Some medicinal substances that we use on a daily basis are now threatening even isolated marine ecosystems. A scientific study carried out in the Gulf of Eilat, in the Red Sea, has revealed the unexpected presence of chemical residues in coral reefs, revealing insidious pollution. These discoveries raise many questions about the environmental impact of human activities and the vulnerability of coral reefs to such contamination.
by Laurie Henry
Cover photo: Acropora sp. corals grow on artificial substrates in the Red Sea. © Noa Shenkar
Often invisible, marine pollution is a major threat to ocean ecosystems and their biodiversity. Coral reefs are home to a quarter of all marine species and support millions of people who make their living from fishing and tourism. These habitats are under increasing pressure from climate change and chemical pollution. A study by Tel Aviv University and the Steinhardt Museum of Natural History, published in Environmental Pollution, reveals a new form of drug residue contamination in the reefs of the Gulf of Eilat. This pollution, caused by human activity, threatens not only corals but also the ecological balance they maintain. A critical issue for the preservation of our oceans.
Unprecedented contamination of the seabed
In the waters of the Gulf of Eilat, researchers have discovered the presence of no fewer than ten pharmaceutical substances in the tissues of reef corals. The samples, taken from 96 corals of the Acropora and Favites genera, showed widespread contamination with drugs from a variety of categories: antibiotics, antihypertensives, statins, laxatives, proton pump inhibitors, antidepressants and antiplatelet agents. Sulfamethoxazole, an antibiotic used to treat respiratory and urinary tract infections, was ubiquitous, detected in 93% of corals. This contamination is not limited to shallow waters, but also extends to deeper areas, between 30 and 40 metres, where corals are supposed to be protected from such influences.
Favites sp. corals growing on artificial substrates in the Red Sea. © Noa Shenkar
The detection method involved advanced hydro-chemical analyses carried out in collaboration with the university’s water chemistry laboratory. The researchers tested the corals for 18 pharmaceutical compounds identified as commonly used in Israel, revealing that more than half of these substances were present in the samples.
These results highlight the extent to which drug residues are being released into marine environments, mainly from inadequately treated wastewater, agricultural run-off and human excretions in certain tourist areas. The coral reefs of Eilat, often cited for their exceptional resilience to climatic disturbances, are now facing a new insidious threat. ‘ What does the presence of pharmaceutical products in corals really mean? Clearly, the corals haven’t received a prescription for antibiotics from their doctor ’, ironised Professor Shenkar in a press release.
The little-known effects of drugs on marine life
Drugs developed to target specific biological mechanisms in humans do not spare marine life when they enter the oceans. According to the study by G. Navon et al, 2024, the ten active substances found modify certain complex biological processes. They can interact with marine organisms in unpredictable ways. ‘ The oestrogens present in contraceptives feminise male fish and affect their ability to reproduce, while Prozac modifies the behaviour of crabs by making them more aggressive ’, explains Prof. Shenkar. This parallel alerts us to similar risks for corals, even if these impacts are still insufficiently studied.
Graphical summary of the study method and results. Detection of 10 pharmaceutical products in coral reefs. © Gal Navon et al., 2024
Corals, fundamental elements of reefs, depend on precise biological cycles, in particular the synchronisation of their egg-laying which ensures their reproduction. This fragility could be exacerbated by prolonged exposure to chemical substances. The study stresses that these disturbances, which are often invisible in the short term, could compromise the survival of coral populations in the long term.
Prof. Shenkar warns: ‘ If these products alter the synchronisation of egg-laying, we may not discover the damage until it is too late to intervene ’. These observations reveal a silent threat that requires urgent attention to better understand the extent of the cumulative effects of this invisible pollution on marine ecosystems.
Implications for biodiversity and human activities
Coral reefs, the lungs of the oceans, are at the heart of marine biodiversity. They are home to almost 25% of marine species ranging from fish to crustaceans, as well as serving as nurseries and breeding grounds for a wide variety of organisms. These habitats are also crucial to millions of people, providing livelihoods through fishing and attracting tourism that is essential to the economies of many coastal regions.
Now the ecological and economic role of these corals is under threat from a combination of environmental stresses, exacerbated by the presence of drug residues. ‘ These already fragile ecosystems, which are under increasing pressure from overfishing, global warming and pollution, now face an insidious chemical threat ,’ stresses Gal Navon, a doctoral student involved in the study.
Antibiotics such as sulfamethoxazole can alter the symbiotic bacterial communities that are essential to coral health, weakening their immunity to disease. Bioaccumulation of these products in the food chain could also affect higher-level marine predators, including humans, if they consume contaminated fish.
The origin of this drug contamination reflects the cumulative impact of human activities. Inadequately treated wastewater remains the main means of transporting these drug residues to the oceans. ‘ It is clear that these medicines save lives, and we have no intention of asking people to reduce their consumption,’ says Professor Shenkar. ‘ However, we need to develop new wastewater treatment methods that effectively treat pharmaceutical compounds. In addition, each and every one of us must dispose of out-of-date medicines in a way that does not harm the environment ’.
An environmental and social emergency
Research into contaminated coral in the Gulf of Eilat reveals invisible and alarming pollution. There is a striking parallel with a recent discovery in Brazil, where sharks Rhizoprionodon lalandii living off Rio de Janeiro and vulnerable according to the IUCN, were exposed to high concentrations of cocaine and its metabolites from coastal waters contaminated by the effluents of clandestine laboratories and urban waste. This powerful stimulant disrupts their behaviour, increases their aggressiveness and unbalances predator-prey interactions, with impacts comparable to the disruption to coral reproduction and health caused by substances such as antibiotics. These chemical pollutants, whether from medicines or illicit drugs, have a similar effect on the biological foundations of marine ecosystems.
Faced with this growing threat, immediate action is crucial. Corals and sharks are sentinels of ocean health. Their contamination reflects the extent of the human footprint on marine environments. Improving wastewater treatment infrastructures, limiting the discharge of toxic substances into the environment and strengthening international regulations are becoming imperative to preserve these key species and the balance of ocean ecosystems.
Source : Gal Navon et al., “Detection of 10 commonly used pharmaceuticals in reef-building stony corals from shallow (5–12 m) and deep (30–40 m) sites in theRed Sea”, Environmental Pollution (2024)