Marin Glad

Indoor air quality (IAQ) in educational facilities is shaped by a dynamic interplay of microbial, chemical and physical factors, all of which influence health and cognitive performance. This study explored IAQ in university classrooms by combining microbiological, chemical and physical measurements to better understand microbial–chemical interactions in such environments. Samples ( N = 33) were collected from 11 rooms of different sizes, including lecture halls, classrooms and computer labs. Bacteria and moulds were quantified using standard microbiological procedures, while CO₂, O₂, CH₄, temperature, relative humidity and pressure were monitored by portable analysers. MALDI‐TOF MS was applied to identify airborne bacterial and fungal species, providing insight into microbial diversity and sources. The average CO₂ concentration was 906 ppm (range 509–1462 ppm). Although the overall mean was below the recommended 1000 ppm limit, more than half of the monitored rooms recorded CO₂ levels above this threshold. Mean bacterial and mould loads were 572 CFU/m ³ (range 50–1376 CFU/m ³ ) and 130 CFU/m ³ (range 56–260 CFU/m ³ ), respectively. Oxygen remained stable at 20.6 vol.%, while methane concentrations were negligible (mean 2.5 ppm). Relative humidity varied between 25% and 55%. Identified microorganisms were dominated by human‐associated bacteria ( Staphylococcus, Micrococcus ) and environmental fungi ( Cladosporium, Penicillium ), with noticeable differences between occupied and unoccupied rooms. Correlation analysis showed significant positive associations between CO₂ and bacterial load ( ρ = 0.56, p < 0.05), as well as relative humidity and bacterial abundance ( ρ = 0.67, p < 0.05). Species richness was negatively correlated with occupancy ( ρ = –0.77, p < 0.01), indicating microbial homogenisation in crowded conditions. Multiple regression analysis identified CO₂ and relative humidity as significant independent predictors of bacterial load ( p < 0.05). These findings highlight the importance of integrating microbial and physico‐chemical monitoring in IAQ assessments. CO₂ and relative humidity emerged as key controllable indicators, offering practical targets for improving air quality and limiting microbial contamination in educational environments.

Marine sediments are a key component of aquatic ecosystems, linking diverse water uses, functions, and services. Chemical contamination of sediments is a global concern, with many jurisdictions striving to prevent future pollution and manage existing contamination. This study evaluates the contamination status of Rovinj’s coastal waters using an integrated approach that combines sediment and biota chemical analyses. Sediments were analyzed to assess long-term contaminant accumulation (D8.C1), while the Mediterranean mussel (Mytilus galloprovincialis) served as a bioindicator of bioavailable contaminants and their cumulative effects on marine habitats (D8.C2). Sediment samples were collected from five sites (S1–S5), and mussels were caged using Mussel Watch installations for approximately 120 days at a control site (Lim Bay) and within Rovinj harbor. Both matrices were analyzed for heavy metals (As, Cd, Cu, Cr, Hg, Ni, Pb, and Zn), polycyclic aromatic hydrocarbons (16 PAHs), and polychlorinated biphenyls (PCBs), following the EU Water Framework Directive. All sampled locations showed a reduction in sediment contamination relative to 2011 data, with most concentrations below ecotoxicological thresholds. Exceptions included elevated ΣPAH and PCB concentrations in the harbor (S1 = 3.18 mg/kg DW; 0.33 mg/kg DW) and marina (S2 = 3.64 mg/kg DW; 0.89 mg/kg DW), as well as Ni levels (S3 = 30 mg/kg DW; S4 = 34 mg/kg DW). Despite higher contaminant loads at some locations, mussel contaminant bioaccumulation remained limited, and their vitality and survival were only moderately affected in the harbor. Although localized increases in some contaminants were detected, all calculated Q_PECm values remained below 1.0, indicating no significant ecological risk. However, a moderate-to-high probability of toxic effects (P) may occur with long-term exposure for biota inhabiting harbor and marina areas. The results of this study demonstrate continued improvement in the environmental quality of Rovinj’s coastal waters compared to the previous decade.

Escherichia coli (E. coli) and intestinal enterococci (ENT) are the indicator bacteria used to test the microbiological quality of bathing water. In Croatia, the quality of bathing water is assessed by parametric method i.e. on the basis of the 90th and 95th percentile values which are calculated using the corresponding arithmetic mean and standard deviation of the logarithmic bacterial concentrations. There are also non-parametric methods for determining the value of a particular percentile, and one of them is the so-called Hazen method. In this work, we study how the different methods of percentile calculation affect the assessment of coastal bathing water quality. We have chosen a "problematic" location with frequently elevated bacterial concentrations as a test site.The results show that in the case of E. coli, the 95th percentile values calculated using the Hazen method are significantly lower than those calculated using the parametric method (Wilcoxon rank test, p < 0.05), while for ENT there was no statistically significant difference. For case of annual assessment, the difference in coastal bathing water quality was statistically significant for both ENT and E. coli (McNemar test, p=0.004 and p=0.02 respectively). In the final classification, the difference in coastal bathing waters quality was statistically significant only in the case of E. coli (McNemar test, p=0.025).

The bacterium Legionella pneumophila is a ubiquitous microorganism naturally present in water environments. The actual presence of this opportunistic premise plumbing pathogen in recreational swimming pools and hot tubs in the northwestern part of Croatia has not been investigated. This study aimed to analyze the presence of the opportunistic pathogen L. pneumophila in public swimming pool water in Primorje-Gorski Kotar County (N = 4587) over a four-year period (2018–2021). Additionally, the second aim was to investigate the connection between the presence of L. pneumophila and pool water physicochemical parameters using mathematical predictive models. The presence of L. pneumophila was detected in six pool samples. Five positive samples were found in the water of indoor hot tubs filled with fresh water, and one positive sample in an outdoor recreational saltwater pool. A predictive mathematical model showed the simultaneous influence of chemical parameters dominated by the temperature in saltwater and freshwater pools, as well as the significant influence of free residual chlorine and trihalomethanes. Our results pointed out that keeping all physicochemical parameters in perfect harmony is necessary to reach the best disinfection procedure and to avoid the optimum conditions for L. pneumophila occurrence.

A comparative study of the two northeastern ports of the Adriatic Sea indicated that the port of Rijeka is microbiologically more loaded than the port of Pula and posing a greater threat to other ports through a potential transfer of pathogens by ballast water. Fecal indicator bacteria, Escherichia coli and intestinal enterococci, were investigated seasonally in 2014–2015 in the ports and during the bathing season monitoring in the two bays where ports are located in 2009–2020. In addition, the indicators and pathogens related to human health were determined in the ports’ seawater and sediment. The determined factors contributing to microbiological pollution were higher number of tourists and locals, potential wastewater and ballast water discharge and enclosed port configuration, with high solar radiation and low precipitation reducing the negative effects. Our research points to the necessity of including Clostridium perfringens in monitoring beach sand during the bathing seasons and a wider list of pathogens in port monitoring due to a potential transfer by shipping ballast water.

Legionellae are gram-negative bacteria most commonly found in freshwater ecosystems and purpose-built water systems. In humans, the bacterium causes Legionnaires’ disease (LD) or a Pontiac fever. In this study, the different waters (drinking water, pool water, cooling towers) in which Legionella pneumophila has been isolated were studied to assess the possible risk of bacterial spreading in the population. The influence of physical and chemical parameters, and interactions with Acanthamoeba castellanii on L. pneumophila, were analyzed by Heterotrophic Plate Count, the Colony-forming units (CFU) methods, transmission electron microscopy (TEM), and Sequence-Based Typing (SBT) analysis. During the study period (2013–2019), a total of 1932 water samples were analyzed, with the average annual rate of Legionella-positive water samples of 8.9%, showing an increasing trend. The largest proportion of Legionella-positive samples was found in cooling towers and rehabilitation centers (33.9% and 33.3%, respectively). Among the isolates, L. pneumophila SGs 2–14 was the most commonly identified strain (76%). The survival of Legionella was enhanced in the samples with higher pH values, while higher electrical conductivity, nitrate, and free residual chlorine concentration significantly reduced the survival of Legionella. Our results show that growth in amoeba does not affect the allelic profile, phenotype, and morphology of the bacterium but environmental L. pneumophila becomes more resistant to pasteurization treatment.

Considering the fact that water is a basic need of every living being, it is important to ensure its safety. In this work, the data on the presence of the opportunistic pathogen P. aeruginosa in drinking water (n = 4171) as well as in pool water (n = 5059) in Primorje-Gorski Kotar County in Croatia in the five-year period (2016–2020) were analysed. In addition, the national criteria were compared with those of neighboring countries and worldwide. The proportion of P. aeruginosa-positive samples was similar for drinking water (3.9%) and pool water (4.6%). The prevalence of this bacterium was most pronounced in the warmer season. P. aeruginosa-positive drinking water samples were mostly collected during building commissioning, while pool samples were from entertainment and spa/hydromassage pools. Outdoor pools showed a higher percentage of positive samples than indoor pools, as well as the pools filled with freshwater rather than seawater. The highest P. aeruginosa load was found in rehabilitation pools. Croatia, Serbia and Montenegro are countries that have included P. aeruginosa in their national regulations as an indicator of the safety of water for human consumption as well as for bottled water, while Slovenia and Bosnia and Herzegovina have limited this requirement to bottled water only. In the case of swimming pool water, this parameter is mandatory in all countries considered in this study.

Europe is one of the leading tourist destinations where tourism is one of the key economic sectors. The quality of bathing waters is a very important factor when choosing a vacation destination. Croatia recognized this early and was one of the first Mediterranean countries to start systematic monitoring of bathing waters. On the other hand, monitoring of inland bathing waters is relatively new and includes a much smaller number of sites (41) compared to coastal waters (894). The aim of this paper was to summarize and analyze the water quality of inland and coastal bathing sites of Croatia, closer regions (non-EU Member States) and in the EU for the last decade. The share of excellent water quality in EU Member States increased by 10.1% and 6.6% for inland and coastal waters, respectively (2011–2020). Germany recorded the highest proportion of excellent water quality for inland waters (92.2%) and Cyprus for coastal waters (99.3%). Looking at the 10-year average of the proportion of bathing waters with excellent quality, the proportion of coastal bathing sites exceeds that of inland waters by 7.1%. It is clear that additional efforts should be made to improve the management and monitoring of inland waters.