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The management of water resources in hyper-arid coastal regions is a challenging task because proper information regarding groundwater recharge and water budget is needed for maintaining the hydraulic balance in optimal conditions, avoiding salinization and seawater intrusion. Thus, this article deals with the estimation of the hydraulic recharge and the study of the effects of salinization on the dynamics of major and trace elements in an alluvial aquifer located in the world's driest zone, the northern Atacama Desert. The result of stable water isotopes (δD and δ 18 O) and tritium ( 3 H) indicated that groundwater in the area is not recent, whereas 14 C results estimated a groundwater residence time ranging between 11,628 and 16,067 yBP. The estimation of the artificial recharge coming from the urban water-supply-system leaks and wastewater/river-water/groundwater infiltration during irrigation was about 19.84 hm 3 /year, which represents an annual negative water balance of 177 hm 3 /year for the aquifer. The groundwater salinization triggered by seawater intrusion (up to 32.6 %) has caused the enrichment of Li, Rb, Ca, Ba, and Sr in groundwater by cationic exchange, where the excess of aqueous Na is exchanged by these elements in the aquifer sediments. Other elements such as B, Se, Si, and Sb are enriched in groundwater by ionic strength and/or anionic exchange during salinization. The heightened B concentrations derived from the B-rich alluvial sediments were higher than the limit suggested by international guidelines, representing a risk to consumers. Vanadium seems to be unaffected by salinization, whereas Pb, Mo, As, U, and Zr did not show a clear behavior during saline intrusion. Finally, this article highlights the consequences of conducting improper water management in coastal hyper-arid regions with exacerbated agriculture., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Abstract An amorphous sodium titanate (ST) nano-particle was prepared via the facile hydrolytic process with the addition of sodium hydroxide and firstly used for ammonia nitrogen (NH 3 -N) removal from wastewater. ST exhibited satisfactory adsorption efficiency for NH 3 -N simulative wastewater (20 mg·L−1) at a wide range of pH 3.0–9.0, within a minimum contact time of 10 min. The Langmuir isotherm showed that the maximum adsorption capacity (298 K) of the adsorbent was reach up to 44.54 mg·g−1. Concentrated competing cations had some interferences with NH 3 -N adsorption at the order of Ca2+ > K+ > Mg2+ > Na+ according to their competition on adsorption sites. During the adsorption process, cation exchange between Na+ and NH 4 + played a powerful role for the NH 3 -N removal and the contribution of Ti-OH groups was also involved in the adsorption. The regeneration test showed that the saturated adsorbents could be conveniently regenerated just by NaOH or NaCl solution treatment and there was no obvious decline of the adsorption capacity after reused for five times. The facile method of fabrication and regeneration, the rapid adsorption process and the satisfactory adsorption efficiency make sodium titanate a promising adsorbent for low concentration NH 3 -N minimization. Graphical abstract Unlabelled Image Highlights • Sodium titanate (ST) was facilely synthesized for the removal of NH 3 -N from water. • ST exhibited excellent adsorption capacity and fast adsorption property for NH 3 -N. • Cations exchange and Ti-OH are the main contribution for NH 3 -N adsorption. • Exhausted ST exhibited good reusability with the help of NaOH or NaCl. [ABSTRACT FROM AUTHOR]

Abstract Constraining sources and site-specific processes of trace elements in speleothem geochemical records is key to an informed interpretation. This paper examines a 10-year data set of drip water solutes from Harrie Wood Cave, south-eastern Australia, and identifies the processes that control their response to El Niño-Southern Oscillation events which varies the site water balance. The contributions of aerosol and bedrock end-members are quantified via hydrochemical mass balance modelling. The parent bedrock is the main source for the drip water solutes: Mg, Sr, K and trace elements (Ba, Al, V, Cr, Mn, Ni, Co, Cu, Pb and U), while atmospheric aerosol inputs also contribute significantly to drip water trace elements and Na, K and Zn. A laboratory investigation evaluating water-soluble fractions of metals in soil samples and soil enrichment factors provided a basis for understanding metal retainment and release to solution and transport from the soil zone. These results identified the role of the soil as a sink for: trace metals, Na and K, and a secondary source for Zn. Further, soil processes including: cation exchange, K-fixation, metal adsorption to colloids and the release of Zn associated with organic matter degradation further modify the chemical composition of the resultant drip waters. This research is significant for the south-eastern Australian region, as well as other sites in a karst setting with clay-rich soil. In particular these results reveal that the response of drip water chemistry to hydroclimatic forcing is non-linear, with the greatest response observed when the long-term gradient in the cumulative water balance reverses. This longer-term drip water monitoring dataset is significant because it provides the pivotal framework required to reliably identify suitable trace element proxies for interpretation in geochemical speleothem records on multi-decadal timescales. Graphical abstract Unlabelled Image Highlights • Atmospheric inputs contribute to drip water: Na, K, Zn and other trace elements. • K-fixation in soils controlled drip water K during the Millennium Drought. • Na and K respond to soil processes and to higher water flux at drought termination. • Zn colloidal mobilisation is linked to a decrease in soil pH. • Na, K and Zn show promise as speleothem palaeo-climate proxies. [ABSTRACT FROM AUTHOR]

Abstract Subsurface iron removal (SIR) is an in-situ technique to lower the iron content of extracted groundwater. Through cyclic injection of oxygenated water ferrous iron oxidises and precipitates as iron hydroxide in a zone surrounding the extraction well, enhancing the sorptive capacity of the aquifer. During subsequent pumping phases, groundwater traverses the oxidation zone and ferrous iron sorbs to available and newly formed exchange and sorption sites, thereby retarding the breakthrough of dissolved iron. The process is well-understood in regards to the retardation of iron. Less well understood, however, is the behavior of a number of trace metals and metalloids during SIR operations, foremost arsenic (As). In this study, we analyse major and minor ion and trace metal concentrations from a number of SIR tests in a sand aquifer near Leuven, Belgium. We use reactive transport modelling to evaluate conceptual models of trace metal release and arrest. The test data, underpinned by model results, show that metal release, namely arsenic and barium (Ba), occurs through the oxidation of trace amounts of sulphide minerals during the injection phase. Sorption through cation exchange retards Ba while complexation lowers dissolved As concentrations. Arsenic is mobilized again during the pumping phase through varying phosphate concentrations in the native groundwater, despite available sorption surfaces, while Ba remains adsorbed. Concentrations, however, remain below WHO guideline values for As and Ba (10 μg/l and 0.7 mg/l), respectively. The developed conceptual model of As fate reveals a high propensity for As mobility during SIR due to desorption reactions and delivers an explanation as to why many SIR operations fail to show substantial As removal, despite efficient iron removal. Other monitored trace elements showed no mobilisation, including Zn, Al, Cd, Cr, Cu, F, Hg, Ni, Pb, Sb and Se. Graphical abstract Unlabelled Image Highlights • Arsenic (As) and Barium (Ba) are released during subsurface iron removal operations. • Sorption through cation exchange retards Ba; complexation lowers total As concentrations. • As is mobilized despite available sorption surfaces during injection and recovery. • Study shows high propensity for As mobility during SIR due to desorption. [ABSTRACT FROM AUTHOR]

Tyramine (TY) adsorption on a Ca-montmorillonite (SAz-2) was investigated with batch experiments and complementary analyses utilizing ultra-high performance liquid chromatography, ion chromatography, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetry (TG). The adsorption reached equilibrium in 8 h, complying with the pseudo-second-order rate equation, and came to an adsorption capacity of 682 mmol kg −1 at pH 6–8.1, utilizing the Langmuir isotherm model. The adsorption of TY and desorption of exchangeable cations exhibited a linear relationship with a slope of 0.9, implying that the adsorption was largely influenced by a cation exchange mechanism. The effective adsorption was further verified by the characteristic TY bands in the FTIR spectra and the signals of mass loss due to TY decomposition in the TG measurements of the clay after adsorption experiments. Intercalation of hydrated TY into the clay interlayer was confirmed by XRD and TG analyses of the heated samples loaded with TY. The adsorption reached only 0.57 cation exchange capacity of the clay which was probably limited by the low charge density of TY as compared to the negative charge density of the clay surface and by the steric effects arising from the hydration of TY that increased its molecular size. Adsorption of TY on montmorillonite can make TY more resistant to thermal decomposition and possibly better preserved in aquatic and soil environments. [ABSTRACT FROM AUTHOR]

Abstract: Analyses of substratum samples under a landfill were performed to assess the pollution impact of waste over a clay–sand material after nine years of exposure. These samples presented different illite/kaolinite ratios and an acid pH, especially low near the waste/soil contact in a 1–1.5m soil thickness with low density and despite the basic pH of the collected actual methanogenic leachate. This study has raised the effects of a presumably acid stage in the waste leachate on the substratum final quality of clay and its physical–chemical properties as an attenuation buffer. These effects were the dissolution of carbonate minerals, decrease of dry density, increase of hydraulic conductivity, release of metals and formation of clays with low cationic exchange capacity (CEC) as kaolinite. The large presence of H+ and Al(OH)3−x x+ depleted the neutralizing capacity of the substratum and occupied exchangeable sites, decreasing therefore the available sites for retaining leachate pollutants, which traveled further than the first-meter depth of the substratum. In order to combat and prevent pollution as well as to preserve the good barrier properties under new landfills it is proposed to select illitic materials better than kaolinitic substratum, to avoid acid landfilling and if not possible to add lime. [Copyright &y& Elsevier]

Increasing background salinity in watersheds has largely been attributed to road salt retention in groundwaters due to their long residence times. However, laboratory studies demonstrate that soils temporarily store salts, either in porewater or adsorbed onto particles. Field studies of road salt retention in soils are nevertheless rare, and mechanisms of salt transport across multiple hydrological reservoirs (e.g., from soil to groundwater) are unknown. Thus, we collected roadside soil porewater and karst spring water weekly for ~1.5 yr to determine salt transport through the vadose zone into the phreatic zone. We observed dual retention mechanisms of sodium (Na+) and chloride (Cl−) in soils due to slow porewater movement, causing ion movement through the soil as slow as 1.3 cm/day, and cation exchange processes, leading to initial Na+ retention followed by later release months after application. Cation exchange processes also caused base cation loss from exchange sites into mobile porewater. Rapid Na+ and Cl− delivery to groundwater occurred through karst conduits during the winter. However, elevated background levels of salt ions in groundwater during the non-salting months indicated accumulation in the catchment due to slower porewater flow in the soil and rock matrix and delayed Na+ release from soil exchange sites. Unlabelled Image • Deicer retention in soil occurs via slow porewater flow and ion exchange reactions. • Ion exchange with Na+ from NaCl causes loss of soil base cations and nutrients. • Retention in soil delays road salt delivery to groundwater by months. • Karst conduit flow paths cause rapid release of salt ions to groundwater. • Karst systems feature dual road salt delivery pathways to aquifers. [ABSTRACT FROM AUTHOR]

Winter deicing salt application has led to water quality impairment as stormwater carries salt ions (Na+ and Cl−) through watersheds. Green infrastructure (GI) is a promising urban stormwater management practice, but its efficacy in managing salt is unknown. GI is not yet designed to remove salt, but may have potential to mitigate its loading to surface waters. Two roadside infiltration-based GI practices in Northern Virginia (bioretention and bioswale) were monitored year-round over 28 precipitation events to investigate the transport of salt through modern stormwater infrastructure. Stormwater runoff volumes and concentrations of salt ions entering and exiting each GI were monitored to determine reductions of salt ions. Both the bioretention and bioswale significantly reduced effluent surface loads of Cl− and Na+ (76% to 82%), displaying ability to temporarily retain and infiltrate salts and delay their release to surface waters. Changes in bioretention soil chemistry revealed a small percentage of Na+ was stored long-term by ion exchange, but no long-term Cl− storage was observed. Limited soil storage along with groundwater observations suggest the majority of salt removed from stormwater by the bioretention infiltrates into groundwater. Infiltration GI can buffer surface waters from salt, but are also an avenue for groundwater salt loading. Unlabelled Image • Salt transport monitored year-round through infiltration-based green infrastructure. • Green infrastructure displayed significant surface effluent salt load reduction. • Majority of inlet salt load transferred from surface to groundwater. • Soil stored some Na+ but no Cl− long-term. • NaCl induced cation exchange in soil. [ABSTRACT FROM AUTHOR]

Silver nanoparticles (Ag NPs) are among the most common forms of nanoparticles in consumer products, yet the environmental implications of their widespread use remain unclear due to uncertainties about their fate. Because sulfidation of Ag NPs results in the formation of a stable silver sulfide (Ag 2 S) product, it is likely an important removal mechanism of bioavailable silver in natural waters. In addition to sulfide, the complete conversion of Ag NPs to Ag 2 S will require dissolved oxygen or some other oxidant so dispersed metal sulfides may be an important pool of reactive sulfide for such reactions in oxygenated systems. The reaction of Ag NPs with zinc sulfide (ZnS) was investigated using a voltammetric method, anodic stripping voltammetry (ASV). ASV provided sensitive, in situ measurements of the release of zinc (Zn2+) cations resulting from the cation exchange reaction between Ag NPs and ZnS. The effects of Ag NP size and surface coatings on the initial rates of sulfidation by ZnS were examined. Sulfidation of smaller Ag NPs generally occurred faster and to a greater extent due to their larger relative surface areas. Sulfidation of Ag NPs capped by citrate and lipoic acid occurred more rapidly relative to polyvinylpyrrolidone (PVP) and branched polyethylene (BPEI). This study demonstrates the utility of voltammetry for such investigations and provides insights into important factors controlling Ag NP sulfidation such as availability of dissolved oxygen, Ag NP size and Ag NP surface coating. Furthermore, this work demonstrates the importance of cation exchange reactions between silver and metal sulfides, and how the environmental release of Ag NPs could alter the speciation of other metals of environmental significance. Unlabelled Image • Reactions between zinc sulfide and various forms of nanosilver were monitored. • Anodic stripping voltammetry was used to measure zinc released from the reaction. • Small nanoparticle size resulted in faster and more complete sulfidation. • Metal sulfides serve as an important reactant for nanosilver sulfidation. [ABSTRACT FROM AUTHOR]

Single solute sorption mechanisms of metformin (MET) and guanylurea (GUA) were investigated in six soils and three model sorbents (kaolinite, bentonite and humic acid) at varying initial pH and background electrolyte (Ca 2+ ) concentrations. Electrostatic interaction and cation exchange were proposed as mechanisms of MET sorption. At initial solution pH between pKa 1 and pKa 2 , electrostatic interaction is the dominating mechanism of MET sorption. However, as pH approaches pKa 1 , cation exchange becomes a significant mechanism of sorption as evidenced by the increased distribution coefficient (K d ) values in Matawhero (130-fold) and Nelson (2000-fold) soils with high cation exchange capacities (CEC) and permanently negative charged sites and when equilibrium pH < pKa 1 where the divalent cationic form dominates in the solution. Furthermore, results showed higher sorption of MET on bentonite with effective distribution coefficient (K d eff ) value of 14.92 L/kg with high permanent negative charges than on kaolinite (K d eff  = 6.70 L/kg), a variable charge clay. Increased MET sorption at low equilibrium pH on kaolinite (K d  = 20.86 L/kg) further suggest cation exchange is also possible at pH < pKa eff . On the other hand, two lines of evidence suggest cation exchange as an important mechanism of GUA sorption: (a) the positive correlation between cation exchange capacity and K 7  L/kg) and humic acid (K d eff  = 20.86 L/kg) further suggest cation exchange is also possible at pH < pKa 1 . On the other hand, two lines of evidence suggest cation exchange as an important mechanism of GUA sorption: (a) the positive correlation between cation exchange capacity and K d eff values and (b) decreased K d eff values as the Ca 2+ concentration in solution was increased in all soils. Biosolids amendment of three soils resulted in contrasting effects on sorption affinities with a decrease for MET and increase for GUA, further confirming sorption mechanisms and significance of solution pH and CEC on the sorption of MET and GUA, respectively., (Copyright © 2018 Elsevier B.V. All rights reserved.)