The Crocodile River rises near Dullstroom, flows through the Nelspruit industrial area, feeds the Lowveld’s farms and winds through the Kruger National Park en route to Mozambique. (Wikipedia)
Every drop of river water tells a story, says scientist Shaskia John — and it’s not just about nature.
“It’s a story about the kinds of medicine that we take, the kinds of chemicals that we use and about the kind of lifestyle choices that we make,” she says. “What we consume, we excrete and the wastewater plants will reflect that … Our rivers are lifestyle markers.”
John, an aquatic ecologist who graduated from the department of nature conservation at Tshwane University of Technology, spoke to the Mail & Guardian on the sidelines of last week’s Oppenheimer Research Conference where she made a presentation on legacy and emerging contaminants in the Crocodile River catchment.
Now in its 14th year, the conference — convened by Oppenheimer Generations Research and Conservation — brought together researchers, policymakers and conservation leaders to advance African-led solutions to the biodiversity and climate crisis.
John’s study examined seasonal shifts in water quality, testing chemical loads in surface water and fish muscle tissue. She screened for 22 metals, 274 pesticides and 21 pharmaceuticals — uncovering alarming levels in the ecologically critical river catchment.
“Rivers are the veins of ecosystems,” she said. “They sustain livelihoods, they sustain biodiversity — but the Crocodile River catchment is slowly becoming a chemical cocktail.”
The Crocodile River rises near Dullstroom, flows through the Nelspruit industrial area, feeds the Lowveld’s farms and winds through the Kruger National Park en route to Mozambique.
There is varied land use in the Crocodile River itself: industrial use, urban use, agricultural use and then there are also ecological zones or buffer zones. “The agricultural, industrial and urban areas bring in chemicals, pharmaceuticals and pesticides as well as fertilisers into the river.”
The river is ecologically important as it supports two key ecological zones in its lower portion — the Krokodilpoort Nature Reserve and it forms the southern border of the Kruger National Park — while sustaining farms, industries and expanding towns. “It’s one of the most used rivers in South Africa.
“It’s a transboundary river,” John added. “That means we have an international obligation to maintain certain water standards because the water supports communities and ecosystems downstream.”
Over a year, John sampled the entire catchment from Machadodorp, near Dullstroom, all the way to Komatipoort during April 2022 and again in October 2022 to compare high and low-flow seasons.
“In April, I sampled 15 sites from the relatively untouched headwaters near Dullstroom down to the heavily impacted industrial and urban zones near Mbombela,” she said.
“By October, I added five more sites where thousands of fish had died in a fish die-off.”
Her aim is to determine chemical loads and test whether human pressure drives ecological risk. Samples were analysed using liquid and gas chromatography mass spectrometry, while fish muscle samples were sent to a commercial lab.
A chemical mirror of society
One of the key findings was that legacy contaminants still haunt South Africa’s rivers. Pesticide testing in fish revealed the bioaccumulation of banned chemicals DDT and DDE, its main environmental breakdown product.
“DDE was present in all three fish species I sampled — largescale yellowfish, tigerfish and redbreast tilapia — while DDT was found in tigerfish only,” said John.
“The higher levels of DDE in tigerfish show biomagnification through our trophic levels [the food chain]. There’s also differences in the concentration among species, which might be due to physiological factors such as their metabolic uptake.”
Urban influences were stark, with illicit drugs prevalent near urban areas and wastewater treatment plants, reflecting the inefficiencies of their removal.
“I found methaqualone, or Mandrax, at 78% of my sites. I also found cocaine and its metabolite benzoylecgonine, which was even more widespread than cocaine itself. Cocaine is better processed in wastewater plants, but its metabolite isn’t, so it becomes more concentrated in the treated water flowing out,” John related.
She also detected “ridiculous amounts” of acetaminophen, or paracetamol — 25 000 nanograms per litre — alongside methamphetamines, anti-inflammatories such as diclofenac (21% of sites) and antibiotics like sulfamethoxazole (40% of sites).
“I found a lot of anti-consulvant medication, which was carbamazepine, at 51% of my sites. These persistent pharmaceutical compounds [diclofenac, sulfamethoxazole and carbamazepine] are very difficult to remove from wastewater,” she said, noting that they create pollution hotspots with implications for antibiotic resistance and aquatic toxicity.
“I found antidepressants and antihistamines in the water and, very concerningly, I found a lot of antiretroviral drugs (ARVs) … It’s a good thing that we see that our communities are taking these drugs and managing this very tragic illness so well.
“But again, our wastewater treatment plants are proving inefficient in removing these ARVs because I’m finding them at extremely high concentrations in the water as well as in the detection percentage.”
In rural areas, contamination also comes from runoff and informal sanitation.
“A lot of time there’s just drop toilets, no facilities, so it ends up just going into the rivers. It’s a combination of inefficient wastewater treatment management as well as unregulated water dumping.”
Pesticides were absent in John’s April 2022 water samples “but in October we did find perchlorates as well as chlorates”.
Metal contamination
“Seasonal changes led to fluctuations in the input and runoff in the river, causing variations in our metal concentrations between sampling seasons.
“In both April and October, the target water quality range set out by the then department of water affairs and forestry showed that aluminium, lead and arsenic all exceeded the acceptable amount for ecological health,” John said.
She found arsenic at high levels, likely linked to the Kaap River’s legacy of legal and illegal mining, as well as lead, which is highly poisonous to aquatic life.
“Arsenic and lead are extremely toxic and aluminium can have a lot of negative effects at high levels as well,” she said, noting that, even if the aluminium occurs naturally, “they still exceeded the target water quality range that is acceptable for healthy ecosystems”.
John’s research underscores the urgent need for improved wastewater management to curb chemical risks to freshwater ecosystems and human health.
“There are still legacy contaminants being discovered in our rivers and new contaminants are emerging faster than we are able to manage,” she warned.
“We need improved wastewater treatment facilities that are upgraded and updated regularly. We also need ongoing monitoring of legacy and emerging contaminants.”
During her sampling, roughly 75% of wastewater treatment plants were non-functional.
“It’s really shocking. Yes, we have the law, but we don’t have the enforcement of policy and regulation,” she said.
“We need to strengthen enforcement for our water quality standards and contaminant limits. These haven’t been updated since the department of water affairs and forestry dissolved into the department of water and sanitation. We’re finding new things all the time that have zero recommended limits that are acceptable to ecology or the environment.”
For John, one solution lies in integrating ecological restoration with community livelihoods.
“We can’t stop humans from existing. We can’t stop ecology from thriving. We have to balance short-term land-use pressures with long-term restoration goals and the livelihoods of our people.”
She believes awareness is the first step. “We have to talk about this in a way that reaches more than just the scientists in the room. Awareness drives change … We need to be able to promote responsible medication disposal and sustainable practices.”
Despite the grim data, she still finds hope in the river’s resilience. “We see the river recovers a bit because of the two ecological zones that act as buffer zones, the Kruger National Park and then the Krokodilpoort, because there’s not a lot of human influence and human impact in those areas, so it gives the river … temporal and spatial capacity to be able to right itself.”