Combination of multivariate data analysis and mixing modelling to assess tracer potential of contaminants of emerging concern in aquifers.

Collected evidence has shown that contaminants of emerging concern (CECs) in conjunction with more conventional tracers (major ions, nutrients, isotopes etc.) can be used to trace pollution origin in aquatic systems. However, in highly mixed aquifer systems signals obtained from conventional tracers overlap diminishing their potential to be used as tracers. In this study, we present an approach that incorporates multivariate statistical analysis (principal component analysis (PCA) and Kohonen's Self-Organizing Map method (SOM)) and mixing modelling to identify the most suitable CECs to be employed as anthropogenic tracers. The study area is located in the Besòs River Delta (Barcelona, NE Spain) and represents the highly mixed aquifer system. A one-year monthly based monitoring campaign was performed to collect the information about the concentrations of 105 CECs as well as major and minor ions in the river and along the groundwater flow. The dimensionality of the obtained dataset was reduced to 25 CECs, based on their estimated health risk effects, for multivariate data analysis. The obtained results showed the overlap of conventional tracers' signals obtained from PCA. In case of CECs, PCA revealed differences in their distributions allowing the differentiation of the roles of natural attenuation processes, local and regional flows on their occurrence in different parts of the aquifer. This was not possible to do using solely CECs' distribution profiles. SOMs provided the lacking information about the modality of the distribution of each CECs, revealing their ability to represent factors controlling the groundwater hydrochemistry, which assist in defining their tracer potential. Based on the obtained results four identified persistent CECs, two with unimodal (lamotrigine and 5-Desamino-5-oxo-lamotrigine) and two with bimodal (carbamazepine and diazepam (higher modality was not revealed)) distributions, were selected to run a mixing model to compare their tracer performance.

Contaminants of emerging concern in the urban aquifers of Barcelona: Do they hamper the use of groundwater?

Urban aquifers are an alternative to obtain freshwater, but they are frequently polluted by contaminants of emerging concern (CECs). Therefore, there is a need to ascertain whether CECs are a water management challenge as they might limit the use of groundwater as safe drinking water even at ng L-1 concentration levels. To answer this question, it is required to evaluate human health-risk effects of measured CECs in the groundwater and to understand their behaviour at a field-scale. This study compiles data about the presence of CECs in the aquifers of Barcelona and its metropolitan area, evaluates health risk effects of measured CECs in the groundwater and presents approaches implemented to identify and quantify the coupled hydro-thermo-chemical processes that govern their fate in the subsurface. Some CECs might be harmful to humans, such as 5-methyl-1H-benzotriazole and the pharmaceuticals azithromycin valsartan, valsartan acid, lamotrigine, gabapentin, venlafaxine and lidocaine, which show very high to intermediate health risk effects. The number of harmful CECs and the level of their hazard increase from the groups of adults and 14-18 years old teens to the groups of 4-8 years old and 1-2 years old children. Thus, some CECs can limit the use of groundwater in Barcelona as potential drinking water source. Finally, knowledge gaps in understanding the integration of these processes into urban water resources management plans are identified, which will help to define groundwater potential uses and to assure the adequate protection of the human health and the environment.

Potential of low-enthalpy geothermal energy to degrade organic contaminants of emerging concern in urban groundwater.

Low-enthalpy geothermal energy (LEGE) is a carbon-free and renewable source to provide cooling and heating to infrastructures (e.g. buildings) by exchanging their temperature with that of the ground. The exchange of temperature modifies the groundwater temperature around LEGE installations, which may contribute to enhancing the capacity of aquifers to degrade organic contaminants of emerging concern (OCECs), whose presence is significantly increasing in urban aquifers. Here, we investigate the impact of LEGE on OCECs and their bioremediation potential through numerical modelling of synthetic and real-based cases. Simulation results demonstrate that: (i) LEGE facilities have the potential to noticeably modify the concentrations of OCECs; and (ii) the final impact depends on the design of the facility. This study suggests that optimized LEGE facility designs could contribute to the degradation of OCECs present in urban aquifers, thus improving groundwater quality and increasing its availability in urban areas.

An advection-reaction model of emerging contaminants in ground and surface waterbodies with known topology: a data-based approach.

A simple data-based advection-reaction (reactive transport) model applicable to both rivers and aquifers monitoring networks is proposed. It is built on (a) available monitoring data, and (b) graph-theoretical concepts, specifically making use of the Laplacian matrix to capture the network topology and the advection process. The method yields useful information regarding the dynamic spatial behavior of the variables monitored, expressed in terms of quantitative parameters like characteristic length, entropy, first-order decay constants, synchronization between sites, and the external inputs/outputs to the system. The model was tested in an unconfined shallow aquifer located in the lower Besòs River (Spain), in which 37 pharmaceutical compounds were monitored at 7 sites, alongside two campaigns (February and May 2021). Characteristic lengths were, on average, of the same order (24.5 m) as the mean distance between consecutive monitoring sites (33.6 m), thus reflecting an adequate monitoring network design. From an estimated mean advection velocity (0.24 m·h-1), first-order decay constants were calculated for each compound and campaign, with mean values of 0.025 h-1 (February) and 0.005 h-1 (May). Whereas entropy was generally slightly larger values in February than in May (mean values of 1.02 and 0.9 entropy units respectively), synchronization showed the opposite trend (mean values of 62.4% and 68.8% respectively). The input/output profiles were generally site-dependent, regardless of the compound, and campaign considered. • A new advection-reaction modeling approach directly based on experimental data obtained from monitoring campaigns together with the network topology is proposed. • The method yields new quantitative information regarding the dynamic behavior of the variables monitored, useful for both research and management purposes.

Occurrence, data-based modelling, and risk assessment of emerging contaminants in an alluvial aquifer polluted by river recharge.

This research presents the occurrence and fate of 121 contaminants of emerging concern (CECs) in an urban aquifer polluted by river recharge through a data-base modelling. Afterwards, risk quotients (RQs) are computed to determine the risk posed by CECs to human health. To this end, groundwater and river water samples were collected in four campaigns conducted from February to May 2021. Results show that 46 CECs are ubiquitous in groundwater and their concentrations vary several orders of magnitude, ranging from below the limit of quantification to 44.5·103 ng/L for iopamidol. Transformation products (TPs) are usually detected at lower concentrations than those of the parent substances but there are some exceptions (i.e., fipronil sulphide, fipronil sulfone and O-desmethylvenlafaxine). River concentrations are higher than those detected in groundwater for some CECs, indicating the occurrence of natural attenuation processes when river water infiltrates the aquifer. A data-based advection-reaction modelling is proposed and tested for ca. 40 substances with detection frequencies higher than 90%. It provides useful quantitative information regarding the dynamic behaviour of the variables monitored, expressed in terms of characteristic length, entropy and synchronized state contribution. Finally, risk quotients (RQs) are used to assess the human health risk posed by the ubiquitous CECs in groundwater. Most CECs do not pose any risk to the different life stages considered, as the RQs evaluated are lower than 0.01. However, the pharmaceuticals valsartan and its TP valsartan acid show RQs higher than 1, indicating that these substances might be harmful to human beings.

Dynamics of nitrous oxide with depth in groundwater: Insights from ambient groundwater and laboratory incubation experiments (Hesbaye chalk aquifer, Belgium).

Aquifers under agricultural areas are considered to be an indirect source of nitrous oxide emission (N2O) to the atmosphere, which is the greenhouse gas (GHGs) characterized with the highest global warning potential and acts as a stratospheric ozone depletion agent. Previous investigations performed in the Cretaceous Hesbaye chalk aquifer in Eastern Belgium suggested that the dynamics of N2O in the aquifer is controlled by overlapping biochemical processes such as nitrification and denitrification. The current study aims to obtain better insight concerning the factors controlling the distribution of N2O concentration along a vertical dimension in the aquifer, and to capture and quantify the occurrence of nitrification and denitrification processes in the groundwater system. Low-flow groundwater sampling technique was undertaken at different depths in the aquifer to collect groundwater samples aiming at obtaining information about ambient aquifer hydrogeochemical conditions and their effect on the accumulation of GHGs. Afterwards, laboratory stable isotope experiments, using NO3- and NH4+ compounds labeled with heavy 15N isotope, were applied to quantify the rates of nitrification and denitrification processes. Ambient studies suggest that the occurrence of N transformation was related to denitrification while laboratory incubation experiments did not detect it. Such controversial results might be explained by the discrepancy between real aquifer conditions and lab design studies. Thus, additional in situ tracer experiments should be carried out in areas where natural groundwater fluxes do not flush the injected tracer too rapidly. In addition, it would be useful to conduct microbiological studies to obtain better insight into the nature of subsurface biofilm biotope.

Effect of land use changes on non-carcinogenic health risks due to nitrate exposure to drinking groundwater.

This study aimed to determine the effect of land-use changes on the non-carcinogenic health risk of nitrate ion exposure of underground drinking water resources in Shiraz (Iran). To this end, 175 chemical samples for the nitrate analysis were regularly taken from 35 drinking water wells of Shiraz from 2013 to 2017, and their results were zoned using GIS. Hazard quotient (HQ) induced by nitrate ion exposure was determined in four age groups: infants, children, adolescents, and adults. Area changes of four types of land-use, including residential, agricultural and green space, industrial, and bare land within a radius of 400 m of drinking water wells, were determined using the GIS and Google Earth software. Then, all data was imported to Matlab 2018 for statistical analysis. The results showed that mean nitrate concentration increased by 2.5 mg L-1 from 2013 to 2017. According to the zoning map, 5 and 11.4% of the area in 2013 and 2017, respectively, exceeded the drinking water standard set by nitrate (i.e., 50 mg/L). Air temperature and precipitation variations also influenced nitrate concentrations and HQ changes (Rtemperature = 0.67). Children's age group was the most vulnerable, and during the study period, this vulnerability was an increasing trend, so that the HQ from 0.93 in 2013 to 0.97 in 2017 has increased. The rate of land-use changes in agricultural, industrial, bare, and urban was -1.8%, 1.3%, -4.6%, and 2.1%, respectively, and the highest correlation was observed between HQ and Diff.l residential land use (Rinfant = 0.55). According to the results, the most influential factor in HQ was air temperature (R = 0.66), and urban land-use change (R > 0.44). To sum up, this study's results showed that land-use changes, especially urban and residential development, significantly affect groundwater nitrate concentration and its degree of HQ. Moreover, increasing temperature and decreasing annual precipitation can also increase the severity of this risk.

Groundwater quality changes in peri-urban areas of the Walloon region of Belgium.

An extensive survey of groundwater quality was performed at the regional scale in peri-urban and industrial contexts of the Walloon Region (Belgium). To this end, 243 sampling locations from 8 areas located in different geological contexts and different peri-urban areas of the region were sampled outside pollution hotspots related to contaminated sites. Each groundwater sample was analyzed for 19 inorganic trace elements, 59 organic micro-pollutants and 8 major and minor elements. Five physico-chemical parameters were measured in the field, at the time of sampling to determine the environmental conditions prevailing in groundwater. Existing groundwater chemical data available outside such peri-urban and industrial areas were also compiled from existing groundwater quality databases for comparison. Most of the organic and inorganic pollutants are detected and their levels of occurrence are described statistically. Cumulative distribution function plots allow comparing the distributions of inorganic trace elements in and outside the urbanized and industrialized areas and among the different prevailing geological contexts. Two indicators are introduced, one quantifying the impact on inorganic trace elements of diffuse pollution in urban and industrial areas, the other reflecting the influence of lithology on concentrations in groundwater. Results show that the composition of groundwater is altered in peri-urban and industrial areas with increased concentrations for several organic pollutants and for most inorganic trace elements. However, the results clearly indicate that for the inorganic trace elements, anthropogenic influence is not limited to increased discharge of pollutants in the urban and industrial areas but also to significant changes in environmental conditions, with more reducing and acidic conditions observed in groundwater. The influence of lithology is also marked in the data set. From a more pragmatic point of view, the data set has been also used to derive upper limits of pollutant background concentrations to be used in decision-making related to the management of contaminated groundwater in urban and industrial environments in the Walloon Region.

Fate and risk assessment of sulfonamides and metabolites in urban groundwater.

Antibiotics, such as sulfonamides (SAs), have recently raised concern as wastewater treatment plants (WWTPs) partly remove them, and thus, SAs continuously enter the aquifers. In this context, the aims of this work are to (1) investigate the temporal evolution of SAs and metabolites in an urban aquifer recharged by a polluted river; (2) identify the potential geochemical processes that might affect SAs in the river-groundwater interface and (3) evaluate the ecological and human health risk assessment of SAs. To this end, 14 SAs and 4 metabolites were analyzed in river and urban groundwater from the metropolitan area of Barcelona (NE, Spain) in three different sampling campaigns. These substances had a distinct behavior when river water, which is the main recharge source, infiltrates the aquifer. Mixing of the river water recharge into the aquifer drives several redox reactions such as aerobic respiration and denitrification. This reducing character of the aquifer seemed to favor the natural attenuation of some SAs as sulfamethoxazole, sulfapyridine, and sulfamethizole. However, most of the SAs detected were not likely to undergo degradation and adsorption because their concentrations were constant along groundwater flow path. In fact, the intensity of SAs adsorption is low as the retardation factors are close to 1 at average groundwater pH of 7.2 for most SAs. Finally, risk quotients (RQs) are used to evaluate the ecological and human health risks posed by single and mixture of SAs in river water and groundwater, respectively. Life-stage RQs of the SAs detected in groundwater for the 8 age intervals were low, indicating that SAs and their mixture do not pose any risk to human beings. Concerning the environmental risk assessment, SAs do not pose any risk for algae, fish and crustaceans as the RQs evaluated are further lower than 0.1.

Occurrence of pathogens in the river-groundwater interface in a losing river stretch (Besòs River Delta, Spain).

The aim of this study is to investigate the occurrence of faecal indicator and microbial pathogens (bacteria and virus) in the shallow urban aquifer of the Besòs River Delta (NE Spain). To this end, human adenovirus (HAdV) and Norovirus of genogroups I and II (NoV GI and NoV GII) as well as the faecal indicator bacteria (FIB) Escherichia coli (EC) and faecal enterococci (FE) were monitored in groundwater and in the River Besòs in December 2013 and in July 2104. None of the targeted pathogens were detected in groundwater in December 2013 but contamination of human origin was observed in approximately 50% of the points sampled in July 2014 reaching concentrations up to 99 GC/100 mL for HAdV. Generally, microbial concentrations in river water were higher than those detected in groundwater. This observation indicates that pathogens are naturally attenuated when river water infiltrates and flows through the aquifer, however HAdV were detected at a sampling point located at 380 m from the river in the absence of FIB. The presence of human viral contamination may represent a risk for the use of groundwater as a drinking water source. Further research is needed to understand the dynamics of pathogens in river-groundwater interface over long time periods and a wide range of flow conditions (wet and dry periods) since the urban groundwater of this aquifer might be a valuable drinking water resource in Barcelona especially during drought periods. The methodology followed in this research can be applied to other urban aquifers with similar purposes since the scarcity and contamination of freshwater resources are worldwide issues.

Parametric assessment of hydrochemical changes associated to underground pumped hydropower storage.

Underground pumped hydropower storage (UPHS) using abandoned mines is an alternative to store and produce electricity in flat regions. Excess of electricity is stored in form of potential energy by pumping mine water to a surface reservoir. When the demand of electricity increases, water is discharged into the mine (i.e., underground reservoir) through turbines producing electricity. During the complete operational process of UPHS plants, hydrochemical characteristics of water evolve continuously to be in equilibrium successively with the atmosphere (in the surface reservoir) and the surrounding porous medium (in the underground reservoir). It may lead to precipitation and/or dissolution of minerals and their associated consequences, such as pH variations. Induced hydrochemical changes may have an impact on the environment and/or the efficiency (e.g., corrosions and incrustations affect facilities) of UPHS plants. The nature of the hydrochemical changes is controlled by the specific chemical characteristics of the surrounding porous medium. However, the magnitude of the changes also depends on other variables, such as hydraulic parameters. The role of these parameters is established to define screening criteria and improve the selection procedure of abandoned mines for constructing UPHS plants. This work evaluates the role of the main hydrogeological factors for three different chemical composition of the porous medium. Results are obtained by means of numerical reactive transport modeling. Potential impacts on the environment (mainly on groundwater and surface water bodies) and on the efficiency of the UPHS plants vary considerably from a hydraulic parameter to another showing the need for a detailed characterization before choosing locations of future UPHS plants.

Occurrence, fate and environmental risk assessment of the organic microcontaminants included in the Watch Lists set by EU Decisions 2015/495 and 2018/840 in the groundwater of Spain.

This paper aims to review the existing occurrence data in Spanish groundwater (GW) for the emerging organic contaminants (EOCs) defined in the surface water Watch Lists of Decisions 2015/495/EU and 2018/840/EU since these contaminants are likely to reach GW bodies because surface waters show close interaction with GW. These two lists include 20 substances: 9 pesticides (5 neonicotinoids, 2 carbamates, 1 oxadiazole and 1 semicarbazone), 6 pharmaceuticals (diclofenac and 5 antibiotics), 3 estrogens, 1 UV filter (2-ethylhexyl-4-methoxycinnamate, EHMC) and 1 antioxidant (2,6-di-tert-butyl-4-methylphenol, BHT). Most of these substances are usually detected at low ng/L concentration range or not detected in the GW bodies of Spain. However, eventually they are reported at concentrations>100ng/L (e.g., imidacloprid, methiocarb, diclofenac, macrolide antibiotics, ciprofloxacin, EHMC and BHT). Consequently, it is required to set up drinking water standards, and/or GW threshold quality values because GW is a valuable water resource worldwide. Overall, GW is less contaminated than other water bodies, such as rivers, suggesting that aquifers possess a natural attenuation capacity and/or are less vulnerable than rivers to contamination. Nevertheless, the natural hydrogeochemical processes that control the fate and transformation of these substances during infiltration and in the aquifer have been barely investigated so far. The concentrations of the target EOCs are used to calculate hazard quotients (HQs) in the Spanish GW bodies as an estimation of their ecotoxicity and in order to compare somehow their chemical quality with respect to those of surface water. Due to the limited ecotoxicity data for most EOCs, HQs can only be calculated for few substances. The results pointed out the risk posed by the anti-inflammatory diclofenac towards Ceriodaphnia dubia (HQ=21) and the medium risk associated to the antibiotic erythromycin for Brachionus calyciflorus (HQ=0.46).

Isotopic composition of nitrogen species in groundwater under agricultural areas: A review.

This work reviews applications of stable isotope analysis to the studies of transport and transformation of N species in groundwater under agricultural areas. It summarizes evidence regarding factors affecting the isotopic composition of NO3-, NH4+ and N2O in subsurface, and discusses the use of 11B, 18O, 13C, 34S, 87Sr/86Sr isotopes to support the analysis of δ15N values. The isotopic composition of NO3-, NH4+ and N2O varies depending on their sources and dynamics of N cycle processes. The reported δ15N-NO3- values for sources of NO3- are: soil organic N - +3‰-+8‰, mineral fertilizers - -8‰-+7‰; manure/household waste - +5‰ to +35‰. For NH4+ sources, the isotopic signature ranges are: organic matter - +2.4-+4.1‰, rainwater - -13.4-+2.3‰, mineral fertilizers - -7.4-+5.1‰, household waste - +5-+9‰; animal manure - +8-+11‰. For N2O, isotopic composition depends on isotopic signatures of substrate pools and reaction rates. δ15N values of NO3- are influenced by fractionation effects occurring during denitrification (ɛ=5-40‰), nitrification (ɛ=5-35‰) and DNRA (ɛ not reported). The isotopic signature of NH4+ is also affected by nitrification and DNRA as well as mineralization (ɛ=1‰), sorption (ɛ=1-8‰), anammox (ɛ=4.3-7.4‰) and volatilization (ɛ=25‰). As for the N2O, production of N2O leads to its depletion in 15N, whereas consumption - to enrichment in 15N. The magnitude of fractionation effects occurring during the considered processes depends on temperature, pH, DO, C/NO3- ratio, size of the substrate pool, availability of electron donors, water content in subsoil, residence time, land use, hydrogeology. While previous studies have accumulated rich data on isotopic composition of NO3- in groundwater, evidence remains scarce in the cases of NH4+ and N2O. Further research is required to consider variability of δ15N-NH4+ and δ15N-N2O in groundwater across agricultural ecosystems.

Occurrence of greenhouse gases in the aquifers of the Walloon Region (Belgium).

This work aims to (1) identify the most conductive conditions for the generation of greenhouses gases (GHGs) in groundwater (e.g., hydrogeological contexts and geochemical processes) and (2) evaluate the indirect emissions of GHGs from groundwater at a regional scale in Wallonia (Belgium). To this end, nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) concentrations and the stable isotopes of nitrate (NO3-) and sulphate were monitored in 12 aquifers of the Walloon Region (Belgium). The concentrations of GHGs range from 0.05µg/L to 1631.2µg/L for N2O, 0µg/L to 17.1µg/L for CH4, and 1769 to 100,514ppm for the partial pressure of CO2 (pCO2). The highest average concentrations of N2O and pCO2 are found in a chalky aquifer. The coupled use of statistical techniques and stable isotopes is a useful approach to identify the geochemical conditions that control the occurrence of GHGs in the aquifers of the Walloon Region. The accumulation of N2O is most likely due to nitrification (high concentrations of dissolved oxygen and NO3- and null concentrations of ammonium) and, to a lesser extent, initial denitrification in a few sampling locations (medium concentrations of dissolved oxygen and NO3-). The oxic character found in groundwater is not prone to the accumulation of CH4 in Walloon aquifers. Nevertheless, groundwater is oversaturated with GHGs with respect to atmospheric equilibrium (especially for N2O and pCO2); the fluxes of N2O (0.32kgN2O-NHa-1y-1) and CO2 (27kgCO2Ha-1y-1) from groundwater are much lower than the direct emissions of N2O from agricultural soils and fossil-fuel-related CO2 emissions. Thus, indirect GHG emissions from the aquifers of the Walloon Region are likely to be a minor contributor to atmospheric GHG emissions, but their quantification would help to better constrain the nitrogen and carbon budgets.

Dynamics and emissions of N2O in groundwater: A review.

This work reviews the concentrations, the dynamics and the emissions of nitrous oxide (N2O) in groundwater. N2O is an important greenhouse gas (GHG) and the primary stratospheric ozone depleting substance. The major anthropogenic source that contributes to N2O generation in aquifers is agriculture because the use of fertilizers has led to the widespread groundwater contamination by inorganic nitrogen (N) (mainly nitrate, NO3-). Once in the aquifer, this inorganic N is transported and affected by several geochemical processes that produce and consume N2O. An inventory of dissolved N2O concentrations is presented and the highest concentration is about 18.000 times higher than air-equilibrated water (up to 4004µg N L-1). The accumulation of N2O in groundwater is mainly due to denitrification and to lesser extent to nitrification. Their occurrence depend on the geochemical (e.g., NO3-, dissolved oxygen, ammonium and dissolved organic carbon) as well as hydrogeological parameters (e.g., groundwater table fluctuations and aquifer permeability). The coupled understanding of both parameters is necessary to gain insight on the dynamics and the emissions of N2O in groundwater. Overall, groundwater indirect N2O emissions seem to be a minor component of N2O emissions to the atmosphere. Further research might be devoted to evaluate the groundwater contribution to the indirect emissions of N2O because this will help to better constraint the N2O global budget and, consequently, the N budget.

Occurrence, fate and risk assessment of personal care products in river-groundwater interface.

This work presents the occurrence and fate of selected personal care products (PCPs) in the urban river-groundwater interface. To this end, urban river and groundwater samples were collected in Sant Adrià del Besòs (NE of Spain) and a total of 16 PCPs were analyzed including benzophenone derivatives, camphor derivatives, p-aminobenzoic acid derivatives, triazoles and parabens in three different campaigns (from May 2010 to July 2014). These compounds reach the aquifer through the recharge of Besòs River that receives large amounts of effluents from waste water treatment plants. Results have shown that most of the compounds were not or barely detected (maximum concentrations around 200ng/L) in groundwater samples during the different sampling campaigns. Only two triazoles, namely benzotriazole (BZT) and methyl benzotriazol (MeBZT) were found at high concentrations in groundwater samples (maximum concentration around 2000ng/L). The fate of PCPs in the aquifer was assessed using mixing analysis considering the seasonal variability of the Besòs River. Overall, measured groundwater concentrations were significantly much lower than those estimated by the mixing of the river water. This observation suggested that most of the PCPs are naturally removed when river water infiltrates the aquifer. However, some compounds were more persistent in the aquifer. These compounds were in descending order: the triazoles BZT and MeBZT followed by the camphor derivative 4MBC and the paraben MePB. The measured concentrations allowed us to assess the environmental risk posed by the selected UV-filters and parabens in the river and groundwater samples. Hazard Quotients (HQs) for different aquatic species were calculated in order to characterize the ecotoxicity potential of the studied compounds in the river-groundwater interface. HQ values were always below 1 indicating that at the concentrations observed in the surface or aquifer water of Besòs River these compounds pose no risk to the selected aquatic organisms.

Quantifying chemical reactions by using mixing analysis.

This work is motivated by a sound understanding of the chemical processes that affect the organic pollutants in an urban aquifer. We propose an approach to quantify such processes using mixing calculations. The methodology consists of the following steps: (1) identification of the recharge sources (end-members) and selection of the species (conservative and non-conservative) to be used, (2) identification of the chemical processes and (3) evaluation of mixing ratios including the chemical processes. This methodology has been applied in the Besòs River Delta (NE Barcelona, Spain), where the River Besòs is the main aquifer recharge source. A total number of 51 groundwater samples were collected from July 2007 to May 2010 during four field campaigns. Three river end-members were necessary to explain the temporal variability of the River Besòs: one river end-member is from the wet periods (W1) and two are from dry periods (D1 and D2). This methodology has proved to be useful not only to compute the mixing ratios but also to quantify processes such as calcite and magnesite dissolution, aerobic respiration and denitrification undergone at each observation point.

Urban groundwater contamination by residues of UV filters.

The occurrence and fate of UV filters (UV F) in an urban aquifer in correlation with (1) the spatial distribution of UV F in Barcelona's groundwater, (2) the depth of the groundwater sample, (3) the physicochemical properties of the target compounds, (4) the recharge sources, and (5) the redox conditions of the Barcelona aquifers, were studied for the first time. The highest groundwater concentrations and the largest number of detected UV F were observed in an aquifer recharged by a polluted river (around 55 ng/L in SAP-4). In contrast, the urbanized areas had lower concentrations (around 20 ng/L in MPSP-1). Two pathways can be identified for UV F to enter the aquifers: (1) leakage of row sewage from the sewage network in urbanized areas and (2) wastewater treatment plant (WWTP) effluents discharged into the river. Measured concentrations of UV F were significantly much lower than those estimated from the waste water proportion in groundwater samples suggesting that UV F might undergo transformation processes in both reducing and oxidizing conditions.

Occurrence of carbamazepine and five metabolites in an urban aquifer.

This paper deals with urban groundwater contaminated with carbamazepine (CBZ) and five of its human metabolites in Barcelona. Groundwater samples were accordingly collected in the aquifers of Poble Sec and Besòs River Delta. Higher concentrations and more compounds were found in the Besòs River Delta aquifer, which is recharged by a river contaminated with treated effluent from numerous treatment plants. By contrast, the urban area of Poble Sec presented lower concentrations and fewer compounds. The results showed that CBZ could be attenuated in the Poble Sec aquifer since concentrations in groundwater were lower than those evaluated from mixing of the recharge sources. Conversely, CBZ and its human metabolites were not removed under the reducing conditions of the Besòs River Delta aquifer probably because of the short residence time in this aquifer.