“Hidden” antibiotics in river fish: A new food safety alert

Antibiotics in the aquatic environment and food chain

Research on antibiotic residues in fish in Brazil

A new study in Brazil has sounded the alarm on an overlooked danger: the accumulation of antibiotics in aquatic environments and their potential to enter the food chain. Beyond detecting these substances in river water, scientists also found them in fish—a common human food source. More alarmingly, some substances banned in livestock farming were still present, showing that the contamination is not only present but also persistent over time.

First, the study shows that antibiotics are widely present in the Piracicaba River, a major river in the state of São Paulo. These are not isolated traces, but rather multiple classes of antibiotics originating from human activities such as healthcare and livestock farming. During the dry season, as water levels drop, these pollutants become even more concentrated, increasing exposure levels for aquatic organisms in the river. Notably, these substances do not merely "float" in the water; they also accumulate in fish tissues, demonstrating that strong bioaccumulation is taking place. This means humans could indirectly ingest antibiotics through food without ever knowing it.

To find a solution, scientists experimented with a common aquatic plant called Salvinia auriculata to purify water. Initial results were quite positive: this plant species is capable of removing most of certain antibiotics, especially enrofloxacin, in just a few days. The main mechanism lies in the root system, where pollutants are absorbed and retained. However, for more "stubborn" compounds like chloramphenicol, the treatment efficiency was significantly lower and the persistence in the environment was longer. This shows that not all antibiotics can be effectively treated using the same method.

However, the complexity of the issue lies in the fact that reducing antibiotic concentrations in water does not equate to reducing risks for aquatic organisms. Experiments show that each type of antibiotic behaves very differently once inside fish tissues. Enrofloxacin is relatively "easy to handle", accumulates less, and is eliminated more quickly. In contrast, chloramphenicol tends to persist in the body, accumulate in tissues, and is difficult to excrete. Particularly, in the presence of Salvinia auriculata, a paradox emerges: even though the water is cleaner, fish may absorb antibiotics more rapidly. The reason is believed to be that plants alter the chemical form of these substances, making them "more bioavailable" to aquatic organisms.

Not stopping at accumulation levels, the study also delved into the biological impacts of these substances. Results showed that chloramphenicol can cause DNA damage in fish, manifested through abnormalities in blood cells. This is a sign indicating long-term risks to the health and reproductive capacity of organisms. However, one positive aspect is that in the presence of Salvinia auriculata, this level of damage is significantly reduced. Scientists suggest that this may be because plants help reduce toxic intermediates or release antioxidant compounds, thereby curbing biological stress in fish. Nevertheless, this benefit does not apply to all antibiotics, particularly more persistent compounds like enrofloxacin.

From the above results, it can be seen that nature-based solutions such as utilizing aquatic plants offer great potential, but they are not a "panacea". One of the major challenges lies in handling the biomass after plants have absorbed contaminants. If not properly harvested and treated, these plants themselves could become a source of antibiotic re-release back into the environment. Therefore, the implementation of such solutions must go hand in hand with stringent management protocols.

More broadly, this study not only reflects an environmental issue but also raises major questions about food safety and public health. The presence of antibiotics in fish shows that the boundary between the environment and the human dining table is increasingly fragile. At the same time, it emphasizes that pollution management solutions must be comprehensively evaluated, as seemingly beneficial interventions can sometimes lead to unforeseen consequences.