Layout 1 Introduction Water is a fundamental determinant of health and one of the most vulnerable elements of our planet with regard to the ongo- ing climate changes. The impact of these changes on the avail- ability, quality, and hygienic safety of water resources is well documented. The United Nations (UN) recognizes water as a universal human right, a principle reiterated in the Drinking Water Directive (2020/2184) issued by the European Union in December 2020 and subsequently transposed into Italian law through the Legislative Decree (LD) 18/2023 (LD, 2023). Based on these considerations, the Department of Hygiene and Health Prevention of the Local Brianza Health Protection Agency (ATS) has initiated a comprehensive monitoring program on the most at-risk water supply points. This initiative aimed at enhanc- ing the effectiveness, efficiency, and appropriateness of policies in place within ATS Brianza that protect the safety of water in- tended for human consumption. This project engages with the challenge posed by the UN Agenda 2030 in ensuring universal access to drinking water, reducing the release of pollutants and harmful substances, including emerging contaminants, while ex- ploiting a risk-based approach through the drafting of a Water Safety Plan (WSP) (Lucentini et al., 2014). The investigation was conducted during the period 2022- 2023 on potable waters in the Provinces of Lecco and Monza Brianza. The specific objectives were to identify and assess sources of vulnerability and quantify the risk of contamination of supply sources from: i) cyanobacteria and their toxins, with particular attention to the class of microcystins; ii) viruses such as bacteriophages, the subgroup of somatic coliphages; iii) spore-forming bacteria particularly resistant to treatment processes such as Clostridium perfringens, as well as the classic indicators of fecal contamination (Escherichia coli and Entero- cocci) in water supply sources near surface water bodies. In the province of Lecco, water distribution for human con- sumption is managed by Lario Reti Holding SPA, with the pri- mary water supply system being the Intermunicipal Aqueduct Brianteo. This system includes a sole lake water intake which, through auxiliary works and connections to local networks, di- rectly serves 64 municipalities across the provinces of Lecco, Como, and Monza. The Brianteo water treatment system origi- nates from the facility located at the end of the Lecco branch of Lake Como. It extracts and treats lake water at a rate ranging from 500 to 1,100 liters per second. Additional water sources in the Lecco province include numerous springs and wells, some situated near water basins and others adjacent to the Adda River’s bed. The water provided by Lario Reti Holding exhibits varying characteristics across different municipalities, but can be gener- SPECIAL SECTION Potentially toxic cyanobacteria blooms in the Southern Alps and the Italian peninsula Safety of water for human consumption: a case study from Northern Italy Mariano Nasello,1 Eleonora Masala,2 Gaia Villa,2 Anna Di Lauro,2 Samuele Peraboni,2 Simona Vercelloni,2 Franca Facchini,2 Anna Molinari,2 Nicoletta Castelli1 1SC Igiene Alimenti Nutrizione, Agenzia di Tutela della Salute della Brianza, Desio; 2Laboratorio di Prevenzione, Agenzia di Tutela della Salute della Brianza, Oggiono, Italy ABSTRACT Water is essential for health, and climate change can compromise its quality. The Local Brianza Health Protection Agency (ATS) has initiated a biennial monitoring project of water supply sources to ensure safe and clean water access, in line with the United Nations (UN) Agenda 2030. The project has identified vulnerabilities in the water supply chain, finding the presence of cyanobacteria in 19.7% of samples. Risk assessment results show that climatic conditions could influence the vulnerability of sources. Corresponding author: Eleonora Masala, Laboratorio di Preven- zione, Agenzia di Tutela della Salute della Brianza, Oggiono, Italy. E-mail: eleonora.masala@ats-brianza.it Key words: water treatment system, cyanobacteria, potable water, microcystins. Authors’ contributions: all the authors made a substantive intellec- tual contribution. All the authors have read and approved the final version of the manuscript and agreed to be held accountable for all aspects of the work. Conflict of interest: the authors declare no potential conflict of in- terest. Funding: none. Availability of data and materials: all data generated or analyzed during this study are included in this published article. Received: 29 August 2024. Accepted: 20 December 2024. Publisher’s note: all claims expressed in this article are solely those of the authors and do not necessarily represent those of their affil- iated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher. ©Copyright: the Author(s), 2025 Licensee PAGEPress, Italy Advances in Oceanography and Limnology, 2025; 16:12986 DOI: 10.4081/aiol.2025.12986 This work is licensed under a Creative Commons Attribution- NonCommercial 4.0 International License (CC BY-NC 4.0). Safety of water for human consumption: a case study from Northern Italy 7 ally classified into four main types, based on geographic origin and hydrogeological criteria: i) water from springs in the pre- Alpine area north of the Orobic Line (Alpine metamorphic rocks); ii) water from springs in the pre-Alpine area south of the Orobic Line (pre-Alpine sedimentary rocks); iii) water from wells in the hills and plain areas; iv) water from the inter-mu- nicipal aqueduct. Materials and Methods The 61 monitored points have been distributed across 31 types of facilities, including wells and springs. Of these, 14 fa- cilities are located at Lake Como, 9 along the River Adda, 4 at Lake Annone, and 2 at Lake Bosisio. For every 61 study sites, 11.5 L of water were collected, in- cluding: i) 0.5 L for physicochemical analyses (pH, conductivity, and THMs Trihalomethanes), following Ottaviani and Bonadonna (2007) and the limits specified in LD (2023); ii) 1 L in sterile containers for microbiological analyses (methods and limits according to LD (2023) and for somatic coliphages (method and limits according to UNI EN (2001) and LD (2023), respectively); iii) 10 L in dark containers; 5 L were used for mi- croscopic counting and identification of cyanobacteria according to UNI EN (2006), and the remaining 5 L were concentrated to a ratio of 1:500 by filtration with nylon membrane (pore size 1.2 µm) and used for Microcystin (MSs) and Nodularin (NOD) de- tection through ELISA testing, following the limits outlined in LD (2023). The risk of vulnerability was calculated by assigning a score of 0 for samples that tested negative for all parameters over the two-year period; a score of 1 for each positive parameter, except for the presence of cyanobacteria or microcystins, which were assigned a score of 2 for every year of positivity. The partial scores were summed, and based on the values obtained, three risk ranges were hypothesised: low 0-1; medium 2-3; high >3. Results and Discussion The analytical results obtained in 2022 and 2023 are shown in Figure 1. Regarding cyanobacteria, 14.9% and 9.1% of the sampling points tested positive in 2022 and 2023, respectively. The most common species in the two years were Planktothrix (with the highest density of 170,000 cells L-1 In Malgrate well after treatment) and Pseudanabaena. Cyanotoxins (MCs and NOD) concentrations were <0.15 µg L-1 in all cases. Regarding the other microbiological parameters examined, positive results were found for Clostridium perfringens (8.3% positivity in 2022 and 1.8% in 2023), Escherichia coli, and En- terococci, each not examined in 2022 and with 15% positivity in 2023. The highest frequency of positivity was for somatic col- Figure 1. Monitoring results. The bars show the percentages of positivity for pathogenic bacteria, cyanobacteria and cyanotoxins out of the total number of samples analysed. M. Nasello, et al.8 iphages, which were detected in 70% and 15% of the points an- alyzed in 2022 and 2023, respectively. The trends in positivity rates may suggest that vulnerability could be influenced by meteoclimatic conditions (not explicitly considered in this work), which in turn lead to significant vari- ations in the flow of the main reservoirs and consequently of secondary ones. Monitoring campaigns were conducted from June to September: in 2022, precipitations were very scarce, while in 2023, the situation was the opposite, with abundant rainfall in both provinces. Two sampling points in Giussano and Besana Brianza (MB), approximately 20 km far from Lake Como, tested positive for bacteriophages and cyanobacteria in both years. The source of contamination remains unclear, particularly regarding the cyanobacterium Planktothrix rubescens. Two possible explana- tions warrant further investigation, including a malfunction of the Brianteo water treatment plant that may have allowed cyanobacteria to enter the water network from the water column above the intake where they are normally present; cyanobacteria then adapted to survive even in the absence of light by activating a heterotrophic metabolism (Perez-Garcia et al., 2011). Alterna- tively, hydrogeological continuity with the main water body may have caused the contamination of the well. The analysis of the data allowed an assessment of the vul- nerability at the investigated supply points (Table 1). In partic- ular, 24.6% of the points monitored over the two-year period showed a high level of criticality, with 60% (7 high-risk points out of 15) attributed to the presence of cyanobacteria. In collab- oration with the water management authority, a monitoring fre- quency has been established based on vulnerability: i) twice a year for critical points (24.6%); ii) annually for moderately crit- ical points (11.5%); iii) every two years for low vulnerability points (63.9%). Given the nature of the waters in the investigated territory, it was deemed important to study the cyanobacteria density, as it represents a useful indicator for assessing the quality of water intended for human consumption. Excessive cyanobacterial bio- mass, in addition to the inconveniences caused by the production of foul-smelling substances (Bowmer et al.,1992), has signifi- cant negative consequences for aquatic resources utilization due to the risk associated with the production and release of toxic compounds (cyanotoxins), which may also transfer along trophic and food chains. The definition and quantitative assessment of risk depend on the autecology of the dominant cyanobacterial species (Cerasino et al., 2012; Chorus et al., 2021), including the dynamics of bloom formation, the presence of toxic strains, types of toxins produced, and the intended use and the corre- sponding aqueduct system. Acute or short-term effects associated with the consumption of contaminated water may arise from inefficient water treat- ment processes in the removal of cyanobacteria and cyanotoxins. Significant levels of cyanotoxins in raw water may result from both natural cellular lysis consequent to bloom senescence and artificial lysis due to inappropriate purification treatments. Stud- ies on the impact of these pollutants on human health are still limited, primarily due to challenges in establishing a temporal link adequate to demonstrate cause-effect associations. The few documented cases concern incidents that occurred in Brazil, Australia, and the US (Metcalf et al., 2012). In industrialized countries, where drinking water is strictly controlled, chronic exposure remains the most likely risk, with the cause-effect re- lationship being particularly challenging to demonstrate from an epidemiological perspective (Svircev et al., 2009). Conclusions The monitoring data showed considerable variability between sampling points in the concentration of cyanobacteria, colony- forming units of bacteria, and plaque-forming units of viruses. The project has allowed for an in-depth understanding of water supply sources and their associated vulnerabilities, but does not allow for conclusions to be drawn regarding the causes of the variability in the analytical data obtained. It will therefore be necessary to collect further experimental data that will enable a statistical analysis of the potential impact of weather variability on water quality, and to conduct a hydrogeological study to ex- plore the interconnections between the supply sources and the main reservoirs. References Bowmer KH, Padovan A, Oliver RL, et al., 1992. Physiology of geosmin production by Anabaena circinalis isolated from the Murrumbidgee River, Australia. Water Sci Technol. 25:259-67. Cerasino L, Salmaso N, 2012 Diversity and distribution of cyanobacterial toxins in the Italian subalpine lacustrine dis- trict. Oceanol Hydrobiol Studies. 41:54-63. Chorus I, Fastner J, Welker M, 2021. Cyanobacteria and cyan- otoxins in a changing environment: Concepts, controversies, challenges. Water. 13:2463. LD, 2023. Legislative Decree 18/2023. Attuazione della direttiva (UE) 2020/2184 del Parlamento Europeo e del Consiglio, del 16 dicembre 2020, concernente la qualità delle acque destinate al consumo umano. (23G00025) (GU n.55 del 6- 3-2023) Lucentini L, Achene L, Fuscoletti V, et al., 2014. Guideline for risk assessment and management within the drinking water chain according to Water Safety Plans, xi, 89 p. Rapporti IS- TISAN 14/20. Metcalf JS, Codd GA. Cyanotoxins. In: Whitton BA (Ed.), 2012. Ecology of Cyanobacteria II: Their diversity in space and time. Springer; Dordrecht, The Netherlands. Ottaviani M, Bonadonna L, 2007. Reference analytical methods for water intended for human consumption according to the Italian Legislative Decree 31/2001. Chemical methods., vii, 328 p. Rapporti ISTISAN 07/31. Perez-Garcia O, Escalante FME, de-Bashan LE, Bashan Y, 2011. Table 1. Summary of risk assessment findings. Risk assessment Low Medium High Total N° 39 7 15 61 % 63,9 11,5 24,6 Monitoring frequency Biennial Annual Half yearly Safety of water for human consumption: a case study from Northern Italy 9 Heterotrophic cultures of microalgae: metabolism and po- tential products. 45:11-36. Svircev Z, Krstic S, Miladinov-Mikov M, et al., 2009. Freshwa- ter cyanobacterial blooms and primary liver cancer epidemi- ological studies in Serbia. J. Environ. Sci. Health C. Environ. Carcinog. Ecotoxicol. Rev. 27:36-55. UNI EN, 2001. UNI EN ISO 10705-2:2001 Water quality - De- tection and enumeration of bacteriophages - Enumeration of somatic coliphages. UNI EN, 2006. UNI EN 15204:2006 Water quality - Guidance standard on the enumeration of phytoplankton using in- verted microscopy (Utermohl technique).