Luxembourgish groundwater aquifers have recently been impacted by high concentrations of several pesticide transformation products (TP) that led to regulatory issues for about 1/3 of the drinking water supplies (Luxembourg considers all transformation products to be relevant and applies the 100 ng/L legal threshold). The consequent application restrictions or complete bans of certain pesticides triggered switches in compound uses in several cultures. A leaching risk analysis had been conducted to orient agricultural counselling on the least impacting parent compounds and transformation products. However, since the leaching simulations relied on literature environmental property data of the pesticides (like fraction of TP generated), there was some uncertainty on the true impact of the identified TPs. Residence times of groundwaters in the main aquifer spanning on average between 10 and 20 years (with proportional recovery times once these waters are contaminated), a faster validation approach was needed. The hypothesis was established that the interflow component in surface waters would be a good indicator to estimate the amount of transformation products available for groundwater leaching. In that perspective passive sampling campaigns were established on four river basins of distinct hydrogeology to quantify the masses of parent compounds and transformation products transported during an entire year and supported by grab sampling in the descending limbs of seasonal flood waves. Additional parameters included conductivity, DOC, Abs280 and macro-anions. All the predicted transformation products were identified and their occurrence varied in amount and timing in the different catchments according to their application, metabolization in soils and hydrogeological setting. This contribution discusses the influences of spatial use variability and hydrological connectivity of agricultural source plots to the magnitude of the occurrences as well as its potential link to the leaching modelling and its parametrization.

How to cite: Gallé, T., Bayerle, M., Pittois, D., Huck, V., and Farlin, J.: Pesticide transformation product occurrences in surface waters as ground water pollution risk indicators in the context of an extended residence time aquifer, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7699, https://doi.org/10.5194/egusphere-egu23-7699, 2023.

South Africa is the leading user of pesticides in Sub-Saharan Africa. Consequently, there is an urgent need to improve our understanding of which pesticides persist in the environment and how they are being transported to non-target environments. The presence of pesticides in non-target environments, such as surface water or groundwater, could be detrimental to aquatic ecosystems and human health.

Our research focuses on monitoring for pesticides in the rivers of three agricultural catchments (Grabouw, Hex River Valley, and Piketberg) within the Western Cape, South Africa. Passive samplers are being deployed from March 2022 to March 2023, adding to a pre-existing dataset of analytical and pesticide application data from 2017 to 2019. Laboratory methods are being developed and validated at Stellenbosch University (SU) to analyze for pesticides using Liquid Chromatography-Mass Spectrometry. Duplicate samples were analyzed at the Swiss Federal Institute of Aquatic Research (Eawag), as a quality control step. Limits of Quantification were lower at Eawag and measured concentrations were typically higher compared to SU. These differences are likely due to variations in the instrument used and sample extraction procedure. 

Results from 2017-2019 indicate that 83% of samples contained five or more pesticides. In every year of sampling, total pesticide concentrations were typically attributable to a single/few compounds per catchment. Six pesticides exceeded Environmental Quality Standard (EQS) values in at least one of the sampling periods. Imidacloprid was highlighted as a pesticide of concern since it consistently exceeded EQS values over all sampling periods. Detection/exceedances of pesticides generally coincided with their application and rainfall events, except for imidacloprid and terbuthylazine. This suggests that alternate transport pathways, such as storage and input from groundwater, may be relevant. Recent results from 2022 sampling indicate that the concentrations of imidacloprid are decreasing; however, they are still exceeding EQS values. Lastly, expansion of the analytes in 2022 led to the detection of two new pesticides, dimethomorph and diphenylamine.

Our results suggest that establishing a long-term data set regarding aquatic pesticide pollution in the Western Cape will lead to a better understanding of the trends and risks of pesticide use. This improved knowledge will lead to the development of targeted mitigation measures for more sustainable agricultural practices in South Africa and beyond.

How to cite: Chow, R., Davies, E., Fuhrimann, S., and Stamm, C.: Evaluating trends and risks of aquatic pesticide pollution in the Western Cape, South Africa, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9553, https://doi.org/10.5194/egusphere-egu23-9553, 2023.

Atrazine is one of the most frequently found pesticides in groundwater and surface water. Under natural light, the half-life of this herbicide in aqueous medium is around 250 days. Atrazine has shown the potential to alter food webs, decrease diversity, and can interfere with species composition. In the current study, electrocoagulation powered by solar energy was used to eliminate atrazine from the aqueous solution. Aluminum and copper electrodes were used to investigate the effect of different operating parameters such as contact time (10-60 min), applied voltage (5-25 V), initial pH (3-11) of the feed water, types and concentration of supporting electrolyte like NaCl, Na₂SO₄ (100-500 mg/L) on the removal of atrazine. The loss of electrode mass and sludge generation were also evaluated. The effect of the initial concentration of atrazine was observed in the range of 3-15 mg/L. The pH of feed water solutions in all the experiments increased, indicating the necessity for neutralization after electrocoagulation.

The possible mechanisms of atrazine removal were explored using several techniques such as X-ray Diffraction (XRD), Fourier Transform Infra-Red (FTIR) spectroscopic analysis. The particle size, surface structure, and shape of dried sludge particles were analyzed using a scanning electron microscope. The energy consumption and operating cost calculations of the electrocoagulation process infer that this technique is not energy-demanding. Kinetic analysis demonstrated that atrazine removal followed first-order rate kinetics. Removal of atrazine from real river water matrices was also assessed in the current research. Current work indicated that solar-powered electrocoagulation is a promising approach for the elimination of atrazine in the treatment of water and wastewater in decentralized mode. 

How to cite: Biswas, B. and Goel, S.: Atrazine removal from river water using direct current and solar-powered electrocoagulation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6156, https://doi.org/10.5194/egusphere-egu23-6156, 2023.

Urban biocides, such as terbutryn, are widely used in facade paints and renders to reduce algae growth and are released with each rain event. Cities are increasingly adopting sustainable stormwater management associated to the sponge city concept, involving infiltration and retention systems and less water in sewer systems. Although biocides and their transformation products have been detected in groundwater, knowledge of the distribution and the infiltration of biocides and transformation products on the district scale is currently missing. Here we aimed at comparing classical and sustainable stormwater management (i.e., infiltration trench and pond) in terms of distribution and hot spots of biocide infiltration at the district scale (2.4 ha). In addition, we assessed the transport of biocides and their transformation products (TP) from facades to soil and stormwater retention systems. We combined a field campaign (6 months), including regular soil and water sampling and description of the water balance using hydroclimatic parameters and land use data, with a modelling approach to estimate and predict biocides leaching and degradation over three decades. The concentrations of terbutryn and TP (from 3 to 300 ng.L^-1)in water regularly exceeded the predicted no effect concentrations (PNEC) of terbutryn. Our modelling approach underscored prevailing (27-73%) biocide infiltration towards groundwater close to facades while a smaller biocide fraction (7-39%) reached the infiltration trench and the pond. The model enabled estimating the distribution of biocides and transformation products among urban compartments, i.e., topsoil close to facades, infiltration and retention systems and deeper soils toward groundwater, for various urban surface-soil interfaces. The interfaces included infiltration through gravel layer close to facade, pavements and vegetated soils and infiltration through trenches, ponds and wells. By comparing integrated scenarios of water management and painting of facades, our results are a first step to evaluate the chronic emission of biocides and TP from facades to evaluate risks and benefits of transition scenarios towards a biocide-free city.

How to cite: Laura, S., Tobias, J., Sylvain, P., and Gwenael, I.: Emissions of the urban biocide terbutryn from facades to soil and stormwater system estimated over three decades, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14583, https://doi.org/10.5194/egusphere-egu23-14583, 2023.

In Ireland, 82% of public water supplies originate from surface water sources which often contain elevated concentrations of dissolved organic matter (DOM) from a range of allochthonous (e.g., leaf leachate, manure) and autochthonous (e.g., macrophytes, biofilms, algae) catchment sources. During disinfection, this DOM may react with chlorine to produce potentially carcinogenic disinfection byproducts (DBPs) such as trihalomethanes (THMs), haloacetic acids (HAAs) and a range of nitrogen-containing species such as haloacetonitriles (HANs) and halonitromethanes (HNMs). As a result, Ireland has the highest reported number of total THM exceedances, (e.g., concentrations in excess of 100 μg L^-1) in potable water across European Union member states. Removal of DOM precursors from raw water prior to chlorination has shown to be effective in mitigating DBP formation. However, significant infrastructural challenges remain in Ireland with many small treatment plants requiring costly upgrades. Hence, there is an urgent need for low-cost proactive monitoring tools to quantify DOM composition and concentration of source water to aid in the production of safe drinking water.

The overall aim of the present study is to better understand the spatiotemporal dynamics of DOM precursors and associated DBP formation at the scale of small river catchments (e.g., <50 km²) typical of drinking water source areas. To achieve this, we investigated two sub-catchments (34 km² and 18 km²) of the River Lee basin, Republic of Ireland, which serve water treatment plants known to be at risk of THM exceedances. High resolution field sampling and measurement of DBP precursors (DOC, DIC, DON, NH₄⁺, Cl^– and Br^–) and DOM optical properties using UV-vis and fluorescence excitation−emission matrix (EEM) spectroscopy were combined with 214 three-day batch chlorination experiments from 36 monitoring points (including 12 groundwater) from February to November 2021. A machine learning ensemble including bagging tree, generalized boosted regression and neural networks models was developed to explore and predict DBP formation potential using EEM parameters, including parallel factor analysis (PARAFAC) components and the measured DBP concentrations from the batch chlorination experiments. Therefore, we could predict with on average of 13% and 6% precision and error, respectively, the concentration of twenty DBPs produced from chlorination including four THMs, nine HAAs, four HANs, one HNM and two haloketone species. In addition, DOM molecular size distribution was measured on 25 samples by size exclusion – organic carbon – nitrogen detection (LC-OCD-OND) to explore the composition of DOM sources. Our findings highlight potential opportunities for DBP risk reduction through proactive online monitoring of source water using fluorescence EEM spectroscopy. This knowledge will help to organize appropriate mitigation strategies at the catchment level as well as aid in treatment process optimization using fluorescence EEM spectroscopy which surpasses the capabilities of traditional online UV-vis spectroscopy. Overall, the findings of our research will help to decrease the number of total THM exceedances in Ireland and better protect consumer health in relation to drinking water chemical quality around the world.

How to cite: Droz, B., Fernandez-Pascual, E., Emma, G., O'Dwyer, J., Harrison, S., O'Driscoll, C., and Weatherill, J.: Predicting multi-species disinfection byproduct formation at small catchment scale using fluorescence spectroscopy data analyzed by machine learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7315, https://doi.org/10.5194/egusphere-egu23-7315, 2023.

Managed Aquifer Recharge (MAR) is a viable method that has gained recognition for storing alternative waters in aquifers for subsequent recovery or environmental benefits. It has the potential to increase the supply of fresh water and protect aquifers from overexploitation and degradation, but it might also carry the risk of contaminating groundwater since the recharge water used may contain a wide range of organic and inorganic contaminants. Therefore, it is important to carefully assess the quality of these alternative sources of water (such as runoff water) used for MAR and implement appropriate treatment measures to remove or neutralize any contaminants that may be present. The purpose of this research is to conduct a preliminary feasibility study of MAR as a potential mitigation measure in the Hesbaye chalk aquifer since this major source of drinking water for the region of Liège (Belgium) is threatened both in terms of quantity and quality. In the first phase of the study, the quality of runoff waters collected from stormwater basins along national roads and in a national airport area was analysed and certain contaminants of emerging concerns were detected at concentrations close to drinking water limits or environmental safety guidelines. In particular, contaminations with PFAS compounds have been detected in stormwater basins in the airport area with maximum values reaching up 490, 330 and 250 ng/L for PFECHS, PFPeA and 6:2 FTS respectively. Other contaminants of emerging concerns such as alkylphenols and organophosphate flame retardants have been detected as well. In a second phase, estimates of expected recharge rates were determined through in-situ experimentation using a small infiltration pond with a pressure sensor and innovative active-DTS measurements with buried optical fiber cables to monitor the infiltration of water into the loess (eolian loam) sediments overlaying the Hesbaye chalk aquifer. Finally, these input data have been used to perform 1D transport modelling simulations in order to make a preliminary evaluation of the risk of groundwater deterioration in the case where these raw runoff waters are infiltrated without pre-treatment. Column infiltration tests are planned to get a better estimation of the soil attenuation capacity in the unsaturated zone. This study is unique in that i) it explores the feasibility of MAR in a country in which the method is not well-developed yet, ii) the use of airport runoff water as a potential source of recharge water is novel and has not been widely examined in previous MAR studies and iii) aquifer-soil treatment in loess sediments overlaying a chalky fractured aquifer is a unique hydrogeological setting to perform MAR operations.

How to cite: Glaude, R., Simon, N., Orban, P., and Brouyère, S.: Chemical characterization of urban waters aimed for managed aquifer recharge in the Hesbaye chalk aquifer (Liège, Belgium), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2642, https://doi.org/10.5194/egusphere-egu23-2642, 2023.

Recent years have seen increasing interest in Per- and Polyfluoroalkyl Substances (PFAS) in the urban water cycle. PFAS are human-manufactured chemicals that have been employed globally in industrial and household products with outstanding chemical stability and mobility. This study set out a one-year monitoring scheme as a basis to better understand the sources, transport and fate of PFAS at a large catchment scale. The monitoring results will further assist the development of a contamination distribution model.

Nine Danube tributary sites including regions with low and high pollution risk were selected, based on the existing monitoring results from other research and inventories of hotspots like industries and landfills, to investigate the appearance of pollutants along the surface water of the catchment. Two locations on the Danube mainstream were targeted for more frequent monitoring of surface water and connected groundwater, furthermore, bank-filtration models will be built for these sites. In the case of point sources, five municipal wastewater treatment plants, four direct industrial dischargers and four legacy landfill sites were selected to identify the impact of these hotspots. Surface runoff at three small catchments dominated by either arable land, grassland or forests, together with samples of atmospheric deposition at three city sites were collected to cover potential diffuse pathways of PFAS transport in the catchment.

At the current stage, two-thirds of the sampling has been carried out for the Danube locations and the rest of the sites are approaching completion. Targeted analysis method using liquid chromatography mass spectrometry (LCMS) was employed, to assess the presence of thirty-two different PFAS compounds.

Despite the fact of being restricted in the EU, PFOA and PFOS were still detected in most samples. Additionally, short-chain perfluoroalkyl carboxylic (PFCA) and sulfonic (PFSA) acids were prominently detected in 110 surface and groundwater samples, while 97% of the total concentration exceeds the newly proposed EQSD(Environmental Quality Standards Directive) of 4.4 ng/L to EU in 2022. What stands out in the results is that, at a site downstream of an industrial hotspot region in the upper part of the catchment, samples show a total PFAS concentration greater than 2700 ng/L, a significant proportion of which came from two replacement compounds, ADONA and GenX. This “signal” is still observed far downstream. In contrast to most of the tributaries, ADONA and GenX were detected in all samples from the two Danube sites and accounted for the largest proportion of the total concentration. Analysis of twelve groundwater samples below one landfill site observed a median total concentration of 110 ng/L, meanwhile three landfill leachate samples were analysed showing amounts greater than 720 ng/L. In addition to the compounds mentioned above, the presence of 6:2 fluorotelomer sulfonate (FTS), Perfluorooctanesulfonamide (FOSA) and sulfonamidoacetic acid (FOSAA) were not negligible in these samples. Wastewater samples are still under evaluation and details will be shown at the conference.

The monitoring results indicate the significant contribution of hotspot regions and point sources to the PFAS contamination in the river, but at the same time, diffuse inputs must not be ignored.

How to cite: Liu, M., Saracevic, E., Krlovic, N., Zoboli, O., Kittlaus, S., Rab, G., Obeid, A., Oudega, T., Derx, J., and Zessner, M.: Comparative assessment of PFAS concentrations in emission pathways, surface and groundwater in the upper Danube Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2267, https://doi.org/10.5194/egusphere-egu23-2267, 2023.

Sulfonamides are widely used antiobiotics and a threat to water resources and related ecosystems. While the direct discharge from untreated sewer or wastewater to surface water is a well-known pathway to the aquatic environment, only a limited number of studies have looked at the discharge and fate of sulfonamides from a contaminant plume to surface water so far.

In this study, we investigated a sulfonamide contaminant plume discharging to a stream in Denmark. The sulfonamides (originating from a former production facility), are transported through a multilayered sandy aquifer and discharge to a groundwater-fed stream located down gradient. Our objectives were to evaluate if a screening using fluorescence properties could be used to delineate the sulfonamide contaminant plume and support the contaminant mass discharge estimation (both by transect method and in-stream measurements).

Direct push technics in combination with a fluorescence screening allowed a relatively unexpensive coarse delineation of high concentrations areas (as opposed to laboratory analysis) down to 15 m.b.g.s. and ergo optimization of monitoring wells / screen locations in the transect. Chemical analyses were combined with slug test and hydraulic gradient estimates via continuous monitoring to quantify the sulfonamide flux and its temporal variations in a 2 km-long transect along the stream (24 monitoring wells with 3 - 6 screens).

The estimated sulfonamide mass discharge (transect based) is in good agreement with the mass discharge calculated from in-stream measurements, highlighting the relevance of the screening approach to select appropriate measurement point locations. Furthermore, the comparison between the flux in both stream and groundwater compartments shows that the degradation of sulfonamides seems relatively limited in the near-stream and hyporheic zone, with the exception of the sulfanilic acid. The results of this study will be used for the prioritization of remedial actions along the main discharge zones.

How to cite: Lemaire, G. G., Vinther, L., Thrane, B. B., Harrekilde, D., Ottosen, C. B., Hansen, J. L., Broholm, M. M., Bjerg, P. L., Dissing, L., and Pedersen, J. K.: Optimized flux estimation of a sulfonamide contaminant plume discharging to a stream using fluorescence screening , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16407, https://doi.org/10.5194/egusphere-egu23-16407, 2023.

Water and sediment transport minerals, micro-plastics, heavy-metals, pathogens, DNA, RNA, and emerging contaminants through river networks. We would like to use point observations of these concentrations to determine where and how much of these are entering the network. However, downstream samples are mixtures of all the potential upstream sources. Separating out the contribution of an individual source requires "unmixing" the network's waters or sediments.

Here, we describe a very efficient approach to perform such an unmixing, identifying the contribution from each nested sub-catchment in a drainage basin. First, we abstract the sub-catchments defined by our sampling sites into a directed acyclic graph. Each node (sub-catchment) in the graph is defined as having an upstream area, which we know, and a tracer source concentration, whose value we want to find. If we assume that when two rivers meet their tracers' fluxes are combined conservatively then downstream concentrations are the mixture of all upstream concentrations, weighted by upstream area.

To solve for the source concentration of each sub-catchment we define a convex optimisation problem, minimising the relative difference in the predicted and observed tracer concentration at each sample site. Due to its convexity, this optimisation problem can be solved in less than a second for networks of a 100 nodes. Uncertainties can be estimated using a Monte-Carlo style approach. We have made an open-source, Python implementation of this algorithm available on GitHub. This implementation requires as input (1) a spreadsheet containing sample site locations and observed tracer concentrations and (2) a D8 flow-direction raster map. This is a powerful approach for locating and quantifying the sources of conservatively mixed tracers or pollutants in drainage networks.

How to cite: Lipp, A. and Barnes, R.: Identifying tracer and pollutant sources in drainage networks from point observations using an efficient convex unmixing scheme, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5368, https://doi.org/10.5194/egusphere-egu23-5368, 2023.