Comprehensive characterization of anthropogenic impacts on Mediterranean intermittent streams using cheminformatics and environmental risk assessment approaches

Abstract

[eng] Intermittent streams, characterized by variable and discontinuous flow regimes, are becoming increasingly common in the Mediterranean region due to climate change, population growth and land use changes, which further decrease water availability. As a result, the natural dilution capacity of streams is limited, making them highly vulnerable to both anthropogenic pressures and climate-driven hydrological variability. Among the key stressors, wastewater treatment plants (WWTPs) are one of the major sources of contaminants of emerging concern (CECs) and their transformation products (TPs). These are continuously being released into the environment and their detection in surface water can pose significant environmental risk due to their persistence, bioactivity, and incomplete removal during wastewater treatment. In this context, this thesis aimed to develop and apply robust analytical techniques for the detection, quantification and characterization of CECs and TPs, as well as to assess their potential environmental risks in Mediterranean freshwater systems, including both surface and groundwater, with a particular focus on under- studied regions as the Middle East North African (MENA) region. An analytical method based on solid phase extraction combined with liquid chromatography coupled to high resolution mass spectrometry was developed and validated for the detection and quantification of 116 CECs. The method demonstrated high sensitivity and broad applicability in both surface and groundwater samples. It was applied for the analysis of samples collected across multiple locations in Southern European countries (Spain, Italy, France) and MENA countries (Algeria, Tunisia), enabling a comparative assessment of water quality between northern and southern Mediterranean regions. Special attention was given to MENA countries, where comprehensive monitoring efforts have been previously lacking. Through an integrated approach combining chemical, ecological, and hydrological indicators, the study highlighted the cumulative impact of wastewater discharges on aquatic ecosystems and emphasized the need for region-specific monitoring frameworks. The importance of considering hydrological variability, particularly in low flow conditions, where natural dilution capacities of streams are limited was also emphasized, especially as water scarcity increases. The correlations between various indicators were assessed where CECs concentrations and benthic indices (ecological) revealed a moderate positive relationship. Environmental risk assessments were conducted by calculating risk quotients to evaluate the potential ecological impact associated to the detected concentrations. This approach enabled the identification of several priority pollutants, including diclofenac, losartan and azithromycin, which were consistently found in surface water at ecologically relevant concentrations, posing potential environmental risks across the five Mediterranean countries studied. In Tunisian groundwater, compounds including azithromycin, ibuprofen and caffeine were also detected at concentration levels indicating potential ecological risks. Notably the overlap in potential ecological risk, driven by the presence of common compounds as azithromycin in both Tunisian groundwater and surface water systems, underscores the ongoing pressures on the studied basin where agriculture, industry and tourism activities predominate. The findings reinforce the urgent need for increased monitoring frameworks, both regionally and internationally, to better manage and mitigate the impact of CECs on the environment. Additionally, to investigate the fate and transformation pathways of CECs and their TPs in intermittent streams, open-source cheminformatics approaches were applied. A combination lab-scale experiments, data curation and prediction models were used to assess the environmental behaviour of TPs. N-oxide transformation products were found to remain persistent along the stream and were observed to be derived from WWTP point sources rather than in-stream formation. Unfortunately, lab-scale experiments did not successfully predict the high occurrence of N-oxide TPs observed in field studies. Suspect and non-target screening approaches, supported by open-source tools, were performed as complementary and valuable tools, to expand the target analysis and provide a deeper insight of the presence of TPs and other unknowns. These approaches enabled the identification of compounds not initially included in the analytical method, offering a broader understanding of the contaminant profiles in intermittent streams. Overall, the findings presented in this thesis underscore the necessity of interdisciplinary strategies and adaptive water management to protect vulnerable freshwater, both intermittent streams and groundwater resources across the Mediterranean Basin.

[cat] Les rieres intermitents, caracteritzades pel seu cabal variable i discontinu, són cada cop més freqüents a la conca mediterrània a causa del canvi climàtic, el creixement poblacional i els canvis d’ús del sòl. Aquestes alteracions redueixen la capacitat de dilució natural dels cursos d’aigua intermitents, fent-los especialment vulnerables tant a les pressions antropogèniques com a la variabilitat hidrològica. Les estacions depuradores d’aigües residuals (EDARs) són una de les fonts principals de contaminants emergents (CECs) i dels seus productes de transformació (TPs). Aquests s’alliberen contínuament al medi ambient degut a l’eliminació incompleta durant els processos de tractament, fet que pot suposar un risc ambiental a causa de la seva persistència i bioactivitat. Aquesta tesi té com a objectiu desenvolupar i aplicar tècniques analítiques per detectar, quantificar i caracteritzar els CECs i els seus TPs en cursos d’aigua intermitents de la regió del mediterrani, especialment en regions poc estudiades com els països MENA (Orient Mitjà i Nord d’Àfrica). Es va desenvolupar i validar un mètode d’alta sensibilitat i àmplia aplicabilitat mitjançant l’extracció en fase sòlida i cromatografia líquida acoblada a espectrometria de masses d’alta resolució per a 116 CECs. Diferents països del Mediterrani van ser estudiats incloent Espanya, Itàlia, França, Algèria i Tunísia. Els resultats van mostrar l’impacte de les descàrregues d’aigües residuals sobre els ecosistemes aquàtics i la necessitat de marcs de seguiment específics per cada regió, destacant la importància de tenir en compte la variabilitat hidrològica, sobretot en condicions de baix cabal, quan la capacitat de dilució natural es veu limitada. Diversos compostos com el diclofenac, el losartan i l’azitromicina es van detectar en concentracions ecològicament rellevants en aigües superficials, indicant un risc ambiental a diversos països mediterranis. A Tunísia, també es van identificar riscos ecològics a les aigües subterrànies, fet que evidencia la necessitat de millores en la gestió dels recursos hídrics. Per estudiar el destí i la transformació dels CECs i els seus TPs en rieres intermitents, es van utilitzar eines quimioinformàtiques de codi obert, experiments a escala laboratori i models de predicció de TPs. L’ús combinat d’anàlisi de cribratge de sospitosos i no dirigit va permetre aprofundir en la identificació i el comportament ambiental de TPs i altres compostos desconeguts en rieres intermitents.