The effects of road salt on freshwater ecosystems and solutions for mitigating chloride pollution - A review

Effects of salinity on the adsorption of cadmium and zinc to tire and road wear particles in water - Significance for river systems and road runoff treatment

Tire wear particles (TWP) are potential pollutants of emerging concern. Therefore, the EU is set to regulate the TWP emissions under the new Euro 7 emission standard. For Germany it is estimated that up to 20,000 t TWP reach the aquatic environment. Main transport pathways are via road runoff and separate sewage systems. Studies indicate that, apart from ecotoxicological concerns, the negatively charged surface of TWP can adsorb heavy metals like Cr, Ni, Zn, Cd and Pb, potentially deteriorating the chemical water quality of rivers. As rivers usually undergo a salt gradient from their source to the sea this may change the adsorption of heavy metals. We investigated the influence of salinity on the heavy metal adsorption on TWP using water samples from the Freiberger Mulde (Saxony, Germany), enriched with NaCl to simulate the salinity representative of different rivers in the Elbe catchment area, and additional water samples (Elbe, Saale, Bode, Schlenze). The adsorption of Cd and Zn appear to be highly salt-dependent. Above 12 mg L-1 Cl-, no significant adsorption was observed. It is assumed that both metals form [MCl4]2- complexes which are repelled from the negative surface of TWP. The potential in building these complexes is high enough to dissolve previously adsorbed Cd from TWP. These findings are important for assessing water quality of river systems as well as runoff filtration and water retention systems. In winter, for instance, when de-icing salt is applied, Cd and Zn bound on TWP may be mobilized entering water systems.

Groundwater Safety and Availability Index (GSAI) and its association with salinity indicators

This study assesses the quality of groundwater in the Odra River Basin in Poland, focussing on environmental health risks, temporal variability, and their association with salinity indices. A new indicator, the Groundwater Safety and Availability Index (GSAI), was developed to evaluate groundwater resources by integrating health risk and resource quantity factors, providing a novel tool for ranking water resources and informing environmental and administrative decision-making. Groundwater samples were collected between 2005 and 2021 and analysed in accordance with national standards. The results demonstrate an improvement in groundwater quality over time, indicated by a reduction in Health Index (HI) values, particularly in Lower Silesia, Lubusz, and Silesia. Significant correlations were found between HI and NO₃- (τ-Kendall = 0.40) and arsenic (τ-Kendall = 0.55). GSAI values varied across regions, with West Pomerania showing the highest groundwater safety and availability, while Silesia had the lowest. Elevated concentrations of contaminants such as arsenic and nitrates were found to significantly impact water safety, particularly during hydrogeological droughts. These findings support the need for region-specific management strategies to ensure sustainable groundwater use and mitigate health risks, with the GSAI serving as a valuable tool for policymakers and environmental planners.

Effects of short-term salt exposure on gill damage, serum components and gene expression patterns in juvenile Largemouth bass (Micropterus salmoides)

The Largemouth bass (Micropterus salmoides; LMB) is a freshwater fish that plays a significant role in aquaculture, and its cultural base is expanding into inland saline water areas. To study the effect of short-term salt exposure on LMB, fish with an average body weight of 11.69 (±1.82) g were cultured for 14 days at three different salt concentrations (0 ‰, 6 ‰, and 12 ‰). After 14 days, the second gill arch was collected for tissue sectioning and transcriptome sequencing, while serum samples were collected to analyze serum components. The results showed that the mortality rate in the 0 ‰ and 6 ‰ groups was 0 %, whereas the mortality rate in the 12 ‰ group was 62 %. In the gill tissue sections, no apparent damage was observed in the 0 ‰ and 6 ‰ groups. However, in the 12 ‰ group, the secondary lamellae became shorter, thicker, and exhibited a disordered arrangement. The serum component test results showed that osmolality and K+ significantly increased in the 12 ‰ group, while Na+, K+, and Cl- concentrations showed slight increases, but the differences were not significant. Comparative transcriptome analysis revealed that, along the salinity gradient, gene expression exhibited five profiles. Genes related to ion transport and immunity were highly expressed in the 6 ‰ and 12 ‰ groups, while genes associated with biosynthesis and ATP production showed decreased expression levels as salinity increased. Notably, seven solute carrier genes, two Na+/K+-ATPase genes, and two insulin-like growth factor genes were significantly highly expressed in the 12 ‰ salinity group, playing important roles in the transmembrane transport of ions. Based on the results, the LMB can acclimatize to a salt concentration of at least 6 ‰. However, exposure to 12 ‰ salinity can lead to a series of adverse effects, including organ damage, reduced energy metabolism efficiency, and disruption of ion homeostasis.

Designing a monitoring plan for microbial water quality and waterborne antimicrobial resistance in the Akaki catchment, Ethiopia

The Akaki River, in Ethiopia, becomes a source of antimicrobial-resistant (AMR) pathogens and genes that are spreading to receiving water. Water quality monitoring (WQM) is limited in Akaki, and the available evidence is based on short-term monitoring of inconsistent sampling sites and water quality parameters. Therefore, we designed a suitable WQM plan for the Big Akaki River receiving wastewater from rural, urban, and peri-urban areas. WQM plan was designed by employing multiple approaches including literature review, field observations, spatial analysis, and pollutant "hotspot" identification. Information was extracted through a systematic review of 48 articles, selected through a screening process, to guide the selection of suitable monitoring sites. Field observation was used to inspect previously sampled sites and identify pollution sources and exposure routes to antibiotic-resistant bacteria and zoonotic pathogens. For validation, water samples were collected from 40 sites identified from the literature review and field observation, and results were refined during a stakeholder consultation workshop. Hotspots were identified based on chemical oxygen demand, dissolved oxygen, ammonia, and extended-spectrum βeta-lactamase (ESβL)-producing Escherichia coli and Salmonella enteritidis/Shigella flexneri data. Cluster analysis of the water quality data categorized the 40 sites into three groups, and the number of sites for future monitoring to 20, including possible pollutant hotspots, reference sites, known pollution sources, exposure routes, and availability of river discharge data. The WQM plan will help AMR and zoonotic pathogens monitoring and mitigation in the study sites. Our approach can be replicated to design WQM plans for other rivers.

Effect of tunnel wash water treatment processes on trace elements, organic micropollutants, and biological effects

Tunnel wash water (TWW) contains high levels of trace elements and organic micropollutants, especially in the dissolved fraction. Discharge poses significant environmental risks. This field study aimed at improving conventional sedimentation treatment by addition of novel secondary treatments: bag filtration, ceramic microfiltration, or granular activated carbon (GAC) filtration. Removal of nine trace elements, 16 polycyclic aromatic hydrocarbons (PAHs), 38 per- and polyfluoroalkyl substances (PFASs), seven benzothiazoles (BTHs), seven benzotriazoles (BTRs), five bisphenols (BPs), and five benzophenones was investigated. Primary sedimentation significantly reduced particles and associated contaminants, achieving over 73 % average removal for trace elements, 65 % for PAHs, and 71 % for PFASs. Subsequent GAC removed over 70 % of dissolved Cr, Cu, Pb, and Zn and over 92 % of dissolved PFASs, BTHs, BTRs, and BPs, including several persistent, mobile and toxic compounds. Following GAC filtration, Cr, Ni, Pb, anthracene, fluoranthene, perfluorooctanesulfonic acid, and bisphenol-A were below environmental quality standards (EQS). GAC consistently reduced responses in in vitro bioassays with endpoints activation of the aryl hydrocarbon receptor, oxidative stress response, and neurotoxicity below effect-based trigger values for surface water. GAC filtration is thus recommended for future TWW treatment. Assessing water quality remains a challenging task due to lack of EQSs for many chemicals.

Chloride accumulation in inland rivers of China and its toxic impact on cotton

The escalation of major ion concentrations in freshwater and soil poses diverse effects on ecosystems and the environment. Excessive ions can exhibit toxicity to aquatic organisms and terrestrial plants. Currently, research on ion toxicity primarily focuses on cation toxicity. Notably, there is a noticeable research gap in understanding the impact of chloride ion (Cl-) on plant growth and development, as well as on the defense mechanisms against Cl- toxicity. In the present study, sampling was conducted on major rivers in China to measure Cl- concentrations. The results revealed that certain rivers exhibited excessive levels of Cl-, emphasizing the critical need to address Cl- toxicity issues. Subsequently, when salt-tolerant cotton seedlings were subjected to various chloride treatments, it was observed that excessive Cl- severely hindered plant growth and development. A combined analysis of transcriptomic and metabolomic data shed light on significantly enriched pathways related to galactose metabolism, arginine and proline metabolism, carotenoid metabolism, and alpha-linolenic acid metabolism under chloride stress. In summary, this research provides a scientific foundation and references for environmental management and water resource protection and offers novel insights for mitigating the adverse impacts of Cl-, thereby contributing to the preservation of ecosystem health.

Mangrove fungi in action: Novel bioremediation strategy for high-chloride wastewater

Bioremediation of extremely high-chloride wastewater poses significant challenges due to the adverse effects of elevated salt concentrations on most microorganisms, where chloride levels can be as high as 7% (w/v). Mangrove wetlands derived fungus, Aspergillus aculeatus, emerged as a promising candidate, capable of removing approximately 40% of chloride ions in environments with concentration of 15% (w/v), representative of industrial wastewater conditions. Transcriptomics and biochemical assays conducted under increasing salt conditions revealed that elevated chloride concentrations induce the expression and activity of S-adenosyl methionine-dependent methyltransferase, which facilitates the conversion of chloride into chloromethane. This is the first report characterizing the biological mechanism behind high salt tolerance and chloride removal capacity of Aspergillus aculeatus. This salt remediation mechanism may work as a starter for developing future bioremediation strategies to treat high-chloride wastewater using fungi, offering an eco-friendly alternative to traditional physical or chemical methods.

Freshwater salinisation: unravelling causes, adaptive mechanisms, ecological impacts, and management strategies

Freshwater salinisation is a growing problem worldwide, affecting surface and groundwater resources. Compared with other global environmental issues, freshwater salinisation has been studied extensively in North America, Australia, and Europe but less so in South America, Asia, and Africa. Both the natural and anthropogenic sources can contribute for freshwater salinisation, through the concentration of dissolved salts in water rising above its normal levels. This review provides a comprehensive assessment of the causes of freshwater salinisation, the impacts on freshwater communities and ecosystem functions, the adaptive mechanisms for survival in an increasingly saline environment, and the management strategies available to control freshwater salinisation. Many human activities contribute to freshwater salinisation, including road salt use, agricultural practices, resource extraction, reservoir construction, and climate change. Aquatic organisms have evolved mechanisms to survive in increasingly saline environments, but excessive salinity can lead to mortality and non-lethal effects. Such effects can have cascading impacts on the structure and function of aquatic communities and ecosystem services. Therefore, monitoring programmes and chemical fingerprinting are needed to identify highly salinised areas, determine how various human activities contribute to freshwater salinisation, and implement management strategies. Furthermore, current research on freshwater salinisation has been limited to a few regions of the world. It is essential to expand the research further into exploring the impacts of salinisation on freshwater resources in unexplored geographic areas of the world that are mainly impacted by climate change scenarios.

Accumulation of road salt in a calcareous fen: Kampoosa Bog, western Massachusetts

Road salt poses a threat to the quality of soils and water resources. Wetlands located in salt contaminated areas are at risk of experiencing lower plant and animal species diversity. Therefore, it is critical to understand how modifications to salt application rates and hydrological events impact wetland water quality. Here, we use chloride mass flux, discharge, groundwater chloride concentration, meteorological, and salt application data from 2012-2020 to estimate chloride accumulation and outflux rates in the Kampoosa Bog subwatersheds, located in Stockbridge and Lee, Massachusetts, and bordered by major highways (Interstate-90 and U.S. Route 7). We also investigate the correlation between wetland size and chloride retention rate. During the 2018-2019 period, mean annual chloride application rates in the major watershed increased from 363000 kg/year (2012-2017) to 479000 kg/year. This led to a net chloride accumulation (KB100 subwatershed: 339000 kg; KB150 subwatershed: 188000 kg) and increased groundwater chloride concentrations in the fen. Chloride outflux from these subwatersheds was primarily driven by discharge. We found that the relationship between wetland percent cover and chloride retention is complex. Although the percent wetland cover is greater in the KB100 main wetland region compared to the KB150 subwatershed, high precipitation in 2018 resulted in similar chloride retention efficiencies (~26%). During the drier year (2019), chloride retention was higher in the wetland region due to its gentle slopes which promote water accumulation and consequently higher evaporation rates which lowers discharge and chloride outfluxes. The chloride steady-state concentration analysis also suggests that there is potential for chloride accumulation to continue because the watershed has not yet reached steady-state chloride concentrations. Without major modifications to salting practices, chloride concentrations will continue increasing and potentially promote the re-growth of invasives (Phragmites) and continued growth of salt tolerant species (Typha angustifolia/xglauca) that diminish plant diversity.

Salt Belt Index (SBI): A biotic index for streams within the North American "salt belt," with proposed baseline chloride thresholds

Road salt (commonly NaCl, CaCl2, and MgCl2) is widely used in the northern United States as a deicing agent for roadways and other byways. Millions of tons of road salt are used annually in the United States, resulting in drastic increases in freshwater salinity. This study aims to determine the chloride optima and tolerance ranges of macroinvertebrates using publicly accessible stream monitoring data from the US EPA. We assigned taxa region-specific tolerance values, which we then used to calculate the Salt Belt Index (SBI). In addition to the SBI, we determined new, region-specific, chronic Cl- thresholds, determined using threshold indicator taxa analysis (TITAN). Using generalized linear models, we found the SBI was highly accurate at estimating chloride concentration (mg/L Cl-) across the salt belt states. Macroinvertebrate community richness exhibited a significant negative relationship with increasing chloride concentrations. Newly proposed chloride thresholds, based on the richness-chloride relationship, were far lower than current thresholds. The SBI was able to differentiate between Low-, Medium-, and High-Impact sites, grouped based on proposed chloride thresholds. Based on our findings, it is clear current salinity thresholds are too high, and management practices should factor in regional variability, taxon-specific physiology, and historical instream chemistry when implementing salinity thresholds.

Regulated Inductively Coupled Plasma–Optical Emission Spectrometry Detectible Elements in Utah Lake: Characterization and Discussion

During the 2021 (n = 15) and 2022 (n = 13) summers, we measured the total and dissolved (<0.45 μm) concentration of 25 elements in Utah Lake using Inductively Coupled Plasma–Optical Emission Spectrometry (ICP-OES) with detection limits in the order of a few parts-per-billion (ppb). This resulted in 1400 measurements, which is a unique dataset in terms of sensitivity and temporal resolution. Regulated elements are not commonly measured at the ppb-level; thus, these data provide insight into both the behavior and existence of these elements in an aquatic environment and have implications for both the management and regulation of the lake. Utah regulates twelve of these elements. While ICP-OES has ppb-level sensitivity, it is not the approved regulatory analysis method for these elements. All regulations are for dissolved concentrations, except aluminum (Al) and phosphorus (P), which are for total recovery. We found total Al above the allowable concentration, but dissolved concentrations were well below allowable concentrations. We attribute high total concentrations to suspended clays. This suggests that regulatory methods should be reviewed for lakes with a high suspended-solid content. Dissolved copper (Cu) concentrations were below regulatory levels in 2021, but some samples were above regulatory levels in 2022. This could be related to the use of Cu-based algaecide treatments, or from other sources. Lead (Pb) data were inconclusive; dissolved Pb concentrations were well below the acute (1 h average) limit, but the chronic concentration limit (4 h average) was below the ICP-OES minimal detection limit. Arsenic (As) concentrations exhibited a seasonal trend that we attribute to groundwater inflows—they were below regulatory levels for aquatic environments but around the levels for drinking water. This ppb-level study with high temporal resolution provides insight into regulated elements in Utah Lake previously not available due to the high sensitivity of the method and measurements of both total and dissolved concentrations.

Salt pollution reduces turbidity, dissolved organic matter, and cyanobacteria in experimental vernal pool communities

Anthropogenic activities such as the over-application of road deicers are causing an increase in the concentration of salts in historically fresh waters. Experimental and field investigations demonstrate that freshwater salinization disrupts ecosystem functions and services, causing the death of freshwater organisms and changes to nutrient conditions. Wetland habitats are one system negatively affected by salt pollution, including ephemeral wetlands (vernal pools) that fill with salt-polluted water after snowmelt. In urbanized areas, the degradation of these ecosystems could result in irreversible ecological damage including reduced water quality and a reduction in biodiversity. To investigate the effects of freshwater salinization on vernal pool communities, we exposed soils from vernal pools to water containing no salt (control), or four concentrations of three salts standardized by chloride concentration (50 mg Cl- L-1, 100 mg Cl- L-1, 200 mg Cl- L-1, and 400 mg Cl- L-1; magnesium chloride, calcium chloride, and sodium chloride). The results of this experiment suggest that emerging zooplankton communities in vernal pools are sensitive to low concentrations of salt pollution, and that alternative salts such as magnesium chloride and calcium chloride are more toxic than sodium chloride. We did not find positive or negative changes in the abundance of eukaryotic phytoplankton but did find negative effects of salt on cyanobacteria abundance, possibly due to corresponding reductions in turbidity which might be needed as a fixation site for cyanobacteria to form heterocysts. Finally, we found that salt pollution likely caused flocculation of Dissolved Organic Matter (DOM), resulting in reduced concentrations of DOM which could alter the buffering capacity of freshwater systems, light attenuation, and the populations of planktonic heterotrophs.

Systematic tracking of nitrogen sources in complex river catchments: Machine learning approach based on microbial metagenomics

Tracking nitrogen pollution sources is crucial for the effective management of water quality; however, it is a challenging task due to the complex contaminative scenarios in the freshwater systems. The contaminative pattern variations can induce quick responses of aquatic microorganisms, making them sensitive indicators of pollution origins. In this study, the soil and water assessment tool, accompanied by a detailed pollution source database, was used to detect the main nitrogen pollution sources in each sub-basin of the Liuyang River watershed. Thus, each sub-basin was assigned to a known class according to SWAT outputs, including point source pollution-dominated area, crop cultivation pollution-dominated area, and the septic tank pollution-dominated area. Based on these outputs, the random forest (RF) model was developed to predict the main pollution sources from different river ecosystems using a series of input variable groups (e.g., natural macroscopic characteristics, river physicochemical properties, 16S rRNA microbial taxonomic composition, microbial metagenomic data containing taxonomic and functional information, and their combination). The accuracy and the Kappa coefficient were used as the performance metrics for the RF model. Compared with the prediction performance among all the input variable groups, the prediction performance of the RF model was significantly improved using metagenomic indices as inputs. Among the metagenomic data-based models, the combination of the taxonomic information with functional information of all the species achieved the highest accuracy (0.84) and increased median Kappa coefficient (0.70). Feature importance analysis was used to identify key features that could serve as indicators for sudden pollution accidents and contribute to the overall function of the river system. The bacteria Rhabdochromatium marinum, Frankia, Actinomycetia, and Competibacteraceae were the most important species, whose mean decrease Gini indices were 0.0023, 0.0021, 0.0019, and 0.0018, respectively, although their relative abundances ranged only from 0.0004 to 0.1 %. Among the top 30 important variables, functional variables constituted more than half, demonstrating the remarkable variation in the microbial functions among sites with distinct pollution sources and the key role of functionality in predicting pollution sources. Many functional indicators related to the metabolism of Mycobacterium tuberculosis, such as K24693, K25621, K16048, and K14952, emerged as significant important factors in distinguishing nitrogen pollution origins. With the shortage of pollution source data in developing regions, this suggested approach offers an economical, quick, and accurate solution to locate the origins of water nitrogen pollution using the metagenomic data of microbial communities.

Impact of road transport system on groundwater quality inferred from explainable artificial intelligence (XAI)

Road networks constitute a vital component of modern society, facilitating rapid transportation and driving economic activities by enabling the smooth movement of goods and people. However, the expansion of road systems carries significant environmental considerations, particularly regarding its impact on groundwater quality. Thus, it is crucial to understand the complex relationship between groundwater quality and the road traffic system. This paper aims to identify the impact of road transport systems on groundwater quality using a data-driven approach. Specifically, road network and groundwater chemistry data in Texas were obtained from an open data portal. This study was carried out in two phases: the explainable artificial intelligence (XAI) modeling phase and the multivariate analysis phase. In the XAI modeling phase, a prediction model was developed using eXtreme Gradient Boosting (XGB), with groundwater chemistry parameters as output features and road transport attributes as input features, i.e., elevation, annual average daily traffic, distance, lane-miles, speed limit and well depth. Furthermore, the relationships between groundwater chemistry parameters and road transport attributes were examined using feature importance and accumulated local effect (ALE). In the multivariate phase, Piper diagrams and principal component analysis (PCA) were utilized to identify the source of the selected groundwater chemistry parameters from the XAI models. The results of the prediction model showed that five groundwater chemistry parameters were significantly impacted by road transport systems with below a mean absolute percentage error of 0.20, including, pH, temperature, aluminum (Al), bicarbonate (HCO3-), and alkalinity. Additionally, XAI models were developed to understand the relationship between the road transport attributes on five selected parameters. The findings collectively indicated that the Texas groundwater qualities are greatly impacted by road transport systems within a distance of 50-meters and a well depth of 100-meters. This study provides a novel contribution to monitoring point sources of groundwater pollution using XAI techniques.

Impacts of sequential salinity and heat stress are recovery time-specific in freshwater crustacean, Daphnia pulicaria

Stressors can interact to affect animal fitness, but we have limited knowledge about how temporal variation in stressors may impact their combined effect. This limits our ability to predict the outcomes of pollutants and future dynamic environmental changes. Elevated salinity in freshwater ecosystems has been observed worldwide. Meanwhile, heatwaves have become more frequent and intensified as an outcome of climate change. These two stressors can jointly affect organisms; however, their interaction has rarely been explored in the context of freshwater ecosystems. We conducted lab experiments using Daphnia pulicaria, a key species in lakes, to investigate how elevated salinity and heatwave conditions collectively affect freshwater organisms. We also monitored the impacts of various recovery times between the two stressors. Daphnia physiological conditions (metabolic rate, Na+-K+-ATPase (NKA) activity, and lipid peroxidation level) and life history traits (survival, fecundity, and growth) in response to salt stress as well as mortality in heat treatment were examined. We found that Daphnia responded to elevated salinity by upregulating NKA activity and increasing metabolic rate, causing a high lipid peroxidation level. Survival, fecundity, and growth were all negatively affected by this stressor. These impacts on physiological conditions and life history traits persisted for a few days after the end of the exposure. Heat treatments caused mortality in Daphnia, which increased with rising temperature. Results also showed that individuals that experienced salt exposure were more susceptible to subsequent heat stress, but this effect decreased with increasing recovery time between stressors. Findings from this work suggest that the legacy effects from a previous stressor can reduce individual resistance to a subsequent stressor, adding great difficulties to the prediction of outcomes of multiple stressors. Our work also demonstrates that cross-tolerance/susceptibility and the associated mechanisms remain unclear, necessitating further investigation.

Urban lake water quality responses to elevated road salt concentrations

Road salt runoff from de-icing applications is increasingly impacting water quality around the globe. Excess salt (especially chloride) concentrations can negatively impact the biological, chemical, and physical properties of freshwater ecosystems. Though road salt pollution is a prevalent issue affecting many northern temperate lakes, there are few studies on how freshwater salinization interacts with other ecological stressors such as eutrophication. We investigated how chloride from road deicers influences water quality in an urban lake. We sampled a tributary and lake receiving large amounts of road salt runoff from a nearby highway in Grand Rapids, Michigan over a 20-month period. Chloride concentrations in the deepest part of the lake consistently exceeded the US EPA chloride chronic toxicity threshold of 230 mg/L, at times reaching up to 331 mg/L. These high chloride concentrations appear to be responsible for preventing part of the lake from complete mixing, and causing hypoxia in the deepest regions of the lake. Total phosphorus concentrations near the surface averaged 35 μg/L but exceeded 7500 μg/L in the deepest part of the lake, which occupies 3-5 % of total lake volume. Phosphorus release rates from the sediments were low and unlikely to be a current source of the high phosphorus concentrations. Rather, both phosphorus and chloride likely have been accumulating in the hypolimnion over a relatively long period of time. Lake management actions will require control of both internal and external phosphorus and chloride sources in the future. We recommend that phosphorus be addressed first to avoid the extremely high phosphorus concentrations from reaching the photic zone and stimulating algal blooms, which would occur if salt was removed first and the halocline broke down. Our findings and recommendations are applicable to other lakes facing similar issues.

Physicochemical properties of mountain streams in the High and Western Tatras

The aim of this study was to measure the physicochemical properties of 28 mountain streams in Tatra National Park, Slovakia. Sampling sites (119) were selected based on a previous study conducted in 2010. Physical properties (e.g., temperature, conductivity, total dissolved solids, pH, and dissolved oxygen) and chemical components (e.g., nitrogen oxides, ammonia oxides, chloride compounds, and chemical oxygen demand) of the water were determined. Environmental parameters of streams (elevation, slope, aspect, width, depth, flow accumulation, watershed size, bedrock, and presence of mountain lakes) at sampling sites were examined. While comparing results from both periods (2010 and 2017), we found a correlation in data trends, concluding that elevation plays a significant role in almost all investigated parameters. Downstream, streams were more saturated by dissolved solids, CaCO3, and nitrates, increasing the pH level. Despite this well-known trend, we observed significant higher levels of ammonias and chlorides in the alpine zone, especially at sites where higher water temperature and lower values of dissolved oxygen were observed. This occurred in the Eastern Tatras, below mountain lakes, and where watersheds had granite origins. There are indications that denitrification processes were significantly stronger in 2017, but, on the other hand, increased chlorides resulted in stronger inhibition of nitrification processes in alpine zones at sites below mountain lakes.

Efficacy of urban road salt reduction strategies on public supply well quality

Long-term road salt application has increased chloride (Cl-) concentrations in public drinking water wells in many cold climate communities. A range of Best Management Practices (BMPs) have been adopted to mitigate the impact of road deicing compounds on groundwater quality. Chronic increases in chloride levels have been observed in several municipal well fields within the southern Ontario Regional Municipality of Waterloo (RMOW). In response, the RMOW and City of Kitchener implemented a plan to reduce salt application on roads by 25% within the local capture zones of one of the impacted well fields, the Greenbrook Well Field. Here the influence of salt reduction BMPs on subsurface water quality are examined by documenting changes in pore water Cl- concentrations and stored salt mass in vadose zone core samples collected at sites near the well field both before and after the implementation of the BMPs. The data indicate that ~6 years after salt reduction measures were initiated, average pore water Cl- concentration and average cumulative stored chloride mass in the vadose zone had decreased by approximately 60% and 40%, respectively. Groundwater samples collected from shallow monitoring wells installed at each field site showed similar post-BMP reductions in shallow groundwater Cl- concentration (~35%). Long-term (1973-2022) trends in raw water Cl- concentration data from the deeper public drinking water supply wells clearly demonstrate a slow, time-lagged response of the municipal supply wells to the salt reduction BMPs. The combined results suggest that controlled reductions in road salt applications within vulnerable, capture zone regions of public supply wells can reduce the impact of road salt deicing practices on municipal groundwater supplies over time.

Road salt pollution alters sex ratios in emerging mosquito populations

De-icing road salt is a persistent emerging pollutant in temperate freshwater systems, where winter salting is necessary for road and pedestrian safety. Experts argue that road salts may increase salt-tolerant mosquito populations and, potentially, disease transmission in urban areas. Only adult females consume bloodmeals and may carry zoonotic diseases. While there are some species with naturally occurring male-biased sex ratios, it is unclear whether road salt differentially affects male and female mosquitoes to alter sex ratios. We hypothesized that road salts would masculinize emergence sex ratios and decrease female success because females may face higher exposure to stressors during their lengthy juvenile development compared to males. We measured mosquito emergence sex ratios of control (0 g/L added salt) and salt (4.5 g/L added salt) mesocosms in southern Ontario, Canada across the West Nile Virus season (May to October). We found female-biased sex ratios (i.e., <50% male frequency) in both 0 and 4.5 g/L. While mosquito abundance was significantly higher in 4.5 g/L compared to 0 g/L, road salt significantly increased the proportion of emerging males from 32.8% to 40.8% (Negative Binomial Model; Estimate ± SE = 0.283 ± 0.108; P = 0.009); mosquitoes shift their sex ratios from female-biased towards parity (50:50) in response to salt. Our study illustrates the need to evaluate sex-specific abundance in pollution-related mosquito population studies. By showing a shift toward more male mosquitoes emerging in high salinity compared to control treatments, our results suggest that road salts may have the potential to decrease female mosquito success and indirectly reduce disease transmission in cities.

Freshwater salinization syndrome limits management efforts to improve water quality

Freshwater Salinization Syndrome (FSS) refers to groups of biological, physical, and chemical impacts which commonly occur together in response to salinization. FSS can be assessed by the mobilization of chemical mixtures, termed "chemical cocktails", in watersheds. Currently, we do not know if salinization and mobilization of chemical cocktails along streams can be mitigated or reversed using restoration and conservation strategies. We investigated 1) the formation of chemical cocktails temporally and spatially along streams experiencing different levels of restoration and riparian forest conservation and 2) the potential for attenuation of chemical cocktails and salt ions along flowpaths through conservation and restoration areas. We monitored high-frequency temporal and longitudinal changes in streamwater chemistry in response to different pollution events (i.e., road salt, stormwater runoff, wastewater effluent, and baseflow conditions) and several types of watershed management or conservation efforts in six urban watersheds in the Chesapeake Bay watershed. Principal component analysis (PCA) indicates that chemical cocktails which formed along flowpaths (i.e., permanent reaches of a stream) varied due to pollution events. In response to winter road salt applications, the chemical cocktails were enriched in salts and metals (e.g., Na+, Mn, and Cu). During most baseflow and stormflow conditions, chemical cocktails were less enriched in salt ions and trace metals. Downstream attenuation of salt ions occurred during baseflow and stormflow conditions along flowpaths through regional parks, stream-floodplain restorations, and a national park. Conversely, chemical mixtures of salt ions and metals, which formed in response to multiple road salt applications or prolonged road salt exposure, did not show patterns of rapid attenuation downstream. Multiple linear regression was used to investigate variables that influence changes in chemical cocktails along flowpaths. Attenuation and dilution of salt ions and chemical cocktails along stream flowpaths was significantly related to riparian forest buffer width, types of salt pollution, and distance downstream. Although salt ions and chemical cocktails can be attenuated and diluted in response to conservation and restoration efforts at lower concentration ranges, there can be limitations in attenuation during road salt events, particularly if storm drains bypass riparian buffers.

In situ monitoring of internal water storage reveals nitrogen first flush phenomena, intermittent denitrification, and seasonal ammonium flushing

Internal water storage (IWS) can be included in bioretention practices to increase storage capacity or promote denitrification-the microbial reduction of nitrate to nitrogen gas. IWS and nitrate dynamics are well studied in laboratory systems. However, the investigation of field environments, consideration of multiple nitrogen species, and determination between mixing versus denitrification is lacking. This study employs in situ monitoring (∼24 h duration) of water level, dissolved oxygen (DO), conductivity, nitrogen species, and dual isotopes of a field bioretention IWS system for nine storms events over a year period. Rapid peaks in IWS conductivity, DO, and total nitrogen (TN) concentrations occurred along the rising limb of the IWS water level and indicated a first flush effect. TN concentrations generally peaked during the first ∼0.33 h of sampling and the average peak IWS TN concentration (C_max = 4.82 ± 2.46 mg-N/L) was 38% and 64% greater than the average TN along the IWS rising and falling limb, respectively. Dissolved organic nitrogen (DON) and nitrate plus nitrite (NO_x) were the dominant nitrogen species of IWS samples. However, average IWS peak ammonium (NH₄⁺) concentrations August through November (0.28 ± 0.47 mg-N/L) demonstrated statistically significant shifts compared to February through May (2.72 ± 0.95 mg-N/L). Average lysimeter conductivity measurements were more than ten times higher February through May. The sustained presence of sodium observed in lysimeters, from road salt application, contributed to NH₄⁺ flushing from the unsaturated media layer. Dual isotope analysis showed denitrification occurred for discrete time intervals along the tail of the NO_x concentration profile and the hydrologic falling limb. Longer antecedent dry periods (17 days) did not correlate to enhanced denitrification but did correspond to more leaching of soil organic nitrogen. Results from field monitoring highlight the complexities of nitrogen management in bioretention systems. First flush behavior into the IWS suggests management to prevent TN export is most critical during the onset of a storm.

Argentometric chloride determination by inductively coupled plasma-optical emission spectroscopy in a wide range of sample matrices

Chloride determination is of great importance, as chloride plays important roles in human health, pitting corrosion, environmental processes, and agriculture. However, chloride determination by inductively coupled plasma-optical emission spectroscopy (ICP-OES), one of the premier techniques used for elemental analysis, is currently limited to specific instrument types or requires the use of additional equipment. This work presents an argentometric method for the indirect measurement of chloride, applicable to any ICP-OES instrument. The initial Ag⁺ concentration added to samples is of great importance, as it affects both the method's limit of quantification (LOQ) and the top limit of its working range. The developed method found 50 mg L^-1 of Ag⁺ to be the optimal concentration, providing a working range of 0.2-15 mg L^-1 Cl^-. The method was robust to changes in filtration time, temperature, and sample acidity. Using the argentometric method, chloride was determined in a variety of samples (spiked-purified water, seawater, wine, and urine). For validation, the results were compared to those obtained using ion chromatography and showed no statistical differences. Argentometric chloride determination by ICP-OES is therefore applicable to many types of samples and can be easily performed on any ICP-OES instrument.

Experimental assessment of salinization effects on freshwater zooplankton communities and their trophic interactions under eutrophic conditions

Freshwater ecosystems are becoming saltier due to human activities. The effects of increased salinity can lead to cascading trophic interactions, affecting ecosystem functioning and energy transfer, through changes in community and size structure. These effects can be modulated by other environmental factors, such as nutrients. For example, communities developed under eutrophic conditions could be less sensitive to salinization due to cross-tolerance mechanisms. In this study, we used a mesocosm approach to assess the effects of a salinization gradient on the zooplankton community composition and size structure under eutrophic conditions and the cascading effects on algal communities. Our results showed that zooplankton biomass, size diversity and mean body size decreased with increased chloride concentration induced by salt addition. This change in the zooplankton community did not have cascading effects on phytoplankton. The phytoplankton biomass decreased after the chloride concentration threshold of 500 mg L^-1 was reached, most likely due to direct toxic effects on the osmotic regulation and nutrient uptake processes of certain algae rather than as a response to community turnover or top-down control. Our study can help to put in place mitigation strategies for salinization and eutrophication, which often co-occur in freshwater ecosystems.

Novel SHRP method showed alternative deicers outperform NaCl brine for certain winter roadway maintenance applications

Transportation agencies are responsible for balancing public safety and environmental impacts in their winter roadway maintenance operations. In managing the environmental impact of deicing procedures, a minimum effective dose should be used and less harmful deicing substances should be considered based on rigorous standardized tests. The subject research presents a modified laboratory test procedure and test apparatus for implementation in the evaluation and selection of deicing agents and definition of an appropriate and efficient application rate. The proposed test procedure is less cumbersome, produces more readily controlled experimental conditions, and is expected to provide improved reproducibility compared to current test methods. This modified approach is then used to evaluate the efficacy of several liquid deicing agents which could be used as an alternative to conventional NaCl brine. The comparative testing found that alternative deicing agents performed as well or better than NaCl brine, sometimes even at lower application rates. In particular, the addition of biocomponents or glycerol byproducts was shown to improve performance of chloride deicing agents.

Urbanization drives geographically heterogeneous freshwater salinization in the northeastern United States

Rising trends in freshwater salinity, collectively termed the Freshwater Salinization Syndrome (FSS), constitute a global environmental concern. Given that the FSS has been observed in diverse settings, key questions regarding the causes, trend magnitudes, and consequences remain. Prior work hypothesized that FSS is driven by state factors, such as human-centered land use change, geology, and climate. Here, we identify the fundamental overriding factors driving FSS within the northeastern United States and quantify the diversity of FSS severity within the region. Specifically, we analyzed decadal-scale trends in specific conductance (a salinity proxy) for 333 lotic sites over four decades. Next, we quantified potential variables driving the rising or falling trends, including impervious surface cover (ISC), winter temperature and precipitation, watershed size, and ambient conductance. Temperature and ISC were considered the most likely candidates for predicting FSS severity because road salts have previously emerged as the fundamental regional driver. Most (62.5%) sites exhibited patterns of significantly increasing conductance; thus, the overall regional state reflects advancing FSS. However, others exhibited an absence of change (28.8%) or decreasing values (8.7%), and slope magnitude did change with latitude. Linear modeling demonstrated that two variables-ISC and watershed size-constitute the best predictors of long-term conductance trends and that an intercept not significantly different than zero suggests that the FSS does not reign in the absence of urbanization. We also detected areas with consistently decreasing trends despite moderate ISC. Therefore, within the region, advancing urbanization causes the typical condition of advancing FSS, but heterogeneity also exists.

Effect of Winter Road Maintenance on the Asphalt Road Surface-Experience in Slovakia and the Czech Republic

The properties of asphalt mixtures and the quality of their execution are key factors for their service life and durability in the pavement structure. This research aims to study the effect of deicing chemicals (sodium chloride, NaCl) on asphalt mixtures in laboratory conditions to know the changes in properties when the samples were loaded with a different number of freeze-thaw cycles. The behavior of the standardly used asphalt mixtures and bitumen binders was verified by the exposure to sodium chloride solution (20 g/L NaCl). In the first part of the experiment, penetration, elastic recovery, and softening point tests were performed for paving grade bitumen 50/70 and 70/100, and polymer-modified bitumen PMB 25/55-60. Furthermore, asphalt concrete (AC 11) mixtures with different air voids were subjected to 25, 50, and 75 freeze-thaw cycles to determine the effect on the service life of the pavement structure. Following the Czech standard, CSN 73 6161, and the TP 170 regulation for the design of asphalt pavements, the Marshall test and the stiffness modulus were determined for all asphalt samples. The obtained results show a negative effect of freeze-thaw cycles on the properties of asphalt concrete surface course mixtures and bitumen.

The joint effects of salt and 6PPD contamination on a freshwater herbivore

Using sodium chloride (NaCl) for de-icing roads is known to have severe consequences on freshwater organisms when washed into water bodies. N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, also known as 6PPD, is an antiozonant mainly found in automobile tire rubber to prevent ozone mediated cracking or wear-out. Especially the ozonated derivate, 6PPD-quinone, which is washed into streams after storm events, has been found to be toxic for coho salmon. Studies on other freshwater organisms could not confirm those findings, pointing towards distinct species-specific differences. Storm events result in greater run-offs from all water-soluble contaminants into freshwater bodies, potentially enhancing the concentrations of both chloride and 6PPD during winter. Here we show that these two contaminants have synergistic negative effects on the population growth of the rotifer Brachionus calyciflorus, a common freshwater herbivore. Hence, while only high concentrations of 6PPD and even higher concentrations of 6PPD-quinone, beyond environmentally relevant concentrations, had lethal effects on rotifers, the addition of NaCl enhanced the sensitivity of the rotifers towards the application of 6PPD so that their negative effects were more pronounced at lower concentrations. Similarly, 6PPD increased the lethal effect of NaCl. Our results support the species-specific toxicity of 6PPD and demonstrate a synergistic effect of the antiozonant on the toxicity of other environmentally relevant stressors, such as road salt contamination.

Impact of road transport on groundwater quality

Road transport is one of the sources of groundwater pollution. The aim of the article is to find out whether the largest roads in Poland have a negative impact on groundwater quality and to assess the extent of their influence. The water chemistry in the area of roads with heavy traffic in north-west and central Poland in 2007-2020 was analyzed. The groundwater quality status and the dynamics of changes in concentrations of selected chemical constituents were assessed. Data was taken from the national chemical monitoring network managed by the Polish Geological Institute - National Research Institute. The results of monitoring tests at 42 selected points were subject to detailed statistical analysis. The mentioned points were located within 100 m from the roads. A statistical analysis of selected chemical parameters and a correlation matrix for selected components were performed. The distribution of electrolytic conductivity in the analyzed 42 points in 2019 is presented in the form of a contour map against the background of the main roads in the analyzed area. Based on archival data, a 7-year prediction of changes in concentrations of selected chemical components, using the autoregressive method, was made. The predicted distribution of concentrations of individual chemical components in groundwater indicates that the vicinity (up to 50 m) of roads may negatively affect the groundwater quality. The increased concentration of chloride and sodium ions was found in most sites. An upward trend was also observed for specific electrolytic conductivity.

Potential for Natural Attenuation of Domestic and Agricultural Pollution in Karst Groundwater Environments

In karst areas, anthropogenic contaminants reach the subsurface with detrimental effects on the groundwater ecosystem and downstream springs, which often serve as drinking water sources for the local human communities. We analyzed the water chemistry and microbial community composition in upstream and downstream locations of five hydrokarst systems (HKS) during four seasons. Conductivity and nitrates were higher in the downstream springs than in the pre-karst waters, whereas the concentration of organic matter, considered here as a pollution indicator, was lower. The microbial community composition varied largely between upstream and downstream locations, with multiple species of potentially pathogenic bacteria decreasing in the HKS. Bacteria indicative of pollution decreased as well when passing through the HKS, but potential biodegraders increased. This suggests that the HKS can filter out part of the polluting organic matter and, with it, part of the associated microorganisms. Nevertheless, the water quality, including the presence of pathogens in downstream springs, must be further monitored to control whether the water is appropriate for consumption. In parallel, the human populations located upstream must be advised of the risks resulting from their daily activities, improper stocking of their various wastes and dumping of their refuse in surface streams.

Review of Chloride Ion Detection Technology in Water

The chloride ion (Cl−) is a type of anion which is commonly found in the environment and has important physiological functions and industrial uses. However, a high content of Cl− in water will do harm to the ecological environment, human health and industrial production. It is of great significance to strictly monitor the Cl− content in water. Following the recent development of society and industry, large amounts of domestic sewage and industrial sewage are discharged into the environment, which results in the water becoming seriously polluted by Cl−. The detection of Cl− has gradually become a research focus. This paper introduces the harm of Cl− pollution in the environment and summarizes various Cl− detection methods, including the volumetric method, spectrophotometry method, electrochemical method, ion chromatography, paper-based microfluidic technology, fluorescent molecular probe, and flow injection. The principle and application of each technology are described; their advantages, disadvantages, and applicability are discussed. To goal of this research is to find a more simple, rapid, environmental protection and strong anti-interference detection technology of Cl−.