Antibiotics in Brazil’s Piracicaba River: Sources, Fish Contamination & Plant-Based Solutions

Concerns are growing over the presence of antibiotics in fish from the Piracicaba River in Brazil, a major waterway in São Paulo state, with a recent study revealing accumulation of these substances in locally caught fish. The research, published in Environmental Sciences Europe, highlights a potential food safety risk, particularly during the dry season when antibiotic concentrations are highest. Even as the study also explored the potential of a common aquatic plant, Salvinia auriculata, to mitigate contamination, the findings underscore the complex interplay between pollutants, the environment, and human health.

Seasonal Shifts in Antibiotic Levels

Researchers from the Center for Nuclear Energy in Agriculture at the University of São Paulo (CENA-USP) discovered a clear seasonal pattern in antibiotic concentrations within the river. During the rainy season, levels of the 12 antibiotics monitored – including tetracyclines, fluoroquinolones, sulfonamides, and phenols – generally fell below detectable limits. Though, as water levels receded during the dry season, these substances became more concentrated, posing a greater risk. This is due to the reduced water volume and the accumulation of contaminants from sources like treated sewage, household wastewater, aquaculture, pig farming, and agricultural runoff, particularly near the Santa Maria da Serra dam and the Barra Bonita reservoir. The study meticulously combined environmental monitoring, analysis of pollutant buildup in organisms, genetic damage assessments, and plant-based remediation experiments to understand the scope of the problem.

A Banned Antibiotic Detected in Fish

Perhaps the most alarming finding was the detection of chloramphenicol in lambari fish (Astyanax sp.) caught by local fishermen. Chloramphenicol’s leverage in livestock is prohibited in Brazil due to its potential toxicity, raising significant concerns about human exposure through consumption of this widely eaten fish. Levels of the antibiotic were found at tens of micrograms per kilogram during the dry season. This discovery builds on growing global concerns about antibiotic resistance, as the presence of these compounds in the environment can contribute to the development of “superbugs” – microorganisms resistant to multiple antibiotics. ScienceDaily reports on the broader implications of this finding.

The Role of Salvinia auriculata: A Complex Picture

The research team investigated whether Salvinia auriculata, a floating aquatic plant, could assist reduce antibiotic contamination. Experiments showed the plant was highly effective at removing enrofloxacin, removing over 95% of the antibiotic from water within days when using higher plant biomass. The half-life of enrofloxacin dropped to just two to three days in these conditions. However, removal of chloramphenicol was slower, with the plant only removing 30% to 45% of the antibiotic, and a half-life ranging from 16 to 20 days. The plant appears to absorb antibiotics primarily through its roots.

Interestingly, the presence of Salvinia auriculata didn’t always translate to reduced antibiotic levels *within* the fish. In some cases, the plant seemed to alter the chemical form of the antibiotics, potentially making them easier for the fish to absorb. This highlights the complexity of using plants as “sponges” for contaminants, as they can change the entire ecosystem and how organisms interact with pollutants. Phys.org details the plant’s impact on genetic damage in fish.

Genetic Damage and Potential Protective Effects

The study also assessed genetic damage in the fish, finding that chloramphenicol significantly increased DNA damage, measured by abnormalities in blood cells. However, the presence of Salvinia auriculata appeared to mitigate this damage, bringing levels closer to those seen in control groups. This suggests the plant may reduce oxidative stress in the fish, potentially through the release of antioxidant compounds. Enrofloxacin, however, did not present the same protective effect, possibly due to its chemical stability and the formation of persistent, toxic metabolites.

Limitations and Future Directions

The researchers emphasize that Salvinia auriculata is not a simple solution. Managing the plant after it absorbs contaminants is crucial; improper removal could release the antibiotics back into the environment. Further research is needed to determine the best methods for harvesting and treating the plant biomass. The study also highlights the demand for a comprehensive approach to address antibiotic pollution, considering not only removal but also the biological and ecological effects of these contaminants. The radiolabeled molecules used in the study were provided by the International Atomic Energy Agency (IAEA), demonstrating the collaborative nature of this research.

Looking ahead, continued monitoring of antibiotic levels in the Piracicaba River and other waterways is essential. Further investigation into the long-term effects of antibiotic exposure on aquatic ecosystems and human health is also warranted. The World Health Organization (WHO) provides extensive resources on antimicrobial resistance and its global impact. Addressing this issue requires a multi-faceted strategy involving responsible antibiotic use in human and veterinary medicine, improved wastewater treatment, and the exploration of nature-based solutions like the use of aquatic plants.

The findings underscore the interconnectedness of human activities and environmental health, and the importance of considering the broader consequences of pharmaceutical pollution. As supervisor Valdemar Luiz Tornisielo notes, the research provides a measurable understanding of a complex problem and points towards the need for integrated solutions.