Per- and polyfluoroalkyl pollution in marine environments: a viewpoint about Africa

INTRODUCTION

Per- and polyfluoroalkyl substances (PFAS) represent a set of anthropogenic organic substances, comprising more than 8,000 distinct acknowledged structures listed in the Toxic Substances Control Act Inventory^[1,2]. These compounds are employed in various utilizations in commercial and industrial sectors dating back to the 1940s^[2]. Owing to their extensive use in numerous consumer items such as food packaging and water-resistant textiles, coatings, and firefighting foams, these elements are now pervasive throughout the environment^[3,4]. Referred to as the “forever chemicals”, PFAS exhibit remarkable persistence in the environment and resist degradation due to the exceptional durability of their carbon-fluorine bonds, making their breakdown particularly challenging. PFAS [e.g., perfluorooctane sulfonate (PFOS) or perfluorooctanoic acid (PFOA)] emissions into the environment originate from multiple sources, including intentional manufacturing, utilization, and disposal processes^[5-7]. Furthermore, PFAS can be present as impurities in substances emitted into the environment or can result from the degradation of precursor substances through abiotic or biotic pathways^[8].

While the focus on PFAS has primarily revolved around their negative effects on human health, there is an increasing awareness of their bioaccumulation in biota, particularly in marine organisms, owing to the growing number of studies highlighting their presence in these ecosystems^[9]. PFAS have demonstrated the capability to disrupt various physiological functions and biochemical routes that are conserved among different phyla, raising concerns regarding their impacts on marine biota^[2,9]. To achieve improved risk management objectives concerning PFAS occurrence, bioaccumulation, and biomagnification, it is imperative to further advance our understanding of uptake and elimination kinetics^[2]. This necessitates obtaining additional information and data on these crucial processes from several parts of the world, including developing countries.

As of the existing global knowledge concerning PFAS, there is growing concern about their impact on marine environments. PFAS, known for their persistence and bioaccumulative properties, have become a significant environmental issue worldwide^[7,10]. Despite extensive research on PFAS pollution, there remains a need to deepen our understanding of their distribution, behavior, and long-term effects on marine ecosystems, particularly in developing countries. In light of the current situation, here we attempted to answer the question: “What is the position of Africa in the current knowledge about PFAS pollution in marine environments?”

CURRENT KNOWLEDGE ABOUT PFAS IN THE MARINE ENVIRONMENT

First, compared with freshwater environments, marine matrices have not attracted significant interest from scientists, especially in Africa^[11]. According to a recent review by Khan et al., the majority of worldwide studies concerning PFAS in the marine environment have primarily focused on water and sediment^[2]. Limited information is available regarding PFAS bioaccumulation in invertebrates, with most data concentrated on crustaceans and mollusks. In fish, PFAS concentrations are commonly recorded in muscle tissue or fillet, primarily addressing concerns related to seafood safety. However, some studies have also investigated PFAS burdens in whole fish and liver. In the case of seabirds, research on PFAS occurrence and bioaccumulation often involves examining levels in eggs, liver, and blood (or plasma). It is recognized that marine mammals can bioaccumulate these compounds at significant levels, particularly in hepatic and circulatory tissues. Thus, the essential origins of PFAS in the marine environment are land-generated, including pesticides, paints, surfactants, textiles, firefighting foams, and fast food packaging, among several others. These chemicals are transported from land into the marine environment via the water cycle^[4]. Then, various ecological phenomena interfere, such as the accumulation in organisms, transfer through food chains, and magnification within ecosystems^[12].

Second, the quantification methods of PFAS involved a series of procedures, including preconditioning, extraction, clean-up, and concentration before the analytical instrumentation. Hence, liquid chromatography (LC) coupled with tandem mass spectrometry (MS/MS) is a widely employed technique for PFAS analysis with notable sophistication as well as meticulous calibration and quality control strategies. Indeed, this technique provides high sensitivity, excellent selectivity, and considerable precision even in complex environmental matrices like seawater and sediment. However, this technique may have limitations in detecting all possible PFAS compounds owing to differences in ionization efficiency and fragmentation patterns among various PFAS species^[13]. LC-MS/MS methods can be technically complex, expensive, and require expertise for operation and maintenance, which is the main reason for the limited number of studies about PFAS in African and developing countries. Table 1 presents examples of field investigations that unveil the presence of PFAS across diverse marine matrices globally, delineating their geographical distribution, study matrix, identification methodology, and the range of occurrence.

WHAT IS AFRICA’S POSITION IN THE GLOBAL KNOWLEDGE ABOUT PFAS IN THE MARINE ENVIRONMENT?

The studies conducted on PFAS in Africa have predominantly focused on terrestrial aquatic ecosystems, primarily rivers, and lakes. Research efforts have been dedicated to understanding the presence, distribution, and potential ecological impacts of PFAS compounds in sediment and freshwater, mainly in South Africa, Nigeria, and Kenya^[31]. Thus, this context forces us to raise relevant questions about the place of marine and coastal environments in the global knowledge of PFAS in Africa. To the best of our knowledge, the two only marine field studies in Africa were carried out in a lagoon area in the north of Tunisia in 2018 and in the Gulf of Guinea in 2022 [Table 1]. The study of Tunisia investigated nine marine species (three fish, two crustaceans, and four mollusks) collected from Bizerte lagoon using (LC-MS/MS) technique, reporting values between 0.20-2.89 ng/g dry weight^[29]. The second study utilized the same technique to quantify the amount of PFAS in four fishery products along the Gulf of Guinea, revealing values between 91 and 1,510 pg/g wet weight^[30]. In a separate investigation, the assessment of PFAS was conducted on marine shellfish farmed in land-based facilities in South Africa. The PFAS concentrations (expressed in ng/g wet weight) varied between 0.12 and 0.49 in abalone, 4.83-6.43 in mussels, 0.64-0.66 in oysters, and 0.22 ng/g ww in lobsters using UHPLC-MS/MS method^[32]. Few other studies included some sampling points in estuaries in global surveys of terrestrial water bodies^[11,13,33].

Unfortunately, the lack of studies in Africa is a significant concern. While PFAS pollution has been extensively researched in various parts of the world, there remains a notable gap in our understanding of the presence and impact of these chemicals on this continent. This group of human-made chemicals is widely used in various industrial and consumer products in Africa for their water and grease-resistance properties^[34,35]. However, their persistent nature and potential adverse health effects have raised global concerns^[36-38] that must not exclude African countries. Despite the growing recognition of PFAS as emerging contaminants, research efforts have predominantly focused on regions such as North America, Europe, and parts of Asia^[18].

With its diverse coastal and marine ecosystems and substantial population relying on fisheries, the African continent should not be overlooked in PFAS research. Marine areas in Africa face unique environmental challenges, including industrial activities, burgeoning urbanization, climate change vulnerability, threatened biodiversity hotspots, and increasing plastic waste generation^[39-41]. These factors can contribute to the release and accumulation of PFAS in coastal waters, sediments, and organisms, potentially posing risks to both human and ecological health. By expanding studies to include African coasts and marine habitats, researchers can gain valuable insights into the presence, distribution, and potential impacts of PFAS in new environmental conditions. It is essential to evaluate the levels of contamination, identify potential sources, and understand the pathways through which PFAS enter the African marine environment. Moreover, the pervasive presence of PFAS poses a significant risk to marine products intended for export, particularly in the context of food safety. Investigations into the accumulation of PFAS in marine biota are crucial to understanding the potential hazards associated with seafood consumption by human populations. As these substances accumulate in marine life, they can find their way into the food supply chain, posing risks to consumers both domestically and internationally. Therefore, comprehensive studies addressing the bioaccumulation of PFAS in marine species are indispensable for safeguarding the integrity of exported marine products and ensuring global food safety standards.

CONCLUSION

Overall, the existing literature on PFAS in the marine environment, particularly in Africa, reveals a noticeable lack of interest and a limited number of studies conducted in this context. The coasts and marine habitats of Africa remain relatively unexplored and understudied. This knowledge gap calls for urgent attention and increased research efforts to understand the potential presence, distribution, and ecological impacts of PFAS chemicals. Addressing the lack of studies on PFAS in the marine environment of Africa requires collaborative efforts among researchers, environmental agencies, and policymakers. It is imperative to foster more robust international collaborations and partnerships with leading scientists in the field from across the world, such as China, the USA, and Europe. Leveraging the expertise and experience of these prominent researchers can facilitate knowledge transfer, exchange of methodologies, and establishment of standardized protocols for PFAS studies in marine environments. Such initiatives can help generate region-specific data, raise awareness about PFAS pollution, and guide the development of appropriate mitigation and regulatory measures. By shedding light on the presence and potential risks of PFAS in African marine environments, we can work towards safeguarding both the environment and the well-being of the communities relying on these vital ecosystems.