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Article

Assessing Pharmaceuticals in Bivalves and Microbial Sewage Contamination in Hout Bay, Cape Town: Identifying Impact Zones in Coastal and Riverine Environments

by
Cecilia Y. Ojemaye
1,2,*,
Amy Beukes
1,3,
Justin Moser
2,
Faith Gara
1,
Jo Barnes
4,
Leslie Petrik
2 and
Leslie Green
1
1
Environmental Humanities South and Department of Anthropology, University of Cape Town, Cape Town 7701, South Africa
2
Environmental and Nano Science Group, Department of Chemistry, University of the Western Cape, Cape Town 7535, South Africa
3
Wits Planetary Health Research Division, Faculty of Health Sciences, University of Witwatersrand, Johannesburg 2193, South Africa
4
Division of Community Health, Stellenbosch University, Stellenbosch 7602, South Africa
*
Author to whom correspondence should be addressed.
Environments 2025, 12(8), 257; https://doi.org/10.3390/environments12080257
Submission received: 19 June 2025 / Revised: 10 July 2025 / Accepted: 24 July 2025 / Published: 28 July 2025
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Abstract

This study investigates the implications of sewage contamination in the coastal and riverine environments of Hout Bay, Cape Town, South Africa. Chemical analyses were applied to quantify the presence of pollutants such as pharmaceutical and personal care products (PPCPs) in sentinel marine organisms such as mussels, as well as microbial indicators of faecal contamination in river water and seawater, for estimating the extent of impact zones in the coastal environment of Hout Bay. This research investigated the persistent pharmaceuticals found in marine outfall wastewater effluent samples in Hout Bay, examining whether these substances were also detectable in marine biota, specifically focusing on Mytilus galloprovincialis mussels. The findings reveal significant levels of sewage-related pollutants in the sampled environments, with concentrations ranging from 32.74 to 43.02 ng/g dry weight (dw) for acetaminophen, up to 384.96 ng/g for bezafibrate, and as high as 338.56 ng/g for triclosan. These results highlight persistent PPCP contamination in marine organisms, with increasing concentrations observed over time, suggesting a rise in population and pharmaceutical use. Additionally, microbial analysis revealed high levels of E. coli in the Hout Bay River, particularly near stormwater from the Imizamo Yethu settlement, with counts exceeding 8.3 million cfu/100 mL. These findings underscore the significant impact of untreated sewage on the environment. This study concludes that current sewage treatment is insufficient to mitigate pollution, urging the implementation of more effective wastewater management practices and long-term monitoring of pharmaceutical levels in marine biota to protect both the environment and public health.

1. Introduction

One of the greatest benefits of organic chemistry is its contribution to society in the form of progress in human pharmacology. But due to the widespread and ever-growing use of pharmaceuticals for health, the increasing occurrence of pharmaceuticals and personal care products (PPCPs) has been noted in aquatic ecosystems [1]. The increase in population and urbanisation has increased the use and disposal of consumer products such as PPCPs in the urban coastal environment [2]. It has become clear that many pharmaceuticals escape their primary target, ending up in unexpected places [3,4,5,6], and most of their ecological effects are not fully understood.
CECs, including both synthetic and naturally occurring chemical substances such as PPCPs, pesticides, industrial chemicals, and microplastics, are increasingly recognised as environmental threats due to their persistence and potential adverse effects on both human and ecosystem health [7,8,9,10]. These chemicals are often found in trace amounts across various environmental media, including water, soil, and air, making them difficult to detect, monitor, and regulate [9,11,12]. Conventional wastewater treatment processes are generally not designed to effectively remove these CECs, often resulting in their release into surface waters and even drinking water sources [13,14]. Studies have shown that CECs such as PPCPs enter the aquatic environment through a variety of pathways, including municipal sewage, industrial waste, and aquaculture, among others [15,16,17,18].
Among these, pharmaceuticals and related compounds are of particular concern due to their widespread and increasing use in daily medical treatments. Following human and veterinary consumption, these substances are excreted either unchanged or as metabolites and subsequently enter the natural environment through wastewater treatment plants (WWTPs), which often lack the capacity to fully remove them [17,19,20].
Initiatives are underway to enhance the comprehension of the potential impacts associated with CECs and to formulate strategies for their effective management and control. This includes improving monitoring and detection methods, developing more effective wastewater treatment processes, and promoting the responsible use and disposal of chemicals [21,22,23].
Regions with arid and semi-arid climates in countries such as South Africa usually present the most extreme exposure scenarios for pharmaceuticals and other CECs because sewage effluent discharges receive insufficient dilution, which increases the exposure of aquatic life to these contaminants [24,25]. The degradation rate of these contaminants in the aquatic environment is insufficiently rapid to offset their rate of introduction, rendering them pseudo-persistent [26]. Hence, the long-term effects of pharmaceuticals and other persistent organic pollutants on non-target organisms in aquatic environments should not be underestimated or ignored.
Invertebrates such as bivalves (mussels, oysters, top shells) are widely consumed because of their nutritional advantages and appealing flavour [27] and play an important role in the food chain of aquatic ecosystems. However, their propensity to bioaccumulate contaminants and toxins such as CECs from the aquatic environment can have negative effects on both human health and the health of marine ecosystems. Moreover, mussels are sentinel species, indicating levels of pollution that may affect diverse marine biota [28].
Once CECs such as pharmaceuticals are introduced into aquatic environments, they can be readily taken up by filter-feeding organisms like bivalves, leading to the bioaccumulation of these substances in their tissues [29,30]. Pharmaceuticals, including antibiotics, hormones, and antidepressants, are particularly concerning due to their biological activity at low concentrations and persistence in the environment. Many studies have confirmed the capacity of bivalves to accumulate these compounds; however, the specific mechanisms and environmental factors influencing their bioaccumulation are not well-understood [31]. The tendency for bivalves and other marine biota to accumulate contaminants and toxins highlights the need for effective management strategies to reduce the release of pollutants into the environment and to monitor and regulate the levels of contaminants in seafood.
South Africa has legislation in place to protect water resources and prevent sewage pollution. The most important legislation includes the National Water Act (Act 36 of 1998) [32,33], the National Environmental Management Act (NEMA) (Act 107 of 1998) [34,35], and the Water Services Act (Act 108 of 1997) [36,37]. These acts establish a framework for managing wastewater, regulating effluent discharge, and holding polluters accountable. There are also municipal bylaws regulating some local aspects of sewage pollution. The most important vehicle for service delivery or failure thereof happens at the municipal level [38].
Hout Bay is a harbour town on the Atlantic seaboard of the Cape Peninsula, South Africa. Before the rapid development of Hout Bay, domestic sewage was managed using septic tank systems, while wastewater from fish factories was directly discharged into the surf zone [39,40,41]. As urbanisation progressed, a more comprehensive wastewater disposal system was needed. In 1986, the Western Cape Regional Service Council (RSC) proposed a centralised wastewater treatment system. A feasibility study in 1984 recommended the installation of a sewage pump station connected to a marine outfall pipeline instead of a treatment plant [39,42]. Despite opposition from residents who argued that the decision bypassed public participation, the marine outfall project was approved after a Supreme Court ruling [43,44].
The marine outfall was completed and became operational in 1991 and 1993, respectively, after the construction of a pump station. This system involves grit and sand removal, as well as the maceration and screening (to 3 mm) of plastic, paper, and debris before discharging the treated effluent (5.7 ML/day) into the marine environment at a depth of 39 m, 2.1 km offshore [41,45]. The outfall was designed to dilute and disperse effluent from fish-processing factories. However, recent findings indicate that this system may not effectively manage contaminants, especially pharmaceutical and personal care products (PPCPs), which were detected in significant volumes [41,42]. In June 2023, South Africa’s Department of Forestry, Fisheries, and the Environment revoked the permit for the Hout Bay outfall, citing insufficient public participation and outdated assessments. The city’s claims that deep-water effluent discharges meet their objectives of reducing ecological and human health risks have been called into question. Moreover, the CLS report (2022) based its dispersion modelling on limited timeframes, not accounting for the continuous nature of the discharges, further complicating the assessment of long-term impacts.
To understand the actual impact zone of the marine outfall and its contribution to pollution in the bay, bivalves, which are an important component of Hout Bay’s marine ecosystem, were evaluated for CECs listed as being present in the effluent discharged by the marine outfall [41,46]. This research investigated various forms of evidence regarding sewage pollution in Hout Bay. Thus, the objective was to investigate the extent of the impact zone by determining levels of pharmaceutical and personal care products (PPCPs) in marine biota (specifically Mytilus galloprovincialis mussels) and assessing microbial indicators of sewage pollution in riverine and coastal water. This comprehensive approach aimed to determine the spatial influence of sewage pollution and identify impacted zones in Hout Bay’s marine and riverine ecosystems. This study also aimed to identify validated evidence that can contribute to decision-making processes concerning coastal pollution and its sources in the area.

2. Material and Methods

2.1. Site Background/Description

Hout Bay, a harbour town on the Atlantic seaboard of the Cape Peninsula, 20 km south of Cape Town, has experienced significant population growth, with an estimated population of 33,438 in 2011 [39,41,47,48,49]. The northern shore of the bay is sandy, while the southeastern and eastern shores are steep rocky cliffs [39,41]. The sandy shoreline is intersected by the Hout Bay or Disa River (it is contentious and largely debated whether the river should be referred to as the Hout Bay River or the Disa River). However, for the purpose of this discussion, it is referred to as the Hout Bay River, which has relatively little catchment and which flows weakly in summer [41]. In 2004, the coastlines of Hout Bay were designated as part of the Table Mountain National Park Marine Protected Area (TMNP MPA) with the aim of promoting the sustainable use of the marine ecosystem for both commercial and recreational purposes [47].
The population had increased by 94.4% since 1990, and a further 41.8% increase occurred since 2000 [50,51]. Hout Bay is segmented into three primary settlement areas: the Valley, Imizamo Yethu (IY), and Hangberg [47]. The Valley and Hangberg communities are predominantly residential areas with access to basic services, while IY is mainly an informal settlement with limited access to basic services such as water and sanitation [47,52,53]. The population of IY was estimated to be 15,538 in 2011, which was almost as much as the rest of the Valley and Hangberg’s population combined, which stood at 17,900 at the time [48], but given the population increase since then, these numbers are an underestimation. Overall, Hout Bay is a town with residential areas as well as economic activities such as fishing [41,49]. The residents of the Valley and Hangberg are mainly rate payers and live in formal residences, whereas many households in IY live below the poverty line [53].
Over the past 40 years, Hout Bay has transitioned from a rural area to a semi-urban settlement, resulting in higher population density and inadequate infrastructure, particularly in the informal settlement of Imizamo Yethu (IY) [49,53]. The growth of the IY settlement post-1994 was driven by land invasions and political factors, leaving it largely unserviced despite efforts to provide formal housing [54,55].
Hout Bay and IY represent a microcosm of the tensions that may arise between ratepaying residents and informal settlements. Ratepayers pay monthly municipal property rates for services and typically pay market-related prices to purchase properties, with loans that are mostly financed by financial institutions. The many informal communities in South Africa, such as IY, typically are without title deeds for their homes and do not pay property rates. Rate payers are treated as customers by municipalities whereas informal settlements are typically either not serviced or receive inadequate service provision [38].
The pollution in the Hout Bay River is largely due to frequent sewage spills, stemming from inadequate sanitation services and decaying infrastructure in the informal settlements [53]. Yet, many formal households still make use of septic tanks instead of being connected to the sewage system that serves most of the formal properties. The municipal sewage reticulation system is linked to the Hout Bay Marine outfall [41], which has no treatment facility.
Hout Bay has been grappling with longstanding challenges of highly polluted and toxic river water. At one point, the Hout Bay River was recognised as the most polluted watercourse in the south peninsula, recording an alarming nine hundred million (900,000,000) E.coli bacteria per 100 mL of water, significantly surpassing levels typically found in standard sewage [56].
The surface water and stormwater system from the informal settlements as well as the higher-income areas in Hout Bay are deemed to be some of the sources of microbial and chemical pollution into the bay and marine biota. However, higher-income areas in Hout Bay do not experience flooding and sanitation challenges, as their grey and black water is today diverted to the marine outfall, which was commissioned in 1993 [53]. Since the sewage reticulation system linked to the marine outfall services about half the Hout Bay population, the outfall can be considered an important source of chemical and microbial contamination into the marine environment. The marine outfall has largely been disregarded as a source of pollution by the community and the municipality because it is out of sight. Hence, river pollution, which enters the ocean from the river mouth, is deemed to be the major source of visible coastal pollution in Hout Bay.
In January 2023, the City of Cape Town (CoCT) temporarily closed Hout Bay beach as a precautionary measure due to possible unsafe levels of pollution [57,58], yet the municipality still refuses to acknowledge the degree of pollution caused by the marine outfall that pumps megalitres of untreated sewage into the bay daily [46]. These incidences and ongoing discharges highlight the danger of infection when coming into contact with sewage-contaminated effluents.

Sampling Sites

Three sites were selected for mussel collection, namely Fish on the Rocks (site 1), a restaurant located in close proximity to the marine outfall pipeline; Mariner’s Wharf (site 2), which is a tourist attraction in Hout Bay, located between the western end of the beach and the adjacent harbour entrance; and the Bronze Leopard Statue (site 3), located near the eastern end of the beach (Figure 1). Samples were collected during low tidal conditions (Table 1). The criteria for selecting the PPCPs investigated in this study were based on their significant detection levels in Hout Bay’s wastewater effluent [41] in order to understand the extent of the sewage-impacted zone because bacterial levels are often contested [38]. Therefore, the selection of sites for the microbiological samples was chosen at crucial source or entry points to indicate the presence of sewage in the riverine and marine environment. The microbiological determinations played a supplementary role in this study. They were meant to confirm that the pollution is of urban sewage origin. Our selection of mussel sampling sites was strategically guided by longstanding concerns regarding the hydrodynamic characteristics of Hout Bay. The bay has often been described by both local residents and scientists as a “bay within a bay,” where discharged effluent from the marine outfall may not disperse effectively into the open ocean but instead recirculates toward the shoreline. These concerns, first raised in the 1990s by environmental scientists and community members, were based on empirical observations of anti-clockwise nearshore current patterns and visible resurfacing of effluent plumes near high-use recreational zones. In response, we strategically positioned our mussel sampling sites at varying distances and orientations relative to the outfall to assess whether these circulation dynamics influence the spatial distribution and bioaccumulation of pharmaceutical and personal care products (PPCPs) in marine biota. Recent hydrodynamic modelling presented in the Hout Bay Marine Outfall Environmental Summary Report (2022) [59] has now formally substantiated these claims, confirming the bay’s limited flushing capacity and the reintroduction of effluent-laden water into ecologically and socially sensitive areas.
While this study examined both biota and water samples, it is important to note that the quantitative analysis of pharmaceutical and personal care products (PPCPs) was limited to mussel tissues. Water samples were collected for microbial analysis only, using E. coli and Enterococcus spp. as indicators of sewage contamination. The determination of pharmaceutical concentrations in seawater or river water was beyond the analytical scope of this present work.
The microbial samples were taken along the course of the Hout Bay River above and below IY and in proximity to the estuary of the Hout Bay River to understand the extent of sewage pollution reaching the beach via riverine transport and its relative contribution to the sewage discharges into the marine environment. One sample was taken near the upper reaches of the Hout Bay River to demonstrate that the pollution was generated along the urban space of Hout Bay and that the river quality was excellent in the pristine natural habitat.

2.2. Microbiological Sampling and Analysis

Sampling of river and seawater occurred in February 2020 and September 2021 for microbiological analysis. The selection of sites for the microbiological samples was chosen at crucial source or entry points to indicate the presence of sewage in the marine environment. All water samples were taken in sterilised bottles according to international requirements [60]. Single water samples of at least 1 L of water were taken at each sample site. These samples were well homogenised before an aliquot was taken from each bottle. This is the standard procedure for analyses intended to indicate the presence of sewage in water sources in South Africa. River samples were taken 30 cm below the water surface, and the sample bottles were opened and closed underwater to avoid floating contamination, such as oil and solid pollutant matter. The sea water samples were taken close to the shore as far as the sampler could wade in—at least at a 60 cm depth. A field blank was performed by pouring a sample of 1 L of distilled water into a sampling container in the field. Samples and the field blank were immediately placed on ice and delivered to the analysing laboratory within three hours of sampling. The analyses were conducted on the same day so as to minimise die-off of microbes in the sample bottles. The independent laboratory conducting the analyses is accredited by the South African National Accreditation System (ISO17025) [61]. Escherichia coli and Enterococcus spp. were determined as indicators of sewage pollution in the water. This was performed according to the South African National Bureau of Standards [61]. For E. coli enumeration, membrane filtration was used (Rapid E. coli 2 Agar) and incubated at 36 °C ± 1 °C for 18–24 h, while for Enterococcus spp., direct plating was used (Rapid Enterococci Agar), and it was incubated at 35 °C ± 1 °C for 18–24 h.
Water testing using RAPID’E.coli 2 Agar consists of a chromogenic medium and a selective supplement. This medium detects two enzymatic activities simultaneously: coliforms (GAL+/GLUC−), which appear as green colonies, and E. coli (GAL+/GLUC+), which form blue to violet colonies because of the overlay of both colours. The selective supplement inhibits the growth of major interfering flora found in water. This makes it particularly useful for testing water intended for human consumption, as well as untreated water from sources such as wells, rivers, and lakes where standard media are less selective [62]. Water testing using RAPID’Enterococcus Agar is a selective chromogenic medium developed for the direct detection and enumeration of intestinal Enterococci in water samples. This medium is designed for testing both potable and untreated water, such as from wells, streams, and lakes where microbial flora are abundant. It works by detecting β-D-glucosidase activity in Enterococci, which results in a blue colour. The combination of selective media and growth conditions suppresses the growth of Gram-negative bacteria and most Gram-positive bacteria, except Enterococci [63].

2.3. Mussel Sample Collection, Handling, and Preservation

Prior to any marine biota sampling, a preliminary ecological survey was conducted at four potential sampling locations in Hout Bay to check for marine organism presence and densities. From this preliminary ecological survey, the sites were selected to sample invasive mussel species in Hout Bay.
Eighty to one hundred mussel samples (Mytilus galloprovincialis) were collected from the intertidal area at three locations in Hout Bay during 2020 and 2021, placed in polypropylene bags, stored on ice, and transported to the laboratory for processing. Upon arrival at the laboratory, the mussel samples collected from each site were removed from their shells (soft tissue), pooled, and homogenised to form a single representative sample per site. The homogenised samples were then stored at −40 °C prior to freeze-drying. After freeze-drying, the samples were manually ground into a fine powder using a mortar and pestle and kept at −40 °C until further analysis. During the 2021 sampling season, a greater number of juvenile mussels were sampled.

2.4. Reagents and Chemicals

The compounds used for this study were chosen as their origin could only be from their presence in sewage influents from households, and their presence was identified in Hout Bay’s marine outfall pump station effluent samples by the CSIR (2017) report. The compounds under investigation were sourced in their highest purity (>95%) from Sigma-Aldrich (Johannesburg, South Africa), which include acetaminophen, carbamazepine, sulfamethoxazole, diclofenac, triclocarban, efavirenz, naproxen, bezafibrate, aspirin, irbesartan, beta-estradiol, and triclosan. The internal standards (ISs) used were acetaminophen-d4, carbamazepine-d10, diclofenac-d4, and sulfamethoxazole-d4. These standards were sourced from Sigma-Aldrich (Steinheim, Germany) and LGC (Middlesex, United Kingdom). Oasis-HLB SPE cartridges (6 cc, 200 mg) were procured from Waters (Microsep, South Africa), while methanol was purchased from Sigma-Aldrich (South Africa). Procedures were carried out using ultrapure water sourced from the Milli-Q system (Millipore, Bedford, MA, USA).

2.5. Sample Preparation (Extraction and Clean-Up)

For each site-specific homogenised sample, triplicate subsamples (n = 3) of 1 g each were independently processed through the extraction and analytical workflow. These independent aliquots were subjected to methanol extraction, ultrasonic treatment, centrifugation, solid-phase extraction (SPE), and LC–MS/MS analysis, as described below. This procedure was implemented to assess intra-sample variability and ensure analytical reproducibility. The method was adopted from an established method [64]: 1 g of the freeze-dried sample was accurately weighed into a 15 mL centrifuge tube, 3 mL of methanol was added, and then it was vortexed for 30 s. The solution was extracted using an ultrasonic bath at 40 °C for 30 min. Afterward, the sample was centrifuged at 8000 rpm for 10 min, and the resulting supernatant was transferred into a 10 mL volumetric flask. The (solid) sample was further extracted two times using the same process. The three combined supernatants were increased to a 10 mL volume with methanol. Then, 1 mL of the supernatant of each sample was respectively diluted with 9 mL of Milli-Q water to form a 10 mL solution. The resulting solution was loaded onto Solid Phase Extraction (SPE) cartridges with reversed-phase tubes (6 cc 200 mg hydrophilic lipophilic balance (HLB) oasis cartridge). Before use, the SPE cartridges were prepared by first flushing with 2 mL of methanol followed by 2 mL of Milli-Q water. Each sample was then loaded onto its respective SPE cartridge at a flow rate of 1 mL/min using a vacuum manifold. The cartridges were subjected to vacuum drying for 20 min. Then, 2 mL of methanol was employed to extract the sample from each SPE cartridge, and the resulting eluate was dried using a stream of nitrogen gas. Next, the samples were reconstituted by adding 250 μL of methanol and 20 μL of a 1 ng/L mixture of internal standard, vortexing for 30 s, and then were transferred into LC vials for analysis.

2.6. Instrumental Method

The chromatographic separations were conducted using Acquity Ultra Performance Liquid Chromatography (UPLC)TM (Waters, Milford, MA, USA). An Acquity UPLC BEH C18 2.1 × 100 mm, 1.7 μm column provided by Waters enabled the simultaneous determination of all target compounds. The column temperature was set to 50 °C. The mobile phase consisted of 0.1% formic acid in water (solvent A) and 0.1% formic acid in methanol (solvent B). Linear gradient elution of 0.30 mL/min was used starting with 100% of solvent A for 8 min. At 9 min, 100% of solvent B was used and maintained to about 10.49 min, and at 10.50 min, 100% of solvent A was used. An injection of 5 μL from each sample was made into the LC/MS system. All samples and standards were subjected to a 12 min chromatographic run.
The UPLC system was connected to a triple quadrupole mass spectrometer (Xevo TQ-MS) equipped with an electrospray ionisation source. During optimisation, a multiple reaction monitoring (MRM) scan mode was established for all analytes. To maximise sensitivity, various conditions, including source temperature, cone voltage, capillary voltage, cone gas flows, and desolvation temperatures, were set to standardised values. This calibration was conducted by directly injecting stock solutions with a concentration of 10 μg/mL.
The settings used included a capillary voltage of 2.5 kV, desolvation gas (N2) flow rate of 900 L/h, collision gas flow rate of 0.15 mL/min, nebuliser gas flow at 7 Bar, source temperature set to 150 °C, and desolvation temperature at 450 °C. Masslynx software was utilised for analytical operation control and data processing.

2.7. Quality Assurance

Evaluation of selectivity was based on qualitative identification of the compound of interest by comparing the sample’s peak spectra and retention time to what was obtained for the standard. Precision and repeatability were evaluated by calculating the relative standard deviation (RSD) of replicate injections (n = 5) of both the standard and sample. The obtained RSD values were below 20%, indicating acceptable reproducibility for environmental sample matrices. The method’s linearity was evaluated using eleven-point calibration curves within a concentration ranging from 0.1 to 1000 ng/L of each target analyte. The resulting correlation coefficient (R2) values obtained from the analysis were greater than 0.99. The extraction efficiency and percentage recoveries were assessed by calculating the comparison of the concentrations of the analyte of interest in pre-spiked samples and those in post-spiked samples at a concentration of 20 ng/g. The results of the recovery analysis for each analyte can be found in Table 2. The method’s limit of detection and quantification were established based on protocol described in our previous paper [65]. To avoid cross-contamination and analytical interference, all equipment and glassware prior to use were rinsed with methanol and water.

2.8. Statistical Analysis

Statistical analyses and graph creation were conducted using Microsoft Excel®. Pharmaceutical concentrations below the limit of quantification (LOQ) or detection (LOD) were excluded from the analysis unless specified otherwise.

3. Results and Discussion

Figure 2 illustrates the concentrations of PPCPs detected in mussels collected from three distinct sites in the marine environment of Hout Bay during two sampling events over a two-year period. The instrument parameters for each analyte, as well as the recovery percentage and limits of detection and quantification, are presented in Table 2.
The concentrations of individual pharmaceuticals measured in the tissue of mussels in 2020 and 2021 from sites 1 to 3 are presented in Figure 2. Aspirin, beta-estradiol, and efavirenz were below the limit of detection. Among the NSAIDs and analgesics, acetaminophen was found to have the highest concentration, ranging from 32.74 ng/g dw to 43.03 ng/g dw. It was also observed that the measured concentrations for all the analysed compounds in 2021 were higher than the observed concentrations in 2020 in all the sites. This indicates that the contamination may be increasing, which could be because of an increase in population and an increase in the usage of these PPCPs in each area/location.
Bezafibrate, an antilipemic agent (lipid-lowering agent), was the dominant compound observed in all the samples from the three sites as well as in both years and ranged from 308.55 ng/g dw to 384.97 ng/g dw. Triclosan and triclocarban, used in personal care products, were also detected at a higher concentration compared to other compounds. This could be a result of their high usage in the area or their greater persistence. Considerable variations in the chemical burden found in bivalves have been demonstrated across different locations and seasons [66,67,68]. Similar studies conducted along the Mediterranean, Italian, and English coasts have shown significant levels of pharmaceuticals in marine mussels, highlighting a pervasive issue in various coastal regions, as well as locally in Camps Bay and False Bay, South Africa [28,30,65,69]. Comparative data from the Baltic Sea also indicate notable levels of pharmaceuticals like diclofenac (560 ng/g) in coastal waters [70]. The levels observed in Hout Bay are lower than those reported in the Baltic region.
A comparison with other coastal regions that have conducted similar studies on mussels was made (Table 3). In the Italian coastal waters of the Tyrrhenian and Adriatic Seas [69], reported concentrations of pharmaceuticals in mussels observed levels of diclofenac reaching up to 109.3 ng/g, and carbamazepine up to 279.6 ng/g. Similarly, off the English coast [30], it was found that mussels contained pharmaceuticals with concentrations ranging from 0.06 to 1.09 ng/g wet weight (ww). Studies from the Portuguese Atlantic coast by Reference [71] have demonstrated diclofenac levels (0.5–4.5 ng/g) in mussels, with spatial variations influenced by local pollution sources. Further, a study in the Belgian coastal zone conducted by Reference [72] demonstrated a range of pharmaceutical contaminant levels in M. edulis, with concentrations of acetaminophen and carbamazepine up to 115 ng/g and 11 ng/g, respectively, while off the Brazilian Coast, concentrations of diclofenac (0.81 ng/g ww) and carbamazepine (0.47 ng/g ww) were seen [73].
In comparison, these findings indicate that the contamination levels in Hout Bay are comparable to those observed in other highly urbanised and industrialised regions of the world. The findings from this study, when compared with those from other coastal regions globally, suggest that the levels of pharmaceutical contaminants in Hout Bay are on par with or exceed those found in many other urbanised coastal environments. This suggests that the pharmaceutical contamination observed in Hout Bay is not only significant but also aligns with trends seen in other global coastal environments exposed to urban wastewater pollution. These comparable levels point to a significant concern regarding the impact of untreated or inadequately treated sewage effluent on marine ecosystems in Hout Bay, as seen in other urban coastal regions.
Although this study assessed microbial pollution in both river and coastal waters, a chemical analysis of PPCPs was performed exclusively on mussel tissue samples due to the study’s focus on bioaccumulation in sentinel organisms. While measuring PPCPs in water could provide valuable additional context, such analyses require different extraction and concentration methods and were outside the scope of this current investigation. Nonetheless, the elevated levels of sewage related PPCPs in mussels, particularly at considerable distances from known discharge points, indicate their persistent presence in the surrounding marine environment, which is influenced by both riverine and outfall sources.
The levels of pharmaceutical contaminants in Hout Bay’s mussels also reflect the ongoing challenges associated with pollution management in semi-enclosed coastal environments: Hout Bay’s “bay within a bay” structure leads to limited water exchange and circulation, which may exacerbate the accumulation of pollutants. The findings highlight the need for enhanced wastewater treatment processes and stricter regulations, similar to those recommended in other regions, to mitigate the impacts of these contaminants on both the environment and public health. By drawing on these studies, we can contextualise the severity of pharmaceutical pollution in Hout Bay, reinforcing the argument that the observed contamination is part of a broader global issue. This highlights the urgency for more effective monitoring, management, and mitigation strategies to address pharmaceutical pollutants in marine environments worldwide.
In addition, the presence of these pharmaceuticals in mussels from Hout Bay is concerning, particularly when considering the bioaccumulation potential and biomagnification up the food chain. Studies have shown that contaminants such as pharmaceuticals, even at trace levels, can accumulate in marine organisms and pose health risks to humans over time [83,84]. Given that mussels are filter feeders and are likely to accumulate higher levels of contaminants, the consumption of these mussels by local communities could lead to chronic exposure to these harmful substances. The results of the microbial analysis are presented in Table 4 and Table 5.
The South African Dept. of Environmental Affairs guideline gives the 90th percentile per 100 mL water for E. coli as ≤ 500 organisms and ≤ 185 organisms for Enterococcus. The United States Environmental Protection Agency, on the other hand, used far more stringent criteria for action: for Enterococcus, the beach action value (BAV) threshold when action should be taken is 60 colony-forming units per millilitre (cfu/mL), and for E. coli, the BAV is 190 cfu/mL (or, for both, the equivalent “most probable number” (MPN/mL) [39,41,87].
By South African standards, the microbial counts for both seasons’ samples taken in the Hout Bay River were significantly above the Enterococci criteria for safety in both Table 4 and Table 5, apart from the sample taken in the higher reaches of the river. One seawater sample in Table 4 taken at the Fish on the Rocks site, which is about 700 m from the marine outfall discharge, was close to the limit for Enterococcus. By US standards, all the river water samples, except the sample taken high up the river, and all three seawater samples would have failed the threshold for Enterococcus spp. The variable microbial count in seawater at the three sampling sites along the Hout Bay coast (Table 4) at a distance greater than the 212 m zone of initial dispersal from both the mouth of the Hout Bay River as well as from the marine outfall was relatively low; thus, E.coli and Enterococcus were not shown to be reliable or sensitive indicators of sewage pollution after dilution in seawater. The results in Table 5, on the other hand, represent a significant deterioration of environmental river water quality over the intervening years. Where the stormwater from the informal settlement of IY joins the river, the water quality represented a high risk to people and the environment. Downriver, where the river crosses the beach to join the sea, the E. coli count was still grossly elevated and presented a risk to beach-goers as well as the marine environment into which it decants. Although IY does have a reticulated sewerage system, the densification of shacks meant that many constructions were erected over the sewer lines, which thus cannot be repaired and are blocked or non-functional in many places, as is manifestly visible on any given inspection day. Sewage regularly runs down IY streets and into the stormwater drains, which drain straight to the Hout Bay River. Thus, the surface run-off of sewage from the informal settlement is the most probable cause of the enormous E. coli count shown in Table 5, where this stormwater joins the Hout Bay River. The Pearce study (1989) concluded that pollution in the surf zone of Hout Bay enters through the Hout Bay River, which is not polluted because of groundwater but because of surface run-off that is sometimes impacted by the run-off of inefficient septic tanks, among many other inputs.

Addressing CECs in Hout Bay’s Marine Environment

This study investigated whether diverse sewage related PPCPs, present in outfall wastewater, were also accumulating in mussels. Samples collected in 2020 and 2021 revealed that many of the same PPCPs detected in the 2017 wastewater samples were also present in mussels, including sites far from the outfall, demostrated a wider impact zone. The findings highlight that the current outfall design may fail to ensure sufficient dilution of chemical and microbial contaminants, exacerbated by population growth. Hout Bay’s unique geography limits the dilution of contaminants and causes polluted water to recirculate, facilitating the accumulation of PPCPs in filter feeders like mussels. These organisms serve as prey for higher trophic levels, thereby magnifying the ecological and potential human health risks.
The presence of PPCPs in Hout Bay is not solely attributed to the marine outfall but may also come from the Hout Bay River due to inadequate wastewater infrastructure and poor sanitation. A recent study by the City of Cape Town (2022) investigated the levels of pharmaceutical compounds and faecal indicator bacteria (FIB) in water samples collected from both the Hout Bay River and nearby beach sites. The river water was found to contain measurable concentrations of pharmaceutical compounds such as acetaminophen, naproxen, hydrochlorothiazide, atenolol, codeine, and ibuprofen, along with elevated FIB levels. In contrast, water samples from Hout Bay beach showed undetectable FIB levels, with fewer pharmaceutical compounds, including acetaminophen, bezafibrate, ofloxacin, salicylic acid, azithromycin, sulfamethoxazole, trimethoprim, and alprazolam.
The City’s study suggests that the PPCPs in nearshore waters were more likely to originate from the Hout Bay River, where frequent sewage spills and runoff from inadequately serviced settlements contribute to the pollution [53]. However, most pharmaceutical compounds detected in the river were not found in wastewater effluent or mussel samples we investigated, with the exception of acetaminophen and naproxen. Although some PPCPs in mussels may have been discharged into the river, the majority of Hout Bay’s serviced population, including the business centre, tourist attractions, and the harbour, disposes of its sewage through the marine outfall. This suggests that PPCPs found in mussel samples could originate from both the marine outfall and, occasionally, the Hout Bay River, where they are subsequently absorbed by marine organisms.
These findings emphasise the need for ongoing monitoring to identify the sources of sewage-related contaminants and suggest that the current design of the marine outfall is insufficient for achieving high levels of dilution and dispersal of contaminants of emerging concern.
The first microbial survey indicated that the river was a source of microbial pollution but also showed microbial pollution in coastal environments furthest from the river and outfall. The second microbial sampling sought to provide additional data to understand the origin of the microbial contamination.
The data in Table 3 and Table 4 clearly show the deteriorating sewage intrusion into the river over the short time between the two sampling sessions. Urban sewage does not only contain human excreta but also a vast variety of chemical compounds, depending on the economic and household activities in the drainage area. The composition changes, sometimes over short periods.
The concentrations of microbiological indicators of sewage pollution in Table 4 also represent a direct health risk, especially to the members of the public using the stretch of river below the dense settlement of IY and the popular beach where the highly polluted river water drains into the sea.
Providing improved sanitation to the informal part of the urban area of Hout Bay would reduce the amount of untreated sewage reaching the bay via the river as well as any overland runoff or contaminated stormwater drainage. That will be an improvement but will not address the very significant volume of persistent pollutants originating from the marine outfall.
Thus, addressing the issue of inadequate wastewater infrastructure and proper sanitation in informal settlements along the river would not be sufficient to solve the problem, as CECs would still be present in wastewater transported through a reticulated sewage system, discharged via the marine outfall pump station, and eventually dispersed into the marine environment through the marine outfall pipeline. The contamination in Hout Bay has not improved in the intervening period, as can be seen from the city’s coastal quality dashboard with the 5-year average water quality rated as poor [88].
To address the issue and presence of CECs in Hout Bay’s marine receiving environment, a more comprehensive approach is needed, as the marine outfall was not designed to handle the ever-increasing volumes of chemical constituents, and no urban river should serve as an open sewer, as the Hout Bay River case demonstrates. This underscores the need for more proactive measures to identify and regulate the release of CECs into the environment, as well as invest in the necessary infrastructure to adequately service all residents so as to address the issue.

4. Conclusions

In summary, our study and other studies have found evidence of various pharmaceutical and personal care product compounds (PPCPs) in Hout Bay’s marine receiving environment, and our study shows conclusively that these compounds bio-accumulate and persist in mussel samples at a considerable distance from the point sources, namely the marine outfall and river mouth. The compounds are present due to their widespread use, as well as excretion from human bodies, transport through wastewater reticulation systems or irregular disposal, and eventual dispersion into the marine environment.
The detection of pharmaceuticals and personal care products in mussel tissues confirms the accumulation of these compounds by sentinel organisms, demonstrating the environmental impact of widespread medication consumption and dispersal through both marine outfall and riverine sewage effluent. The results indicate an extensive impact zone around the outfall and river mouth, with inadequate dispersal to protect the marine or coastal environment. The geographic extent of the plume and concentration gradients of persistent chemicals found at significant distances from the diffusers show that the apparent dilution based on instantaneous modelling of enterococci is not an adequate tool for measuring impacts at any distance from the discharge. The findings indicate that the impact zone around the marine outfall and river mouth is extensive, with inadequate dispersal to prevent contamination of the marine environment. Effective monitoring and mitigation measures are essential to address the widespread dispersal of CECs and microbes in Hout Bay. Since the sewage reticulation system linked to the marine outfall services about half the Hout Bay population, the outfall is an important source of chemical and microbial contamination into the marine environment and cannot be disregarded by the community and the municipality as a significant source of pollution.
The history of municipal decision making in choosing sewage disposal options in Hout Bay that were not acceptable to the residents of this isolated urban suburb of Cape Town has played a significant role in the pollution by sewage of the coastal areas. Moreover, the lack of control of unserviced land invasion has exacerbated the sanitation issues the residents of Hout Bay are exposed to. Furthermore, the use of flawed methods such as instantaneous dispersion modelling to motivate the governmental reissuance of marine outfall highlights the role that contested decision making has had in polluting a once-pristine environment.
While the wastewater infrastructure and sanitation need improvement to reduce the contribution of CECs from the Hout Bay River, the presence of CECs in wastewater processed through a reticulated sewage system and the marine outfall design criteria require further attention to address this issue adequately. The accumulating volumes of CECs in filter-feeders like mussels demonstrate the overarching issue of inadequate dilution in Hout Bay’s “bay within a bay” environment that impacts a host of marine life.
Further research into the extent of the impact zone and the factors that contribute to the extensive dispersion and thus the bioaccumulation of pharmaceutical compounds by bivalves in a marine protected area is needed, in addition to a better understanding of the potential risks associated with consuming these organisms. This study highlights the urgent need to establish the extent of antimicrobial resistance in faecal coliforms found in the riverine and estuarine environment of Hout Bay.

5. Recommendations

The issue of persistent contaminants in wastewater has become increasingly urgent in recent years, especially in the context of the COVID-19 pandemic and the energy crisis. The increased use of certain chemicals during the pandemic has led to higher concentrations of these contaminants in wastewater, which can be harmful to the environment and public health.
A multi-faceted approach is needed to address persistent contaminants in wastewater. This includes updating and adapting wastewater treatment technologies, reducing harmful chemical usage, and implementing effective regulations to control contaminant discharge, especially given emerging challenges like public health pandemics, load-shedding, and increasing population densities. It is crucial that these efforts are prioritised and sustained to ensure the long-term health of our ecosystems and communities. Such challenges can have significant environmental and public health implications, making it essential to invest in upgrading existing systems and developing new technologies.
The urgent need to replace marine outfalls with land-based wastewater treatment systems is a global issue, presenting an opportunity for cross-border collaboration and innovation to develop sustainable solutions. Innovation in wastewater treatment technologies can lead to more efficient and cost-effective solutions that can provide multiple benefits, such as reducing water pollution, conserving resources, generating renewable energy, and promoting public health. Therefore, it is crucial to prioritise research and development in this area and support initiatives that promote sustainable wastewater management practices.
Overall, responding appropriately to the urgent need for upgrading wastewater treatment and providing access to safe and adequate sanitation systems to all communities is critical to safeguarding public health and the environment and promoting sustainable development.

Author Contributions

C.Y.O.: Conceptualisation, Investigation, Methodology, Data curation, Formal analysis, Writing—original draft, Writing—review and editing, A.B.: Investigation, Methodology, Data curation, Writing—review and editing. J.M.: Investigation, Methodology, Visualisation, Writing—review and editing. F.G.: Investigation, Writing—review and editing. J.B.: Investigation, Methodology, Formal analysis, Writing—review and editing, Data curation. L.P.: Conceptualisation, Project administration, Validation, Resources, Supervision, Funding acquisition, Writing—review and editing. L.G.: Conceptualisation, Project administration, Validation, Resources, Supervision, Funding acquisition, Writing—review and editing. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by [National Research Foundation] grant number [118754] and the Science for Africa Foundation’s DELTAS Africa II program (Del:22-010) supported by the Welcome Trust and the Foreign and Commonwealth Development Office of the United Kingdom.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Acknowledgments

We extend our sincere gratitude to the National Research Foundation for funding the project under SANOCEAN Project no: 118754, titled “Marine Sewage Outfalls—Environmental Impact Evaluation.” This research was supported by Critical Zones Africa consortia and funded by the Science for Africa Foundation’s DELTAS II and University of Cape Town Carnegie DEAL Sustainable Development Goals Post-Doctoral Fellowship. We thank Denzil Brent for drawing the map of the study area.

Conflicts of Interest

The authors declare no conflicts of interest.

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Environments 12 00257 g001
Figure 1. Map of the sampling site of Hout Bay.
Figure 1. Map of the sampling site of Hout Bay.
Environments 12 00257 g001
Environments 12 00257 g002
Figure 2. Concentration (n = 3) of pharmaceuticals in mussel samples. Fish on the Rocks—site 1; Mariner’s Wharf—site 2; Bronze Leopard Statue—site 3.
Figure 2. Concentration (n = 3) of pharmaceuticals in mussel samples. Fish on the Rocks—site 1; Mariner’s Wharf—site 2; Bronze Leopard Statue—site 3.
Environments 12 00257 g002
Table 1. Sampling location basic information.
Table 1. Sampling location basic information.
Sampling Site/Name Longitude and LatitudeTime Wind/Speed Direction
2020202120202021
Site 134°03′18.8″ S 18°20′52.2″ E7:35 a.m.6:54 a.m.7 km/h S 10 km/h S
Site 234°02′51.4″ S 18°20′56.0″ E8:30 a.m.8:00 a.m.7 km/h S 10 km/h S
Site 334°02′55.6″ S 18°21′38.8″ E9:15 a.m.9:10 a.m.7 km/h S 10 km/h S
Table 2. Instrument parameters and target analyte information.
Table 2. Instrument parameters and target analyte information.
Compound NameMolecular Weight (g/mol)Molecular StructureLog KowRT (min)Ion Transition (m/z)Ionisation ModeCE (eV)LOD (ng/g)LOQ (ng/g)% Recovery
Acetaminophen151.16Environments 12 00257 i0011.103.22152 > 93152 > 110ES+240.431.3098.5
Carbamazepine236.27Environments 12 00257 i0022.676.43237 > 135
237 > 179		237 > 194ES+100.20.599.2
Sulfamethoxazole253.28Environments 12 00257 i0031.314.50254 > 147254 > 156ES+250.3198.9
Diclofenac296.15Environments 12 00257 i0044.069.12296 > 215296 > 250ES+150.7299.1
Triclocarban315.58Environments 12 00257 i0055.288.76313 > 126313 > 160ES-200.61.997.2
Efavirenz315.67Environments 12 00257 i0064.847.11316 > 168316 > 244ES+309.93090.4
Naproxen230.26Environments 12 00257 i0073.007.68231 >149231 > 185ES+200.20.598.5
Bezafibrate361.82Environments 12 00257 i0083.819.06360.12 > 273.9360.12 > 273.9ES-200.82.598.9
Aspirin180.16Environments 12 00257 i0091.199.2136.7 > 64.6136.7 > 92.7ES-204.91590.1
Irbesartan428.53Environments 12 00257 i0104.509.80429.1 > 206.9429.1 > 206.9ES+200.20.598.9
Beta-estradiol272.4Environments 12 00257 i0114.139.25271 > 183271 > 183ES-209.93096.2
Triclosan289.54Environments 12 00257 i0125.179.20289 > 34.8289 > 35ES+559.93097.5
Quantification ion in bold.
Table 3. Concentration of pharmaceuticals from other studies. nd: not detected; LOD: limit of detection; ww: wet weight; dw: dry weight.
Table 3. Concentration of pharmaceuticals from other studies. nd: not detected; LOD: limit of detection; ww: wet weight; dw: dry weight.
LocationCompoundsConcentrationReferences
San Francisco BayCarbamazepine
Sulfamethoxazole
Triclocarban		1.3–5.3 ng/g ww
<LOD
<LOD–1.5 ng/g ww		[74]
Ebro Delta, Tarragona, SpainTriclosan
Carbamazepine
Sulfamethoxazole		1106.44 ng/g dw
453.2 ng/g dw
81.3 ng/g dw		[75]
Ebro Delta (Spain)Sulfamethoxazole<LOQ[76]
False Bay, South AfricaAcetaminophen
Sulfamethoxazole
Carbamazepine
Diclofenac		46.7–85.5 ng/g dw
36–272 ng/g dw
26.06–66.00 ng/g dw
67.67–232.33 ng/g dw		[65]
Northwestern Adriatic SeaCarbamazepine
sulfamethoxazole		2 ng/g
43 ng/g		[77]
Ebro Delta, Tarragona, EuropeSulfamethoxazolend–<LOQ[78]
SingaporeCarbamazepine<LOQ–0.1 ng/g[79]
Italian coastDiclofenac
carbamazepine		<1.4–171.1 ng/g dw
<1.0–299.7 ng/g dw		[69]
Coastal lagoon (Ravenna, Italy)Diclofenac2.1–4.6 ng/g ww[80]
Brazilian coastsNaproxen
Carbamazepine
Diclofenac
Bezafibrate		nd–1.6 ng/g ww
nd–0.9 ng/g ww
nd–3.0 ng/g ww
nd–5 ng/g ww		[73]
Benalmádena (S Spain)Bezafibrate<LOQ–2.7 ng/g dw[81]
Gulf of Gdansk (southern Baltic Sea)Diclofenac
Naproxen		560 ng/g dw
473 ng/g dw		[70]
USATriclocarban1.02–46.2 ng/g ww[82]
Table 4. Samples for microbiological analyses from the Disa River and the sea at Hout Bay on 27 February 2020.
Table 4. Samples for microbiological analyses from the Disa River and the sea at Hout Bay on 27 February 2020.
Sampling Site—NameSourceResults
cfu/100 mL
E. coliEnterococcus
Disa River at Disa River Street bridgeRiver100727
Disa River at Victoria Street bridgeRiver14002420
Fish on the RocksSea100150
Mariner’s WharfSea1824
Bronze Leopard StatueSea1624
* South Africa Limit-≤500≤185
* USEPA Limit (freshwater)-12633
* USEPA Limit (marine water)--35
* South Africa Limit—Reference [85]; * USEPA Limit—Reference [86].
Table 5. Samples for microbiological analyses from the Disa River and the sea at Hout Bay on September 2021.
Table 5. Samples for microbiological analyses from the Disa River and the sea at Hout Bay on September 2021.
Sampling Site—NameTypeE. coli
(cfu/100 mL)
Hout Bay top of valley (weir below cascade)RiverNone detected
At Victoria Street BridgeRiver300
At the join of stormwater from Imizamo YethuRiver8,300,000
Estuary on beach, short distance from seaEstuary (semi-saline)50,000
* South Africa Limit ≤500
* USEPA Limit 126
* South Africa Limit—Reference [85]; * USEPA Limit—Reference [86].
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MDPI and ACS Style

Ojemaye, C.Y.; Beukes, A.; Moser, J.; Gara, F.; Barnes, J.; Petrik, L.; Green, L. Assessing Pharmaceuticals in Bivalves and Microbial Sewage Contamination in Hout Bay, Cape Town: Identifying Impact Zones in Coastal and Riverine Environments. Environments 2025, 12, 257. https://doi.org/10.3390/environments12080257

AMA Style

Ojemaye CY, Beukes A, Moser J, Gara F, Barnes J, Petrik L, Green L. Assessing Pharmaceuticals in Bivalves and Microbial Sewage Contamination in Hout Bay, Cape Town: Identifying Impact Zones in Coastal and Riverine Environments. Environments. 2025; 12(8):257. https://doi.org/10.3390/environments12080257

Chicago/Turabian Style

Ojemaye, Cecilia Y., Amy Beukes, Justin Moser, Faith Gara, Jo Barnes, Leslie Petrik, and Leslie Green. 2025. "Assessing Pharmaceuticals in Bivalves and Microbial Sewage Contamination in Hout Bay, Cape Town: Identifying Impact Zones in Coastal and Riverine Environments" Environments 12, no. 8: 257. https://doi.org/10.3390/environments12080257

APA Style

Ojemaye, C. Y., Beukes, A., Moser, J., Gara, F., Barnes, J., Petrik, L., & Green, L. (2025). Assessing Pharmaceuticals in Bivalves and Microbial Sewage Contamination in Hout Bay, Cape Town: Identifying Impact Zones in Coastal and Riverine Environments. Environments, 12(8), 257. https://doi.org/10.3390/environments12080257

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