Point Of Water Research Articles

The MD study of water short-range order during liquid-liquid transition: Toward the second critical point

Full-scale thermodynamic experimental investigations of the liquid-liquid transition and different water phases remain challenging due to spontaneous crystallization and the complexity of studies on the nanosecond time scale. Moreover, the specific position of the second critical point in water is still unclear. This study used molecular dynamics to reproduce the structural properties of both low- and high-density waters and to characterize changes in the order parameters, average number of hydrogen bonds, and ordering of neighboring molecules during liquid-liquid transitions and in regimes of supercooled waters. A rapid change in calculated parameters under increased pressure could be attributed to a first-order phase transition. In addition, we provided evidence that low-density water becomes dissolved in high-density water inclusions as the temperature or pressure increases. The presumed location of the second critical point has been identified as TC ≈ 220 K, PC ≈ 1.5 kbar, and ρC ≈ 1.02 g/cm3.

Incidence of per- and polyfluoroalkyl substances (PFAS) in private drinking water supplies in Southwest Virginia, USA

Per- and polyfluoroalkyl substances (PFAS) are a class of man-made contaminants of human health concern due to their resistance to degradation, widespread environmental occurrence, bioaccumulation in living organisms, and potential negative health impacts. Private drinking water supplies may be uniquely vulnerable to PFAS contamination in impacted areas, as these systems are not protected under federal regulations and often include limited treatment or remediation, if contaminated, prior to use. The goal of this study was to determine the incidence of PFAS contamination in private drinking water supplies in two counties in Southwest Virginia, USA (Floyd and Roanoke) that share similar bedrock geologies, are representative of different state Department of Health risk categories, and to examine the potential for reliance on citizen-science based strategies for sample collection in subsequent efforts. Samples for inorganic ions, bacteria, and PFAS analysis were collected on separate occasions by participants and experts at the home drinking water point of use (POU) for comparison. Experts also collected outside tap samples for analysis of 30 PFAS compounds. At least one PFAS was detectable in 95 % of POU samples collected (n = 60), with a mean total PFAS concentration of 23.5 ± 30.8 ppt. PFOA and PFOS, two PFAS compounds which presently have EPA health advisories, were detectable in 13 % and 22 % of POU samples, respectively. On average, each POU sample contained >3 PFAS compounds, and one sample contained as many as 8 compounds, indicating that exposure to a mixture of PFAS in drinking water may be occurring. Although there were significant differences in total PFAS concentrations between expert and participant collected samples (Wilcoxon, alpha = 0.05), collector bias was inconsistent, and may be due to the time of day of sampling (i.e. morning, afternoon) or specific attributes of a given home. Further research is required to resolve sources of intra-sample variability.

Analysis of the instability of the characteristics of a standard platinum resistance thermometer in the interval between verifications and a method for reducing the measurement error

The standard platinum resistance thermometer is currently the most accurate contact temperature sensor. One of the most important characteristics of its error is the instability of resistance during the interval between calibrations. In this work, the task was set to analyze the data from periodic calibration of 27 thermometers performed at the D. I. Mendeleev Institute for metrology for several years. Based on the analysis, it was concluded that the instability of the resistance of thermometers at the triple point of water for most thermometers exceeds ±0.002 °C, sometimes reaching several hundredths of a degree. The work analyzes the reasons for the instability of resistance, as well as the instability of the relative resistance of thermometers. Based on data analysis of the thermometer error at the temperatures between calibration points and graphs of changes in the interpolation function during the interval between the calibrations in the entire measurement range, it was shown that the error associated with the instability of the thermometer can be reduced from hundredths to thousandths of a degree when used as a measured parameter relative resistance of the thermometer. It is proposed to include in the regulatory documents on the verification methods of Standard platinum resistance thermometers an additional periodic calibration of the thermometers at the triple point of water.

Autoclave Design for Microgravity Hydrothermal Synthesis

Microgravity offers an enticing synthetic knob for materials scientists to explore—however, this environment creates major challenges in hardware development that can turn a simple 3-day experiment into a 3-year long nightmare. This paper provides an overview of engineering an autoclave, compatible with NASA’s Solidification Using a Baffle in Sealed Ampoules (SUBSA) furnace, to enable microgravity hydrothermal synthesis—an acceleration-sensitive technique that processes aqueous samples above the boiling point of water. Hydrothermal synthesis is a universal chemical transformation technique that is used to produce a range of advanced materials with applications in alternative energy, healthcare, and the food industry. In this work, we use the synthesis of graphene hydrogel as a case study to verify our hardware design on Earth before launching to the International Space Station for microgravity testing. The design addresses pertinent challenges which include enabling thermal expansion while preventing air bubble formation in solution and implementing a pressure fail-safe above the maximum operating temperature. Our goal in presenting this autoclave design is to provide a step forward towards commercial-of-the-shelf microgravity hardware.

Orienting Electron Fillings in d Orbitals of Cobalt Single Atoms for Effective Zinc–Air Battery at a Subzero Temperature

AbstractThe missions in extreme environments such as the moon, the Arctic/Antarctic, and the plateau require the operation of batteries at low temperatures even below the freezing point of water. Herein, it is reported that compressively stressed Co single atoms exhibit enhanced oxygen reduction reaction (ORR) activity and enable the effective operation of zinc–air battery at a subzero temperature. The compressive strain is generated by depositing Co single atoms on highly arced carbon layers with ultra‐small curvature radii ≈2 nm. The locally compressive strain on Co single atoms redistributes the electron fillings in d orbitals with different spatial orientations, thereby strengthening the adsorption of active intermediates and enhancing the activity toward ORR. As expected, compressively stressed Co single atoms outperform Co single atoms on a flat support without strain in terms of kinetic current density (31.09 mA cm−2 vs 0.35 mA cm−2) at 0.85 V during ORR. The integration of the catalyst into a Zn–air battery generates a superior power density of 54.8 mW cm−2 than the commercial Pt/C counterpart (24.1 mW cm−2) at −40 °C.

Beyond Local Structures in Critical Supercooled Water through Unsupervised Learning.

The presence of a second critical point in water has been a topic of intense investigation for the last few decades. The molecular origins underlying this phenomenon are typically rationalized in terms of the competition between local high-density (HD) and low-density (LD) structures. Their identification often requires designing parameters that are subject to human intervention. Herein, we use unsupervised learning to discover structures in atomistic simulations of water close to the liquid-liquid critical point (LLCP). Encoding the information on the environment using local descriptors, we do not find evidence for two distinct thermodynamic structures. In contrast, when we deploy nonlocal descriptors that probe instead heterogeneities on the nanometer length scale, this leads to the emergence of LD and HD domains rationalizing the microscopic origins of the density fluctuations close to criticality.

Evaluation of Ion Recombination Correction for Indigenously Developed Farmer Ion Chamber in Flattening Filter-Free Photon Beams.

Modern generation linear accelerator (linac) either generates X-rays with a flattening filter (WFF beam) or without flattening filter free (FFF beam). The FFF beams are associated with a significantly higher dose per pulse compared to WFF beams due to the absence of a flattening filter and the corresponding attenuation caused by it. This results in increased ion recombination and a larger saturation correction factor (ks). In accordance with the IAEA TRS 398 dosimetry protocol, ks is necessary for the accurate measurement of absorbed dose at a point in water. The objective of this study was to evaluate the ks for the indigenous FAR 65-GB ion chamber (IC) for the FFF X-rays. The study was carried out on TrueBeam linac (Varian, A Siemens Healthineers company) which offers 6 MV WFF, 6 MV FFF, 10 MV WFF and 10 MV FFF beams. The two-voltage method was employed to measure ks in a solid water phantom at a depth of 10 cm for a FAR 65-GB and SNC 600c and 0.6cc PTW 30013 Farmer chambers at 100 cm and 150 cm source-to-chamber distances for a 10 cm × 10 cm field size. The ks values for the FAR 65-GB, PTW 30,013, and SNC 600c were 1.0055 (1.0113), 1.0051 (1.0071), and 1.0033 (1.0066) for the 6 MV WFF (FFF) beams, respectively, and 1.0066 (1.0178), 1.0061 (1.0137), and 1.0035 (1.0119) for the 10MV WFF (FFF) beams, respectively. The ks values calculated by two-voltage method matches with ks values obtained from Jaffe's plot. The chamber exhibited a linear dose-response up to 3000 cGy, beyond which a saturation effect was observed. Our study reveals that this chamber is suitable for the reference dosimetry for the FFF beams.

Thermodynamic Simulation of Cascade Cooling System for Vacuum Freeze Drying

Vacuum freeze drying (VFD) is a drying method carried out at pressures and temperatures below the triple point of water. Drying occurs by sublimation. The results of the VFD method are able to maintain the quality of dry ingredients (taste, colour, nutrient, etc.). To achieve a condition below the triple point of water, it is conditioned so that the pressure is under a partial pressure of 6.11657 mbar at a temperature of 0.01°C. The refrigeration system is simulated using refrigerants R-134a and R-22. The purpose of the simulation is to obtain the optimum system conditions. The variables varied were the saturated temperature of the LTC (Low-Temperature Circuit) evaporator, the saturation temperature of the HTC (High-Temperature Circuit) evaporator, the difference in the temperature of the pinch point between the LTC condenser and the HTC evaporator and the temperature of the HTC condenser. The simulation results are the saturated temperature of the LTC evaporator -30°C, the saturation temperature of the HTC evaporator -15°C, the difference in the temperature of the pinch point between the LTC condenser and the HTC evaporator 10°C and the temperature of the HTC condenser 40°C. The highest Coefficient of Performance (COP) of the cascade cooling system with these parameters is 2.55 using a combination refrigerant R22 in HTC and R134a in LTC.

Groundwater development and management constraints in drought prone Chiredzi and Zvishavane Districts, Zimbabwe

Communities in drought-prone areas continued to fall into new vulnerability traps due to increasing water demand and stress. The study assessed groundwater development and management constraints in the Chiredzi and Zvishavane districts of Zimbabwe. Groundwater development and management activities implemented in the study area were supported by the Government of Zimbabwe, development partners, humanitarian agencies, private sector corporate social responsibility, and individual households. Interpretivism and realism philosophical positionalities were employed in the study. Whilst interpretivism’s inductive approach enabled an in-depth qualitative methodology and understanding of the groundwater constraints, the direct realism provided quantitatively driven scientific and statistical data to answer the research questions exhaustively. Quantitative data was gathered through a household questionnaire administered to randomly selected respondents. Qualitative data was gathered using focus group discussions, key informant interviews, direct field observations and measurements. Respondents to the key informant interview were drawn from district-level government officials, local authorities, traditional leaders, village pump minders and water point committee members.Due to climate change, communities have experienced an increase in the decline in groundwater levels during the dry season evidenced by demand surpassing supply. Temperature increase and rainfall decline experienced by 97%, and 73% of respondents from Chiredzi and Zvishavane districts, respectively, resulted in increased withdrawal and reduced groundwater recharge. Participants revealed that groundwater withdrawal is on the increase while recharge is declining as evidenced by the increase in conflicts at waterpoints. The 85% coverage by low groundwater-yielding basement hydrogeological formation suggested a slight reduction in groundwater recharge due to reduced rainfall and increased community vulnerability to drought. Village Pump Minders and Water Point Committees experienced operational challenges that affected the maintenance of groundwater sources. This was mainly due to the incapacitation of local institutions in terms of financial resources, equipment, and skills. The study recommends a groundwater replenishment model to improve groundwater aquifer recharge. Strengthening of local institutions improves the management of groundwater using integrated water resources management (IWRM) framework that promotes coordination between competing uses.

Enhancing Rubber Vulcanization Cure Kinetics: Lowering Vulcanization Temperature by Addition of MgO as Co-Cure Activator in ZnO-Based Cure Activator Systems.

Vulcanization is a chemical modification of rubber that requires a considerable amount of thermal energy. To save thermal energy, the kinetics of rubber vulcanization should be improved. In this article, the curing properties of rubber vulcanization are thoroughly investigated using the moving die rheometer (MDR) technique. To enhance the kinetics in different stages of ZnO-based sulfur vulcanization systems, small amounts of MgO were added. The results revealed that the small amount of 1 to 2 phr (per hundred grams of rubber) of MgO in the controlled 5 phr ZnO-based curing systems can significantly improve the curing kinetics. For example, the optimum curing time of 1 phr MgO added to the 5 phr ZnO-containing semi-efficient vulcanization system at different temperatures was more than half that of the controlled 5 phr ZnO-only compound. While maintaining a similar rate of vulcanization, the vulcanization temperature can be reduced by up to 20 °C by using MgO as a co-cure activator, which exhibits similar or better rheometric mechanical properties compared to the controlled compounds. With the addition of MgO as a co-cure activator, the vulcanization reactions become very fast, enabling vulcanization to be completed, even at the boiling point of water (100 °C) with an affordable curing time (<1 h). By reducing the vulcanization temperature, the scorch safety time can be enhanced in the ZnO/MgO-based binary cure activator-containing vulcanizates. Overall, MgO could be a potential candidate as a co-cure activator with ZnO for the vulcanization of rubber, offering better economical and eco-friendly methods.

Assessment of the coating quality in a top-spray fluidized bed coater: An experimental study

The effects of multiple factors on the coating process in a top-spray fluidized bed coater were systematically investigated. The intra-particle coating variability could be assessed by the SEM measurement. Fluidizing gas temperature (0.5–0.9, normalized by the boiling point of water), injection velocity (0.115–0.397 m/s) and concentration (2.1–5.2 wt%) of the coating liquids, atomizing pressure (1.0–3.0 bar) and nozzle height (378 and 470 mm) were found to impact particle agglomeration, coating efficiency and thickness dramatically. Their impact trends and mechanisms were analyzed in detail. The effect of the particle size (0.22–1.26 mm) on particle agglomeration behavior was highlighted. Critical injection velocities and the corresponding agglomeration ratios were experimentally determined. Finally, it was established that there were no universal optimum conditions for the spray coating process, and they can be experimentally determined according to the attributes of interest.

Understanding the conversion mechanisms in supercritical water conditions of PET as a model compound of plastic wastes

In this work, polyethylene terephthalate (PET) was used as a model compound for understanding the conversion mechanism of plastic wastes through supercritical water gasification (SCWG) for producing: i) a gas rich in methane/hydrogen; and ii) for obtaining valuable molecules to be recycled in chemical processes (e.g., benzoic and acetic acids).The experiments were conducted at two different temperatures (above the critical point of water): 450 °C and 600 °C, in order to study the influence of this parameter on the conversion yield. The holding time in the reactor was set at 30 min for all trials. The experimental data were compared to the thermodynamic equilibrium calculations and the results showed that increasing the temperature from 450 °C to 600 °C, the total gas yield is highly improved (from 8.6 mol gas/kg of dried feedstock to 22 mol gas/kg of dried feedstock). The experiments with Raney-nickel catalyst indicated a significant improvement of the carbon conversion yield, which led to a higher gas production from mild to higher temperatures. The maximum total gas yield obtained with this catalyst was 63.4 mol gas/kg of dried feedstock at 600 °C, which is almost 3 times higher than that obtained at the same operating conditions without catalyst. The HHV of the obtained gas at 600 °C with the catalyst was 64.7 MJ/kg gas and 57.9 MJ/kg gas at 450 °C. Additionally at mild operating temperatures (450 °C), the obtained performance with the catalyst was even higher than that obtained at 600 °C without catalyst (50 mol gas/kg dried feedstock and 22 mol gas/kg dried feedstock, respectively), which is the major contribution of this work. At mild temperatures (450 °C) the methane production is highly favored, meanwhile at 600 °C the hydrogen production is enhanced. The methane yield obtained at 450 °C was 21.3 mol CH4/kg dried feedstock and the hydrogen yield obtained at 600 °C was 20.6 mol H2/kg dried feedstock. In the aqueous phases obtained from the experiments performed without catalyst at 450 °C, it was found valuable intermediate species such as benzoic and acetic acids (at a concentration of 4462 mg/L and 946 mg/L, respectively). This study represents a sustainable approach for valorizing plastic wastes by catalytic SCWG process.

Quantitative observation of water phase transition in gas diffusion layers utilizing advanced in situ differential scanning calorimetry

The study investigates the freezing behavior of supercooled water in gas diffusion layers (GDLs) of polymer electrolyte fuel cells (PEFCs). Using an innovative advanced in situ differential scanning calorimetry (advanced DSC) technique, we analyze phase transitions within GDLs at a single-cell scale, excluding impacts of catalyst layers and membranes. This method overcomes the limitations of traditional DSC, allowing variable water saturation and distribution. We find that freezing-thawing and drying-saturating cycles contribute to noticeable variations in the freezing temperature (Tonset) of supercooled water, ranging from −6 °C to −15 °C, attributed to the heterogeneous surface of GDL and water redistribution. Repeated drying-saturating cycles remove nucleation seeds, lowering the freezing point of water − a "cleaning effect." The freezing probability reduces at lower saturation levels, influenced by waterproof treatment uniformity on GDLs. Residual ice can be detrimental to the cold-start capability of PEFCs, as it promotes freezing of supercooled water around −1 °C. Our findings enhance understanding of water behavior in GDLs and its impact on PEFC cold-start performance. Applying this technique to other cell components, such as the catalyst layer, could further elucidate water freezing dynamics in PEFCs and guide the innovation of more reliable cell components for PEFC applications in broader climates.

Prediction of Phase Equilibrium Conditions and Thermodynamic Stability of CO2-CH4 Gas Hydrate

With the large-scale promotion and application of CO2 flooding, more and more engineering problems have emerged. Due to the high CO2 mole fraction, the associated gas of CO2 flooding very easily forms solid hydrates, compared to conventional natural gas. This has resulted in production decline or shutdown. Understanding the phase equilibrium conditions for hydrate formation in production fluids is crucial for hydrate prevention and control. In this study, accurate predictions of CO2-CH4 mixed gas hydrate formation conditions were performed using theoretical models. The temperature and pressure ranges for hydrate formation were calculated for different CO2 mole fraction, ranging from −11.5 °C to 20.85 °C and from 0.81 MPa to −28.1 MPa, respectively. Based on the calculated phase equilibrium data, a multi-parameter empirical model was developed using polynomial fitting. The calculation errors for the multi-parameter empirical model were 3.09%. The multi-parameter empirical model established in this study can avoid complex thermodynamic equilibrium calculations and has the advantages of simplicity, high accuracy, and wide coverage of downhole conditions. Based on the calculated phase equilibrium data, the dissociation enthalpy of CO2-CH4 hydrate below and above the freezing point of water was calculated. The results showed that an increase in CO2 mole fraction led to an increase in hydrate dissociation enthalpy and enhanced thermodynamic stability, making hydrate prevention more challenging. Our work can contribute to the optimization of CO2 production fluid treatment processes and the development of hydrate prevention and control technologies.

Animal welfare on Argentinean dairy farms based on the Welfare Quality® protocol framework

Animal welfare is a multidimensional concept that comprises animal health, mental state and natural living conditions and plays an essential role in dairy production. On dairy farms, animal welfare can be assessed with different available protocols. The goal of this study was to describe the animal welfare strengths and hazards of dairy farms in Argentina using the Welfare Quality® protocol as a framework. We conducted a literature search using the Scopus database to find articles related to the measures included in the protocol for Argentinean farms. Furthermore, we included data from national statistics. The data available were grouped according to the four principles of the protocol: good feeding, good housing, good health, and appropriate behavior. The results suggest that cows are well nourished; however, water provision is limited because grazing cows need to walk long distances, between 244 m and 460 m, to access a water point. Heat stress is a notable constraint affecting the welfare of cows, as the temperature-humidity index is greater than 72 for at least 100 days during the year. The prevalence of lameness and downer cows was estimated to be 2.2% and 0.7%, respectively, which are below the thresholds for ensuring good welfare. The annual average somatic cell count was 385,000/ml, close to the cutoff recommended for good health. The mortality rate of the cows was higher than recommended. The main strength of Argentinean dairy farms in relation to animal welfare is access to pasture throughout the year for 90% of the farms.

Identification of local structures in water from supercooled to ambient conditions.

Studies of water thermodynamics have long been tied to the identification of two distinct families of local structures, whose competition could explain the origin of the many thermodynamic anomalies and the hypothesized liquid-liquid critical point in water. Despite the many successes and insights gained, the structural indicators proposed throughout the years were not able to unequivocally identify these two families over a wide range of conditions. We show that a recently introduced indicator, Ψ, which exploits information on the hydrogen bond network connectivity, can reliably identify these two distinct local environments over a wide range of thermodynamic conditions (188-300K and 0-13 kbar) and that close to the liquid-liquid critical point, the spatial correlations of density fluctuations are identical to those of the Ψ indicator. Our results strongly support the idea that water thermodynamic properties arise from the competition between two distinct and identifiable local environments.

Determinants of the operational performance of community-managed handpumps in rural Mozambique: An analysis of five years of cross-sectional sustainability assessments

Improving rural water supply sustainability in sub-Saharan Africa remains a major challenge. This study analysed five-years of cross-sectional sustainability check data collected annually between 2011 and 2016 (except 2015) to investigate factors influencing the operational performance of community-managed handpumps in rural Mozambique. Logistic and negative binomial regression was performed using multiple outcome measures of functionality, reliability and continuity. Average marginal effects (AMEs) were estimated to assess the effects of the predictors and mediation analysis was conducted to examine the role of women's participation.Higher levels of handpump performance were associated with financial records quality and update frequency, water committees with spare parts in stock, and committee annual revenue. The AME of high quality or recently updated financial records for non-functionality was estimated to be −0.40 (95% confidence interval [CI], −0.56 to −0.25), which is interpreted as a 40% lower probability of a water point being non-functional compared to the reference group. Water committees with a spare part stock exhibited a preventive effect on both non-functionality and breakdowns in the past 12 months, reducing their probability by 10% (AME, 95% CI, −0.17 to −0.03) and by 18% (AME, 95% CI, −0.30 to −0.05), respectively. Annual committee revenue up to 2,000 MZN (57 USD) reduced the probability of breakdowns by 25% (AME, 95% CI, −0.45 to 0.05). Handpumps were 10% (AME, 95% CI, 0.03 to 0.17) more likely to be non-functional when women were in the committee management positions. Conversely, female maintenance group members were associated with reduced breakdowns in the multivariate regression analysis (odds ratio, 0.48; 95% CI, 0.24 to 0.95).Increasing outreach of post-construction support on capacity building for water committees, particularly on user fee collection, maintaining financial records, replenishing spare parts, and increased participation of women in the maintenance group, may contribute to greater sustainability of rural water points.

Evaluation of vulnerable zones to water pollution in the lower Soummam alluvial aquifer, Bejaia, Algeria

Abstract Understanding the critical relationship between the Soummam River and its alluvial aquifer is crucial for the protection of this vital water resource. The approach is based on monitoring the spatial and temporal evolution of physico-chemical parameters and identifying their origin through correlation with the geology and piezometry of the alluvial aquifer; this will be achieved using differential gauging and hydrogeochemical tracing. This will provide valuable information for the management and protection of this precious water resource. The case study focuses on the alluvial aquifer of the lower Soummam Valley in Bejaia, Algeria, where a unique natural barrier upstream creates a close hydraulic relationship between the river and the aquifer. This allows for water exchange, which we investigated through two sampling campaigns (high and low water) at 32 water points (boreholes, wells and stations). By tracking the movement of special chemical tracers in both the Soummam River and the underlying alluvial aquifer, this study confirms a direct hydraulic connection between them. This means that water can flow from the river into the aquifer, highlighting the potential risk of water pollution. This has helped us to identify areas where pollution from the river could seep into the groundwater, threatening the drinking water supply.

Study of surface flow discharge in the bompon sub watershed, Magelang District

Background: The Bompon sub-watershed can be divided into 3 parts, namely upstream, middle and downstream and has a catchment area in residential areas and mixed gardens. The five river areas in the Bompon Sub-watershed have different levels of water discharge. This is influenced by the area size, rainfall, land cover, slope, shape of the watershed area, and density of rivers in the watershed area. This research was conducted in Margoyoso Village, with the aim of knowing the amount of river water discharge in the upstream, middle and downstream Bompon Sub-watershed, residential catchment areas and mixed gardens. Methods: In this research, water flow discharge was calculated using the Area-velocity Method using floats. This study uses a quantitative approach. The object of this research is the amount of flow discharge in the five river sections, while the subject of this research is the observation water points in the five river sections in the Bompon Sub-watershed. Findings: The results of this research show that the largest discharge magnitude is in the downstream section. Meanwhile, the smallest discharge amount is in the middle section, because the river order in the downstream section is a meeting between several river orders in the upstream and middle sections. Conclusion: Then for measuring surface flow discharge in the water catchment area, it shows that the amount of discharge in residential areas does not contain flowing water. This is caused by land use factors around the weir which are dominated by residential areas, where there are buildings which make it difficult for water to enter the ground. Meanwhile, in mixed plantation areas there is a fairly large amount of discharge, because the water supply comes from subsurface flows or seepage.

Frostbite incidence is a selective term and dependable on methodology — a narrative review

Introduction: Frostbite is freezing of the tissue that mostly affects skin but also the underlying tissues. It results from prolonged exposure to temperatures below the freezing point of water (0°C). One of the many consequences of climate change is extreme cold events, which increase the risk of frostbite in the general population, particularly among individuals who are involuntarily exposed to cold for prolonged periods of time. Although frostbite has been a known phenomenon for a long time, occurring as early as 5000 years ago, the exact incidence of frostbite is not known. This is partly due to variable internal (frostbite susceptibility, hydration status, protective garments) and external etiological factors (wind chill, precipitation, altitude), that never coincide all at the same time. Objectives: The objective was to compare the incidence rates of frostbite in the published studies that focused on frostbite incidence. Methods: Out of a total of 61 studies using the keywords “frostbite” and “incidence” on PubMed, we selected seven that dealt with frostbite incidence over 20 years. We briefly summarized and compared the results of the studies. Results: The comparison of the seven studies shows a great variability of frostbite incidence depending on the population, its size, and the method of data collection. Studies that included civilian populations have significantly lower frostbite incidence rates than studies focusing on individuals who are exposed to temperatures below 0°C for extended periods, such as mountaineers, military personnel, workers in cold storage houses or homeless people. The results highlight different incidence rates for different populations and indicate that retrospectively collected data are insufficiently comparable among studies. Frostbite incidence, expressed as the ratio of injured individuals to non-injured inhabitants, is only comparable in studies using the same methodology. Enhanced frostbite susceptibility is a confirmed fact and was generally not considered in most of the studies. Conclusions: Frostbite incidences of the included studies are insufficiently comparable to draw any conclusions on possible general frostbite incidence in a population. To enhance our ability to estimate or predict frostbite occurrences within the general population, establishing an international or national frostbite registry in high-risk countries could be helpful.