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Biomonitoring of surface water quality in Africa: contamination levels by chemical pollutants, including emerging pharmaceutical compounds and heavy metals, and the use of biomarkers – a literature review

Afoussatou Amadou, Nelly Kelome et Victorien Tamègnon Dougnon
Cet article est une traduction de :
Biosurveillance de la qualité des eaux de surface en Afrique : niveaux de contamination en polluants chimiques dont les composés pharmaceutiques émergents et les métaux lourds et utilisation de biomarqueurs, une revue de littérature []

Résumés

La pollution chimique des eaux de surface représente un défi majeur en Afrique, notamment dans les zones urbaines et industrialisées. L’utilisation des biomarqueurs pour surveiller cette pollution apparaît comme une approche efficace pour évaluer la qualité de l’eau et ses impacts sur les écosystèmes aquatiques. Cette revue de littérature vise à renforcer les connaissances sur l’application des biomarqueurs dans le suivi des polluants chimiques particulièrement des composés pharmaceutiques émergents (CPE) et des métaux lourds en Afrique. Une analyse de 50 articles scientifiques publiés entre 2010 et 2025 a été réalisée. Les résultats montrent que les biomarqueurs permettent de détecter les effets des polluants chimiques sur les organismes aquatiques. Une augmentation de l’activité enzymatique a été observée chez les poissons exposés aux contaminants, traduisant une réponse biologique au stress chimique. De plus, les biomarqueurs de stress oxydatif se révèlent particulièrement utiles pour évaluer l’impact de la pollution en mesurant les radicaux libres et les antioxydants dans les tissus des poissons. L’intégration des biomarqueurs dans le suivi de la pollution chimique en Afrique constitue un outil puissant pour évaluer la qualité des eaux et les conséquences des activités humaines sur les écosystèmes aquatiques. Ces données fournissent des bases solides pour orienter les recherches futures et renforcer les politiques de gestion de la qualité de l’eau à l’échelle continentale.

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We would like to thank the African Centre of Excellence for Water and Sanitation (C2EA), National Water Institute, University of Abomey-Calavi (Benin), for the financial support provided for this study. We also extend our thanks to the International Academy of Francophone Science (AIFS) for their assistance in submitting this research.

Introduction

1Chemical pollution of surface waters is a major problem in Africa, particularly in urban and industrial areas (Afsa et al., 2022). This pollution can originate from various sources, including emerging pharmaceutical compounds (EPCs) and heavy metals, which are of increasing concern due to their potential impact on human and environmental health (Santana et al., 2018a; Martínez et al., 2023). EPCs, such as antibiotics, anti-inflammatories, analgesics and hormonal contraceptives, anticonvulsants and psychotropic drugs, radiological contrast agents, and antiretrovirals, are often poorly removed by wastewater treatment systems, and some end up in surface waters (Kartal and Bildik, 2022; Ogunlaja et al., 2022). Several African studies highlight the presence of significant concentrations of CPEs and heavy metals in surface waters (Baguma et al., 2022; Hossein and Ripanda, 2025). A study in West Africa reports total concentrations of pharmaceuticals and personal care products in surface waters reaching approximately 100 µg/L in some urban/peri-urban sites (Cangola et al., 2024). Another literature review in the Central and East African region reports ecotoxicological risks from substances such as estradiol, spiramycin, and diclofenac in surface waters (Mheidli et al., 2022a). In a study in Benin conducted on rivers and lagoons around Cotonou, Gbotche et al. (2023) identified concerning concentrations of mercury, lead, and cadmium in sediments. These studies suggest that exposure of aquatic fauna to EPCs and heavy metals in African urban areas could lead to toxicological effects, bioaccumulation, and even antibiotic resistance (Shaalan and Sayed, 2025).

2The implementation of effective biomonitoring is a reliable way to rapidly identify pollution sources and understand their effects on aquatic ecosystems. This environmental approach involves measuring biological changes in living organisms (humans, animals, plants, etc.) to detect the effects of pollution (Muñiz-González et al., 2021). Various techniques are used to assess the quality of aquatic environments, including physicochemical, microbiological, and ecotoxicological approaches. However, among the most recent and promising tools is the use of biomarkers, which enable early detection of the biological effects of contaminants on aquatic organisms (Olajuyigbe et al., 2020; Afsa et al., 2022; Nyaaba et al., 2023).

3Biomarkers, whether biochemical, physiological, or molecular, provide early information on the interactions between contaminants and aquatic organisms before visible signs of toxicity appear. Their application extends to various model organisms such as fish, mollusks, and crustaceans (Mheidli et al., 2022; Ogunlaja et al., 2022). The specificity of biomarkers for environmental pollutants depends on the targeted metabolic or endocrine pathways. For example, anti-inflammatory and analgesic drugs stimulate biotransformation enzymes (glutathione transferase), indicating oxidative stress; psychotropic drugs and beta-blockers affect the nervous system via the inhibition of acetylcholinesterase (AChE); while compounds with estrogenic activity induce vitellogenin (VTG) or alter thyroid hormones. These biomarkers make it possible to associate each class of EPC with a specific toxic mechanism, thus constituting a mechanistic approach that links emerging pharmaceutical compounds to the biological and metabolic pathways they disrupt.

4Although still underdeveloped in Africa, this approach shows strong potential for characterizing exposure to and sublethal effects of pharmaceutical residues in aquatic ecosystems (Ripanda et al., 2022; Martínez et al., 2023). This systematic literature review aims to synthesize and expand knowledge on the use of biomarkers for monitoring surface water pollution by emerging pharmaceutical compounds (EPCs) and heavy metals in Africa. It is structured around the biomonitoring of aquatic ecosystems, the presence and impact of EPCs, the biomarkers used, and their advantages and limitations.

Methods

5A literature search was conducted on Google Scholar, PubMed, Scopus, ScienceDirect, and Web of Science to identify studies related to surface water biomonitoring in Africa, using the keywords: "biomonitoring," "surface water," "biomarkers," "Africa," "chemical pollution," "emerging pharmaceutical compounds," and "heavy metals." The selection criteria for articles were as follows: articles published between 2010 and 2025, available in English or French, and presenting relevant data related to the topic. The PRISMA method was applied (Moher et al., 2009).

6A total of 200 articles were selected, including 145 original articles and 55 review articles, of which 80 were retained. The studies originated from 16 African countries (Figure 1) and focused on physicochemical, bacteriological, molecular, histological, immunological, and enzymatic parameters. The organisms studied included water, sediments, fish, and plants.

Figure 1: Map showing countries that have conducted biomonitoring studies of surface water pollution in Africa

Figure 1: Map showing countries that have conducted biomonitoring studies of surface water pollution in Africa

Results and discussion

Biomonitoring of aquatic ecosystems in Africa

7Surface water biomonitoring in Africa varies considerably from country to country and depends on numerous factors, including available resources, geographical, climatic, and demographic contexts, environmental priorities, public policies, and technical and institutional capacities (Adjagodo et al., 2018; Baguma et al., 2022). Despite progress in some regions, biomonitoring remains a relatively recent concern, often considered secondary to other environmental emergencies such as solid waste management or industrial emission reduction (Sousa et al., 2018). Limited financial, human, and technical resources, combined with significant institutional fragmentation, hinder the implementation of coherent and sustainable environmental monitoring programs in Africa. Indeed, the lack of coordination among key stakeholders (ministries of the environment, research institutes, universities, and civil society organizations) leads to a dispersion of initiatives and a lack of harmonization of collected data (Weiss et al., 2016). This situation limits the scope, continuity, and quality of surface water biomonitoring programs (Mangadze et al., 2019; Domingo-Echaburu et al., 2021). Consequently, it becomes difficult to obtain an accurate and integrated assessment of the state of aquatic ecosystems and to reliably measure the impact of anthropogenic pressures on their functioning (Patel et al., 2020).

8Biotic and abiotic factors (Figure 2) (living and non-living elements) play a crucial role in the quality of aquatic ecosystems. Contamination levels, which simultaneously affect soils, water, and living organisms, reflect the diversity and intensity of anthropogenic pressures and influence the evolution and persistence of contaminants over time (Anjanapriya et al., 2021). Biotic factors, such as microbial activity and bioaccumulation in aquatic organisms, also contribute to the transformation, retention, or redistribution of pollutants (Anjanapriya et al., 2021; Domingo-Echaburu et al., 2021). Thus, the contamination of aquatic environments is a dynamic process, modulated both by the intrinsic properties of contaminants and by ecological and climatic variations that determine their fate in the environment.

9The main pollutants involved are heavy metals (lead, mercury, cadmium, chromium) and organic compounds (pesticides, solvents, pharmaceuticals) presented in Table 1, mainly originating from industrial, mining, agricultural, and domestic activities that are often poorly regulated. In addition, nutrients (nitrogen, phosphorus) from fertilizers and wastewater contribute to eutrophication, as does recurring microbial contamination ( E. coli, Salmonella, Vibrio cholerae ), an indicator of health risks related to fecal contaminants in water (Lawani et al., 2017; Anjanapriya et al., 2021). The most widely used analytical methods, including high-performance liquid chromatography (HPLC), mass spectrometry (MS), and molecular biology, enable the accurate detection of chemical and biological contaminants (Kasonga et al., 2021; Ogunlaja et al., 2022; Ripanda et al., 2022). However, in Africa, their use remains hampered by the high cost of equipment, the shortage of specialized laboratories, and the lack of technical training in several African countries.

Figure 2: Factors influencing the contamination of the aquatic ecosystem over time

Figure 2: Factors influencing the contamination of the aquatic ecosystem over time

Inspired by Anjanapriya et al., 2021.

Table 1. Pollutants found in aquatic ecosystems in Africa

Ecosystem

Type of pollutants

Contaminants

Source of contamination

Diagnostic methods

References

Soil, water, aquatic plants, fish

Heavy metals

Lead, mercury, argon, cadmium, copper, manganese, chromium and zinc

Industrial, mining, agricultural or domestic sources

HPLC, MS

Farombi et al., 2007; Yang et al., 2021

Soil, water,

Nutrients

Phosphorus and nitrogen

Agriculture and wastewater.

Spectrophotometry

Paré and Bonzi-Coulibaly, 2013

Soil, water, aquatic plants, fish

Organic chemicals

Pesticides, herbicides, solvents and pharmaceuticals

Industrial, agricultural or domestic sources.

HPLC, MS

Olisah, 2020; Kasonga et al., 2021; Ogunlaja et al., 2022; Ripanda et al., 2022

Soil, water,

Case suspended

Sediments, mud and debris

Soil erosion, construction or mining.

Spectrometry

Antoinette et al., 2018; Kairigo et al., 2020

Soil, water, aquatic plants, fish

Microorganisms

Escherichia coli, Salmonella and Vibrio cholerae

Wastewater and animal waste.

Molecular biology, Bacteriology

Sousa et al., 2018; Ekelund Uggeet al., 2022; Mheidli et al., 2022

Biomonitoring of chemical pollution: the regional approach in Africa

10Given the complexity and variability of chemical pollutants across regions, it is essential to examine the manifestation of local pollution, as the types and intensity of contaminants depend heavily on human activities, climate, the level of urbanization, and agricultural practices (Mesbah, 2015). Biomonitoring of aquatic ecosystems in Central Africa is crucial in the face of increasing pressures related to industrialization, rapid urbanization, and intensive agriculture. A regional approach allows for the identification of the most vulnerable areas and the adaptation of prevention and remediation strategies to each specific context. We have identified four main regions: Central Africa, which includes the Democratic Republic of Congo and Cameroon; West Africa, which includes Nigeria, Ghana, and Benin; East Africa, which includes Kenya, Uganda, Tanzania, Ethiopia, and Uganda; and finally, Southern Africa, which includes the country of South Africa.

Central Africa

11Although specific data on pharmaceutical pollution remain limited in this region, some studies indicate a concerning presence of organic compounds, pathogens, nitrates, phosphates, pesticides, pharmaceuticals, heavy metals, and hydrocarbons in surface waters (Pare and Bonzi-Coulibaly, 2013). However, the majority of available studies have focused more on metal pollution. In particular, mercury, lead, and cadmium are among the most frequently found pollutants in waterways, especially in mining areas. In the Democratic Republic of Congo, rivers surrounding mining activities have mercury concentrations in fish tissues exceeding the limits tolerated by the World Health Organization (WHO) (Guemou, 2021; Nyakabeji et al., 2023). In Cameroon, artisanal gold mining along the Sanaga and Nyong rivers has caused significant lead contamination, detected in fish living in these areas (Branchet, 2018). The scarcity of available data masks a significant risk from the simultaneous presence of heavy metals and antibiotics in the environment, which could promote the emergence of resistant bacteria and amplify the danger to human and animal health.

West Africa

12In West Africa, biomonitoring of aquatic ecosystems has become a priority in the face of the accelerated degradation of aquatic environments under the effect of demographic pressure, mining, agricultural, and industrial activities (Bezerra et al., 2019). Studies on watercourses in West Africa, particularly in Nigeria, Ghana, and Benin, have identified heavy metals (lead, cadmium, mercury, copper, zinc, etc.) as major contaminants, mainly from industrial activities and toxic waste dumps (Mesbah, 2015; (Kèlomè et al., 2012). In Nigeria, the study by Ogunlaja et al. on the Ogun River revealed high concentrations of lead in sediments and fish tissues, exceeding the limits recommended by the WHO (Ogunlaja et al., 2022). In another study conducted on rivers and lagoons around Cotonou, Gbotche et al. (2023) identified high levels of mercury, lead, and cadmium in the sediments. Another recent study by Deguenon et al. (2022) explored the presence of antibiotics, including sulfamethoxazole and ciprofloxacin residues, in several urban rivers in Benin. These antibiotics, mainly from hospital waste and ineffective wastewater treatment plants, have been found at concentrations sufficient to induce bacterial resistance in aquatic microorganisms and disrupt natural microbial communities (Koudokpon et al., 2021).

East Africa

13Lake Victoria, Africa's largest lake, shared by Kenya, Uganda, and Tanzania, is a priority area for environmental monitoring due to population density and increasing industrialization in its surrounding areas. Hossein and Ripanda (2025) demonstrated an increased presence of antimicrobial pollutants in the region's waters, particularly in Tanzania, Kenya, and Uganda. According to the authors, untreated pharmaceutical effluents and agricultural runoff contribute to the emergence of antimicrobial resistance (AMR), highlighting the urgent need for an integrated "One Health" approach to limit the spread of AMR (Hossein and Ripanda, 2025). Furthermore, Nantaba et al. (2024) identified pharmaceutical residues in Lake Victoria sediments in Uganda. This study quantified these contaminants and assessed their ecotoxicological risks in this critical ecosystem for the region (Nantaba et al., 2024). In Ethiopia, analyses have shown that the Nile basin is contaminated by various pollutants, including heavy metals and organic substances, with concentrations exceeding the limits recommended by the WHO for drinking water, irrigation, and support of aquatic life (Kipsang et al., 2024). Heavy metal contamination also poses a major threat in Uganda. Nakhle (2021) highlighted the presence of lead, mercury, and cadmium in the Nakivubo River and their bioaccumulation in fish and aquatic invertebrates. In Tanzania, biomonitoring research has shown that industrial and agricultural pollution severely affects the biodiversity of river and lake systems (Ekaka Azanga et al., 2016).

North Africa

14North Africa, with its arid climate and densely populated coastal areas, faces increasing environmental challenges in managing aquatic ecosystems. Key threats identified in the region include pollution from heavy metals, hydrocarbons, pesticides, and persistent organic pollutants, which affect not only aquatic wildlife but also the food security and health of human populations dependent on these resources (Ogunlaja et al., 2022). The Mediterranean coast of North Africa, which includes countries such as Algeria, Tunisia, and Egypt, is particularly affected by industrial and urban pollution. A systematic literature review conducted in 2022 identified 210 pharmaceutical compounds in aquatic compartments in the Middle East and North Africa between 2008 and 2022. These compounds are considered emerging contaminants due to their impacts on the aquatic environment and human health. However, the risk assessment associated with these compounds has not been quantified in the region (Mheidli et al., 2022). Kabir et al. (2025) revealed that North Africa has lead (Pb) levels in sediments reaching 5.94 mg/kg, exceeding the recommended limits for drinking water quality, agricultural irrigation, and supporting aquatic life. The authors emphasize the need for an integrated approach to combat the spread of antimicrobial resistance in the region (Kabir et al., 2025).

South Africa

15In South Africa, chemical and pharmaceutical pollution poses a major threat to water quality, the health of aquatic organisms, and the human populations that depend on these resources. Munzhelele et al. highlighted the presence of pharmaceutical contaminants in South African wastewater and waterways, specifying their sources, exposure pathways, geographic distribution, and impacts on ecosystems (Munzhelele et al., 2024). The main pollutants detected include antibiotics (ciprofloxacin, ampicillin, sulfamethoxazole), antiretrovirals, analgesics, and other drugs for human and veterinary use (Munzhelele et al., 2024). Concentrations range from nanograms to micrograms per liter, with higher levels in densely populated urban areas. Urban rivers, such as the Stiebeuel River in the Western Cape, receive runoff from informal settlements, resulting in high concentrations of ammonia, total organic matter, and E. coli, exceeding South African water quality standards. These areas are significant sources of pharmaceutical pollution, confirming the presence of multiple drugs in the water, including antibiotics and antiretrovirals (Maraj et al., 2025). Munzhelele et al., who conducted a systematic literature review, identified more than 100 pharmaceutical compounds in wastewater and aquatic environments in South Africa, primarily in the Gauteng and KwaZulu-Natal provinces. This study shows that South Africa accounts for approximately 60% of the available data on pharmaceutical pollution in Africa (MDPI), highlighting the importance of strengthening biomonitoring programs and improving the management of chemical and pharmaceutical pollution (Munzhelele et al., 2024).

CPE and heavy metals in Africa

16In Africa, as in many countries worldwide, the main sources of contamination include discharges of domestic, industrial, and hospital wastewater. Wastewater treatment systems are often inadequate for effectively removing CPEs and heavy metals. Furthermore, the disposal of pharmaceutical waste and expired medications is unregulated in many countries, resulting in these chemicals being released into the aquatic environment without any treatment. Despite considerable knowledge about the toxicity of these compounds, particularly from laboratory tests (Madikizela et al., 2017), very little data is available on their presence and levels of contamination in natural environments.

CPE and heavy metals in water

17In Central Africa, Waleng and Nomngongo (2022) detected high concentrations of amoxicillin and ibuprofen (sulfamethoxazole) in the waters of several countries in the region, highlighting the transboundary spread of these contaminants (Waleng and Nomngongo, 2022). Matongo et al. (2015) demonstrated the presence of ibuprofen and clozapine in the waters and sediments of the Msunduzi and Umgeni rivers, with concentrations reaching 117 µg/L in wastewater and 659 ng/g in sediments in South Africa. The review conducted by Munzhelele et al. (2024) documented the sources, exposure pathways, occurrence, and ecological impacts of these contaminants, confirming their widespread distribution in South African aquatic environments. In West Africa, a systematic review conducted by Cangola et al. (2024) analyzed the presence of pharmaceuticals and personal care products (PPCPs) in water. The study covered 58% of the countries in the region, identifying drug residues in wastewater, rivers, and groundwater. Total concentrations measured varied greatly depending on the water compartment studied, ranging from 12 to 700,000 ng/L in groundwater, from 0.42 to 107,800,000 ng/L in surface water, and from 8.5 to 121,310,000 ng/L in wastewater. Furthermore, spot water quality analyses in Ghana have revealed high concentrations of certain pharmaceuticals (approximately ibuprofen ~28 µg/L, diclofenac ~27.2 µg/L, and paracetamol ~22.03 µg/L in local studies), confirming the existence of localized urban sources that can contribute to bioaccumulation in organisms (Sackey et al., 2024). These results reveal the extent of pharmaceutical contamination in various water types and underscore the need for rigorous monitoring and appropriate management of these contaminants to protect both ecosystems and human health.

CPE and heavy metals in the soil

18Soil contamination by pharmaceutical compounds and heavy metals is an environmental problem, particularly in urban areas and around landfills. Residues of drugs such as diclofenac, caffeine, and paracetamol originate primarily from hospital effluents, untreated domestic waste, and certain agricultural practices involving the spreading of sewage sludge. These substances enter the soil through runoff, sewage systems, and leaching from waste storage sites (Dankwa et al., 2024). In the Sekondi-Takoradi metropolitan area, soil analysis revealed caffeine concentrations of up to 2.7 mg/kg, diclofenac concentrations of up to 0.9 mg/kg, and paracetamol concentrations of up to 2.1 mg/kg (Opoku et al., 2025). According to Akinsorotan et al. (2023), the intensive use of pharmaceuticals in urban areas leads to a significant accumulation of these residues in soils, disrupting ecosystems and posing a risk to human and animal health. Simultaneously, soils also exhibit concentrations of heavy metals such as lead (Pb), cadmium (Cd), mercury (Hg), and chromium (Cr), originating from industrial activities, the use of fertilizers and pesticides, and vehicle pollution (Mesbah, 2015). In the Owabi and Barekese reservoirs (Kumasi), a study detected paracetamol in sediments with a detection frequency of 66.7% and a mean concentration of 3.32 ± 4.55 µg/kg (Gyesi et al., 2022). The interaction between pharmaceutical compounds and heavy metals in soils can alter the bioavailability and toxicity of these contaminants. Heavy metals can slow the degradation of pharmaceutical residues, while certain pharmaceutical compounds influence metal mobility. These complex interactions, as suggested by Akinsorotan et al. (2023), require further investigation to better understand their ecotoxicological impacts and to develop effective strategies for the management and remediation of contaminated soils (Akinsorotan et al., 2023; Chouti et al., 2020; Kèlomè et al., 2012).

CPE and heavy metals in aquatic organisms

19Contamination of aquatic environments by heavy metals and CPEs persists in ecosystems, accumulates in aquatic organisms, and causes various physiological and ecotoxicological effects (Hossein and Ripanda, 2025). Heavy metals such as cadmium (Cd), lead (Pb), copper (Cu), zinc (Zn), iron (Fe), and mercury (Hg) are often detected in fish tissues at levels exceeding food safety standards (Akinsorotan et al., 2023; Kèlomè et al., 2012). Jamil Emon et al. (2023) report that heavy metal concentrations in fish muscle can range from 0.1 to several µg/g (µg per gram, or mg/kg) depending on the species, metal, and study site (Jamil Emon et al., 2023). Regarding CPEs, direct data on their accumulation in the tissues of aquatic organisms are still limited in West Africa. In South Africa, according to Waleng and Nomngongo (2022), the persistence of antibiotics in the environment and chronic exposure of organisms to these chemicals have ecotoxicological effects on the ecosystem. Maremane et al. (2024) report that concentrations of azithromycin at 935 ng/L, prednisone at 433 ng/L, prednisolone at 0.66 ng/L, and dexamethasone at 360 ng/L have been measured in surface waters, levels that suggest the possibility of bioaccumulation in exposed aquatic organisms (Maremane et al., 2024). These levels result in risk/effect ratios (RQ) classified as "medium to high" for several aquatic organisms (daphnia, algae, fish) (Gyesi et al., 2022).

20These results clearly show that heavy metals and CPEs coexist in aquatic environments and can interact, amplifying toxic effects through oxidative stress, enzyme inhibition, and ionic imbalance. The observed accumulation (sometimes > 2 µg/g for certain metals) and environmental drug concentrations (hundreds of ng/L) underscore the urgent need for rigorous ecotoxicological monitoring in discharge areas.

Biomarkers in biomonitoring of surface waters and aquatic ecosystems

21As mentioned above, biomarkers are valuable tools for monitoring polluted waters. They are biological responses that allow us to measure the effects of exposure to a contaminant in the environment (Kadim and Risjani, 2022). Recent literature highlights the use of biomarkers to detect the effects of various pollutants, such as heavy metals, pesticides, and emerging pharmaceutical compounds (EPCs), on aquatic biodiversity (Kumari and Khare, 2017; Kadim and Risjani, 2022; Salcedo-Bellido et al., 2021). In the context of water pollution monitoring, biomarkers are used to detect responses in aquatic organisms exposed to contaminants present in water (Silva et al., 2020). These can be molecules such as enzymes, proteins, nucleic acids, or metabolites produced or modified in response to exposure to a contaminant (Kumar and Khare, 2017). Biomarkers can also indicate a mode of action of contaminants, such as oxidative stress, DNA damage, endocrine disruption, or immune system dysfunction. They thus allow for the assessment of the sensitivity and specificity of contaminant effects on aquatic organisms compared to other water quality monitoring methods. Biomarkers can help identify the chemical contaminants responsible for the observed effect, assess the contaminant dose received by the organism, and detect synergistic or antagonistic effects between different contaminants (Kumar and Khare, 2017).

Integrated analysis of biomarkers of chemical contamination (CPE and heavy metals) in aquatic environments

22The biological indicators listed in Table 2 allow for the early detection of toxic effects at different levels of organization (molecular, cellular, tissue, and systemic), thus providing a broad view of the health of aquatic ecosystems. Different biomarkers are used according to various methods, each based on a specific mechanism of action.

Table 2: Biomarkers used in surface water biomonitoring

Contaminants

Biomarkers

Mechanism of action

Methods used

References

Aquatic organism

Enzymatic biomarkers

Assignment of enzymatic function

Catalase, glutathione-S-transferase and acetylcholinesterase activity by enzymatic methods

Nephale et al., 2023

Water, soil, aquatic organism

Biomarkers of oxidative stress

Increased oxidative stress

Measuring free radical levels using oxidative tests

Meknachi, 2020

Water, soil, aquatic organism

DNA damage biomarkers

Chromosomal aberrations, mutations and DNA breaks

Research on DNA or RNA using molecular biology to identify genetic changes

Dubois and Jacob, 2016

Aquatic organism

Endocrine biomarkers

Disruption of the endocrine system by blocking the action of natural hormones

Measurement of natural hormones

Guedegba et al., 2022

Aquatic organism

Immune response biomarkers

altered immune response

Measurement of immunoglobulin levels using immunological methods

Younis et al., 2023

Aquatic organism

Stress proteins

Production of proteins such as metallothionein and heat shock proteins

Protein quantification in organisms using proteomics

Aquatic organism

Histological biomarkers

Presence of cellular damage, tissue alterations and morphological changes

Measurement of cellular alterations by histological tests

Jiao et al., 2023

Aquatic organism

Bioaccumulation biomarkers

Assessment of pollutant accumulation in the food chain

Pollutant analysis using methods adapted to pollutant types

Vieira et al., 2019

23Enzymatic biomarkers such as catalase (CAT), glutathione S-transferase (GST), and superoxide dismutase (SOD) are among the most widely used for the early detection of oxidative stress and metabolic disturbances. According to El-Hassan Mokhamer et al. (2019), the activity of these enzymes increases significantly in Oreochromis niloticus exposed to high concentrations of lead (Pb), zinc (Zn), copper (Cu), iron (Fe), and cadmium (Cd) in the El-Mahmoudeyia Canal in Egypt, reflecting an adaptive response to chemical stress (Mokhamer et al., 2019). Similarly, a decrease in enzymatic activity has been observed in environments contaminated with pharmaceutical residues. The study by Mauro et al. (2021) on Danio rerio showed that prolonged exposure to a mixture of human drugs induces significant inhibition of GST and catalase, indicating disruption of detoxification mechanisms (Mauro et al., 2021). Furthermore, Gradinariu et al. (2025) confirmed that pharmaceutical residues (azithromycin, oxytetracycline, sulfamethazine, and trimethoprim, even at low environmental concentrations of 2819 ng/L, 399 μg/L, 612 μg/L, 328 μg/L, and 7 μg/L, respectively) alter the oxidative status of fish by inhibiting antioxidant enzymes and accumulating oxidation products.

24From a genotoxic perspective, metallic and pharmaceutical pollutants can induce direct DNA damage. The comet assay used by Mokhamer et al. (2019) revealed a significant increase in DNA breaks in the gills and liver of O. niloticus exposed to heavy metals, demonstrating the ability of these contaminants to disrupt genetic material. In Kenya, biomarkers used included micronucleus assays in fish, which revealed genetic alterations, with significant increases in the frequency of cellular abnormalities in exposed fish (Jenkins et al., 2021). These effects are consistent with those reported in the toxicogenomics literature, which links exposure to cadmium, lead, or chromium to an inhibition of cellular repair mechanisms (Caballero-Gallardo et al., 2016).

25Endocrine biomarkers are essential for detecting hormonal disruption caused by substances with estrogenic or androgenic activity. Adeogun et al. (2016) demonstrated an increase in vitellogenin (Vtg) and zinc-binding protein (Zrp) in male tilapia caught in the Awba Dam in Nigeria, correlated with the presence of heavy metals and other pollutants with hormonal activity (Adeogun et al., 2016). Similarly, experimental studies have shown that chronic exposure to a mixture of pharmaceuticals disrupts the regulation of the hypothalamic-gonadal axis (HPG) in zebrafish (Danio rerio), leading to effects on reproduction and embryonic development (Hamid et al., 2022).

26Immunological biomarkers, although less frequently studied, reflect alterations in the biological defense system. Sibiya et al. (2023) observed, in Labeo rohita exposed to metformin (40 µg/L and 80 µg/L), a decrease in lysozyme levels and white blood cells, suggesting a suppression of the cellular immune response, thus increasing the vulnerability of the fish to pathogens (Sibiya et al., 2023).

27Biomarkers, particularly metallothioneins (MT) and heat shock proteins (HSP), are also key indicators of metal contamination. El-Khayat et al. (2020) demonstrated that MT expression increases significantly in O. niloticus and Biomphalaria alexandrina collected from areas rich in Cd, Cu, and Pb, confirming their role in metal detoxification and intracellular regulation (El-Khayat et al., 2020). HSP proteins, on the other hand, reflect general cellular stress related to heat or toxic agents. Histological alterations constitute a visible manifestation of the cumulative effects of contamination. Histopathological studies have revealed hepatic vacuolization, cellular disorganization, and necrosis in the livers of fish exposed to heavy metals and persistent organic pollutants (Salem et al., 2021). Finally, bioaccumulation biomarkers are essential for establishing a link between environmental contamination and internal concentrations in biological tissues, allowing us to understand the trophic transfer of pollutants. Although some contaminants, such as endocrine disruptors present in water and aquatic resources, are documented as likely to accumulate in the food chain (Ibor et al., 2023), the use of measurable biomarkers in exposed organisms remains necessary to accurately quantify these effects.

Advantages and limitations of biomarkers in biomonitoring

28Integrating different types of biomarkers into water biomonitoring offers a holistic perspective on the exposure, mechanisms of action, and effects of contaminants on aquatic organisms (Ladeira and Viegas, 2016). However, it is essential to consider the specific advantages and limitations associated with each biomarker, to develop multidisciplinary approaches, and to interpret biomarker data within their context alongside other information for a robust assessment of aquatic ecosystem health.

29The use of biomarkers facilitates the early detection of biological effects, the identification of mechanisms of action, and the formulation of appropriate environmental management strategies to reduce risks to ecosystems. Biochemical and enzymatic biomarkers are highly sensitive and allow for the early detection of sublethal effects of contaminants (Pereira et al., 2018). Histological and physiological biomarkers provide information on structural and functional effects at the organ and whole-organism levels, enabling the assessment of chronic impact and the integrity of exposed populations (Mahi et al., 2022). Molecular and genomic approaches provide crucial information on the mechanisms of action of contaminants, genotoxicity, and endocrine disruption (Zhugen et al., 2017). Thanks to its sensitivity and early detection, the combination of biosensors makes it possible to detect the effects of contaminants before the appearance of visible damage, thus facilitating the implementation of preventive management strategies. Phase I and II enzymes (CYP450, GST, esterases) respond rapidly to heavy metals and pharmaceutical residues, indicating activation of detoxification and cellular defense mechanisms (Ali et al., 2025).

30However, the use of biomarkers has methodological limitations, such as inter-individual variability, the influence of environmental factors, analytical complexity, and the sometimes-subjective interpretation of data. These constraints highlight the need for an integrated approach, combining several biomarkers to obtain a reliable toxicity assessment (Dubois and Jacob, 2016).

Conclusion

31Biomonitoring of aquatic ecosystems in Africa, across the various regions studied, highlights chemical water pollution and its negative impacts on aquatic organisms. Research conducted in East, West, North, and Southern Africa shows a worrying prevalence of contaminants such as heavy metals, pharmaceuticals, and organic pollutants. The combined use of biomarkers is a powerful tool for monitoring aquatic ecosystems, particularly in the face of emerging pollutants such as pharmaceutical residues and heavy metals. Indicators such as oxidative stress, enzyme activity levels, and histological abnormalities in aquatic organisms provide valuable information on the impact of human activities on ecosystems. Research in West Africa on rivers and lake ecosystems, as well as research in South Africa on chemical and agricultural contamination, underscores the need for continuous monitoring and sustainable management strategies. Analysis of regional observations reveals an urgent need to strengthen biomonitoring capacity across the African continent. This implies not only improving analytical infrastructures, but also better scientific outreach and effective integration of environmental data into public policies.

32It is crucial to adopt an integrated approach to address these challenges, emphasizing collaboration between researchers, policymakers, and local communities. Furthermore, developing water management policies based on early detection data using biomarkers can help mitigate the effects of pollution and protect aquatic resources for future generations. Developing regional monitoring networks and exchanging data among African countries will be essential to meeting these environmental challenges and ensuring a healthy and sustainable future for the continent's aquatic ecosystems.

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Titre Figure 1: Map showing countries that have conducted biomonitoring studies of surface water pollution in Africa
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Titre Figure 2: Factors influencing the contamination of the aquatic ecosystem over time
Crédits Inspired by Anjanapriya et al., 2021.
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Afoussatou Amadou, Nelly Kelome et Victorien Tamègnon Dougnon, « Biomonitoring of surface water quality in Africa: contamination levels by chemical pollutants, including emerging pharmaceutical compounds and heavy metals, and the use of biomarkers – a literature review »VertigO [En ligne], 25-2 | Octobre 2025, mis en ligne le 24 octobre 2025, consulté le 19 janvier 2026. URL : http://journals.openedition.org/vertigo/50878 ; DOI : https://doi.org/10.4000/15erm

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Auteurs

Afoussatou Amadou

Researcher, Applied Microbiology and Pharmacology of Natural Substances Research Unit, Applied Biology Research Laboratory, Doctoral School of Life and Earth Sciences, University of Abomey-Calavi, Benin, email address: afoussaa82@gmail.com

Nelly Kelome

Full Professor, Laboratory of Geology, Mining and Environment, Faculty of Sciences and Techniques, University of Abomey-Calavi, Benin, email address: nkelome@yahoo.fr

Victorien Tamègnon Dougnon

Senior Lecturer at CAMES Universities, Research Unit in Applied Microbiology and Pharmacology of Natural Substances, Laboratory of Applied Biology Research, Doctoral School of Life and Earth Sciences, University of Abomey-Calavi, Benin, email address: victorien.dougnon@gmail.com

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