastic pollution in fresh water – including purified tap water.

“As plastics are not biodegradable, they never truly disappear but continue to break down into smaller and smaller pieces,” she says, noting that not all plastic is removed during conventional water treatment. 

Ubomba-Jaswa says attempts to understand the biological uptake of fine plastic particles in mammals and humans have not yielded conclusive findings, so it is vital for the science community to conduct more studies into the flow of microplastics from source to sea, their removal during water treatment, and the potential exposure and risks to consumers via drinking water. 

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