The comprehensive evaluation of nitrate origin and transformation pathways in the oxic alluvial aquifer in Serbia.

Accurate pollution source identification is essential for establishing adequate water management strategies, particularly in groundwater with slow flow and prolonged recharge process allowing long-term pollution retention. An integrated study based on hydrogeochemical, dual isotopic (δ15NNO3 and δ18ONO3), and microbiological approaches (DN, IRB, and SRB BART tests) along with the statistical data processing was conducted to determine nitrate origin and fate in oxic alluvial groundwater source Kljuc in Serbia. The findings from a comprehensive investigation, encompassing 20 groundwater sampling locations during the period 2010-2019, delineated three distinct zones - the hinterland (anthropogenic impact area-untreated sewage inflow), the middle zone (area of mixed influence from fertilizer application, accompanied by a mitigated anthropogenic impact), and the zone of riparian denitrification. Significant linear relationship between anthropogenic impact parameters (Na, Cl, B, NO3-, NH4+, and electrical conductivity) along with the isotopic signatures (δ15N-NO3- ranking from + 10.01 to + 11.18‰ and δ18O-NO3- ranking from + 1.15 to + 6.24‰) and grouped sampling objects by cluster analysis indicated that hinterland is burdened by the nitrates originating from anthropogenic impact. The cross-section of groundwater flow data, concurrent increase of NH4+, and pH levels, along with the highest values of δ15N-NO3- (+ 12.90‰) and δ18O-NO3- (+ 9.70‰), indicated area of fertilizers (urea) impact. BART test results, pH increase, and low oxygen concentration, along with the groundwater flow data in riparian zone, indicated the unfolding of denitrification process. Presented research emphasizes the importance, necessities, and advantages of simultaneous and complementary use of hydrogeochemical, microbiological, and isotopic data.

Incremental costs of hospital-acquired infections in COVID-19 patients in an adult intensive care unit of a tertiary hospital from a low-resource setting.

BACKGROUND: Hospital-acquired infections (HAIs) are a global public health problem and put patients at risk of complications, including death. HAIs increase treatment costs, but their financial impact on Serbia's healthcare system is unknown. Our goal was to assess incremental costs of HAIs in a tertiary care adult intensive care unit (ICU) that managed COVID-19 patients. METHODS: A retrospective study from March 6th to December 31st, 2020 included patients with microbiologically confirmed COVID-19 (positive rapid antigen test or real-time polymerase chain reaction) treated in the ICU of the Teaching Hospital for Infectious and Tropical Diseases, University Clinical Centre of Serbia. Demographic and HAI-specific data acquired in our ICU were collected, including total and stratified medical costs (services, materials, laboratory testing, medicines, occupancy costs). Median total and stratified costs were compared in relation to HAI acquisition. Linear regression modelling was used to assess incremental costs of HAIs, adjusted for age, biological sex, prior hospitalisation, Charlson Comorbidity Index (CCI), and Glasgow Coma Scale (GCS) on admission. Outcome variables were length of stay (LOS) in days and mortality. RESULTS: During the study period, 299 patients were treated for COVID-19, of which 214 were included. HAIs were diagnosed in 56 (26.2%) patients. Acinetobacter spp. was the main pathogen in respiratory (38, 45.8%) and bloodstream infections (35, 42.2%), the two main HAI types. Median total costs were significantly greater in patients with HAIs (€1650.4 vs. €4203.2, p < 0.001). Longer LOS (10.0 vs. 18.5 days, p < 0.001) and higher ICU mortality (51.3% vs. 89.3%, p < 0.001) were seen if HAIs were acquired. Patients with ≥ 2 HAIs had the highest median total costs compared to those without HAIs or with a single HAI (€1650.4 vs. €3343.4 vs. €7336.9, p < 0.001). Incremental costs in patients with 1 and ≥ 2 HAIs were €1837.8 (95% CI 1257.8-2417.7, p < 0.001) and €5142.5 (95% CI 4262.3-6022.7, p < 0.001), respectively. CONCLUSIONS: This is the first economic evaluation of HAIs in Serbia, showing significant additional costs to our healthcare system. HAIs prolong LOS and influence ICU mortality rates. Larger economic assessments are needed to enhance infection control practices.

Indicators of Groundwater Potential for Nitrate Transformation in a Reductive Environment.

Increasing nitrate concentration in many shallow aquifers has become a global environmental problem. In order to determine anoxic aquifer sensitivity to nitrate pollution and potential for nitrogen conservation, we have qualified potential nitrate transformation pathways, by conducting field tests, tracer study, physicochemical and microbiological analysis of the groundwater. Combination of in situ measuring and laboratory analysis of physicochemical properties and selected biological activity reactivity tests (BARTTM), has enabled estimation of different pathways of NO3- reduction. During five days of nitrate enrichment experiment there was no observed increase in NO3- concentration, nor any observed decrease of TN (total nitrogen) in the groundwater, while NH4+ production rates increased (with the peak concentrations of 4.97 mg N/L) on the first day of the experiment. We assume that inhibited respiratory denitrification and enhanced DNRA (dissimilatory reduction of nitrate to ammonium) may preserve available nitrogen in a bioavailable form of ammonium.

Massive fish mortality and Cylindrospermopsis raciborskii bloom in Aleksandrovac Lake.

This paper presents a case study of a massive fish mortality during a Cylindrospermopsis raciborskii bloom in Aleksandrovac Lake, Serbia in mid-December 2012. According to a preliminary investigation of the samples taken on November 6 before the fish mortalities and to extended analyses of samples taken on November 15, no values of significant physicochemical parameters emerged to explain the cause(s) of the fish mortality. No industrial pollutants were apparent at this location, and results excluded the likelihood of bacterial infections. Even after freezing, the dissolved oxygen concentration in the water was sufficient for fish survival. High concentrations of chlorophyll a and phaeophytin occurred in the lake, and phytoplankton bloom samples were lethal in Artemia salina bioassays. A bloom of the cyanobacterium C. raciborskii was recorded during November. Although the A. salina bioassays indicated the presence of toxic compounds in the cyanobacterial cells, the cyanotoxins, microcystins, cylindrospermopsin and saxitoxin were not detected.

Evaluation of the origin of nitrate influencing the Kljuc groundwater source, Serbia.

This paper describes the use of the dual isotope method involving δ(15)N and δ(18)O measurements of dissolved nitrates to assess the origin and fate of groundwater nitrate at the Kljuc groundwater source, Serbia. A sampling campaign was conducted in September 2007 during flow conditions obtaining groundwater from observation wells and river water fed by a shallow aquifer hosted in alluvial (sandy-gravel) sediments. Nitrate isotope ratios ranged from +5.3 to +16.9‰ and δ(18)O(NO(3)) values varied from -2.3 to +5.0‰. Two major contamination sources were identified with isotopic compositions characteristic for nitrate derived from nitrification of soil organic nitrogen (+5.3 to +7.8‰ for δ(15)N) resulting in nitrate concentrations of 33.6 and 78.8 mg/L and nitrate derived from animal wastes or human sewage, e.g. via septic systems, yielding δ(15)N values of +9.9 to +11.9‰ and elevated nitrate concentrations of 31.2-245.8 mg/L. The occurrence of nitrification and denitrification was also revealed based on concentration and isotope data for dissolved nitrate.

Spatial and temporal variability of stable isotopes and biological parameters for the Danube River in Serbia.

This paper presents the results of hydrological, physicochemical, biological, and isotopic investigations of the Danube River along the stretch through Serbian territory conducted during four campaigns in September and November 2007, September 2008 and April 2009. The stable isotope values exhibited significant changes both in the Danube (-10.7 to-9.5 per thousand for delta(18)O and-73.7 to-67.1 per thousand for delta(2)H) and in its tributaries (-9.1 to-8.5 per thousand for delta(18)O and-69.4 to-59.4 per thousand for delta(2)H) depending on the time of survey, which could be partly attributed to the influences of seasonal effects. Results emphasise the dominant role of tributaries inflows from aquifers along the Danube. The very narrow range of delta(13)C(POC) (from-28.9 to-27.4 per thousand) was associated with relatively high C/N ratios (C/N>9), and together with delta(15)N(TPN) values, the date suggested that, in early spring, a major fraction of particulate organic matter was derived from allochthonous matter. An orthogonal varimax rotation of the principal components analysis identified four latent factors ('mineral related', 'biological', 'hardness', and 'soil inlets') which are responsible for the data structure covering 79% of the observed variations among the variables studied. A reliable grouping of samples with respect to the season was found.