Airport Deicers: An Unrecognized Source of Phosphorus Loading in Receiving Waters.

Airport ice control products contributed to total phosphorus (TP) loadings in a study of surface water runoff at a medium-sized airport from 2015 to 2021. Eleven airport ice control products had TP concentrations from 1-807 mg L-1 in liquid formulas, while solid pavement deicer had a TP concentration of 805 mg kg-1. Product application data, formula TP concentrations, and surface water sampling results were used to estimate TP concentration and loading contributions from these ice control products to receiving streams. Airport ice control products were found to contribute to TP in 84% of the water samples collected at downstream sites during deicing events, and TP concentrations at those sites exceeded aquatic life benchmarks in 70% of samples collected during deicing. A receiving stream 6 km downstream had TP attributed to airport ice control sources in 78% of the samples. TP loadings at an upstream site and the receiving stream site were greatest during the largest runoff events as is typical in urban runoff, but this pattern was not always followed at airport outfall sites due to the influence of TP in deicer products. Products analyzed in this study are used at airports across the United States and abroad, and findings suggest that airport deicers could represent a previously unrecognized source of phosphorus to adjacent waterways.

Effectiveness of water softening residuals as components of road deicing chemicals: Model analysis of freezing point depression.

Water softening residuals disposal is a worldwide issue due to the lack of effective reuse alternatives. The current principal disposal methods of landfilling and land application are quite costly due to the dewatering and transportation costs involved, and these operations can also cause potential environmental harm from leaching of the additives used in the treatment process. This research is aimed at the use of water softening residuals in the production of biodegradable road deicers that would be beneficial in replacing the highly corrosive and environmentally harmful chloride salts that are currently used for road deicing. Experimental data developed show that calcium magnesium acetate (CMA) and calcium magnesium propionate (CMP) deicers produced using water plant sludges are effective in deicing applications. A mathematical model is developed for predicting freezing point depression of CMA and CMP deicers as a function of molal concentration. The model predictions are found to match well with the experimental data, providing confidence in the use of this model for the effective design water softening sludge based deicers. The information developed herein provides options for the sustainable management of softening residuals and the concommitant mitigation of environmental harm associated with road deicing operations.

Water quality of stormwater generated from an airport in a cold climate, function of an infiltration pond, and sampling strategy with limited resources.

Monitoring pollutants in stormwater discharge in cold climates is challenging. An environmental survey was performed by sampling the stormwater from Luleå Airport, Northern Sweden, during the period 2010-2013, when urea was used as a main component of aircraft deicing/anti-icing fluids (ADAFs). The stormwater collected from the runway was led through an oil trap to an infiltration pond to store excess water during precipitation periods and enhance infiltration and water treatment. Due to insufficient capacity, an emergency spillway was established and equipped with a flow meter and an automatic sampler. This study proposes a program for effective monitoring of pollutant discharge with a minimum number of sampling occasions when use of automatic samplers is not possible. The results showed that 90% of nitrogen discharge occurs during late autumn before the water pipes freeze and during snow melting, regardless of the precipitation during the remaining months when the pollutant discharge was negligible. The concentrations of other constituents in the discharge were generally low compared to guideline values. The best data quality was obtained using flow controlled sampling. Intensive time-controlled sampling during late autumn (few weeks) and snow melting (2 weeks) would be sufficient for necessary information. The flow meters installed at the rectangular notch appeared to be difficult to calibrate and gave contradictory results. Overall, the spillway was dry, as water infiltrated into the pond, and stagnant water close to the edge might be registered as flow. Water level monitoring revealed that the infiltration capacity gradually decreased with time.

Machine learning-assisted chemical design of highly efficient deicers.

The use of deicers in urban areas, on runways and aircrafts has raised concerns about their environmental impact. Understanding the ice-melting mechanism is crucial for developing environmentally friendly deicers, yet it remains challenging. This study employs machine learning to investigate the ice penetration capacity (IPC) of 21 salts and 16 organic solvents as deicers. Relationships between their IPC and various physical properties were analysed using extreme gradient boosting (XGBoost) and Shapley additive explanation (SHAP). Three key ice-melting mechanisms were identified: (1) freezing-point depression, (2) interactions between deicers and H2O molecules and (3) infiltration of ions into ice crystals. SHAP analysis revealed different ice-melting factors and mechanisms for salts and organic solvents, suggesting a potential advantage in combining the two. A mixture of propylene glycol (PG) and sodium formate demonstrated superior environmental impact and IPC. The PG and sodium formate mixture exhibited higher IPC when compared to six commercially available deicers, offering promise for sustainable deicing applications. This study provides valuable insights into the ice-melting process and proposes an effective, environmentally friendly deicer that combines the strengths of organic solvents and salts, paving the way for more sustainable practices in deicing.

Road salt applications mobilize trace elements from roadside soil to shallow groundwater.

In regions where deicers are applied to roadways, micronutrients and toxic trace elements may be mobilized from soil material into soil porewater. These elements may subsequently migrate with soil porewater to surface waters and groundwaters, potentially leaching the soil of micronutrients or introducing toxins to water resources. Our study thus aims to quantify the timing and extent of trace element releases from soil material to soil porewater and groundwater in response to deicing events. We sampled soil porewater near a road at a rural site for trace elements and compared the results to salt applications and soil porewater Na and Cl levels. We also assessed trace element, Na, and Cl concentrations in a karst spring at the rural site and a karst spring at an urban site to evaluate the role of land use in conveying these contaminants to groundwater. We found that certain trace elements (e.g., As, Ba, Fe, Sr) peaked concomitantly with Na and Cl in soil porewater at the rural site after road deicing events, suggesting their release due to excess salt inputs to the soil. We did not observe increases in trace element concentrations at the rural karst spring following individual road salt applications, likely due to low deicer inputs and trace element levels across its recharge basin. However, at the urban site, we observed that other assemblages of trace elements (e.g., As, Cu, Li) in the karst spring peaked with deicing-related Na and Cl pulses. We also found positive and significant correlations between salt applications to the recharge basin and exports of some trace elements (e.g., As, Cu, Li, Se) at the urban karst spring, indicating deicing events triggered trace element releases to groundwater. Overall, we detected road salt-driven trace element release from soil material to soil porewater and groundwater that was exacerbated by urbanization.

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.

Understanding metal concentration and speciation in motorway runoff.

Although highway runoff has historically been extensively studied, the increasing complexity of stormwater management means that there are still significant gaps regarding the reduction of soluble metals. The work reported in this paper addresses these challenges by analysing the presence and behaviour of iron, copper and zinc in runoff from junction 24 of the M1 motorway in the UK (peak traffic flow: 30,000 vehicles per hour) and comparing it with other urban sources of metals found in the same catchment (a local brook and sewage treatment works). The sampling site included an interceptor and a treatment lagoon and the event monitoring indicated a trend by which the metals did not change their concentration or particulate soluble proportion immediately, hence showing that pre- and post-storm conditions are important factors when analysing the solubility of metals and their behaviour. The data provided further evidence of the important influence of storm characteristics on metal concentrations in highway runoff, in particular the effects of an antecedent dry weather period (ADWP). In addition, this study also helped us to better understand how the release of sodium the application of de-icer for road maintenance in winter affects the availability of zinc.

Preparation and Application of a Novel Slow-Releasing with Core-Shell Deicer in Asphalt Mixtures.

The massive application of chloride salts has a direct effect on the corrosion of structures and vehicles and decreases durability as well as road pavement damage. A novel slow-release deicer with a core-shell structure was prepared to reduce the salts' impacts, subsequently characterized by scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), differential scanning calorimetry (DSC), and thermogravimetric analysis (TG). The conductivity evaluation, moisture absorption, and the snow or ice melting performance of the deicer were also tested. The core-shell deicer with different replacement rates was used to prepare the deicing asphalt mixture based on the equivalent volume replacement method. In this study, the high- and low-temperature performance, moisture damage resistance, and snow or ice melting capacity of mixtures were evaluated in the laboratory. The results show that the low-temperature and moisture stability performances decreased, and high-temperature performance improved, as the content of the core-shell deicer was increased. It is confirmed that the replacement rate of the deicer filler should be lower than 75% to meet the specification requirements. The prepared deicing asphalt mixture has good snow and ice melting performance and can reduce the bonding strength between ice and pavement surface. Durability and cost-benefit analysis are expected in further investigations.

Eco-friendly deicer prepared from waste oyster shells and its deicing properties with metal corrosion.

Calcium acetate eco-friendly deicer was prepared using waste oyster shell as a raw reactant material and its physicochemical properties were investigated. The waste oyster shells were converted to a calcium acetate deicer by reaction with acetic acid at ambient temperature. The physicochemical properties of the prepared calcium acetate deicer were analysed using various analytical method. The ice melting and metal corrosion characteristics of the calcium acetate deicer synthesized from the waste oyster shell were evaluated by comparison with those of the calcium chloride and sodium chloride deicers. The chloride deicers severely corroded the metal, but the calcium acetate deicer prepared from the waste oyster shell did not cause metal corrosion. The ice melting performance of calcium acetate prepared from the waste oyster shell was lower than that of calcium chlorides, however, the addition of sodium hydroxide could significantly improve the ice melting capacity.

Toxicological impacts of roadway deicers on aquatic resources and human health: A review.

During winter, snow and ice on roads in regions with cold weather can increase traffic crashes and casualties, resulting in travel delays and financial burdens to society. Anti-icing or deicing the roads can serve a cost-effective method to significantly reduce such risks. Although traditionally the main priorities of winter road maintenance (WRM) have been level of service, cost-effectiveness, and corrosion reduction, it is increasingly clear that understanding the environmental impacts of deicers is vital. One of the most important problems in this regard is environmental contamination caused by cumulative use of deicers, which has many detrimental effects on the aquatic systems. Among the deicers, the chloride-based ones raise the most toxicological concerns because they are highly soluble, can migrate quickly in the environment and have cumulative effects over time. In this review, we summarize and organize existing data, including the latest findings about the adverse effects of deicers on surface water and groundwater, aquatic species, and human health, and identify future research priorities. In addition, the data provided can be used to develop a framework for quantifying some of the variables that stakeholders and agencies use when preparing guidelines and standards for WRM programs. PRACTITIONER POINTS: Pollution from the increasing use of roadway deicers may have detrimental effects on the environment. Of particular concern are the acute and cumulative risks that chloride salts pose to aquatic species. Chloride salts are water-soluble, very difficult to remove, highly mobile, and non-degradable. Deicers cause water stratification, change the chemicophysical properties of water, and affect aquatic species and human health. Current guidelines may not be appropriate for environmental protection and need to be revised.

Palladium release from catalytic converter materials induced by road de-icer components chloride and ferrocyanide.

Environmental levels of platinum group elements (PGEs) are rising due to emissions of vehicle catalytic converter (VCC) materials containing palladium, platinum and rhodium. When these PGE-containing VCC materials are exposed to soil and water, coordination complex formation with ligands present in the environment may mobilize PGEs into solution, particularly Pd. Road de-icing salt contains two ligands with high affinities for Pd2+: chloride (Cl-) from NaCl and cyanide (CN-) from ferrocyanide (Fe(CN)64-) anti-caking agents. Batch leaching studies of VCC materials were conducted with solutions representative of de-icer-contaminated road runoff at pH 8 and room temperature for 48 h. Ferrocyanide (FC) concentrations of 0 µM, 1 µM, 2 µM and 10 µM were tested with background electrolyte concentrations of 0.028 M NaCl (1000 mg/L Cl-) or 0.028 M NaClO4. Palladium release increased with FC concentration, ranging from 0.014 ± 0.002 µM Pd without FC to 5.013 ± 0.002 µM Pd at 10 µM FC. At 0 µM, 1 µM and 2 µM FC, chloride induced further Pd release, but had no effect at 10 µM FC. PHREEQC modeling predicted that the predominant species present in equilibrium with Pd(OH)2(s) were Pd(OH)20 and Pd(CN)42-, and that PdClx2-x complexes had only a minor effect on the total concentration of dissolved palladium. The effect of FC on Pd release was predicted but not the effect of Cl-, indicating possible kinetic control. Platinum was measured above limits of detection (LODs) only at 10 µM FC, and rhodium levels were below LODs, consistent with their slower complexation kinetics.

The influence of road salt on seasonal mixing, redox stratification and methane concentrations in urban kettle lakes.

Influxes of saline water from roads treated with deicers can alter the density structure of urban lakes. This can diminish or halt turnover events, such that lakes may transition from dimixis to monomixis or meromixis. In nutrient-rich lakes, this lack of turnover can produce persistent hypolimnetic anoxia. We hypothesized that diminished turnover in urban lakes impacted by road salt inputs would lead to increased accumulation of methane in the hypolimnia, with the potential for greater release of methane to the atmosphere via ebullition and from larger storage fluxes of methane when turnover events do occur. The lake water columns of two urban lakes (Woods Lake and Asylum Lake), previously suggested to have transitioned to meromixis and monomixis because of road salt deicer inputs, were sampled monthly from March 2016 to June 2017. A nearby rural lake (North Lake) less likely to be impacted by road salt and maintaining seasonal mixing, was also sampled for comparison. Lake column water was analyzed for conductivity, temperature, dissolved oxygen, ferrous iron, manganese, sulfide, calcium, magnesium, sodium, chloride and methane concentrations as a function of depth. All three lakes are eutrophic with at least seasonally anoxic hypolimnia. Our data are consistent with prior studies suggesting that Woods Lake has transitioned to meromixis and Asylum Lake to monomixis due to an influx of dense saline water from roads treated with deicers. In contrast, rural North Lake, which had much lower chloride, sodium and conductivity levels, was dimictic. The diminished or absent turnover in the two urban lakes during fall and spring resulted in persistently anoxic, redox-stratified hypolimnia, with much larger accumulations of methane compared to the rural lake. This study demonstrates that road salt deicers impact lake mixing and biogeochemistry, especially methane concentrations, with the potential for significant increases in greenhouse gas emissions from urban lakes.

The Evaluation of Damage Effects on MgO Added Concrete with Slag Cement Exposed to Calcium Chloride Deicing Salt.

Concrete systems exposed to deicers are damaged in physical and chemical ways. In mitigating the damage from CaCl2 deicers, the usage of ground slag cement and MgO are investigated. Ordinary Portland cement (OPC) and slag cement are used in different proportions as the binding material, and MgO in doses of 0%, 5%, 7%, and 10% are added to the systems. After 28 days of water-curing, the specimens are immersed in 30% CaCl2 solution by mass for 180 days. Compressive strength test, carbonation test, chloride penetration test, chloride content test, XRD analysis, and SEM-EDAX analysis are conducted to evaluate the damage effects of the deicing solution. Up to 28 days, plain specimens with increasing MgO show a decrease in compressive strength, an increase in carbonation resistance, and a decrease in chloride penetration resistance, whereas the S30- and S50- specimens show a slight increase in compressive strength, an increase in carbonation resistance, and a slight increase in chloride penetration resistance. After 180 days of immersion in deicing solution, specimens with MgO retain their compressive strength longer and show improved durability. Furthermore, the addition of MgO to concrete systems with slag cement induces the formation of magnesium silicate hydrate (M-S-H) phases.

New approaches to enhance pollutant removal in artificially aerated wastewater treatment systems.

Freshwater ecosystems sustain human society through the provision of a range of services. However, the status of these ecosystems is threatened by a multitude of pressures, including point sources of wastewater. Future treatment of wastewater will increasingly require new forms of decentralised infrastructure. The research reported here sought to enhance pollutant removal within a novel wastewater treatment technology, based on un-planted, artificially aerated, horizontal subsurface flow constructed wetlands. The potential for these systems to treat de-icer contaminated runoff from airports, a source of wastewater that is likely to grow in importance alongside the expansion of air travel and under future climate scenarios, was evaluated. A new configuration for the delivery of air to aerated treatment systems was developed and tested, based on a phased-aeration approach. This new aeration approach significantly improved pollutant removal efficiency compared to alternative aeration configurations, achieving >90% removal of influent load for COD, BOD5 and TOC. Optimised operating conditions under phased aeration were also determined. Based on a hydraulic retention time of 1.5 d and a pollutant mass loading rate of 0.10 kg d-1 m-2 BOD5, >95% BOD5 removal, alongside final effluent BOD5 concentrations <21 mg L-1, could be achieved from an influent characterised by a BOD5 concentration > 800 mg L-1. Key controls on oxygen transfer efficiency within the aerated treatment system were also determined, revealing that standard oxygen transfer efficiency was inversely related to aeration rate between 1 L and 3 L min-1 and positively related to bed media depth between 1500 mm and 3000 mm. The research reported here highlights the potential for optimisation and subsequent widespread application of the aerated wetland technology, in order to protect and restore freshwater ecosystems and the services that they provide to human society.

Combined effects of road salt and an insecticide on wetland communities.

As the numbers of chemical contaminants in freshwater ecosystems increase, it is important to understand whether contaminants interact in ecologically important ways. The present study investigated the independent and interactive effects of 2 contaminants that frequently co-occur in freshwater environments among higher latitudes, including a commonly applied insecticide (carbaryl) and road salt (NaCl). The hypothesis was that the addition of either contaminant would result in a decline in zooplankton, an algal bloom, and the subsequent decline of both periphyton and periphyton consumers. Another hypothesis was that combining the contaminants would result in synergistic effects on community responses. Outdoor mesocosms were used with communities that included phytoplankton, periphyton, zooplankton, amphipods, clams, snails, and tadpoles. Communities were exposed to 4 environmentally relevant concentrations of salt (27 mg Cl- L-1 , 77 mg Cl- L-1 , 277 mg Cl- L-1 , and 727 mg Cl- L-1 ) fully crossed with 4 carbaryl treatments (ethanol, 0 µg L-1 , 5 µg L-1 , and 50 µg L-1 ) over 57 d. Contaminants induced declines in rotifer and cladoceran zooplankton, but only carbaryl induced an algal bloom. Consumers exhibited both positive and negative responses to contaminants, which were likely the result of both indirect community interactions and direct toxicity. In contrast to the hypothesis, no synergistic effects were found, although copepod densities declined when high concentrations of both chemicals were combined. The results suggest that low concentrations of salt and carbaryl are likely to have mostly independent effects on aquatic communities. Environ Toxicol Chem 2017;36:771-779. © 2016 SETAC.