The research shows that the toxicity of chemical pollutants reaching our rivers increases when interacting with environmental factors such as rising temperatures or the presence of biofilms, calling into question the classical criteria used to establish legal safety limits, which often fail to reflect the complexity of natural ecosystems.
Researcher Amina Khalid recently defended her doctoral thesis “Integrating Ecological Complexity and Physiological Traits into Environmental Risk Assessments” at the University of Girona, co-supervised by Dr Anna Vila (UdG) and Dr Helena Guasch (CEAB-CSIC).
The work analyses the effects of chemical pollution at different biological scales and under diverse conditions, ranging from fish embryos in laboratory settings to fish populations in rivers and streams with significant concentrations of heavy metals, chemical residues or pharmaceuticals.
By combining scales, controlled experiments and field studies, the thesis demonstrates the need to incorporate ecological complexity, as well as the physiological traits of organisms, in order to properly predict the environmental risks posed by chemical residues entering freshwater ecosystems. This ecological perspective is crucial not only to protect biodiversity and ecosystem services, but also to understand the indirect repercussions for human health, in line with the One Health concept, which connects environmental, animal and human health.
Laboratory experiments with zebrafish embryos, a common model in ecotoxicology, confirmed that 1H-benzotriazole —present in plastics, detergents and industrial products such as coolants— exhibited moderate acute toxicity. However, malformations were observed in embryo development, a warning sign pointing to potential long-term effects in fish.
This evidence that the synthetic chemical compound could cause long-term and chronic effects, beyond what standard tests revealed, led the research team to study how the pollutant behaved when interacting with various conditions present in rivers.
In the experimental channels of the Live Organisms Laboratory (LEOV) at CEAB-CSIC and at the Institute of Ecology of the University of Girona, common environmental factors were incorporated, such as temperature changes (recreated in the channels to simulate heatwaves) or the presence of biofilms (by introducing river stones covered with this “green layer” formed by colonies of microorganisms), to better understand the differences in toxicity across complex ecological scenarios.
The study showed that biofilms had a beneficial effect on fish in the absence of pollutants. But when a chemical residue was present, the opposite occurred: biofilms enhanced its toxicity, causing oxidative stress and metabolic alterations in the studied fish.
The research also demonstrated that rising water temperatures synergistically increased the toxicity of pollutants. Thermal stress raised the metabolic demand of fish and reduced their ability to respond to the presence of chemicals, leading to more severe health effects.
Finally, fieldwork was carried out with Barbus meridionalis, a threatened native species. The study, conducted in the Osor stream (Girona, Catalonia, Spain), confirmed that environmental factors such as rising water temperatures enhanced the toxicity of pollutants such as zinc, resulting in a deterioration of the physiological state of the fish.
In summary, the scientific study highlights that current environmental risk assessment protocols may be underestimating the real toxicity of pollutants, as they do not take into account interactions with physiological and ecological factors, such as the baseline health status of flora and fauna, the presence of biofilms or thermal stress. To obtain more reliable predictions, these environmental factors should be incorporated, since they can amplify the harmful effects of pollutants. Rethinking legal thresholds in light of these results is not only an ecological issue, aimed at protecting natural ecosystems and their biodiversity, but also a matter of public health, given that the degradation of freshwater ecosystems has a very direct impact on humans.
The PRORISK project
This research was conducted within the framework of the European PRORISK project (Best chemical Risk assessment professionals for maximum Ecosystem Services benefit), funded by the European Union under the Horizon 2020 programme (Marie Skłodowska-Curie Actions). The project aims to train a new generation of specialists in advanced environmental risk assessment, integrating scientific knowledge on the interactions between pollutants and ecosystems to better protect ecosystem services and, ultimately, the health of all living beings.
