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Heavy metal stars — how artificial mussels are used to monitor water pollution

Heavy metal stars — how artificial mussels are used to monitor water pollution
The plastic basket with vials and weights that Victor Wepener uses to monitor water quality. (Photo: Victor Wepener)
Katie Biggar for Roving Reporters
By Katie Biggar for Roving Reporters
18 Dec 2023
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To monitor platinum concentration in water, scientists are turning to novel technology that mimics the way mussels work.

The Hex River, which owes its name to the Afrikaans word for “witch”, is a pretty little stream when it starts life high in the Magaliesberg bushveld – an area of rugged beauty. But by the time it has meandered north, exited the Olifantsnek Dam, passed through farmlands and under the N4 – the main road to Sun City – to reach Rustenburg, there’s nothing terribly bewitching about it.

At the Boitekong informal settlement, north of Rustenburg, plastic and other rubbish litter the river and its banks. It’s hardly the sort of place you would go for a stroll much less take to the waters. But, hello! What do we have here? Trudging through the cold water, amid the bobbing cooldrink bottles and chip packets, is a tall middle-aged man in waders, sunglasses and a cap. 

If you didn’t know better you might imagine he’s a fisherman. But Victor Wepener is out angling for much more than barbel or kurper. Rather than a rod, he carries a plastic basket. And packed carefully in it is not a single hook or lure, but instead a dozen small vials, sharing space with a buoy, a collection of ropes, cable ties and a weight. 

The vials are made of Perspex tubing, a type of acrylic plastic. And inside these clear tubes are chelex beads – small glass beads – suspended in highly purified water, and enclosed by two polyacrylamide gel layers – a jelly-like substance that lets only certain substances pass through. 

With Professor Wepener, to use his title, is a small band of students. 

For two years, in the dead of winter and when summer swelters, Wepener and his students have been bringing their baskets down to the Hex River and in carefully noted locations, anchoring the vials in its waters.

Sure, the litter is unsightly, but it’s beneath the water surface where things can really turn ugly, and where the team’s attention is focused.

The Hex flows through the heart of South Africa’s platinum belt, home to the majority of the world’s platinum reserves and mines. The precious metal that turned Rustenburg into a boomtown (in the 2000s it was said to be the country’s fastest-growing municipality), can be incredibly toxic to life when it gets into watercourses. Which is why it is vital to keep tabs on concentrations of the metal and others in water.

Wepener, an ecotoxicologist with the Unit of Environmental Sciences and Management at North-West University, and his team have been doing just that.

mussels A living mussel (Perna perna) on the rocky shores of KwaZulu-Natal. Mussels are an important source of protein to coastal communities. (Photo: Nathan Rice)



With their beads, vials and gels, they have fashioned “artificial mussels”. While these look very different from the bivalve molluscs many of us know from the rocky seashore or our dinner plates, there are similarities. Both real and artificial mussels are able to filter water by the gallon – more than 25 litres a day – including toxic heavy metals, such as platinum. 

Bioprospecting


Wepener hopes artificial mussels will make it easier to monitor pollutants. 

“This is a sort of bioprospecting – seeing what makes mussels such an effective water purifier and building it into materials like carbon nanotubes. Mussels are not a very complex organism and it’s well recorded that bivalves play a very important role in maintaining ecosystem services such as water purification,” he says.

Artificial mussels were first developed by Professor Rudolf Wu, of City University in Hong Kong, using coated glass beads to measure concentrations of the heavy metals copper, chromium, lead and zinc in the ocean. 

Wepener has been working with artificial mussels since the early 2000s, when these devices were deployed in a number of South Africa’s harbours. 

In 2017, he joined forces with colleague, Professor Nico Smit of the Water Research Group at North-West University, and Professor Bernd Sures, an aquatic ecotoxicologist from Germany’s Universität Duisburg-Essen, to adapt artificial mussels for freshwater environments, in what they believe is a novel approach to assessing platinum toxicity in aquatic environments. 

‘Natural progression’


“It was a natural progression after working with the artificial mussel for so many years,” says Wepener, who reckons the device is showing real potential for applications in freshwater environments like rivers. 

Advances in the technology come at a time when water quality has been deteriorating – not only in the polluted rivers of the platinum belt, but across South Africa, with mining being a major culprit.

Despite facing various difficulties, including “logistics constraints”, the mining industry remains vital to South Africa’s economy, contributing more than R200-billion (more than $10-billion) to the gross domestic product. But pollution generated by mining has left the country’s rivers overexerted – unable to deal with any more contaminants, says water resource management expert Anja du Plessis. 

“Continued misuse and exploitation of this vital natural resource will have dire consequences in the near future,” she says.

Du Plessis, an associate professor at the University of South Africa, warns that when it comes to water pollution, we can’t keep treating the symptoms, like we are doing now. We have reached a saturation point and drastic action must be taken – which is why monitoring heavy metal levels in freshwater ecosystems is so important. What gets measured gets fixed, or so the old adage goes, and it’s the raison d’être for the Hex River artificial mussels project. 

Proliferating platinum


South Africa is the largest producer of platinum and the world’s main supplier of platinum group elements, such as platinum, palladium and rhodium. These have a wide range of uses in the medical, technological and electronic sectors as well as the automotive industry. 

Over the past few decades platinum levels in the environment have increased globally, mainly due to the introduction of catalytic converters in vehicle exhaust systems (ironically with the intention of reducing airborne pollution), as well as mining and its related activities, such as abstracting water and dumping tailings (mining leftovers). 

Mining in the lower Hex River.JPG

Living organisms exposed to platinum group elements can suffer serious health problems, including asthma, nausea, hair loss, skin diseases and even miscarriages.

But it is not only about monitoring pollutants in our vital fresh water systems. Artificial mussels hold promise for treating wastewater too. Elsewhere in the world, says Wepener, researchers are starting to design artificial mussels for placement in sewage treatment plants. 

Sea link


What goes into rivers – pollution included – eventually reaches the sea. It’s a truth we were reminded of during KwaZulu-Natal’s 2022 floods. The province’s rivers came down in spate, causing more than 400 deaths and displacing more than 40,000 people. Billions of rands worth of  infrastructure was damaged too, including wastewater works and pipelines, releasing untold quantities of untreated sewage into the sea. 

The subsequent massive outbreak of E. coli (Escherichia coli, a bacteria found in the intestines of humans and other animals) forced a ban on bathing at beaches in Durban and on the north and south coasts. This had devastating economic consequences since KwaZulu-Natal relies heavily on tourism and recreational activities. More than 30,000 jobs were lost and people’s livelihoods, food sources and even spiritual connections with the sea were threatened as the authorities closed beaches. 

Du Plessis says the 2022 outbreak was caused not only by the floods, but by poor or nonexistent maintenance of wastewater infrastructure. 

In addition to contaminants like bacteria, more than 80% of the pollution in the ocean originates on land, according to the National Ocean Service and the United Nations. This includes plastics, heavy metals, fertilisers and much more, carried by streams and rivers from mines, farms and factories into bays, harbours, estuaries and finally out to sea.  

Although heavy metals are found naturally in marine systems, man has made matters much worse. And worryingly, while the problem has grown on South Africa’s coast over the past 30 years, the number of studies related to marine pollution monitoring has decreased. 

Du Plessis warns that the country’s water resources are threatened and that basic water services nationwide have been declining steadily over the past 20 years.

Mussels to the rescue


Artificial mussels could be part of the solution. 

Wepener says that at some treatment plants elsewhere in the world, waste water is pumped through membranes similar to those used in artificial mussels. “They’ve actually used a property the mussels have which allows them to retain the substances once filtered.”

The membranes are made from carbon-based nanomaterials onto which a coating like that used on the glass beads of the artificial mussel is placed. The coating is effective in trapping or absorbing various substances, says Wepener.

However, he has yet to hear of the technology applied for this purpose in South Africa and more research is needed. The artificial mussels Wepener works with are not able to absorb pollutants on a scale that would be useful for removing metals – only for monitoring. 

He concedes that a living mussel is more effective at absorbing than an artificial mussel. Artificial mussels only take in dissolved metals whereas real mussels take in dissolved and particulate-bound metals. 

The plastic basket with vials and weights that Victor Wepener uses to monitor water quality. (Photo: Victor Wepener)


A Bronx tale


Living mussels have historically been used to monitor pollution levels and metal concentrations in the water because of their amazing filtering ability. Mussels are filter feeders, which means that to stay alive, they take up molecules from the water, trapping even heavy metals in their tissues. 

In 2012, researchers in New York suspended a raft full of mussels to monitor and filter contaminants in the Bronx River. They anchored the raft downstream of the Hunts Point Wastewater Treatment Plant, in an area where harvesting was prohibited because the waters were severely contaminated by bacteria. 

The study concluded that a fully stocked raft, with more than 300,000 mussels, could potentially sequester more than 60kg of nitrogen in their tissues, shells and bodily fluids. 

Although this represents only a small dent in the yearly nitrogen discharge of Hunts Point, scientists reckon hundreds of rafts could have a real impact. 

Where does the nitrogen come from and what’s its significance?

Our own body waste, food and the things we throw down our sinks and put into our dishwashers, are the main source of nitrogen in sewage. Excessive nitrogen in wastewater causes eutrophication, a build-up of nutrients that can cause algae to spread over the surface of water faster than an ecosystem can handle. This reduces oxygen, putting plant and animal health at risk. 

Food for thought


Mussels need very little space so they can live comfortably on rafts or in mussel cages. Experts believe they are perhaps the easiest bivalve to grow. 

Mussels have long been grown on rafts in South Africa. In Saldanha Bay they have been farmed for the past 15 years. 

Nor is South Africa a stranger to using living mussels for pollution monitoring. 

The Mussel Watch Programme, an initiative started in the US to monitor water quality, has been adopted by many countries. South Africa’s Department of Environmental Affairs and Tourism took up the programme in 1985, monitoring heavy metal concentrations in the tissues of the Mediterranean mussel (Mytilus galloprovincialis) in the Western and Northern Cape. In the early 2000s, the programme was expanded to Durban and East London, but has since been curtailed. 

According to the Department of Forestry, Fisheries and the Environment, the Mussel Watch Programme is still operational, but has evolved into a coastal pollution monitoring programme on the West Coast. Logistical constraints brought an end to sampling on the East Coast in 2017, says the department. It adds that it is engaging with partner institutions to expand the more comprehensive pollution monitoring on the West Coast to elsewhere in the country. 

“The programme is now monitoring four sites, namely Strandfontein, Milnerton, Saldanha Bay and Port Nolloth, in the Western Cape,” says department spokesperson Peter Mbelengwa.

Mussels have their limitations as a monitoring tool, however. Factors including age, sex, reproductive phase, water temperature and salinity can heavily affect the way individual mussels accumulate and filter.  

And there’s another issue: To measure the contaminants, you have to kill the mussel. 

Living Mussel, Perna Perna (Cred Nathan Rice).JPG

With artificial mussels, of course, there’s no killing to assess the pollutants they’ve absorbed. They also offer standardisation and can be deployed in freshwater and marine environments. 

Wepener’s novel approach to measuring toxicity in water bodies has applications not only in North West, but across the country. And he is in the process of validating the tool for measuring mercury in Walvis Bay Harbour and Swakopmund, in Namibia.

Great value


Whether they’re real or artificial, the value of mussels is hard to overstate. 

In South Africa, mussels are a delicacy for some and a staple food for others. Mussel farming is the second-biggest contributor to South African mariculture production. Furthermore, mussel collecting is common all along the East Coast. They represent a rich source of protein in a country where nearly half  the population lives in poverty, according to Statistics South Africa, and where food security remains a pressing concern. 

In 2021, marine scientist Tembisa Jordaan made a film, Ulwandle Lushile – Meeting the Tides. It’s a story of women in the rural community of Sokhulu in KwaZulu-Natal who are continuing a mussel-harvesting legacy years after they were barred from their coastal lands during apartheid. This film encapsulates many South African stories of mussels and people. 

“Mussels are a means of survival for these women and so many other countless people,” says Jordaan. 

“They have an incredibly deep connection with nature and need to be included in all decisions around these animals and ecosystems. It just makes sense.” DM

Katie Biggar is a marine biologist, independent journalist, filmmaker and multimedia writer. 

This story was produced with support from Internews’ Earth Journalism Network (EJN). As part of EJN’s Ocean Media Initiative, Biggar was mentored by EJN associate Lauren Finch and Roving Reporters writing coach Matthew Hattingh. This included helping her think through the story angle, sourcing and structure of the piece, as well as final editing.

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