This year-long research analyzed emerging risks in influent, effluent wastewaters and biosolids from six wastewater treatment plants in Spain’s Valencian Region. Specifically, it focused on human enteric and respiratory viruses, bacterial and viral faecal contamination indicators, extended-spectrum beta-lactamases-producing Escherichia coli, and antibiotic-resistance genes. Additionally, particles and microplastics in biosolid and wastewater samples were assessed. Human enteric viruses were prevalent in influent wastewater, with limited post-treatment reduction. Wastewater treatment effectively eliminated respiratory viruses, except for low levels of SARS-CoV-2 in effluent and biosolid samples, suggesting minimal public health risk. Antibiotic resistance genes and microplastics were persistently found in effluent and biosolids, thus indicating treatment inefficiencies and potential environmental dissemination. This multifaced research sheds light on diverse contaminants present after water reclamation, emphasizing the interconnectedness of human, animal, and environmental health in wastewater management. It underscores the need for a One Health approach to address the United Nations Sustainable Development Goals.

Climate change, unpredictable weather patterns, and droughts are depleting water resources in some parts of the globe, where recycling and reusing wastewater is a strategy for different purposes. To counteract this, the EU regulation for water reuse sets minimum requirements for the use of reclaimed water for agricultural irrigation, including a reduction in human enteric viruses. In the present study, the occurrence of several human enteric viruses, including the human norovirus genogroup I (HuNoV GI), HuNoV GII, and rotavirus (RV), along with viral fecal contamination indicator crAssphage was monitored by using (RT)-qPCR methods on influent wastewater and reclaimed water samples. Moreover, the level of somatic coliphages was also determined as a culturable viral indicator. To assess the potential viral infectivity, an optimization of a capsid integrity PMAxx-RT-qPCR method was performed on sewage samples. Somatic coliphages were present in 60% of the reclaimed water samples, indicating inefficient virus inactivation. Following PMAxx-RT-qPCR optimization, 66% of the samples tested positive for at least one of the analyzed enteric viruses, with concentrations ranging from 2.79 to 7.30 Log₁₀ genome copies (gc)/L. Overall, most of the analyzed reclaimed water samples did not comply with current EU legislation and contained potential infectious viral particles.

Synanthropic rodents are involved in the transmission of several parasitic zoonoses to humans, such as helminth parasites. As part of a multidisciplinary study concerning the rodent population in Barcelona (Spain), 300 specimens of the Norway rat, Rattus norvegicus, were analyzed to elucidate their helminth community, mainly species with a zoonotic potential. The sample included 263 specimens from the sewage system and 37 from public gardens. A total of 253 (84.3%) rats were found to be parasitized, and 206 (68.7%) harbored zoonotic species. Adult rats were found to be more heavily parasitized with zoonotic helminths than juveniles, but the sex and site of capture had no influence. Six zoonotic helminths were identified: Hydatigera taeniaeformis larvae (1.7%), Rodentolepis nana (8.0%), Hymenolepis diminuta (21.3%), Calodium hepaticum (46.3%), Gongylonema neoplasticum (36.7%), and Moniliformis moniliformis (2.3%). Human zoonotic helminth infections often go unreported, so that the role of R. norvegicus in their transmission is unknown. According to our results, it is advisable to monitor and control rodent populations in deprived settlements close to cities and in cities themselves, and to promote good hygienic and sanitary practices, especially among vulnerable populations and workers with high exposure such as sewage workers.

In late October 2024, an extreme Isolated Depression at High Levels (DANA) caused widespread flooding and the failure of wastewater treatment and sewerage systems across several municipalities in the Valencia region (Spain). Researchers from several Spanish National Research Council (CSIC) institutes conducted a six-month monitoring program in Albufera Natural Park and in the Poyo and Picassent gullies, which drain into the lagoon. Microbiological fecal indicators (Escherichia coli, somatic coliphages, and viral markers) showed an immediate and pronounced response to the flooding, indicating substantial inputs of untreated wastewater. Although most indicators gradually declined over subsequent months, several remained above pre-event levels, suggesting incomplete recovery and the persistence of contamination hotspots. Geochemical analyses revealed elevated concentrations of major and trace elements, marked increases in carbon and nitrogen fractions, and significant post-event enrichment of key anions in sediment samples. In water samples, variations in nutrient and anion concentrations were attenuated but clearly distinguishable, reflecting the combined influence of runoff and wastewater overflows. Multiple contamination indices were applied to evaluate changes in water and sediment quality. Differences among indices highlighted their relative nature and the critical role of reference values in interpretation. Integrative indices based on geometric means and relative toxicity (PLI and PERI) indicated moderate to low levels of current geochemical contamination. These findings demonstrate that the 2024 DANA caused significant and persistent microbiological and geochemical disturbances, underscoring the vulnerability of Mediterranean wetlands to extreme hydrometeorological events and the need for improved wastewater management and flood-resilient infrastructure under climate change.