Elevated ammonium (NH₄⁺) concentrations in groundwater (GW) pose significant challenges to existing GW treatment systems, particularly in simplified systems such as household sand filters (HSFs), which are widely used in developing countries. We previously conducted a series of column experiments (sand filter materials collected in Hanoi, Vietnam) mimicking HSFs. These experiments revealed limited and fluctuating NH₄⁺ removal, highlighting the need for a comprehensive process-based model to elucidate the complex interplay of physical and biochemical processes that influence NH₄⁺ concentration dynamics in these systems. Here, we established a one-dimensional advective-dispersive-reactive model conditioned on data from column experiments under laboratory (artificial GW inflow with sand materials from local HSFs) and field conditions (natural GW inflow with sand materials from local supplier), accounting for temporal variations in reaction kinetics, transport processes, and a previously unconsidered inter-phase transfer process for nitrate (NO₃^-). The modeled breakthrough curves capture the complex dynamics of NH₄⁺, nitrite (NO₂^-), and NO₃^- concentrations under both laboratory and field conditions. The reaction rates of the nitrogen species show strong hysteresis in response to substrate (NH₄⁺ and NO₂^-) concentrations, suggesting that potential lags in the biochemical reactions caused by inhibitions and low retention time lead to the incomplete NH₄⁺ removal. Our scenario analysis indicates that, without inhibition effects, the current bio-reactive environment could reduce NH₄⁺ concentrations to the legal target level (within up to eight hours retention time under field conditions). This study represents one of the few process-based modeling efforts mimicking HSFs. Future modeling research should parameterize various inhibition effects into the existing reactive transport models in order to gain quantitative insight into enhancement methods for HSFs.

How to cite: Wei, R., Le, A. V., Liu, B., Azari, M., Nowak, W., Kappler, A., and Oladyshkin, S.: Modeling the Ammonium Removal Processes in Household Sand Filters, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-205, https://doi.org/10.5194/egusphere-egu25-205, 2025.

Cryptosporidium parvum is a pathogen causing gastrointestinal infections, occasionally leading to death in immunocompromised individuals. It can contaminate surface water and groundwater, and consequently drinking water supplies, through agricultural activities such as cattle and dairy farming or the spreading of manure as fertilizer. The importance of removing C. parvum by filtration is of great interest because of its long-term persistence in water as oocysts and its resistance to chemical disinfection owing to its thick cell wall. This is relevant for both subsurface filtration and engineered filtration processes. Therefore, it is necessary to evaluate its removal efficiency in subsurface media and during the filtration stage of drinking water treatment. This study aimed to select an appropriate surrogate for C. parvum oocysts that exhibits similar attenuation and transport behaviour through porous media, is cost-effective, and poses no harm to humans or the environment, enabling its application in engineered installations and field studies.

Bacillus subtilis is commonly used as a conservative surrogate for C. parvum for subsurface transport studies, and aerobic spores have been included by the U.S. Environmental Protection Agency as an indicator for C. parvum in groundwater under the direct influence (GWUDI) of surface water. While B. subtilis may be a cost-effective option, its smaller size (nearly 6 times smaller in diameter), different shape (rod-shaped vs. spherical), and distinct surface characteristics present limitations. This study evaluated the attenuation and transport of B. subtilis spores, oocyst-sized unmodified (yellow-green and yellow-orange) and glycoprotein-coated microspheres, along with UV inactivated C. parvum in columns packed with silica sand. The objective was to determine the significance of size, surface charge, and macromolecules on the cell wall surface, on the reduction of the oocysts. Glycoprotein-coated microspheres, exhibiting similar physicochemical properties (including macromolecules) to oocysts, were found to be the most effective surrogate. The study results highlight the importance of selecting appropriate surrogates for accurate evaluation of the transport of C. parvum in the subsurface and its removal in water treatment through sand filtration.

How to cite: Stevenson, M. E., Pang, L., Farnleitner, A. H., Lindner, G., Kirschner, A. K. T., Blaschke, A. P., and Sommer, R.: Selecting an Appropriate Surrogate for Assessing Filtration Removal of Cryptosporidium parvum for Water Treatment Applications, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3798, https://doi.org/10.5194/egusphere-egu25-3798, 2025.

Abstract

Arsenic (As) contamination in groundwater is a serious environmental and public health issue, particularly in regions where groundwater is a primary source of drinking water. Many Asian countries, particularly Bangladesh, India and parts of Southeast Asia are adversely affected with As contaminated aquifers. The present study thus aims to explore the source, distribution and release mechanism of As into the groundwater in the parts of southern bank of the Upper Brahmaputra floodplains in Assam, India.  Groundwater samples (n=100) were collected from the shallow aquifers (< 30 m) from two the districts Jorhat and Golaghat, and were analysed for major ions (Ca²⁺, Na⁺, K⁺, Mg^2+, Cl^-,HCO₃^-, NO₃^-,SO₄^2-) and trace elements (As, Fe, Mn, Pb, Co, Cu, Zn). Concentration of As, Fe and Mn in the aquifers has exceeded the permissible limits set by WHO (World Health Organisation) posing serious threat to human health. 54% of groundwater samples have exceeded WHO permissible limit of 10 µg/L for As (range: bdl (below detection limit) to 480 µg/L, mean: 31µg/L). While 94% (range: 0.076 mg/L to 41.37 mg/L, mean: 10.92) and 77% (range: 0.002 mg/L to 9.06 mg/L, mean: 0.6 mg/L) of groundwater samples have exceeded the WHO permissible limit of 0.3 mg/L and 0.05 mg/L for Fe and Mn respectively. Aquifers enriched with As was found adjacent to Naga foothills while low As was found near the Brahmaputra river. Aquifer lithology reveals the presence of thick clay layer near the Naga hills (also indicated by higher Al₂O₃ in the sediments) and subsequently minerals like illite and kaolinite was found in these clay layers (confirmed by the XRD peaks). The clay minerals might have acted as the active site for adsorption of As, thus acting as the host for As in the studied region. Moreover, the average value (mean: 80) of Chemical Index of alteration (CIA) indicates intense chemical weathering at the source area in warm and humid condition leading to formation of copious amount of clay minerals like kaolinite. No strong co relation was seen between As and the redox sensitive elements viz; Fe and Mn, nor with HCO₃, NO₃ or SO₄ indicating multitudinous processes or reactions viz competitive exchange with anion, reductive dissolution and pH dependent sorption might have control the release of As in the studied region. Higher LREE compared to HREE indicates the source of these clastic sediments could be from felsic or intermediate composition of rocks. Principle Component Analysis (PCA) and cluster analysis indicated the dominance of geogenic factors as the main contribution of these contaminants in the groundwater of the study area. Regular monitoring and intervention of groundwater in the region is crucial for its prolong use. The present study will assist stakeholders and policy maker in taking evidence-based decision and providing As safe drinking water to the affected communities

Key words: Arsenic; Groundwater; Brahmaputra floodplains; Sediment Geochemistry; Hydrochemistry

How to cite: Medhi, S. and Choudhury, R.: Arsenic toxicity in Groundwater of Brahmaputra Floodplains of Assam, India: Concerns for drinking water quality, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1106, https://doi.org/10.5194/egusphere-egu25-1106, 2025.

The transport of pathogens through rocks is often regarded as negligible unless there are fractures in the medium. However, sedimentary rocks may have a porosity that allows the migration of pathogens even when they are unfractured.
In this work, we investigated the transport behavior of several pathogens (namely Escherichia coli and Enterococci faecalis) through a sedimentary porous rock made of 98.5 wt.% of calcite (CaCO3), hydraulic conductivity 6·10−6 m/s, and porosity 0.43. Core flooding experiments were performed under variable head conditions, ensuring full saturation of the samples. During the experiments, the flow and pathogen concentration were monitored. After an initial stabilization of the core, a suspension containing a known concentration of pathogens was superimposed onto the sample and allowed to drain through. Upon complete suspension drainage, several cycles of sterile saline solution (0.9 vol.%) were performed until the pathogen concentration at the outlet became negligible. A reactive transport model through saturated porous media was developed and implemented to describe the tests. The model couples conservation laws for flow and transport under variable head conditions with constitutive equations of straining and attachment/detachment. The data show significant retention of pathogens within the core during suspension drainage and rapid mobilization during distilled water infiltration. This behavior is well captured by the model and shows that rocks can act as bioreactors for pathogens that favor accumulation and growth during loading and mobilization during flooding with low-salinity water. This may suggest that porous rock deposits may exacerbate contamination of the underlying aquifers under intermittent conditions of accumulation/growth and release rather than protecting underground water resources, as generally assumed.
This topic is the objective of DY.MI.CR.ON. project “Predictive dynamics of microbiological contamination of groundwater in the earth critical zone and impact on human health (DY.MI.CR.ON Project)” funded by the European Union – Next Generation EU, mission 4 component 1, CUP I53D23000500001.

How to cite: Ghirotto, A., Prigiobbe, V., Caputo, M. C., De Giglio, O., Cassiani, G., Ekiz, M. Ç., Turturro, A. C., Savino, A. F., Colella, D., Barboza, G., Milani, M., and Verani, M.: Transport of pathogens in saturated porous rocks under variable flow and salinity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4185, https://doi.org/10.5194/egusphere-egu25-4185, 2025.

Streams and ponds used for local irrigation tend to demonstrate high spatiotemporal variability of water quality. Microbial water quality monitoring becomes overly resource-demanding if the water quality metrics are treated as purely random values. Research on several irrigation ponds and streams showed relatively stable spatial patterns of microbial and other water quality metrics. Detection of those patterns was achieved by setting 20 to 30 monitoring locations, visiting each location seven to ten times during the irrigation season, measuring the water quality metrics at each location with in situ sampling in water samples, computing relative differences between the measurements in each sampling location, computing the average value of those measurements across the water source for each visit, and finally computing the mean relative differences (MRD) for each location over all the visits. Positive MRDs indicated the preponderance of elevated values of water quality variables, and negative MRDs indicated the prevalence of low values. The nearshore locations typically had the largest MRD in ponds, and the locations with more populated stream reaches. 

Unmanned aerial vehicles were used for multispectral imaging of some ponds on each visit to several ponds before the water sampling. Both reflectance and remote sensing indices were determined at the same locations where water quality metrics were measured. The stable temporal patterns were detected for reflectance and remote sensing indices. Strong significant Spearman correlations were found between stable patterns of some water quality variables and remote sensing indices. Those correlations indicate the opportunities to use UAV-based remote sensing of irrigation water sources to inform the design of sampling water across ponds. Correlations between stable patterns of water quality variable patterns may help in developing monitoring design schemas when the more readily available water quality variable patterns are known.

Establishing temporally stable spatial patterns via the mean relative differences points to locations where monitoring locations could be placed to represent the average across the pond or stream. Also, locations with low MRDs of the microbial pollution metrics appeared to be more suitable for establishing the irrigation water intake. Overall, stable water quality patterns, when detected, can provide useful guidance for establishing and monitoring water quality for those water sources.

How to cite: Pachepsky, Y., Stocker, M., Smith, J., Widmer, J., Harriger, D., Jeon, D., Morgan, B., Hong, S., van Tassel, A., Baek, I., Dunn, L., Coffin, A., Pisani, O., and Kim, M.: Temporal stability of microbial water quality in small  irrigation water sources, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7415, https://doi.org/10.5194/egusphere-egu25-7415, 2025.

Transboundary rivers are crucial resources for drinking water, recreation, and irrigation. However, wastewater emissions and global environmental and demographic changes can impair raw water quality and pose risks to public health. This study aims to assess the impact of emissions from wastewater treatment plants, combined sewer overflows (CSOs), and inland waterway transport on microbiological water safety along the upper Danube River Basin (DRB).

To achieve this, we developed a stochastic mathematical model to trace pathogen load emissions throughout the river network. The model predicts concentrations of reference pathogens (Cryptosporidium, Giardia, Campylobacter, norovirus, enterovirus) in the river for current conditions and a future climate scenario represented by a selected CORDEX RCP 8.5 high emission scenario. The study estimates bathing water infection risks and determines the required pathogen logarithmic reduction in raw river water to ensure safe drinking water. The model accounts for exponential pathogen inactivation rates influenced by water temperature, solar ultraviolet radiation, and lake sedimentation (for protozoan cysts/oocysts). High-resolution navigational information based on automated identification system (AIS) data, detailing the number and location of ships, were used to model the impact of inland waterway transport. The data were aggregated into monthly average daily ship volumes across three ship types (cruise, passenger, and freight) along a section of the Danube River. Model validation was conducted using monthly data sets spanning 2–4 years, including cultivation-based standard fecal indicators, human-associated genetic fecal microbial source tracking markers (HF183/BacR287, BacHum), and reference pathogens (Cryptosporidium, Giardia). Additionally, the study investigates whether the crAssphage marker (CPQ_056) serves as a suitable proxy for human viral fecal contamination in water quality modeling, compared to standardized viral indicators such as somatic coliphages. To understand the effects of future changes on water safety, various scenarios and combinations up to the year 2100 are analyzed, including population growth (affecting wastewater emissions), climate change (impacting river discharge and microbial inactivation), advanced wastewater treatment, reduction of CSOs (in line with the recast of the European Urban Wastewater Treatment Directive), and changes in inland navigation and ship wastewater handling.

The findings indicate that tertiary treated municipal wastewater currently has the greatest impact on river water safety. However, if additional disinfection (quaternary treatment) is implemented, other pollution sources, such as ship navigation and CSOs, as well as climate change effects, will play an increasingly significant role in determining microbiological water safety.

How to cite: Derx, J., Valent, P., Steinbacher, S., Ameen, A., König, A.-M., Demeter, K., Linke, R., Sommer, R., Lindner, G., Schmalwieser, A. W., Walochnik, J., Kirschner, A., Mach, R. L., Cervero-Aragó, S., Zessner, M., Kittlaus, S., Blöschl, G., Stevenson, M., Blaschke, A. P., and Farnleitner, A. H.: Resilience to Future Changes: Assessing the Impact of Human Wastewater Emissions on Microbiological Water Safety Along the Danube , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8167, https://doi.org/10.5194/egusphere-egu25-8167, 2025.

To ensure the supply of clean water, we need tools to accurately predict where microorganisms of fecal origin come from, how they move in the environment and where they go to. To date, however, there have been few studies that have looked at bacterial overland transport (BOT). The current state of knowledge is mainly based on data from point sources (sewage treatment plants), whereas little is known about diffuse fecal sources from wildlife and livestock. The aim of this study is therefore to investigate the influence of the type of fecal matter (cow and red deer) as well as storage time and conditions (temperature and moisture) on resuspension and re-mobilization of (genetic) fecal indicators and/or pathogens. For this purpose standardized fecal samples from cow and deer were prepared in the laboratory and stored for different lengths of time (0 to 120 days) under diverse climatic conditions reflecting seasons. Fecal samples were then used in shaking experiments in which the samples were covered with water in Erlenmeyer flasks and placed in a shaking incubator. Different rainfall intensities were simulated by different shaking speeds (60 rpm and 85 rpm) and the effect of the rainfall duration was simulated by the duration of shaking (10 min and 60 min). Cultivation-based methods were used to determine fecal indicator organisms (FIB) such as E. coli, enterococci and Clostridium perfringens spores as well as somatic coliphages in the water. A panel of different qPCR-based DNA and/or RNA markers will then be used to determine host-associated genetic markers (qPCR). This multifactorial experimental approach provides the first quantitative estimates of the persistence and mobility of microbial target organisms in standardized fecal pellets from cattle and deer. The chosen multi-parametric and multi-method approach allows 1) comparison of culture-based with qPCR-based results and 2) comparison of RNA vs. DNA targets. NGS (next generation sequencing) data allows to draw conclusions on intestinal microbial persistence and to evaluate whether they reflect the mobilized load, an important information for the subsequent modelling approach. To summarize, the present study represents the first holistic quantitative approach to determine bacterial overland transport. The state-of-the-art combination of quantitative, microbiological and molecular methods and parameters will provide the scientific basis for accurate prediction of BOT.

How to cite: Linke, R., Zhou, Y., Lindner, G., Hochenegger, N., Borovec, T., Reischer, G., Priselac, K., Hykollari, A., Stalder, G., Sommer, R., Derx, J., and Farnleitner, A.: From the pasture to the water: multiparametric laboratory experiments to determine microbial release from feces, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8224, https://doi.org/10.5194/egusphere-egu25-8224, 2025.

Water contamination caused by enteric microbial pathogens from humans and animals poses serious risks to public health. Rainfall events can induce the release of microorganisms from feces, and the health risks posed by these pathogens to water bodies are highly dependent on their transport and survival characteristics. Novel molecular tools and diagnostic capabilities have rapidly advanced in recent years, offering significant potential to revolutionize the study of microbial contamination and transport in water bodies and to enhance the modeling of overland transport of microorganisms through the application of these advanced diagnostic methods. This study employs rainfall-release experiments and pathogen enumeration in runoff and infiltrated water to investigate bacterial release and overland transport mechanisms from fresh cow feces, aiming to address gaps in advanced molecular techniques and to assess the impacts of fecal shape and aging on the precise quantification of bacterial overland transport (BOT).

Artificial rainfall experiments are conducted on fresh cow pat samples which are placed onto bare surfaces to study bacterial release and onto small scale undisturbed soil plots to study bacterial overland transport. The experimental setup includes three rainfall intensities (40 mm/h, 60 mm/h and 80 mm/h) and two slopes (5% and 25%). In addition, the effects of different fecal shapes are investigated (large and small surface area-to-volume ratios). The quantitative analyses are done for different microbial parameters (FIB, bacterial MST markers) using both culture-based and qPCR-based methods and the effects of experimental setups, microbial parameters, and enumeration methods will be compared and evaluated. The release will be modelled using the Bradford-Schijven model formulations, and Kineros2/STWIR will be used for modelling the BOT.

This study will improve the understanding of the release and transport of manure-borne pathogens from fresh cow pats and provide a more precise quantitative approach to measuring BOT using advanced diagnostic methods.

How to cite: Zhou, Y., Linke, R., Sommer, R., Lindner, G., Strauss, P., Ramler, D., Hykollari, A., Stalder, G., Anton Schatz, R., Priselac, K., Leifels, M., Stevenson, M., Demeter, K., Paul Blaschke, A., Schijven, J., Farnleitner, A., and Derx, J.: Multiparametric Modeling of Bacterial Release and Overland Transport from Feces: Insights from Rainfall Experiments and Molecular Diagnostic Tools , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12690, https://doi.org/10.5194/egusphere-egu25-12690, 2025.

Nitrification (NI) and urease inhibitors (UI) are added as organic trace substances to agricultural land during the application of nitrogen and urea fertilizers. They inhibit the nitrification processes and urease activity in soil and thus ensure a reduced emission of gaseous ammonia and nitrous oxide. The application of UI has been mandatory since 2020 following the amendment to the German Fertilizer Ordinance, which means that increased use is to be expected. The substances can enter surface waters through translocation and leaching processes in soils. So far, the stability of NI and UI in the aqueous phase has only been investigated in ultrapure water and tap water. Therefore, the aim of this study was to investigate the stability of five NI, i. e. 1H-1,2,4-triazoles (triazole), dicyandiamides (DCD), 3,4-dimethylpyrazoles (3,4-DMP), 3-methylpyrazoles (3-MP), N-((3(5)-Methyl-1H-pyrazol-1-yl)methyl)acetamid (MPA) and one UI, i. e. N-(2-nitrophenyl)phosphoric acid triamide (2-NPT), in two natural surface waters at 20 °C and at different pH values (i. e. pH 5, 7 and 9) using batch experiments. We distinguished between the processes of hydrolysis, sorption and microbial degradation. Hence, three differently treated triplicate batch samples were set up after the removal of suspended matter (> 0.63 mm). To investigate hydrolysis, the test water was filtered through a 0.22 μm polyamide membrane. For the investigation of sorption on suspended solids, a sodium azide solution was added to the water to inactivate microorganisms (final concentration in batch samples 100 mg/L). To investigate microbial degradation, the test water was used in its natural composition. pH values were adjusted using dilute HNO₃ and NaOH, respectively. The six inhibitors were added as a mixture to each batch sample with a target concentration of 5 μg/L each. Batch samples were taken, subsequently filtered (0.45 µm, regenerated cellulose) and measured by HPLC-MS/MS over a period of 8 days for the sorption tests and 83 days for the hydrolysis and microbiological degradation experiments.

None of the investigated inhibitors showed any sorption on suspended solids. With regard to hydrolysis and microbial degradation, the results differed depending on inhibitor and pH. For MPA no decomposition by hydrolysis could be detected at all three pH values. However, MPA was microbially degraded at pH 7 and pH 9 and was no longer detectable after about 55 days. 2-NPT was hydrolytically degraded at pH 5 and 9 over the entire test period, but no hydrolysis was observed at pH 7. At pH 7, no microbial degradation could be detected for 70 days. Thus, 2-NPT is persistent at pH 7. At pH 9, our results did not show any microbial degradation for 2-NPT. The stability of inhibitors in surface waters is driven by hydrolysis and microbial degradation and may vary greatly with pH.

How to cite: Michael, L., Flores, E., Pabst, S., and Klitzke, S.: Stability of selected nitrification and urease inhibitors in surface water, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13044, https://doi.org/10.5194/egusphere-egu25-13044, 2025.

Nitrification and urease inhibitors (NI,UI) added to fertilisers can increase the availability of nitrogen to plants. By inhibiting certain processes, they could contribute to a reduction in the emission of N₂O and NH₃ compounds and a reduction in nitrate leaching. Some of these substances have already been detected in surface water and groundwater and are considered to be harmful to human health. The inhibitors are therefore an area of conflict between climate change mitigation and increased fertiliser efficiency on the one hand, and soil and groundwater protection on the other. However, knowledge of their abiotic and biotic degradation in water and saturated sediment systems is currently very limited.

The aim of this study is to determine the fate of the 6 most commonly used inhibitors 1H-1,2,4-Triazol (Triazole), Dicyandiamide (DCD), 3,4-Dimethylpyrazol (3,4-DMP), N-[(3 or 5-methyl-1H-pyrazol-1-)methyl]acetamid (MPA), 3-Methylpyrazol (3-MP) and N-(2-Nitrophenyl) phosphoric triamide (2-NPT) in surface water and saturated sandy sediments.

Triplicate batch samples containing either saturated water-sediment mixtures (solid-solution-ratio 1:3) or surface water only were spiked with six inhibitors (target concentration 1.5 µg/L each). Both sets were maintained under biotic or abiotic (autoclaved water and sediment) conditions at room temperature. The supernatant was sampled periodically for 90 days and analysed for inhibitors, pH, dissolved organic carbon and electrical conductivity.

None of the inhibitors were sorbed to the sediment except Triazole, which showed only minimal sorption of less than 10%. The urease inhibitor 2-NPT was partly decomposed by hydrolysis alone under the studied pH between 7-8.6. Degradation in general was most pronounced in the biotic water-sediment mixture where DCD and MPA were completely degraded and 3,4-DMP, 2-NPT and 3-MP were partially degraded. The Inhibitor MPA was very susceptible to biodegradation even in surface water, however, its forming metabolite 3-MP is not. Triazol was not degraded under any conditions in this study.

With the exception of Triazole, saturated sediments (for instance in a bank filtration scenario) could probably reduce most of the inhibitors’ concentrations if the microbial community is intact. However, four out of six inhibitors were not completely degraded even under biotic conditions within 90 days, making them susceptible to breakthroughs into groundwater. Therefore, their fate in the environment should be studied further.

How to cite: Zieger, A., Flores, E., Pabst, S., and Klitzke, S.: Fate of urease and nitrification inhibitors in surface water and saturated sediment, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13064, https://doi.org/10.5194/egusphere-egu25-13064, 2025.

Pesticides have been found in surface water and groundwater sources for decades. They are not only widely considered as a major threat for these waters, but also for drinking water. Not only pesticides that are still authorized by the European Commission can be found in the sources for drinking water, also banned compounds, such as atrazine (banned in 2007), still cause exceedances of environmental threshold values (as measured in 2020).

A comprehensive study was conducted in Dutch drinking water sources analyzing pesticides and their metabolites in both surface water and groundwater. Observations in surface water sources were divided in intake water and pre-treated water. For groundwater sources, observations were divided in observation wells, individual abstraction wells and all abstraction wells per particular drinking water abstraction station. Dutch drinking water standards were used as a measure of the implications for drinking water production processes.

This study shows that 156 different pesticides or metabolites were found at the nine surface water intake points considered. The standard for this substance group was exceeded on several occasions at all intake points. Pesticide residues have also been found in 40% of groundwater abstractions for drinking water production, particularly in phreatic ones (77%). This also involves a diversity of different substances. Pesticide residues exceeded the standard in 20% of groundwater abstractions. The pressure on surface water quality due to pesticides as indicated by the Removal Requirement Index seems to decrease slightly in recent years, whereas the pressure on groundwater intended for drinking water production seems to increase. Due to the diversity of pesticides found in ground- and surface water, trends are not obvious. Which and how many pesticides were observed differs between observation wells, abstraction wells and the combined abstraction wells, as well as aquifer properties.

How to cite: van Loon, A., van Driezum, I., Pronk, T., and Clevers, S.: Pesticide contamination across drinking water sources in the Netherlands, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16997, https://doi.org/10.5194/egusphere-egu25-16997, 2025.