Glyphosate binding in soil as revealed by sorption experiments and quantum-chemical modeling

Deciphering competitive interactions: Phosphate and organic matter binding on goethite through experimental and theoretical insights

The adsorption of phosphorus (P) onto active soil surfaces plays a pivotal role in immobilizing P, thereby influencing soil fertility and the filter function of soil to protect freshwater systems from eutrophication. Competitive anions, such as organic matter (OM), significantly affect the strength of this P-binding, eventually controlling P mobility and release, but surprisingly, these processes are insufficiently understood at the molecular level. In this study, we provide a molecular-level perspective on the influence of OM on P binding at the goethite-water interface using a combined experimental-theoretical approach. By examining the impact of citric acid (CIT) and histidine (HIS) on the adsorption of orthophosphate (OP), glycerol phosphate (GP), and inositol hexaphosphate (IHP) through adsorption experiments and molecular dynamics simulations, we address fundamental questions regarding P binding trends, OM interaction with the goethite surface, and the effect of OM on P adsorption. Our findings reveal the complex nature of P adsorption on goethite surfaces, where the specific OM, treatment conditions (covering the surface with OM or simultaneous co-adsorption), and initial concentrations collectively shape these interactions. P adsorption on goethite exhibits a binding strength increasing in the order of GP < OP < IHP. Crucially, this trend remains consistent across all adsorption experiments, regardless of the presence or absence of OM, CIT, or HIS, and irrespective of the specific treatment method. Notably, OP is particularly susceptible to inhibition by OM, while adsorption of GP depends on specific OM treatments. Despite being less sensitive to OM, IHP shows reduced adsorption, especially at higher initial P concentrations. Of significance is the strong inhibitory effect of CIT, particularly evident when the surface is pre-covered, resulting in a substantial 70 % reduction in OP adsorption compared to bare goethite. The sequence of goethite binding affinity to P and OM underscores a higher affinity of CIT and HIS compared to OP and GP, suggesting that OM can effectively compete with both OP and GP and replace them at the surface. In contrast, the impact of OM on IHP adsorption appears insignificant, as IHP exhibits a higher affinity than both CIT and HIS towards the goethite surface. The coverage of goethite surfaces with OM results in the blocking of active sites and the generation of an unfavorable electric potential and field, inhibiting anion adsorption and consequently reducing P binding. It is noteworthy that electrostatic interactions predominantly contribute more to the binding of P and OM to the surface compared to dispersion interactions.

Martini-Based Coarse-Grained Soil Organic Matter Model Derived from Atomistic Simulations

The significance of soil organic matter (SOM) in environmental contexts, particularly its role in pollutant adsorption, has prompted an increased utilization of molecular simulations to understand microscopic interactions. This study introduces a coarse-grained SOM model, parametrized within the framework of the versatile Martini 3 force field. Utilizing models generated by the Vienna Soil Organic Matter Modeler 2, which constructs humic substance systems from a fragment database, we employed Swarm-CG to parametrize the fragments and subsequently assembled them into macromolecules. Direct Boltzmann inversion (DBI) facilitated the determination of bonded parameters between fragments. The parametrization yielded favorable agreement in the radius of gyration and solvent-accessible surface area. Transfer free energies exhibited a strong correlation with hexadecane-water and chloroform-water values, albeit deviations were noted for octanol-water values. Comparing densities of modeled Leonardite humic acid systems at coarse-grained and atomistic levels revealed promising agreement, particularly at higher water concentrations. The DBI approach effectively reproduced average values of bonded interactions between fragments. Radial distribution functions between carboxylate groups and calcium ions showed partial agreement, however, reproducing certain peaks was challenging due to fixed bead sizes. Detailed analysis of atomistic systems revealed different configurations between the groups, explaining discrepancies. The present contribution provides a comprehensive insight into the properties, strengths, and weaknesses of the coarse-grained SOM model, serving as a foundation for future investigations encompassing pollutant interactions and varied SOM compositions.

Can calcite play a role in the adsorption of glyphosate? A comparative study with a new challenge

Calcite as a sorbent can interact with both inorganic and organic substances through their functional groups. To measure its adsorption ability, another sorbent, saponite was selected because it can sorb glyphosate, an organic compound with a polar molecule and widely used as a herbicide. In this study, the two sorbents calcite and saponite were saturated by calcium chloride, and characterized by SEM-EDX, X-ray diffraction, and Zeta Potential Analyzer to investigate their capacity to sorb glyphosate. After saturation, the saponite became homoionic Ca-saponite with minor changes in morphology and specific surface area. But, the morphology of calcite transformed from rhombohedron to scalenohedron, with an increase of 75-folds in its specific surface, and the zeta potential became positive in alkaline pH, which contradicts the results of all previous research. The modified sorbents (Ca-calcite and Ca-saponite) were added to two soil samples to investigate each sorbent's effect on glyphosate sorption. Adsorption isotherm and percentage of glyphosate desorbed revealed the difference in binding and adsorption sites. The Langmuir and Temkin models fitted isotherm data in low concentrations better and suggested chemosorption for the uptake of glyphosate. FTIR analyses of samples with and without glyphosate were compared and results suggested that the bulk of adsorption happened in siloxane groups and on calcium carbonates surfaces.

Chemical and Redox Speciation of Uranyl with Three Environmentally Relevant Bifunctional Chelates: Multi-Technique Approach Combined with Theoretical Estimations

Carbon and phosphorous are two primary elements common to the bio-geosphere and are omnipresent in both biotic and abiotic arenas. Phosphonate and carboxylate are considered as building blocks of glyphosate and humic substances and constituents of the cellular wall of bacteria and are the driving functionalities for most of the chemical interactions involving these two elements. Phosphonocarboxylates, a combination of both the functionalities in one moiety, are ideal models to dig deep into for understanding the chemical interactions of the two functional groups with metal ions. Phosphorous and carbon majorly exist as inorganic/organic phosphate and carboxylate, respectively, in the bio-geosphere. Aquatic contamination is a major concern for uranium, and the presence of complexing agents would alter the uranium concentrations in aquifers. Determination of solution thermodynamic parameters, speciation plots, redox patterns, E_h-pH diagrams, coordination structures, and molecular-level understanding by density functional theory calculations was carried out to interpret the uranyl (UO₂²⁺) interaction with three environmentally relevant phosphonocarboxylates, namely, phosphono-formic acid (PFA), phosphono-acetic acid (PAA), and phosphono-propanoic acid (PPA). UO₂²⁺ forms 1:1 complexes with the three phosphonocarboxylates in the monoprotonated form, having nearly the same stability, and the complexes [UO₂(PFAH)], [UO₂(PAAH)], and [UO₂(PPAH)] involve chelate formation of five, six, and seven membered rings, respectively, through the participation of an oxygen each from the carboxylate and phosphonate, strengthened by an intra-molecular hydrogen bonding through the proton of the phosphonate moiety with uranyl oxygen. The complex formations are favored both enthalpically and entropically, with the latter being more contributive to the overall free energy of formation. The redox speciation showed an aqueous soluble complex formation over a wide pH range of 1-8. Electrospray ionization mass spectrometry and extended X-ray absorption fine structure established the coordination modes, which are further corroborated by density functional calculations. The knowledge gained from the present studies provide potential inputs in framing the cleanup, sequestering, microbial, and bio-remediation strategies for uranyl from aquatic environments.

Influence of monoammonium phosphate on glyphosate adsorption-desorption in tropical soils: Effect of the order of sorbate additions

Glyphosate and phosphate compete for the same adsorption sites in the soil because their adsorption mechanisms are similar as the herbicide contains a phosphate group. However, how this competition occurs in relation to the order of addition of the sorbate and the composition of the soils remains unclear. The effect of the soil clay composition and the order of glyphosate and monoammonium phosphate (MAP) additions on glyphosate sorption-desorption was investigated using three inceptisols collected from Colombian rice fields. Glyphosate adsorption isotherms were evaluated using the batch equilibrium method and were modeled applying the Freundlich equation. The values for glyphosate Kfa, when evaluated alone, ranged from 14.39 to 639.86 mg1-na Lna kg-1. An agreement was found between adsorbed glyphosate, chlorites, and low initial phosphorous soil content. Preadsorbed MAP or simultaneous MAP-glyphosate additions to the soil revealed a drastic reduction in glyphosate Kfa values in soil containing the highest amount of 2 × 1 clays, but kaolinitic soils remained practically unaffected. Low desorption values could be associated with soils with the highest kaolinite content. Glyphosate remobilization was favored when the desorbing MAP solution was used in soils containing preadsorbed glyphosate. This study provides new knowledge on the effect of phosphorus fertilizers on glyphosate bioavailability in soils with different mineral compositions.

Phosphate addition enhances alkaline extraction of glyphosate from highly sorptive soils and aquatic sediments

BACKGROUND

Analytical constraints complicate environmental monitoring campaigns of the herbicide glyphosate and its major degradation product aminomethylphosphonic acid (AMPA): their strong sorption to soil minerals requires harsh extraction conditions. Coextracted matrix compounds impair downstream analysis and must be removed before analysis.

RESULTS

A new extraction method combined with subsequent capillary electrophoresis-mass spectrometry for derivatization-free analysis of glyphosate and AMPA in soil and sediment was developed and applied to a suite of environmental samples. It was compared to three extraction methods from literature. We show that no extraction medium reaches 100% recovery. The new phosphate-supported alkaline extraction method revealed (1) high recoveries of 70-90% for soils and aquatic sediments, (2) limits of detections below 20 μg kg-1 , and (3) a high robustness, because impairing matrix components (trivalent cations and humic acids) were precipitated prior to the analysis. Soil and sediment samples collected around Tübingen, Germany, revealed maximum glyphosate and AMPA residues of 80 and 2100 μg kg-1 , respectively, with residues observed along a core of lake sediments. Glyphosate and/or AMPA were found in 40% of arable soils and 57% of aquatic sediment samples.

CONCLUSION

In this work, we discuss soil parameters that influence (de)sorption and thus extraction. From our results we conclude that residues of glyphosate in environmental samples are easily underestimated. With its possible high throughput, the method presented here can resolve current limitations in monitoring campaigns of glyphosate by addressing soil and aquatic sediment samples with critical sorption characteristics.

Glyphosate, AMPA, and metsulfuron-methyl retention in the main horizons of a Typic Argiudoll

Retention is one of the processes controlling the behavior and fate of pesticides in soil. The objective of this work was to evaluate the adsorption and desorption of glyphosate, AMPA, and metsulfuron-methyl in the main horizons of a Typic Argiudoll destined for agricultural use. For this purpose, the batch equilibrium method was used at a range of concentrations for each compound. Desorption was performed in three consecutive steps after the adsorption experiment. The results obtained showed strong adsorption of glyphosate and AMPA in the three horizons, following the trend B > A > C, with weak desorption. Metsulfuron-methyl, on the other hand, showed weak adsorption in the three horizons, following the trend A > B > C, with relevant desorption. Our results allow us to identify metsulfuron-methyl as the compound that poses the greatest environmental risk in terms of the potential contamination of other areas and groundwater. However, despite their strong adsorption and weak desorption, glyphosate and AMPA also represent potential contaminants of other environmental matrices.

Degradation of glyphosate in water by the application of surface corona discharges

Glyphosate (GLP) is one of the most widely applied herbicides, and is found ubiquitously in the environment. The removal of glyphosate from waste water and soil is challenging and can be achieved with chemical or biological methods, which, nevertheless, suffer from different disadvantages. The application of a physical plasma for the removal of GLP in water was examined by the application of surface corona discharges in a wire-to-cylinder setup filled with argon. The plasma was ignited at the liquid surface without any additives. By applying a photometric method, GLP was detected after derivatisation with fluorenyl methoxycarbonyl chloride, whereas phosphate was determined with ammonium molybdate. A GLP degradation rate of 90.8% could be achieved within a treatment time of 30 minutes with an estimated energy efficiency of 0.32 g/kWh.

Interaction of glyphosate in matrices of cellulose and diethylaminoethyl cellulose biopolymers: theoretical viewpoint of the adsorption process

Glyphosate is an herbicide widely used in agricultural activities causing contamination of soils and bodies of water and damage to the biodiversity of ecosystems. In this context, the present study aimed to theoretically study the adsorption potential of the biopolymer cellulose (CE) and its diethylaminoethyl cellulose derivative (DEAEC) with the herbicide glyphosate (GLY). Theoretical calculations were performed using the density functional theory. Molecular electrostatic potential and frontier molecular orbital analyses were performed, which allowed identifying the possible sites of interaction of biopolymers that were in the functional groups -OH and O- of cellulose and in the groups -O- and -NH+(CH2CH3)2 of the DEAEC. Reactivity indices chemical softness and hardness showed that both adsorbents could interact with adsorbate. Simulated IR indicated that the interactions could be evinced in experimental measurements by changes in the bands of glyphosate (ν(P = O), δ(P-O-H), δ(C-N-H)) or in the bands of CE and DEAEC (ν(C-O), ν(C-H), ν(N-H)). The binding energies showed that the GLY interacts more effectively with CE than DEAEC. The ΔH prove that all processes are exothermic and the CE-GLY1 interaction showed value of ΔG < 0. The topological results showed a greater number of interactions with electrostatic nature. The results found in the study show that the theoretical data provides useful information to support the use of biopolymers as matrices for glyphosate adsorption or other contaminants.

Earthworm casts restrained the accumulation and phytotoxicity of soil glyphosate to cowpea (Vigna unguiculata (L.) Walp.) plants

The heavy use of glyphosate during the cultivation of glyphosate-resistant crops, would trigger the so called "pseudo-persistent" glyphosate in soil, thereby threatening agricultural environment, crop production, and human health through food safety. Such that, there is pressing need for the development of strategies for the effective management of glyphosate contamination in soil to promote cleaner agricultural production. In this study, as witnessed via characterizing the bioavailability and phytotoxicity of glyphosate to cowpea plants in soils applied with or without earthworm casts (EWCs), EWCs could significantly facilitate glyphosate desorption from soil, thus enhance its bioaccessibility, nonetheless, sharply decreased rather than increased the accumulation of glyphosate in cowpea plants via reducing the residue pool of glyphosate in the soil. Consequently, in comparison with the glyphosate-alone group, EWCs involvement triggered the increase of chlorophyll content, alleviation of ROS accumulation and lipid peroxidation of membrane, and in turn reduced the activity of a series of stress-tolerance enzymes by means of down-regulating the expression of the corresponding mRNA; ultimately, helped plants to reverse the glyphosate-induced growth suppression. Our findings demonstrated that, EWCs were promising candidate for the cost-effective and easy-to-operate remediation and reuse of glyphosate-contaminated soil, while also being able to improve the quality of the cultivated land and promote crop growth and resistance as a nutrients supplier.

The fate of a hazardous herbicide: a DFT-based ab initio study on glyphosate degradation

Glyphosate degradation has been extensively examined; however, only a few detailed computational studies have been performed on the topic so far. There are substantial differences between the degradation products of glyphosate, as AMPA (aminomethylphosphonic acid) is toxic while sarcosine intermediate is non-toxic. These species can have different effects on the environment and, indirectly, on the human body. We performed calculations using density functional theory and post-Hartree-Fock correlated ab initio methods to find the possible mechanisms for the degradation process by small (hydroxyl, peroxyl, and superoxide) radicals. We found that direct sarcosine formation is strongly dependent on the concentration of the radical species. AMPA and glycine were mostly formed as aldehyde derivatives, while in addition to the former, glyoxylate and bicarbonate are formed alternatively. A significant pH effect was also found for the competitive reactions determined by the calculated rate constants of the elementary steps. Overall barriers showed similarities by DFT but ab initio methods could separate them.

Facilitating effect of heavy metals on di(2-ethylhexyl) phthalate adsorption in soil: New evidence from adsorption experiment data and quantum chemical simulation

In terms of researching and treating farmland pollution, interactions between organic and inorganic pollutants are very important aspects. Herein, the effects of heavy metals on di(2-ethylhexyl) phthalate (DEHP) adsorption in soil were investigated. The presence of Cd²⁺/Cu²⁺ increased the adsorption capacity of DEHP (>23%) in a nonlinear manner. Fourier transform infrared spectroscopy revealed that the stretching vibration of soil functional groups changed under different pollution combinations, while quantum chemical simulation, including an independent gradient model and localized orbital locator, proved that outer-orbital complexes could be formed by electrostatic interaction between Cd²⁺/Cu²⁺ and DEHP. The electron transfer process was analyzed by charge decomposition analyses, and these, combined with bond critical point analyses, revealed that metal ions reduced DEHP stability. The binding energy and binding free energy of different combinations were calculated and analyzed, using the key soil organic matter (SOM) information obtained through pyrolysis gas chromatography mass spectrometry. This effectively explained the adsorption behavior, and showed that SOM polar functional groups played an important role in the effect of heavy metals on DEHP adsorption. The study described here has provided a new basis for understanding the multiple interactions, accumulation, and transformation of pollutants in the soil.

Pesticides in a case study on no-tillage farming systems and surrounding forest patches in Brazil

With the growing global concern on pesticide management, the relationship between its environmental recalcitrance, food security and human health has never been more relevant. Pesticides residues are known to cause significant environmental contamination. Here, we present a case study on long-term no-tillage farming systems in Brazil, where Glyphosate (GLY) has been applied for more than 35 years. GLY and its main breakdown product, aminomethylphosphonic acid (AMPA) were determined in topsoil (0-10 cm) samples from no-tillage fields and nearby subtropical secondary forests by high-performance liquid chromatography coupled with a fluorescence detector. In addition, the presence of carbamates, organochlorines, organophosphates and triazines were also screened for. GLY and AMPA were present in all soil samples, reaching values higher than those described for soils so far in the literature. A significant decrease for AMPA was observed only between the secondary forest and the farm's middle slope for site B. GLY and AMPA were observed respectively at peak concentrations of 66.38 and 26.03 mg/kg soil. GLY was strongly associated with forest soil properties, while AMPA associated more with no-tillage soil properties. Soil texture was a significant factor contributing to discrimination of the results as clay and sand contents affect GLY and AMPA retention in soils. This was the first study to report DDT and metabolites in consolidated no-tillage soils in Brazil (a pesticide fully banned since 2009). Based on human risk assessment conducted herein and the potential risk of GLY to local soil communities, this study offers a baseline for future studies on potential adverse effects on soil biota, and mechanistic studies.

The Binding of Phosphorus Species at Goethite: A Joint Experimental and Theoretical Study

Knowledge of the interaction between inorganic and organic phosphates with soil minerals is vital for improving soil P-fertility. To achieve an in-depth understanding, we combined adsorption experiments and hybrid ab initio molecular dynamics simulations to analyze the adsorption of common phosphates, i.e., orthophosphate (OP), glycerolphosphate (GP) and inositolhexaphosphate (IHP), onto the 100 surface plane of goethite. Experimental adsorption data per mol P-molecule basis fitted to the Freundlich model show the adsorption strength increases in the order GP < OP < IHP, and IHP adsorption being saturated faster followed by GP and OP. Modeling results show that OP and GP form stable monodentate (M) and binuclear bidentate (B) motifs, with B being more stable than M, whereas IHP forms stable M and 3M motifs. Interfacial water plays an important role through hydrogen bonds and proton transfers with OP/GP/IHP and goethite. It also controls the binding motifs of phosphates with goethite. Combining both experimental and modeling results, we propose that the B motif dominates for OP, whereas GP forms M and IHP forms a combination of M and 3M motifs. The joint approach plausibly explains why IHP is the predominant organically bound P form in soil. This study could be considered as a preliminary step for further studies for understanding the mechanisms of how microbes and plants overcome strong IHP–mineral binding to implement the phosphate groups into their metabolism.

The challenge of detecting the herbicide glyphosate and its metabolite AMPA in seawater - Method development and application in the Baltic Sea

The globally used herbicide glyphosate and its metabolite aminomethylphosphonic acid (AMPA) have not yet been reported to occur in the marine environment, presumably due to a lack of suitable analytical methods. In this study, we developed two new methods for the analysis of glyphosate and AMPA in seawater: a small-scale method, which includes an SPE cleanup step that minimizes salt-matrix effects during LC-MS/MS analysis, and a large-scale method that employs an additional SPE preconcentration step. Different SPE materials were evaluated for their suitability to enrich glyphosate and AMPA from saltwater and a molecularly imprinted polymer was selected. Both methods were validated in ultrapure water and environmental seawater. Achieved limits of detection with the small-scale method were 6 and 8 ng/L for glyphosate and AMPA, while the large-scale method achieved 0.12 and 0.22 ng/L, respectively. The small-scale method was used to analyze environmental samples from the Warnow Estuary in Germany. Glyphosate and AMPA could be successfully detected in the samples, but could not be measured beyond the saline estuary due to dilution and degradation effects. A set of samples from the western Baltic Sea was analyzed with the large-scale method. Glyphosate and AMPA could be detected in all Baltic Sea samples, especially at stations close to estuaries. To the best of our knowledge, this is the first report on the occurrence of glyphosate and AMPA in seawater.

Glyphosate adsorption onto kaolinite and kaolinite-humic acid composites: Experimental and molecular dynamics studies

Glyphosate (PMG) has been the most widely used herbicide in the world, and its environmental mobility and fate are mainly controlled by interactions with mineral surfaces. In soil systems, kaolinite is typically associated with humic acids (HAs) in the form of mineral-HA complexes, and hence it is crucial to characterize the molecular-scale interactions that occur between PMG and kaolinite and kaolinite-HA complexes. Batch experiments, Fourier transform infrared spectrum (FTIR) and X-ray photoelectron spectroscopy (XPS), isothermal titration calorimetry (ITC), and molecular dynamics (MD) simulations were performed to decipher the molecular interactions between PMG and kaolinite and kaolinite-HA composites. Our results reveal that kaolinite-HA composites adsorb higher concentrations of PMG than does kaolinite alone, likely due to more adsorption sites existed on kaolinite-HA than on kaolinite. FTIR and XPS analysis reveal that the carboxyl, phosphonyl and amino groups of PMG interacted with kaolinite and kaolinite-humic acid via Hydrogen bonds. The ITC results and interaction energy calculations indicate that the adsorption of PMG onto the kaolinite-HA is more energetically favorable relative to that onto kaolinite. MD simulations suggest that the PMG molecule adsorbs parallel to the surface of kaolinite and the composites through hydrogen bonding. Humic acid increases the adsorption of PMG through the creation of H-bond networks between PMG, the kaolinite surface, and humic acid. The results from this study improve our molecular-level understanding of the interactions between PMG and two important components of soil systems, and hence yield valuable information for characterizing the fate and behavior of PMG in soil environments.

Ab Initio Molecular Dynamics Simulations of the Interaction between Organic Phosphates and Goethite

Today's fertilizers rely heavily on mining phosphorus (P) rocks. These rocks are known to become exhausted in near future, and therefore effective P use is crucial to avoid food shortage. A substantial amount of P from fertilizers gets adsorbed onto soil minerals to become unavailable to plants. Understanding P interaction with these minerals would help efforts that improve P efficiency. To this end, we performed a molecular level analysis of the interaction of common organic P compounds (glycerolphosphate (GP) and inositol hexaphosphate (IHP)) with the abundant soil mineral (goethite) in presence of water. Molecular dynamics simulations are performed for goethite-IHP/GP-water complexes using the multiscale quantum mechanics/molecular mechanics method. Results show that GP forms monodentate (M) and bidentate mononuclear (B) motifs with B being more stable than M. IHP interacts through multiple phosphate groups with the 3M motif being most stable. The order of goethite-IHP/GP interaction energies is GP M < GP B < IHP M < IHP 3M. Water is important in these interactions as multiple proton transfers occur and hydrogen bonds are formed between goethite-IHP/GP complexes and water. We also present theoretically calculated infrared spectra which match reasonably well with frequencies reported in literature.

Assessment of pesticide inputs into surface waters by agricultural and urban sources - A case study in the Querne/Weida catchment, central Germany

Pesticide inputs into surface waters may cause harmful effects on aquatic life communities and substantially contribute to environmental pollution. The present study aimed at evaluating the input pathways in the Querne/Weida catchment (central Germany) to efficiently target mitigation measures of pesticide losses. Relevant pesticide substances were measured in surface waters in agricultural and urban surroundings and in soil samples within the catchment area. Pesticides application data from farmers were analyzed. Additionally, batch tests were performed to determine sorption and degradation of relevant pesticides for site specific soil properties. Frequency of detection, number of pesticides and maximum concentrations were much higher in the surface water samples in mainly urban surroundings compared to those in agricultural surrounding. The most frequently detected substances were glyphosate, AMPA, diflufenican and tebuconazole in surface water samples and diflufenican, boscalid, tebuconazole and epoxiconazole in the topsoil samples. Glyphosate and AMPA contributed to the highest concentrations in surface water samples (max. 58 μg L^-1) and soil samples (max. 0.19 mg kg^-1). In most cases, pesticide detections in surface water and soil were not consistent with application data from farmers, indicating that urban sources may affect water quality in the catchment area substantially. However, it was observed that pesticide substances remain in the soil over a long time supported by sorption on the soil matrix. Therefore, delayed inputs into surface waters could be suspected. For the implementation of reduction measures, both urban and agricultural sources should be considered. Novel findings of the study: pesticide detections were not consistent with application data from farmers, urban sources contributed substantially to pesticide pollution of surface waters.

Molecular level picture of the interplay between pH and phosphate binding at the goethite-water interface

The soil pH plays a substantial role in controlling phosphorus (P) adsorption and mobilization. These processes are strongly affected by the phosphate interaction strength with P-fixing soil minerals such as goethite. The target of the current contribution is to draw a molecular level picture of the interplay between pH and phosphate binding at the goethite-water interface via a joint experimental-theoretical approach. Periodic density functional theory (DFT) calculations were carried out to provide a molecular level understanding of the pH dependence of P adsorption. To validate the modeling approach, adsorption experiments of phosphate at goethite were performed in the pH range of 4-12. There was agreement between experiments and simulations in the description of the adsorption behavior by two pH-dependent successive stages. The adsorption increases along the pH change from 4 to 8. A further increase of pH leads to a decrease of adsorption. By comparing with literature data it is concluded that the first stage will be observed only if there is no significant change of the surface charge at low pH. Moreover, the molecular modeling results point to the abundance of the monodentate (M) binding motif at both extremely low and high pH ranges. Otherwise, the bidentate (B) one is predominant along the intermediate pH range. These observations could resolve the existing debate about the assignment of phosphate-goethite binding motifs. Furthermore, the results point to a decrease of pH upon phosphate sorption due to an induced acidification of soil solution. The present joint experimental-theoretical approach provides a better understanding and description of the existing phosphate sorption experiments and highlights new findings at the atomistic/molecular scale.

Assessment of the Synergic Effect between Lysinibacillus sphaericus S-Layer Protein and Glyphosate in the Lethality of the Invasive Arboviral Vector Aedes albopictus

Glyphosate and glyphosate-based herbicides are among the most used chemicals in plant pest control. Both glyphosate and its main by-product Aminomethylphosphonic Acid (AMPA) are highly environmentally persistent and, through several processes (including surface runoff and bioaccumulation), affect species beyond their intended targets, especially in aquatic ecosystems. Aedes albopictus is a novel invasive arboviral vector in Colombia and has spread to much of the national territory in recent years. Strains of the bacterium Lysinibacillus sphaericus have shown the ability to degrade glyphosate into environmentally inert compounds, in addition to having great larvicidal efficiency in different mosquito species through the production of several proteins, including the surface layer (S-Layer) protein. The S-Layer is a bacterial structure consisting of glycoprotein monomers, and its functions are thought to include bacterial interactions, protection from the outside medium and biological control. The study assessed the entomopathogenic activity of L. sphaericus S-Layer protein on Ae. albopictus larvae, and the effects that glyphosate and its by-products have in this process. To that end, bioassays were performed to compare the larval mortality between different treatments with and without S-Layer, glyphosate, and glyphosate derivates. Comparisons were made through Analysis of variance (ANOVA) and Tukey's Honestly Significant Difference (HSD) analyses. Significant differences were found in larval mortality in the treatments, and larval mortality was greater when the S-Layer protein was present, though glyphosate field-doses (1.69 g/L) alone had a notable toxicity as well. An apparent synergic effect on the mortality of larval Ae. albopictus when exposed to mixtures containing 1500 ppm of the S-Layer protein, glyphosate, and/or glyphosate derivates was found. Further studies are needed for the in-depth understanding of this mechanism and its consequences on aquatic ecosystems.

Molecular modelling of sorption processes of a range of diverse small organic molecules in Leonardite humic acid

Soil organic matter (SOM) is abundant in the environment and plays an important role in several biogeochemical processes, including microbial activity, soil aggregation, plant growth and carbon storage. One of its key functions is the retention and release of various chemical compounds, primarily governed by the sorption process, which strongly affects the environmental fate of nutrients and pollutants. Sorption largely depends on the composition of SOM, as well as its structure, dynamics and the thermodynamic conditions. Although several approaches are available, experimental characterization of sorption mechanisms is not easy. Computational models for predicting sorption coefficients often require a wealth of experimental data for training and are only applicable to compounds and conditions related to the training dataset. Here, we use molecular dynamics (MD) simulations to study the sorption of a range of small organic compounds. As a model SOM system we use the standard Leonardite humic acid (LHA) sample, which physicochemical properties have recently been characterized computationally in detail. This model allowed us to estimate sorption propensities of the systems at two different hydration levels (water activities close to 0 and 1), showing a remarkable correlation with experimental data. Importantly, this molecular modelling approach based on perturbation free-energy calculations is rigorously derived from statistical thermodynamics and requires no experimental sorption data for training. It is therefore in principle applicable to any SOM model or thermodynamic condition. Moreover, the power of MD simulations to provide high-resolution insight into atomistic and molecular interactions was employed to explore how sorbate molecules associate with the LHA matrix and which contacts they form. The heteroatoms of both sorbate and sorbent play an important role and water molecules are identified as further key players in facilitating the sorption process.

HIGHLIGHTS

Modelling of the sorption processes in soil organic matter at atomistic level.Rigorous, physics-based approach applicable to a range of SOM systems and conditions.Remarkable level of matching with experimental data with additional insight into the molecular mechanism.Interactions between the sorbate and local environment strongly affects the sorption process.

Interaction between glyphosate and montmorillonite in the presence of artificial seawater

Glyphosate (N- (phosphonomethyl) glycine) is one of the most widely used herbicides in the world. In the literature, there are several studies describing the interaction between glyphosate and clay minerals. However, there is a lack of data of this interaction in marine environments. In this research, we examined the adsorption of glyphosate onto montmorillonite in the presence of artificial seawater. Mössbauer data showed that the interaction of the phosphonate group of glyphosate with Fe²⁺ of montmorillonite prevents its oxidation to Fe³⁺. X-ray diffractograms showed that glyphosate adsorption takes place only onto the montmorillonite surface and not in its interlayers. Infrared spectroscopy data demonstrate that the interaction between glyphosate and montmorillonite could be through the amino group. FT-IR spectra of aqueous solutions of salts of seawater showed that Ca²⁺ interacts with glyphosate of the phosphonate group, thus causing an increase in its adsorption onto montmorillonite. However, glyphosate dissolved in 0.50 mol L⁻¹ NaCl and 0.034 mol L-1MgCl2 solutions showed the lowest adsorption onto montmorillonite. In addition, the adsorption of glyphosate onto montmorillonite decreased when the NaCl concentration increased. The results fitted the Sips isotherm model, probably because the Ca²⁺ interacts with glyphosate, making the adsorption process more homogeneous. Thus, n values for Freundlich and Sips isotherm models decreased with an increase in ionic strength. Glyphosate and ions of artificial seawater increased the pH_pzc of montmorillonite.

Leaching and degradation of 13C2-15N-glyphosate in field lysimeters

Glyphosate (GLYP), the globally most important herbicide, may have effects in various compartments of the environment such as soil and water. Although laboratory studies showed fast microbial degradation and a low leaching potential, it is often detected in various environmental compartments, but pathways are unknown. Therefore, the objective was to study GLYP leaching and transformations in a lysimeter field experiment over a study period of one hydrological year using non-radioactive 13C2-15N-GLYP labelling and maize cultivation. 15N and 13C were selectively measured using isotopic ratio mass spectrometry (IR-MS) in leachates, soil, and plant material. Additionally, HPLC coupled to tandem mass spectrometry (HPLC-MS/MS) was used for quantitation of GLYP and its main degradation product aminomethylphosphonic acid (AMPA) in different environmental compartments (leachates and soil). Results show low recoveries for GLYP (< 3%) and AMPA (< level of detection) in soil after the study period, whereas recoveries of 15N (11-19%) and 13C (23-54%) were higher. Time independent enrichment of 15N and 13C and the absence of GLYP and AMPA in leachates indicated further degradation. 15N was enriched in all compartments of maize plants (roots, shoots, and cobs). 13C was only enriched in roots. Results confirmed rapid degradation to further degradation products, e.g., 15NH4+, which plausibly was taken up as nutrient by plants. Due to the discrepancy of low GLYP and AMPA concentrations in soil, but higher values for 15N and 13C after the study period, it cannot be excluded that non-extractable residues of GLYP remained and accumulated in soil.

QM/MM simulations of organic phosphorus adsorption at the diaspore-water interface

Phosphorus (P) immobilization and thus its availability for plants are mainly affected by the strong interaction of phosphates with soil components especially soil mineral surfaces. The related reactions have been studied extensively via sorption experiments especially by carrying out adsorption of ortho-phosphates onto Fe-oxide surfaces. But a molecular-level understanding of the P-binding mechanisms at the mineral-water interface is still lacking, especially for forest eco-systems. Therefore, the current contribution provides an investigation of the molecular binding mechanisms for two abundant phosphates in forest soils, inositol hexaphosphate (IHP) and glycerolphosphate (GP), at the diaspore mineral surface. Here a hybrid electrostatic embedding quantum mechanics/molecular mechanics (QM/MM) based molecular dynamics simulation has been applied to explore the diaspore-IHP/GP-water interactions. The results provide evidence for the formation of different P-diaspore binding motifs involving monodentate (M) and bidentate (B) for GP and two (2M) as well as three (3M) monodentates for IHP. The interaction energy results indicated the abundance of the GP B motif compared to the M one. The IHP 3M motif has a higher total interaction energy compared to its 2M motif, but exhibits a lower interaction energy per bond. Compared to GP, IHP exhibited stronger interaction with the surface as well as with water. Water was found to play an important role in controlling these diaspore-IHP/GP-water interactions. The interfacial water molecules form moderately strong H-bonds (HBs) with GP and IHP as well as with the diaspore surface. For all the diaspore-IHP/GP-water complexes, the interaction of water with the diaspore exceeds that with the studied phosphates. Furthermore, some water molecules form covalent bonds with diaspore Al atoms while others dissociate at the surface to protons and hydroxyl groups leading to proton transfer processes. Finally, the current results confirm the previous experimental conclusions indicating the importance of the number of phosphate groups, HBs, and proton transfers in controlling the P-binding at soil mineral surfaces.

Electrochemical method to study the environmental behavior of Glyphosate on volcanic soils: Proposal of adsorption-desorption and transport mechanisms

Glyphosate is used extensively worldwide, but current evidence suggests detrimental effects on the environment, pollinators, and human health. Glyphosate adsorption kinetics and adsorption/desorption were studied through batch sorption experiments in ten typical volcanic ash-derived soils from Andisol and Ultisol orders. Two kinetic models were used to fit the experimental data: i. Models that allowed establishment of principally kinetic parameters and modeling of the adsorption process, and ii. Models described solute transport mechanisms commonly used for remediation purposes. Adsorption kinetic data were best fitted by the pseudo-second-order kinetic model and Two-Site Nonequilibrium model. These models suggest that mechanisms are complex due to rapid surface adsorption in ultisols with mass transfer controlling adsorption kinetics across the boundary layer, as indicated by the highhand lowt_1/2values. High intraparticle diffusion into macropores and micropores was observed for Andisols. The Freundlich model accurately represented adsorption equilibrium data in all cases (R² > 0.9580) with comparatively higher adsorption capacity on Andisols. K_f values (2.50-52.28 μg^1-1/n mL^1/n g^-1) and hysteresis were significant in all studied soils. Taken together, these data suggest that Glyphosate may be adsorbed more on Andisol soils in comparison to Ultisols.

Adsorption of glyphosate on Brazilian subtropical soils rich in iron and aluminum oxides

We investigated the adsorption of glyphosate onto five subtropical soils of Paraná and São Paulo states, Brazil, a region of intense agricultural activities, aiming at the determination of kinetic and isotherm adsorption parameters which enable the evaluation of the potential leaching of the herbicide. The adsorption was fast, being described by the pseudo-second order and intraparticle diffusion models, thus suggesting that mixed mechanisms are involved. The Oxisol containing the highest concentrations of metal oxides (209.5 g kg-1 Fe2O3 and 160.2 g kg-1 Al2O3) was the sample with the highest rate constant, indicating the adsorption sites are readily available. All the soils are rich in aluminum and iron oxides, explaining the Freundlich coefficients (KF) between 642 and 1360 mg1-1/n kg-1 L1/n, which are higher than most of the coefficients described for other soils around the world. The maximum desorption (15% of the adsorbed amount) was observed for the Oxisol. For the other soils, desorption ranged from 2 to 7%. These results suggest that the leaching of free glyphosate to nearby surface and groundwaters is unlikely unless excessive doses are used. The adsorption parameters are useful for managing the right doses applied to the crops, thus avoiding contamination of adjacent areas.

Modeling the mobility of glyphosate from two contrasting agricultural soils in laboratory column experiments

Glyphosate (GLP) currently is one of the most widely used herbicides worldwide. The persistence of GLP and its major metabolite, aminomethylphosphonic acid (AMPA) in the environment has been described by other authors. This study was aimed at comparing the GLP and AMPA behavior in sandy and loamy sand soils after spiking with enhanced (445 µg g-1) concentrations of GLP in herbicide KLINIK® (Nufarm, Austria) and bioaugmentation followed by 40 days weathering and a consistent three-stage leaching in a laboratory column experiment. Soil samples were obtained from mineral topsoil (0-10 cm) within former agricultural lands where soil parent material was formed by glacigenic deposits. The total amount of GLP and AMPA collected during three leaching stages was significantly (p<.05) higher from columns with sandy soil, compared to loamy sand soil. Bioaugmentation resulted in considerably lower concentrations of AMPA in leachates, especially in the sets with sandy soil (p=.01). Leachates were tested using FTIR spectroscopy and Daphnia magna. Statistical analysis of the changes in Ntot, Ctot, K+, Mg2+, Al3+, Ca2+, Mn2+ and Fe3+ concentrations in soils after the leaching experiment revealed that the loamy sand soil was likely to be more sensitive to the addition of GLP and bioaugmentation than sandy soil.

Foliar Roundup application has minor effects on the compositional and functional diversity of soil microorganisms in a short-term greenhouse experiment

The herbicide Roundup (and glyphosate, its active ingredient) is extensively used for weed control on a worldwide scale. It is absorbed after foliar application and quickly translocated inside the plant. In this study, we investigated the effects of Roundup speed, a commercial glyphosate formulation, on the structural composition (dominance of microbial groups, phospholipid fatty acid analysis - PLFA) and functional diversity (use of carbon sources, Multiple Substrate Induced Respiration - MSIR) of soil microorganisms. We specifically aimed at understanding the potential impact of biotic interactions on herbicide effects and included plants, earthworms, and endomycorrhizal fungi in the experimental setup. For this, we grew clover (Trifolium repens) in the greenhouse and added mycorrhizal inoculum (Glomus mosseae) and earthworms (Lumbricus terrestris) to the pots. Two weeks after foliar Roundup application and subsequent plant death, the pots were destructively sampled. The application resulted in a significant increase of microbial respiration (SIR) by approximately 30%. A multivariate analysis of the MSIR data exhibited small but significant differences between the microbial communities of treated and untreated pots, while no significant difference was apparent for the PLFA data. Bacterial PLFAs generally decreased following herbicide application, while mycorrhizal and fungal PLFAs were not affected. We did not find a consistent difference between the fatty acid markers of gram negative and gram positive bacteria. For all investigated parameters, there were highly significant differences between the upper (0-5 cm depth) and lower (5-10 cm) soil layers. The fact that rooting density differed by a factor of 3.5 between the two layers indicated that herbicide effects were especially pronounced in the clover rhizosphere and were likely due to changes in root exudate composition. We found significant, though very small, interactions between Roundup and other experimental factors (especially mycorrhizal inoculum).

Influence of metal ions on glyphosate detection by FMOC-Cl

Glyphosate (GLP, N-(phosphonomethyl)glycine) is the most important broadband herbicide in the world, but discussions are controversial regarding its environmental behaviour and distribution. Residue analyses in a variety of environmental samples are commonly conducted by HPLC-MS where GLP needs to be derivatised with 9-fluoromethoxycarnonyl chloride (FMOC-Cl). Since this derivatisation reaction was suspected to be inhibited by metal ions in the sample matrix, the present study provides a comprehensive experimental study of the effect of metal ions (Al3+, Ca2+, Cd2+, Co2+, Cu2+, Fe2+, Fe3+, Mg2+, Mn2+, Zn2+) on derivatisation and GLP recovery. Results show that some metals (Cd2+, Co2+, Cu2+, Mn2+ and Zn2+) decreased the GLP recovery down to 19 to 59%. Complementary, quantum chemical modelling of 1:1 GLP-metal complexes as well as their reactivity with respect to FMOC-Cl was performed. Here, a decrease in reactivity of FMOC-Cl towards GLP-metal complexes is observed; i.e. the reaction is non-spontaneous in contrast to the free GLP case. The present results are in accord with previous studies and provide an explanation that full GLP recovery in different matrices was never reached. Remedy strategies to compensate for the inhibition effect are explored such as pH adjustment to acidic or alkaline conditions or addition of ethylenediaminetetraacetic acid (EDTA). In general, our results question the use of internal isotopic labelled standards (ILS) since this presupposes the presence of the analyte and the ILS in the same (free) form.

Effect of temperature, pH and total organic carbon variations on microbial turnover of 13C315N-glyphosate in agricultural soil

Glyphosate is the best-selling and the most-used broad-spectrum herbicide worldwide. Microbial conversion of glyphosate to CO2 and biogenic non-extractable residues (bioNER) leads to its complete degradation. The degradation of glyphosate may vary in different soils and it depends on environmental conditions and soil properties. To date, the influence of temperature, soil pH and total organic carbon (TOC) on microbial conversion of glyphosate to bioNER has not been investigated yet. The pH or TOC of an agricultural original soil (pH 6.6, TOC 2.1%) was modified using sulfuric acid or farmyard manure (FYM), respectively. Each treatment: original (I), 3% TOC (II), 4% TOC (III), pH 6.0 (IV) and pH 5.5 (V) was amended with 13C315N-glyphosate and incubated at 10 °C, 20 °C and 30 °C for 39 days. The temperature was the main factor controlling the mineralization and the extractable 13C315N-glyphosate, whereas higher TOC content and lower pH resulted in enhanced formation of 13C-bioNER. After 39 days the cumulative mineralization of 13C-glyphosate was in the range of 12-22% (10 °C), 37-47% (20 °C) and 43-54% (30 °C). Extractable residues of 13C-glyphosate were in the range of 10-21% (10 °C) and 4-10% (20 °C and 30 °C); whereas those of 15N-glyphosate were as follows 20-32% (10 °C) and 12-25% (20 °C and 30 °C). The 13C-NER comprised about 53-69% of 13C-mass balance in soils incubated at 10 °C, but 40-50% in soils incubated at 20 °C and 30 °C. The 15N-NER were higher than the 13C-NER and varied between 62% and 74% at 10 °C, between 53% and 81% at 20 °C and 30 °C. A major formation of 13C-bioNER (72-88% of 13C-NER) at 20 °C and 30 °C was noted in soil amended with FYM. An increased formation of 15N-bioNER (14-17% of 15N-NER) was also observed in FYM-amended soil. The xenobiotic 15N-NER had a major share within the 15N-NER and thus need to be considered when assessing the environmental risk of glyphosate-NER.

Adsorption-desorption and leaching potential of glyphosate and aminomethylphosphonic acid in acidic Malaysian soil amended with cow dung and rice husk ash

This study investigates adsorption-desorption and the leaching potential of glyphosate and aminomethylphosphonic acid (AMPA) in control and amended-addition of cow dung or rice husk ash-acidic Malaysian soil with high oxide mineral content. The addition of cow dung or rice husk ash increased the adsorptive removal of AMPA. The isotherm data of glyphosate and AMPA best fitted the Freundlich model. The constant Kf for glyphosate was high in the control soil (544.873 mg g-1) followed by soil with cow dung (482.451 mg g-1) then soil with rice husk ash (418.539 mg g-1). However, for AMPA, soil with cow dung was high (166.636 mg g-1) followed by soil with rice husk ash (137.570 mg g-1) then the control soil (48.446 mg g-1). The 1/n values for both glyphosate and AMPA adsorptions were < 1 indicating their strong affinity for adsorbents. Desorption of both glyphosate and AMPA occurred only in the control soil. The compounds were not detected in soils with added cow dung or rice husk ash. The addition of cow dung or rice husk ash increased glyphosate mobility. However, ground water ubiquity scores for both control and amended soils were < 2.8. This indicated glyphosate is a transitional herbicide; therefore, its leaching potential in the soil is low, despite the addition of cow dung or rice husk ash. Addition of these wastes decreased the mobility and leaching potential of AMPA. The addition of cow dung or rice husk ash could be beneficial in increasing adsorption and enhancing degradation of these compounds.

Glyphosate Transport in Two Louisiana Agricultural Soils: Miscible Displacement Studies and Numerical Modeling

Glyphosate (N-(phosphonomethyl) glycine) (GPS) is currently the most commonly used herbicide worldwide, and is generally considered as immobile in soils. However, numerous reports of the environmental occurrence of the herbicide coupled with recent evidence of human toxicity necessitate further investigation as to the behavior of GPS in the soil environment. Batch sorption studies along with miscible displacement experiments were carried out in order to assess the mobility of GPS in two Louisiana agricultural soils; Commerce silt loam and Sharkey clay. Batch results indicated a high affinity of both soils for solvated GPS, with greater affinity observed by the Sharkey soil. GPS sorption in the Commerce soil was most likely facilitated by the presence of amorphous Fe and Al oxides, whereas the high cation exchange capacity of the Sharkey soil likely allows for GPS complexation with surface exchangeable poly-valent cations. Miscible displacement studies indicate that GPS mobility is highly limited in both soils, with 3% and 2% of the applied herbicide mass recovered in the effluent solution from the Commerce and Sharkey soils, respectively. A two-site multi-reaction transport model (MRTM) adequately described GPS breakthrough from both soils and outperformed linear modeling efforts using CXTFIT. Analysis of extracted herbicide residues suggests that the primary metabolite of GPS, aminomethylphosphonic acid (AMPA), is more mobile in both soils, although both compounds are strongly retained.

On the degradation pathway of glyphosate and glycine

The degradation in water of the most widespread herbicide, glyphosate, is still under debate. Experimental disagreements on this process exist and there are only a few theoretical studies to support any conclusions. Moreover, the relationship between glyphosate and glycine is underestimated. Besides the structural similarity, glycine is a product of glyphosate degradation; hence, their studies are complementary. In this study, two mechanisms for the decomposition of the glyphosate molecule and glycine molecule in water are proposed. These mechanisms were explored by using quantum mechanical calculations. A combined microsolvation/PCM approach was employed to find and characterize their transition states, by which the reaction pathways were determined via the IRC method. The results have shown that the degradation processes might occur via a C-C bond cleavage, through a concerted mechanism, whereby the proton transfers and the CO2 detachments occur simultaneously. The second mechanism had two consecutive steps, a decarboxylation followed by the proton transfers. The water molecules served as a conduit for the proton transfers, away from the amine group (or the phosphonate, glyphosate case). Their function was to assist the reactions in a water-mediated decarboxylation. In these particular cases, the free energy of activation was 42.68 and 42.28 kcal mol-1 for the glycine structure and the glyphosate structure, respectively. These results agreed with the photodegradation and thermodegradation of glyphosate, as well as with the spontaneous decarboxylation of glycine. A concerted mechanism might be expected to yield C-P and C-N bond cleavages in the glyphosate molecule.

Molecular level investigation of the role of peptide interactions in the glyphosate analytics

The detection of the herbicide glyphosate (GLP) in environmental samples is most often conducted after derivatizing the target molecule with the chromophore 9-fluorenylmethyloxycarbonyl chloride (FMOC-Cl). However, this method is sensitive to all primary and secondary amines, which can occur in the sample matrix as well. In order to quantify the interference of primary and secondary amines on GLP detection, we have used well-defined peptides such as pentaglycine (PG) and albumin as well as mixtures of peptides such as peptone. These peptides have been added to the derivatization solution of GLP at different constant concentration levels and UV extinction coefficients have been determined. Data analysis supported by quantum chemical modeling of the GLP-peptide, FMOC-GLP, and FMOC-peptide complexation reactions facilitated the identification of two interfering impacts of peptide on GLP derivatization: (i) increase of the signal due to reaction with FMOC-Cl leading to an overestimation of GLP concentration and (ii) decrease of GLP recovery due to complex formation and therefore inhibition of GLP derivatization, which leads to an underestimation. Specifically, our results indicated that the GLP-peptide- and peptide-FMOC-interactions are mainly affected by type of interfering peptides as well as concentration of each peptide and GLP in the environmental samples.

Unravelling the nature of glyphosate binding to goethite surfaces by ab initio molecular dynamics simulations

Investigation of the interaction between glyphosate (GLP) and soil minerals is essential for understanding GLP's fate in the environment. Whereas GLP-goethite binding has been discussed extensively, the impact of water as well as of different goethite surface planes has not been studied yet. In this contribution, periodic density functional theory-based molecular dynamics simulations are applied to explore possible binding mechanisms for GLP with three goethite surface planes (010, 001, and 100) in the presence of water. The investigation included several binding motifs of monodentate (M) and bidentate (B) type. It was found that the binding stability increases in the order M@001 < M@010 < (2O + 2Fe) B@100 < M@100 < (1O + 2Fe) B@001 < (2O + 1Fe) B@010. This behavior has been traced to the presence of intramolecular H-bonds (HBs) in GLP as well as intermolecular HBs between GLP and water, GLP and goethite, and water and goethite. These interactions are accompanied by proton transfer from GLP to water and to goethite, and from water to goethite as well as water dissociation at the goethite surface. Further, it was observed that the OH^- species can replace the adsorbed GLP at the goethite surface, which could explain the well-known drastic drop in GLP adsorption at high pH. The present results highlight the role of water in the GLP-goethite interaction and provide a molecular level perspective on available experimental data.