The Mediterranean Sea, one of the most enclosed basins on the planet, accumulates constant human pressure: mass tourism, maritime traffic, sewage discharges, and agricultural runoff. This combination of factors transforms its waters into a breeding ground for chemical substances that end up in marine organisms. A recent study by the University of Córdoba (UCO) has focused on four species commonly consumed in the Mediterranean diet: horse mackerel, sardines, red mullet, and hake. The results, published in the Journal of Hazardous Materials , reveal that these fish harbor a cocktail of up to 81 polluting compounds , many of which have been barely monitored until now.
The team, led by Ayman N. Saber, Noelia Caballero Casero, and Soledad Rubio from the Department of Analytical Chemistry at the Chemical Institute for Energy and the Environment (IQUEMA), analyzed 120 specimens. To do so, they developed a screening platform for suspected contaminants that allowed them to trace approximately 11.000 potential substances, including original pollutants and their metabolites. The research not only confirms the presence of plasticizers, flame retardants, pesticides, pharmaceuticals, and personal care products, but also highlights a disturbing finding: almost half of the compounds detected are metabolites —products that arise after the fish itself processes the contaminant. In many cases, no traces of the original contaminant were even found, suggesting that routine monitoring may be overlooking a significant portion of actual exposure.
A comprehensive analysis of 11.000 substances
The methodology used combines supramolecular solvent extraction with high-resolution mass spectrometry. This technique allows for the detection of a wide range of substances without the need to analyze them individually, thus multiplying the detection capacity. Of the 11.000 potential substances, 81 were identified in the fish tissues. These include plasticizers such as phthalates, flame retardants, pesticides, pharmaceuticals, illicit drugs, cosmetic ingredients, and persistent industrial compounds. The presence of these chemicals does not automatically imply a health risk, but it does underscore the need to study their long-term impact, especially when it comes to metabolites, whose effects on the human body are much less well documented.
One of the most striking findings of the study is the abundance of methylated metabolites. Methylation is not considered a common detoxification mechanism in fish, so the researchers raise the need to investigate its origin and the processes that generate it. This finding opens a new avenue of research, since these compounds could have a different toxicity than their precursors and are not included in current food safety assessments.
Metabolites: the hidden footprint in food safety
The research reveals that limiting controls to the original contaminants provides an incomplete picture. Metabolites, being the result of chemical transformation within the fish, can accumulate in tissues and go undetected by conventional analyses. In this study, almost half of the compounds found were metabolites, and in many cases, no trace of the parent substance was found. This suggests that fish actively metabolize contaminants, but the resulting byproducts can remain in the body and reach the consumer. The authors emphasize that the presence of a contaminant does not equate to an immediate health problem , but understanding its behavior and potential effects is crucial for assessing the actual risk of human exposure.
Furthermore, the study reveals that the mix of pollutants varies considerably among species. The jack mackerel, which feeds on both pelagic and benthic prey, exhibits the broadest spectrum, including plasticizers, industrial compounds, and pesticides. The red mullet, which stirs up coastal sediments, accumulates primarily plasticizers and pharmaceuticals. The hake, at the top of the food chain, shows a lower volume of pollutants but a higher presence of persistent industrial substances that are difficult to degrade. These differences reflect the influence of habitat and diet on chemical accumulation.
Each species, a different mix
The Mediterranean, due to its semi-enclosed basin nature, is particularly vulnerable to the accumulation of pollutants. Wastewater, industrial activity, and agricultural runoff constantly release substances that enter the food chain. As fish feed, they ingest these particles and accumulate them in their tissues. The UCO study demonstrates that each species has a unique chemical profile , further complicating risk assessment. For example, horse mackerel, by consuming prey from different depths, is exposed to a wider variety of pollutants. Red mullet, by stirring up sediment, comes into contact with compounds that settle on the seabed. Hake, as a predator, concentrates persistent substances that biomagnify throughout the food chain.
The researchers emphasize that these findings should not be interpreted as a call to stop consuming fish, but rather as a call to improve monitoring systems. Including metabolites in routine analyses would provide a more realistic picture of marine pollution and the risk to public health. Furthermore, the study opens the door to investigating the origin of methylated metabolites, a little-known phenomenon that could have toxicological implications.
In short, this work highlights the complexity of pollution in the Mediterranean and the need to advance our understanding to protect both the ecosystem and consumers. Science continues to make strides in unraveling the effects of emerging pollutants, and this study is a clear example of how research can contribute to safer food and a healthier sea.
