Hout Bay mussels contaminated with hidden toxins and sewage
Hout Bay, a coastal suburb of Cape Town, is facing a growing pollution crisis in its waterways, with increasing levels of pharmaceuticals and other toxins detected in mussels, according to a new study.
The study, by scientists from UCT, Wits, the University of the Western Cape and Stellenbosch University, investigated contamination in the coastal and riverine environments of Hout Bay by assessing pharmaceutical and personal care products in mussels and microbial indicators in water samples.
The researchers set out to determine the extent of the pollution's impact zone. Their analysis of samples taken between 2020 and 2021 found contamination from the Hout Bay marine outfall, inadequate riverine sanitation and other sources indicated an urgent need for upgraded wastewater treatment and infrastructure to protect public and environmental health.
The findings underscored the 'significant impact' of untreated sewage on the environment, the researchers said.
The numbers are stark
Acetaminophen, a common painkiller, was detected at concentrations ranging from 32.74 to 43.02 nanograms per gram of dry mussel tissue (ng/g dw)
Bezafibrate, a drug to lower cholesterol, was by far the most common contaminant, reaching concentrations as high as 384.96 ng/g dw.
Triclosan, an antibacterial found in many personal care products, was also high, at 338.56 ng/g dw.
The results show that marine organisms are consistently being contaminated by medicines and personal care products. The increasing concentrations over time are likely because of more people moving to the area and the growing use of these kinds of products.
The microbial analysis conducted as part of the study detected exceptionally high levels of E. coli in the Hout Bay River, specifically in areas receiving stormwater from the Imizamo Yethu settlement, with counts reaching more than 8.3 million colony-forming units per 100ml (cfu/100 mL).
What it means for residents
Because of the high levels of contamination, regularly eating the mussels and other seafood could lead to chronic exposure to these harmful chemicals, which may cause chronic illness and organ damage, the study says.
However, the effects are far more prominent in marine organisms and marine environments.
According to the study, Hout Bay's contamination levels are comparable to those in other highly urbanised and industrialised regions of the world.
Leslie Petrik, a professor of chemistry at UWC and one of the study's authors, advised residents and beachgoers to 'stay away – the risk is consistently present'.
Petrik said trends indicate that the quality of the water is deteriorating, increasing the risks for recreational users as well as commercial and tourism activities.
'Each of us has a duty for environmental stewardship. The toxicity of these persistent compounds is well documented and should preferably be substituted,' she said.
The city's response
City of Cape Town Deputy Mayor and mayoral committee member for spatial planning and environment, Eddie Andrews, told Daily Maverick that the challenge of the removal of pharmaceutical and product chemicals from wastewater was by no means unique to Hout Bay or Cape Town.
'Wastewater treatment works globally do not generally effectively remove contaminants of emerging concern from sewage, irrespective of the level of treatment,' said Andrews.
Advanced techniques can remove some contaminants, but Andrews said these were costly, energy intensive and impractical at scale for municipal systems.
The city has been investigating long-term options to replace marine outfall pipelines with new wastewater treatment works, but no decisions have been made on the timing of these replacements.
Andrews said that Cape Town faced many competing priorities, with underserved areas requiring basic sanitation upgrades and that the 'prioritisation of limited funding' needed to be weighed up in this context.
An environmental monitoring programme was under way and the sampling of both water and tissue at sites near the marine outfall was providing insight into this issue, he said.
Extensive impact zone
The researchers found that chemicals in pharmaceuticals, including those in antibiotics, antidepressants and hormones, as well as those found in personal care products, are not being adequately diluted or dispersed. Instead, they pass through wastewater systems largely untreated.
As a result, they accumulate and persist in marine environments and organisms, such as the mussels studied, even at significant distances from where the waste enters the waterways.
The main source of contamination is the Hout Bay marine outfall, which releases about 5.7 million litres of screened sewage into the ocean every day, 2.1km from shore at a depth of 39m.
Contamination is also from the polluted inflows from the Disa River and other tributaries, which are heavily affected by the ineffective sanitation infrastructure, especially in informal settlements such as Imizamo Yethu.
The study found that the impact zone around the outfall and river mouth was extensive.
These zones are 'too pervasive for truly safe, consistent recreational use', said Petrik.
The researchers warn that the current sewage treatment is not enough to curb the pollution, and that the marine outfall 'was not designed to handle the ever-increasing volumes of chemical constituents'.
Growing informal housing built over sewer lines means these systems are often blocked or broken, leading to raw sewage routinely flowing down streets and into stormwater drains, which feed directly into the river.
Another key factor identified is Hout Bay's unique geography as a 'bay within a bay', which limits water exchange and circulation. Instead, it acts as a trap, causing pollutants to recirculate back to the shoreline rather than being flushed out to sea.
Improving wastewater systems
Zahid Badroodien, the city's mayoral committee member for water and sanitation, said that Cape Town was committed to continually improving its wastewater systems: 'While the Hout Bay marine outfall currently operates within its design parameters and complies with national discharge regulations, we recognise that CECs [contaminants of emerging concern], including pharmaceutical and personal care products, pose new challenges globally.'
Research on the treatment of these contaminants was ongoing across the world, she said, and the city was 'evaluating multiple long-term options that may address this in the future' at all of its wastewater treatment works.
Petrik said that the study aimed to focus attention on the peculiar way that the city measured impact zones, using a single snapshot model of enterococci levels, which are used to detect faecal contamination. But, she said, the marine outfall and the Disa River released untreated raw sewage continuously, '24/7/365'.
Petrik said that the city should rather trace the chemical fingerprint of sewage to properly understand the impact zones.
'The city keeps claiming that the marine outfall dispersal works according to its design criteria, but the measure of dispersal they use is vastly inadequate.
'Enterococci die off after a while, whereas the persistent contaminants give a far clearer, longer-lasting and traceable measure of the dispersal and thus the impact zones around these point sources of sewage discharge,' said Petrik.
River pollution
The city acknowledged that the Hout Bay River, also known as the Disa River, was in a very poor state due to periodic and ongoing pollution from a number of sources.
'It receives flows from a catchment of approximately 37 square kilometres, which includes natural upper slopes in the Table Mountain National Park, formal residential areas and smallholdings on both sides of the Hout Bay River, formal housing with backyard dwellers in Imizamo Yethu and Hangberg areas, and informal dwellings in Imizamo Yethu, which includes a fairly large informal settlement with limited services,' said Andrews.
City's plan to improve sanitation services in Hout Bay, particularly in informal settlements like Imizamo Yethu
Immediate actions: Increased, proactive cleaning, rapid response to spills, door-to-door inspections to enforce by-laws, and public education campaigns.
Medium-term plans: Exploration of temporary solutions like diverting flows at the Victoria Road pump station and investigating the feasibility of in-line water treatment.
Long-term strategy: A feasibility study in 2028/2029, which will focus on a major upgrade of the Disa River sewer pipe to increase its capacity and resilience.
Badroodien said these efforts were part of a broader R1.25-billion city-wide investment in sanitation infrastructure for the current financial year, with R355-million allocated for sewer pipe replacements and R241-million to upgrade pump stations across Cape Town.
Andrews said that they agreed with the authors of the study that further research into the bioaccumulation of pharmaceutical compounds by bivalves, such as mussels, in a marine protected area was needed.
He said measures of when these contaminants should be considered to be at a level that was harmful both to people and the environment were not yet established, but that the city remained 'engaged in this emerging science as it develops globally'. DM
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Leslie Petrik, a professor of chemistry at UWC and one of the study's authors, advised residents and beachgoers to 'stay away – the risk is consistently present'. Petrik said trends indicate that the quality of the water is deteriorating, increasing the risks for recreational users as well as commercial and tourism activities. 'Each of us has a duty for environmental stewardship. The toxicity of these persistent compounds is well documented and should preferably be substituted,' she said. The city's response City of Cape Town Deputy Mayor and mayoral committee member for spatial planning and environment, Eddie Andrews, told Daily Maverick that the challenge of the removal of pharmaceutical and product chemicals from wastewater was by no means unique to Hout Bay or Cape Town. 'Wastewater treatment works globally do not generally effectively remove contaminants of emerging concern from sewage, irrespective of the level of treatment,' said Andrews. Advanced techniques can remove some contaminants, but Andrews said these were costly, energy intensive and impractical at scale for municipal systems. The city has been investigating long-term options to replace marine outfall pipelines with new wastewater treatment works, but no decisions have been made on the timing of these replacements. Andrews said that Cape Town faced many competing priorities, with underserved areas requiring basic sanitation upgrades and that the 'prioritisation of limited funding' needed to be weighed up in this context. An environmental monitoring programme was under way and the sampling of both water and tissue at sites near the marine outfall was providing insight into this issue, he said. Extensive impact zone The researchers found that chemicals in pharmaceuticals, including those in antibiotics, antidepressants and hormones, as well as those found in personal care products, are not being adequately diluted or dispersed. Instead, they pass through wastewater systems largely untreated. As a result, they accumulate and persist in marine environments and organisms, such as the mussels studied, even at significant distances from where the waste enters the waterways. The main source of contamination is the Hout Bay marine outfall, which releases about 5.7 million litres of screened sewage into the ocean every day, 2.1km from shore at a depth of 39m. Contamination is also from the polluted inflows from the Disa River and other tributaries, which are heavily affected by the ineffective sanitation infrastructure, especially in informal settlements such as Imizamo Yethu. The study found that the impact zone around the outfall and river mouth was extensive. These zones are 'too pervasive for truly safe, consistent recreational use', said Petrik. The researchers warn that the current sewage treatment is not enough to curb the pollution, and that the marine outfall 'was not designed to handle the ever-increasing volumes of chemical constituents'. Growing informal housing built over sewer lines means these systems are often blocked or broken, leading to raw sewage routinely flowing down streets and into stormwater drains, which feed directly into the river. Another key factor identified is Hout Bay's unique geography as a 'bay within a bay', which limits water exchange and circulation. Instead, it acts as a trap, causing pollutants to recirculate back to the shoreline rather than being flushed out to sea. Improving wastewater systems Zahid Badroodien, the city's mayoral committee member for water and sanitation, said that Cape Town was committed to continually improving its wastewater systems: 'While the Hout Bay marine outfall currently operates within its design parameters and complies with national discharge regulations, we recognise that CECs [contaminants of emerging concern], including pharmaceutical and personal care products, pose new challenges globally.' Research on the treatment of these contaminants was ongoing across the world, she said, and the city was 'evaluating multiple long-term options that may address this in the future' at all of its wastewater treatment works. Petrik said that the study aimed to focus attention on the peculiar way that the city measured impact zones, using a single snapshot model of enterococci levels, which are used to detect faecal contamination. But, she said, the marine outfall and the Disa River released untreated raw sewage continuously, '24/7/365'. Petrik said that the city should rather trace the chemical fingerprint of sewage to properly understand the impact zones. 'The city keeps claiming that the marine outfall dispersal works according to its design criteria, but the measure of dispersal they use is vastly inadequate. 'Enterococci die off after a while, whereas the persistent contaminants give a far clearer, longer-lasting and traceable measure of the dispersal and thus the impact zones around these point sources of sewage discharge,' said Petrik. River pollution The city acknowledged that the Hout Bay River, also known as the Disa River, was in a very poor state due to periodic and ongoing pollution from a number of sources. 'It receives flows from a catchment of approximately 37 square kilometres, which includes natural upper slopes in the Table Mountain National Park, formal residential areas and smallholdings on both sides of the Hout Bay River, formal housing with backyard dwellers in Imizamo Yethu and Hangberg areas, and informal dwellings in Imizamo Yethu, which includes a fairly large informal settlement with limited services,' said Andrews. City's plan to improve sanitation services in Hout Bay, particularly in informal settlements like Imizamo Yethu Immediate actions: Increased, proactive cleaning, rapid response to spills, door-to-door inspections to enforce by-laws, and public education campaigns. Medium-term plans: Exploration of temporary solutions like diverting flows at the Victoria Road pump station and investigating the feasibility of in-line water treatment. Long-term strategy: A feasibility study in 2028/2029, which will focus on a major upgrade of the Disa River sewer pipe to increase its capacity and resilience. Badroodien said these efforts were part of a broader R1.25-billion city-wide investment in sanitation infrastructure for the current financial year, with R355-million allocated for sewer pipe replacements and R241-million to upgrade pump stations across Cape Town. Andrews said that they agreed with the authors of the study that further research into the bioaccumulation of pharmaceutical compounds by bivalves, such as mussels, in a marine protected area was needed. He said measures of when these contaminants should be considered to be at a level that was harmful both to people and the environment were not yet established, but that the city remained 'engaged in this emerging science as it develops globally'. DM
