Synthetic phenolic antioxidant additives are commonly used to prevent oxidative degradation in various materials, but they present significant challenges due to their non-renewable origins and potential health risks. This study explores the synthesis of novel arylindane diols-specifically diisoeugenol (DiE) and diisoallylsyringol (DiAS)-and evaluates their potential as safer and more sustainable alternatives. Using zeolite catalysis, a highly selective pathway for synthesizing DiE through the dimerization of the lignin-derived monomer isoeugenol (IE) was demonstrated. The synthesis of DiAS and diisoallylphenol (DiAP) enabled further exploration of how structural differences, such as o-methoxy groups, affect the physicochemical and toxicological properties of these arylindanes. The antioxidant activity of the compounds was tested using ABTS and DPPH assays, revealing strong radical-scavenging capabilities. Furthermore, oxidation onset temperature (OOT) measurements in polypropylene (PP) formulations containing these antioxidants showed improved thermal stability, matching or surpassing that of commercial antioxidants. Toxicological evaluations, including cytotoxicity tests on human gingival fibroblasts and an estrogenic activity (EA) screening using the CALUX assay, indicated low levels of EA and cytotoxicity. These results highlight the potential of DiE and DiAS as effective, renewable, and safe lignin-derived antioxidants for industrial applications.

Metal concentrations and distributions in a Belgian agricultural soil and the impact of manure application were studied. Most metal contaminants, except Pb and Co, reached their highest levels in winter (between 1.7 and 5.3 times higher than in other seasons) due to manure application. The vertical metal profiles in the soil also varied seasonally because of agricultural activities and plant growth. Meanwhile, sequential extraction on the soil solid phase pointed out that on an annual basis, Cd, Co, and Mn were primarily present in the exchangeable fraction at 42, 34 and 41 % respectively (also Ni was quite present in the exchangeable fraction at 20 %), that Pb was in the reducible fraction at 52 %, while Cr and Fe were more enriched in the residual fraction at 66 and 64 %, respectively. In addition, metal interactions between soil porewater and solid phase were investigated by using the passive sampling technique of Diffusive Gradients in Thin-films (DGT) and the one-dimensional DGT-induced flux in sediments (1D-DIFS) model. These results suggest a high release rate of Cd, Co, Mn and Ni from the soil solid phase to the pore water, and a low release rate of Cr, Cu, Fe and Pb. Therefore, the first group of metals poses a much greater risk for plant uptake and intoxication than the second group of metals.

Polycyclic aromatic hydrocarbons (PAHs) and their methylated derivatives (Me-PAHs) are (semi-)persistent environmental pollutants with significant toxicological risks. While targeted and non-targeted analyses are effective at identifying individual compounds, they fail to assess the combined biological effects of complex mixtures. This study developed an H1L7.5c1 cell line-based reporter gene assay. Key parameters such as cell density, exposure time, and exposure medium were optimized to enhance the assay sensitivity, precision, and robustness. Our bioassay achieved a limit of detection (LOD) of 0.13-nM benzo[a]pyrene (BaP) equivalents and an effective concentration (EC50) of 1.1 ± 0.1 nM BaP. A relative potency (REP) library was built for 16 PAHs and 5 Me-PAHs. Application to groundwater and wastewater effluent revealed correlations between bioassay-derived and chemically-derived bioequivalent quantity. A close match was observed in groundwater, but more complex wastewater effluent matrices suggested the presence of additional AhR-active compounds. A mixture analysis using a Generalized Response Addition model revealed no significant synergistic or antagonistic interactions among the sample mixtures. This study highlights the potential of using H1L7.5c1 cell line-based bioassay as a rapid and sensitive screening tool for (Me-)PAHs monitoring in environmental samples. It offers a valuable tool for Effect-Based Monitoring and assessment under the EU Water Framework Directive.

In this study, a reactive transport model using HYDRUS-2D is built for an agricultural field in Kinrooi (Belgium), irrigated with treated wastewater through a sub-irrigation system. The model evaluates groundwater level fluctuations and transformations of NH₄⁺, NO₂⁻, and NO₃⁻ within the unsaturated zone and groundwater over a three-year period. Hydrodynamic and reactive transport components were calibrated against high-resolution groundwater level time series and nitrogen compound concentrations. Model shows that sub-irrigation raised groundwater levels by up to 0.4 m during dry periods, while after irrigation ceased, groundwater levels declined nonlinearly, with roughly half of the increase dissipating within the first month and the remainder gradually returning to baseline over the following three months. Although sub-irrigation slightly affected nitrogen transport and leaching, these impacts were spatially limited to irrigated zone and diminished one month after irrigation ended where concentrations within unsaturated zone for NH₄⁺ and NO2⁻ decreases by 10 %. Groundwater concentrations remained below permitted threshold values in both irrigated and non-irrigated zones. Elevated background nitrate from long-term fertilizer use reduced the relative effect of sub-irrigation on groundwater nitrate. Scenario analyses further revealed that natural processes, including plant uptake, sorption, and particularly nitrification and denitrification play a key role in regulating NH₄⁺ and NO₃⁻ concentrations, while their absence leads to higher concentrations due to reduced transformation and retention.

The expansion and development of aquaculture activities in the Tam Giang–Cau Hai lagoon system, including the Thuy Tu and Cau Hai lagoons, has generated waste that impacts the natural environment. This research focused on assessing the isotopic compositions of carbon and nitrogen in suspended organic matter within the aquaculture ponds and surrounding ecosystems of the Thuy Tu and Cau Hai lagoons. The isotopic fingerprints of organic carbon and nitrogen in suspended matter showed significant differences between the Thuy Tu and Cau Hai lagoons, depending on the sampling period (March and July). The ratio of particulate organic carbon to particulate nitrogen (POC/PN) in suspended matter indicated a substantial contribution from phytoplankton. A mixing model was applied to determine the impact of aquaculture waste on the Thuy Tu and Cau Hai lagoons. By quantifying the contributions of each carbon and nitrogen source, this study successfully evaluated the significant influence of artificial fertilizer source on both lagoons for the first time. Fertilizer contributions relating to aquaculture activities increased progressively with distance in Thuy Tu lagoon, while in the Cau Hai lagoon, the impact of fertilizers came from both aquaculture activities and agricultural production.

ObjectivesResin composites may release bisphenol A (BPA) due to impurities present in the monomers. However, there is a lack of knowledge regarding the leaching characteristics of BPA from resin composites. Therefore, experimental resin composites were prepared with known amounts of BPA. The objective of this study was (1) to determine which amount of BPA initially present in the material leaches out in the short term and, (2) how this release is influenced by the resin composition.MethodsBPA (0, 0.001, 0.01, or 0.1 wt%) was added to experimental resin composites containing 60 mol% BisGMA, BisEMA(3), or UDMA, respectively, as base monomer and 40 mol% TEGDMA as diluent monomer. Polymerized samples (n = 5) were immersed at 37 °C for 7 days in 1 mL of water, which was collected and refreshed daily. BPA release was quantified with UPLC-MS/MS after derivatization with pyridine-3-sulfonyl chloride.ResultsBetween 0.47 to 0.67 mol% of the originally added BPA eluted from the resin composites after 7 days. Similar elution trends were observed irrespective of the base monomer. Two-way ANOVA showed a significant effect of the base monomer on BPA release, but the differences were small and not consistent.SignificanceThe released amount of BPA was directly proportional to the quantity of BPA present in the resin composite as an impurity. BPA release was mainly diffusion-based, while polymer composition seemed to play a minor role. Our results underscore the importance for manufacturers only to use monomers of the highest purity in dental resin composites to avoid unnecessary BPA exposure in patients.

Estrogens are contaminants in the Scheldt estuary due to a dense population and intense industrial and anthropogenic activities, but their levels and evolution in this estuary are not well studied. Here we investigated estrogenic activity (EA) in the dissolved, particulate and sediment compartments of the estuary using the Estrogen Receptor (ER)-Chemical Activated Luciferase Gene Expression (CALUX) bioassay, in recent and historical samples. EA ranges between 7-168, 2.16-22.5 and 1.8-38.2 pg E2-equivalents g-1 in the dissolved, particulate and sediment phases of the Scheldt, respectively. The partitioning coefficient (Kd) between the particulate and dissolved phases is about 2000 L kg-1. EA levels in the estuarine sediments decreased during the last 40 years, but the strongest decrease, from 112 to 28 pg E2-equivalents g-1, is observed in the upper estuary. The mass loadings of dissolved and particulate estrogens discharged into the North Sea amount to 7.5 and 1.6 μg s-1, respectively. Future monitoring of the estrogen levels in various compartments of the Scheldt is necessary considering its strong environmental impact on living organisms and human beings.

In this study, hazardous wastes including fluff, dust, and scrubbing sludge were sampled in 2019 from two metal shredding facilities located in Wallonia, Belgium. To assess the extent of the contamination, a global approach combining chemical and biological techniques was used, to better reflect the risks to health and the environment. The samples investigated induced significant in vitro aryl hydrocarbon receptor (AhR) agonistic bioactivities and estrogenic receptor (ERα) (ant)agonistic bioactivities in the respective CALUX (chemical activated luciferase gene expression) bioassays. The mutagenicity of the samples was investigated with the bacterial reverse gene mutation test using the Salmonella typhimurium TA98 and TA100 strains. Except for the sludge sample (site 3), all samples induced a mutagenic response in the TA98 strain (± S9 metabolic fraction) whereas in the TA100 strain (+ S9 metabolic fraction), only the sludge sample (site 2) showed a clear mutagenic effect. The in vivo toxicity/teratogenicity of the shredder wastes was further evaluated with zebrafish embryos. Except for the dust sample (site 2), all samples were found to be teratogenic as they returned teratogenic indexes (TIs) > 1. The high levels of contamination, the mutagenicity, and the teratogenicity of these shredder wastes raise significant concerns about their potential negative impacts on both human health and environment.

Increased human activity in the Antarctic Peninsula combined with accelerated melting of its glaciers highlights the importance of monitoring trace element concentrations. Surface sediment samples were collected around King George Island, Hope Bay and in the Bransfield Strait in February 2020 and were analysed by X-ray fluorescence spectroscopy and inductively coupled plasma mass spectrometry. The methods display a good correlation. Our results show clear distinctions between these regions for selected elements with high local heterogeneities. Hope Bay exhibited lower concentrations of Fe, Mn, Co, V, Zn while most stations in the Bransfield Strait and around King George Island showed moderate to significant enrichment in Cu, As and Cd. Twelve stations presented a moderate ecological risk. The consistency of our values supports a natural rather than anthropogenic origin, possibly related to volcanism and the geology of the area. However, our results suggest an increase in Cr that should be further investigated.

Dental composites remain under scrutiny regarding their (long-term) safety. In spite of numerous studies on the release of monomers both in vitro and in vivo, only limited quantitative data exist on the in vivo leaching of degradation products from monomers and additives. The aim of this observational study was for the first time to quantitatively and qualitatively monitor the release of parent compounds and their degradation products in saliva from patients undergoing multiple restorations. Five patients in need of multiple large composite restorations (minimally 5 up to 28 restorations) due to wear (attrition, abrasion, and erosion) were included in the study, and they received adhesive restorative treatment according to the standard procedures in the university clinic for Restorative Dentistry. Saliva was collected at different time points, starting before the restoration up until 24 h after the treatment with composite restorations. Saliva extracts were analyzed by liquid chromatography–mass spectrometry. Leaching of monomers and degradation products was highest within 30 min after the placement of the restorations. The highest median concentrations of monomers were recorded for UDMA, BisEMA-3, and TEGDMA; yet, besides BisEMA-3 and TEGDMA, no monomers could be detected after 24 h. Mono- and demethacrylated degradation products remained present up to 24 h and concentrations were generally higher than those of monomers. In patients with multiple restorations, degradation products were still present in the sample taken before the next operation, several weeks after the previous operation. Exposure to residual monomers and degradation products occurs in the first hours after restoration. Monomers are present in saliva shortly after restoration, but degradation products can be detected weeks after the restoration confirming a long-term release. Future research should focus more on the release of degradation products from monomers and additives from resin-based materials given their prolonged presence in saliva after restoration.

Under the pressure of global droughts and water shortage, it is essential to evolve toward a sustainable and robust water system. One possible avenue is the maximum reuse of treated wastewater, but the quality of which determines its reuse. Therefore, inorganic (Cd, Pb, Cr, Ni, Cu, and As) and organic (xenoestrogens and polycyclic aromatic contaminants, PACs) contaminants were monthly monitored in an effluent of the wastewater treatment plant (WWTP), the surrounding surface waters and the local groundwater in Belgium. Dissolved and particulate concentrations of inorganic contaminants in these water bodies were analyzed. In addition, Diffusive Gradients in Thin-films (DGT) was used in situ to obtain bioavailable metal fractions. In the WWTP effluent and surface waters, only Ni exceeds the Annual Average-Environmental Quality Standard (AA-EQS), while in the groundwater, dissolved As was the predominant element. Moreover, in the surface and effluent waters the highest lability degrees were observed for Cd and Ni. The concentrations of these metal species in the effluent water were lower than in the other water bodies. Micro-organic pollutants, xenoestrogens and PACs were analyzed by dual Estrogen and Aryl hydrocarbon Receptor - Chemical Activated LUciferase gene eXpression (ER & AhR-CALUX) assays. Since the annual averaged (AA) bioequivalent concentration of E2 (0.18 ng/L) is below the AA-EQS standard (0.4 ng/L), and the bioequivalent concentration of benzo[a]pyrene never exceeded the maximum admissible concentration (MAC), the reclamation and reuse of treated wastewater for groundwater replenishment and agricultural irrigation should pose no environmental problems, at least in a short-term.

Bisphenol A (BPA) is an industrial chemical that has been used for the manufacturing of polycarbonate plastics, epoxy resins and other consumer products, including food contact materials and dental resins. However, its petrochemical origin and adverse health effects, such as xeno-oestrogenic activity (EA), pose a challenge for sustainability. Here we show a green synthetic pathway towards genuinely sustainable BPA alternatives from a renewable lignin source. At the heart of this production route is a selective alkylation reaction between bio-based arene (for example, guaiacol) and alkene (for example, isoeugenol) molecules, catalysed by a recyclable zeolite catalyst H-USY. Zeolite catalysis favours regioselectivity and prompts higher reaction rate and chemoselectivity, enabling high yields of bisguaiacols. The synthesized bisguaiacols can be valorized into high-molecular-weight thermoplastic and thermosetting polymers with promising thermophysical properties, showcasing their potential as BPA replacements. This work progresses beyond the state of the art by demonstrating that renewability is not only a goal but also a means for safer chemicals. Bisphenol A (BPA) is an essential building block for manufacturing plastics, but its adverse health effects have become a major concern. Here the authors show a zeolite-catalysed synthetitic route to bio-renewable BPA alternatives that feature excellent safety and preserve efficacy of function.

Estrogenic substances (ES) in an urban river Zenne (BE) dominated by wastewater effluents were assessed over the course of one year. To measure the bioequivalent (BEQ) 17 β-estradiol (E2) concentrations of ES, the biological effect-based methodology - the Chemical-Activated LUciferase gene eXpression (CALUX) bioassay was used. Daily water discharges were collected from January 2015 to February 2016 at or near the sampling stations in the Brussels Capital Region. An annual water budget shows that approximately 50% of the Zenne River flow downstream is from wastewater effluent. The estrogenic activity and yearly average ES load in influents and effluents of wastewater treatment plants (WWTPs) located in the North and South, combined sewer overflows (CSOs) and the Zenne River, were assessed for upstream and downstream of two WWTPs of Brussels. Both WWTPs with activated sludge treatment remove more than 90% of the ES. The influent concentrations of ES at the South and North WWTPs ranged from 30-359 and 18-55 ng E2 eq./L, respectively. The effluent concentrations of ES ranged from 1.0-2.1 and 1.1-6.6 ng E2 eq./L at WWTP-S and -N, respectively. The yearly average ES loads were 0.05-0.14 and 0.39-1.5 g E2 eq./d for WWTP-S and -N, respectively. The temporal variation of E2-eq concentrations at the river stations Z3 and Z5 (upstream) ranged from 1 to 2 ng E2 eq./L, while the ES activity at sites Z9 and Z11 (downstream) varied from 2-17 ng E2 eq./L and from 1-8 ng/L ng E2 eq./L, respectively. The relative ES loads to the Zenne River are as follows: WWTPs (31%), CSOs (27%), upstream Zenne (15%), a missing source (14%), and local tributaries (13%). ES in the Zenne River behave in a pseudo-persistent manner because of continuous input from the WWTPs and slow degradation in the 18 km river stretch. The BEQ concentration of E2 exceeds the EU environmental quality standards (EQS) of 0.4 ng E2/L throughout the Zenne River.

Introduction: Many natural or synthetic compounds used in foods, dietary supplements, and food contact materials (FCMs) are suspected endocrine disruptors (EDs). Currently, scientific evidence to predict the impacts on biological systems of ED mixtures is lacking. In this study, three classes of substances were considered: i) phytoestrogens, ii) plant protection products (PPP) and iii) substances related to FCMs. Fourteen compounds were selected based on their potential endocrine activity and their presence in food and FCMs.Methods: These compounds were evaluated using an in vitro gene expression assay, the ERα-CALUX, to characterize their responses on the estrogen receptor alpha. Cells were exposed to fixed ratio mixtures and non-equipotent mixtures of full and partial agonists. The concentration-response curves measured for the three classes of compounds were characterized by variable geometric parameters in terms of maximum response (efficacy), sensitivity (slope) and potency (median effective concentration EC50). To account for these variations, a generic response addition (GRA) model was derived from mass action kinetics.Results: Although GRA does not allow us to clearly separate the concentration addition (CA) and independent action (IA) models, it was possible to determine in a statistically robust way whether the combined action of the chemicals in the mixture acted by interaction (synergy and antagonism) or by additive behavior. This distinction is crucial for assessing the risks associated with exposure to xenoestrogens. A benchmark dose approach was used to compare the response of phytoestrogen blends in the presence and absence of the hormone estradiol (E2). At the same time, 12 mixtures of 2–5 constituents including phytoestrogens, phthalates and PPPs in proportions close to those found in food products were tested. In 95% of cases, the response pattern observed showed a joint and independent effect of the chemicals on ER.Discussion: Overall, these results validate a risk assessment approach based on an additive effects model modulated by intrinsic toxicity factors. Here, the CA and IA approaches cannot be distinguished solely based on the shape of the concentration response curves. However, the optimized GRA model is more robust than CA when the efficacy, potency, and sensitivity of individual chemical agonists show large variations.

Objectives: There is still much debate about the release of bisphenol A (BPA) from resin-based dental materials. Therefore, this study aimed to quantify BPA present as an impurity and to evaluate whether their degradation by salivary, bacterial, and chemical challenges could increase its release. Methods: BPA was determined in three different amounts (300, 400, and 500 mu g) of eight unpolymerized resinbased materials (four composites, one fissure sealant, two adhesives and one root canal sealer). Next, polymerized samples (n = 5) of each material were immersed in 1 mL of whole human pooled saliva collected from adults, Streptococcus mutans (2 x 107 CFU/mL), and acidic (0.1 M HCl), alkaline (0.1 M NaOH), and control media, respectively. The amount of BPA was quantified using an UPLC-MS/MS method including derivatization of BPA by pyridine-3-sulfonyl chloride. Results: Only the composites contained trace amounts of BPA above the limit of quantification (ranging from 301 +/- 32 pg PBA/mg to 1534 +/- 62 pg BPA/mg), most likely as impurity from the synthesis of the monomers. The amounts of BPA released from polymerized materials upon salivary and bacterial degradation were too low for accurate quantification, but in water, quantifiable amounts of BPA were released from all materials. In alkaline media, the BPA release from two composites was significantly decreased, while the release from one adhesive was significantly increased, compared to water. Conclusions: BPA already present in unpolymerized resin-based materials may account for the release of BPA after polymerization. There was no clear indication that short-term material degradation leads to increased release of BPA.

Effluents of sewage treatment plants (STPs) are an important source of estrogenic substances to the receiving water bodies affecting their ecological safety. In this study, steroids, bisphenol A (BPA) and phthalates were assessed in the secondary (SE) and tertiary effluent (TE) of three typical urban STPs in Beijing (China). In addition, the overall estrogenic activity in these effluents was assessed by an in-vitro bioassay (ERE-CALUX). Results showed that the concentrations and activities of estrogenic compounds in TE were lower than those in SE. The residual concentration of 178-estradiol (E2) was the highest among the detected steroids, accounting for 51.6 +/- 5.1% in SE and 57.5 +/- 24.8% in TE. The residual level (25.2-41.6 ng/L) of BPA in effluents was significantly higher than that of steroids (0.2-28.8 ng/L). The residual concentration of diethyl phthalate was the highest among the detected phthalates accounting for 47.1 +/- 5.1% in SE and 37.6 +/- 11.5% in TE. Steroids and BPA had a higher removal rate (83.5% and 96.7%) in secondary and tertiary treatment than phthalates (68.8% and 83.1%). The hydrophobic characteristics of these estrogenic compounds determined the removal mechanism. The removal of steroids, BPA, dimethyl phthalate and diethyl phthalate (LogKow= 1.61-4.15) mainly occurred through biodegradation in the water phase, while the removal of dibutyl phthalate, butylbenzyl phthalate and di(2-ethylhexyl) phthalate (LogKow= 4.27-7.50) mainly occurred in the solid phase after adsorption on and sedimentation of the suspended particulate matter. According to ERE-CALUX, the estrogenic activity in the final STP effluents was 3.2-45.6 ng E2-equivalents/L, which is higher than reported levels in the effluents of European STPs. Calculation of estrogenic equivalents by using substance specific chemical analysis indicated that the dominant contributor was E2 (56.4-88.4%), followed by 17 alpha-ethinylestradiol (EE2) (4.1-34.8%), both also exerting a moderate risk to the aquatic ecosystem. While the upgrade of treatment processes in STPs has efficiently reduced the emission of estrogenic substances, their ecological risk was not yet phased out.

Objectives: Only little is known about degradation of methacrylate monomers. Therefore, using in vitro chemical and saliva degradation this study aimed to identify the degradation products of organic compounds present in resin-based dental materials. Methods: Ten dental monomers and nine polymerized dental resin-based materials were immersed for 24 h in chemical media (0.1 M HCl, 0.1 M NaOH) and human pooled saliva in order to identify leached monomers and degradation products from chemical and saliva degradation. Samples were analyzed using liquid chromatography coupled to high -resolution mass spectrometry to identify previously unknown degradation products. Results: During in vitro chemical degradation, uncured monomers were rapidly hydrolyzed into monoand demethacrylated degradation products. During chemical degradation in alkaline conditions of polymerized materials, considered the worst-case scenario, only degradation products could be detected. In acidic conditions, monomers and their degradation products were detected. In addition, different additives such as EDMAB, DMPA and HMBP were present in acidic degradation samples. Degradation in human pooled saliva for 24 h to mimic the in vivo situation, resulted in the identification of both monomers and their degradation products.

Re-use of treated wastewater is receiving increasing attention as method to reduce water stress resulting from population growth, socio-economic development and climate change. In 2018, the European Commission issued a policy strategy entailing minimum water quality requirements for water re-use for agriculture and aquifer recharge. However, the environmental impact of such solution is yet to be determined. The VUB in collaboration with private and public sector partners set up a field experiment in Kinrooi (Belgium) in which the effects of re-using treated domestic wastewater for sub-irrigation of an agricultural field are monitored. This is an interdisciplinary project which includes analyses of the effects on water quality and quantity in the subsurface saturated and unsaturated zone and nearby surface water, the effects on crops as well as research on the public perception. Within this project, one of the aims is to create an advection-dispersion groundwater transport model to investigate how the chemical composition of the shallow groundwater would change after the treated domestic wastewater is applied through sub-irrigation. Observation data of tracers of the re-used water in the groundwater are needed to calibrate the transport model. Therefore, it is critical to choose a suitable tracer, allowing to unambiguously tell apart the effluent and groundwater end members. Literature suggests the use of chemical properties such as stable isotopes and Cl/Br ratios to use as wastewater tracers. Stable isotopes of hydrogen and oxygen are investigated, but the focus is currently on the use of Cl/Br ratios, which shows promising results. The use of this ratio as tracer is based on the close to ideal conservative behaviour of bromide and chloride ions in water caused by their small size and hydrophilic characteristics. This implies that physical processes such as dilution and evaporation happening in the environment influence the absolute concentrations of the ions but leaves their ratio constant. At the moment, 21 monitoring wells are installed on the field of which 9 monitoring wells have been sampled for data on Cl/Br tracers. In general, the results indicate that finding a suitable tracer is not straightforward because chemical and isotopic compositions of the groundwater and treated wastewater are often similar. Therefore, the research continues to focus on improving the analytical methods used to analyse the currently used tracers (e.g. Cl/Br ratio and stable isotopes) and on the selection of other tracers such as anthropogenic organic compounds (e.g. pharmaceuticals and artificial sweeteners) to quantify the influence of the effluent end member and to enhance modelling performance.

The population of the semi-arid areas of the countries in the East African Rift Valley (EARV) is faced with serious problems associated with the availability and the quality of the drinking water. In these areas, the drinking water supply largely relies on groundwater characterised by elevated fluoride concentration (> 1.5 mg/L), resulting from interactions with the surrounding alkaline volcanic rocks. This geochemical anomaly is often associated with the presence of other naturally occurring potentially toxic elements (PTEs), such as As, Mo, U, V, which are known to cause adverse effects on human health. This study reports on the occurrence of such PTEs in the groundwater on the populated flanks of Mt. Meru, an active volcano situated in the EARV. Our results show that the majority of analysed PTEs (Al, As, Ba, Cd, Cr, Cu, Fe, Mn, Ni, Se, Sr, Pb, and Zn) are within the acceptable limits for drinking purpose in samples collected from wells, springs and tap systems, suggesting that there is no immediate health risk associated with these PTEs. However, some of the samples were found to exceed the WHO tolerance limit for U (> 30 μg/L) and Mo (> 70 μg/L). The sample analysis also revealed that in some of the collected samples, the concentrations of total dissolved solids, Na+ and K+ exceed the permissible limits. The concerning levels of major parameters and PTEs were found to be associated with areas covered with debris avalanche deposits on the northeast flank, and volcanic ash and alluvial deposits on the southwest flanks of the volcano. The study highlights the need to extend the range of elements monitored in the regional groundwater and make a more routine measurement of PTEs to ensure drinking water safety and effective water management measures.

It took several consecutive years of devastating droughts sweeping through Europe, causing substantial economic losses, for many to realise how urging it is to improve the water directives, making critical sectors like agriculture more resilient to a changing climate. Shrinking water supplies and growing demand further forced stakeholders to seek alternative sources, drawing their attention to projects previously considered economically unjustified. Therefore, water re-use and reclamation became one of the EU’s priorities fulfilling the ambitions of the European Green Deal to implement circular water management strategies. To facilitate the transition and support new legislation, in-depth research in the feasibility and environmental impacts of aquifer recharge with reclaimed wastewater is essential. The GROW project investigates this issue on multiple levels, among which the effect of reclamation of wastewater through aquifer recharge on local and regional scale groundwater levels. At the experimental site in Kinrooi, Belgium, the groundwater levels are closely monitored with automatic submersible data loggers installed in 21 monitoring wells distributed on the investigated agricultural field and its vicinity. Data on water levels in the underlying Quaternary, porous aquifer are collected hourly and are verified through monthly manual measurements taken to ensure an unhindered operation of the infrastructure. A distributed, transient-state flow model is used to simulate the groundwater table’s response to the effluent sub-irrigation at the desired rate. The model’s flexibility also allows making predictions of the aquifer behaviour under changing climatic conditions by augmenting the soil-water balance model with revised weather data. The model’s performance is tested against the high temporal resolution dataset obtained from the monitoring network. Attention is also paid to the experiment’s effect on the water levels in the adjacent hydrological network, while the effluent is partly rerouted from the hitherto used surface water discharge to the sub-irrigation system. The data collected in our experiment is used to determine the capability of the aquifer to store and recover the reclaimed wastewater during drought periods. That would reduce the demand for traditional, inefficient surface irrigation and increase the climate resilience of the agricultural sector in Flanders. Together with data from similar projects carried out throughout Europe, our results can be used to facilitate long-expected EU legislation enabling circular water use. To support this process, we also investigate the impact of the re-use of treated wastewater for agriculture on groundwater quality and the public perception of this sensitive issue.