MLe-KCNQ2: An Artificial Intelligence Model for the Prognosis of Missense KCNQ2 Gene Variants.

Despite the increasing availability of genomic data and enhanced data analysis procedures, predicting the severity of associated diseases remains elusive in the absence of clinical descriptors. To address this challenge, we have focused on the KV7.2 voltage-gated potassium channel gene (KCNQ2), known for its link to developmental delays and various epilepsies, including self-limited benign familial neonatal epilepsy and epileptic encephalopathy. Genome-wide tools often exhibit a tendency to overestimate deleterious mutations, frequently overlooking tolerated variants, and lack the capacity to discriminate variant severity. This study introduces a novel approach by evaluating multiple machine learning (ML) protocols and descriptors. The combination of genomic information with a novel Variant Frequency Index (VFI) builds a robust foundation for constructing reliable gene-specific ML models. The ensemble model, MLe-KCNQ2, formed through logistic regression, support vector machine, random forest and gradient boosting algorithms, achieves specificity and sensitivity values surpassing 0.95 (AUC-ROC > 0.98). The ensemble MLe-KCNQ2 model also categorizes pathogenic mutations as benign or severe, with an area under the receiver operating characteristic curve (AUC-ROC) above 0.67. This study not only presents a transferable methodology for accurately classifying KCNQ2 missense variants, but also provides valuable insights for clinical counseling and aids in the determination of variant severity. The research context emphasizes the necessity of precise variant classification, especially for genes like KCNQ2, contributing to the broader understanding of gene-specific challenges in the field of genomic research. The MLe-KCNQ2 model stands as a promising tool for enhancing clinical decision making and prognosis in the realm of KCNQ2-related pathologies.

Multiclass Determination of Endocrine-Disrupting Chemicals in Meconium: First Evidence of Perfluoroalkyl Substances in This Biological Compartment.

Major concerns have been raised about human exposure to endocrine-disrupting chemicals (EDCs) during pregnancy. Effective methodologies for the assessment of this exposure are needed to support the implementation of preventive measures and the prediction of negative health effects. Meconium has proven a valuable non-invasive matrix for evaluating cumulative exposure to xenobiotics during the last two trimesters of pregnancy. The study objective was to develop a novel method to determine the presence in meconium of perfluoroalkyl substances (PFASs), bisphenols, parabens, and benzophenones, EDCs that are widely used in the manufacture of numerous consumer goods and personal care products, including cosmetics. Ten PFASs, two bisphenols, four parabens, and four benzophenones were measured in meconium samples prepared by using a combination of Captiva Enhanced Matrix Removal (EMR) lipid cartridges with salt-assisted liquid-liquid extraction (SALLE) and dispersive liquid-liquid microextraction (DLLME) before the application of liquid chromatography-tandem mass spectrometry (LC-MS/MS). Experimental parameters were optimized by applying different chemometric techniques. Limits of detection ranged from 0.05 to 0.1 ng g-1, and between-day variabilities (relative standard deviations) ranged from 6.5% to 14.5%. The method was validated by matrix-matched standard calibration followed by a recovery assay with spiked samples, obtaining percentage recoveries of 89.9% to 114.8%. The method was then employed to measure compounds not previously studied in this matrix in 20 meconium samples. The proposed analytical procedure yields information on cumulative in utero exposure to selected EDCs.

Molecular dynamics simulations of the calmodulin-induced α-helix in the SK2 calcium-gated potassium ion channel.

The family of small-conductance Ca2+-activated potassium ion channels (SK channels) is composed of four members (SK1, SK2, SK3, and SK4) involved in neuron-firing regulation. The gating of these channels depends on the intracellular Ca2+ concentration, and their sensitivity to this ion is provided by calmodulin (CaM). This protein binds to a specific region in SK channels known as the calmodulin-binding domain (CaMBD), an event which is essential for their gating. While CaMBDs are typically disordered in the absence of CaM, the SK2 channel subtype displays a small prefolded α-helical region in its CaMBD even if CaM is not present. This small helix is known to turn into a full α-helix upon CaM binding, although the molecular-level details for this conversion are not fully understood yet. In this work, we offer new insights on this physiologically relevant process by means of enhanced sampling, atomistic Hamiltonian replica exchange molecular dynamics simulations, providing a more detailed understanding of CaM binding to this target. Our results show that CaM is necessary for inducing a full α-helix along the SK2 CaMBD through hydrophobic interactions with V426 and L427. However, it is also necessary that W431 does not compete for these interactions; the role of the small prefolded α-helix in the SK2 CaMBD would be to stabilize W431 so that this is the case. In conclusion, our findings provide further insight into a key interaction between CaM and SK channels that is important for channel sensitivity to Ca2+.

Do calmodulin binding IQ motifs have built-in capping domains?

Most calmodulin (CaM) targets are α-helices. It is not clear if CaM induces the adoption of an α-helix configuration to its targets or if those targets are selected as they spontaneously adopt an α-helical conformation. Other than an α-helix propensity, there is a great variety of CaM targets with little more in common. One exception to this rule is the IQ site that can be recognized in a number of targets, such as those ion channels belonging to the KCNQ family. Although there is negligible sequence similarity between the IQ motif and the docking site on SK2 channels, both adopt a similar three-dimensional disposition. The isolated SK2 target presents a pre-folded core region that becomes fully α-helical upon binding to CaM. The existence of this pre-folded state suggests the occurrence of capping within CaM targets. In this review, we examine the capping properties within the residues flanking this core domain, and relate known IQ motifs and capping.

An epilepsy-causing mutation leads to co-translational misfolding of the Kv7.2 channel.

BACKGROUND: The amino acid sequence of proteins generally carries all the necessary information for acquisition of native conformations, but the vectorial nature of translation can additionally determine the folding outcome. Such consideration is particularly relevant in human diseases associated to inherited mutations leading to structural instability, aggregation, and degradation. Mutations in the KCNQ2 gene associated with human epilepsy have been suggested to cause misfolding of the encoded Kv7.2 channel. Although the effect on folding of mutations in some domains has been studied, little is known of the way pathogenic variants located in the calcium responsive domain (CRD) affect folding. Here, we explore how a Kv7.2 mutation (W344R) located in helix A of the CRD and associated with hereditary epilepsy interferes with channel function. RESULTS: We report that the epilepsy W344R mutation within the IQ motif of CRD decreases channel function, but contrary to other mutations at this site, it does not impair the interaction with Calmodulin (CaM) in vitro, as monitored by multiple in vitro binding assays. We find negligible impact of the mutation on the structure of the complex by molecular dynamic computations. In silico studies revealed two orientations of the side chain, which are differentially populated by WT and W344R variants. Binding to CaM is impaired when the mutated protein is produced in cellulo but not in vitro, suggesting that this mutation impedes proper folding during translation within the cell by forcing the nascent chain to follow a folding route that leads to a non-native configuration, and thereby generating non-functional ion channels that fail to traffic to proper neuronal compartments. CONCLUSIONS: Our data suggest that the key pathogenic mechanism of Kv7.2 W344R mutation involves the failure to adopt a configuration that can be recognized by CaM in vivo but not in vitro.

Subcutaneous ivermectin for the treatment of the hyperinfection syndrome by Strongyloides stercoralis / [Ivermectina subcutánea en el tratamiento de un síndrome de hiperinfección por Strongyloides stercoralis].

Strongyloidiasis is a disease caused by the nematode Strongyloides stercoralis that is endemic in rural regions in tropical and subtropical countries. Immunosuppressed patients have an increased risk of infection by this parasite and are at risk of developing a hyperinfection syndrome which involves a higher risk of death. The syndrome is treated with ivermectin, however, there is no parenteral presentation of this medication for human use in Colombia or the world, which is an important problem in patients who have compromised enteral absorption, for instance, those with intestinal obstructions. We present a case of hyperinfection syndrome by Strongyloides stercoralis in Colombia, which was treated with subcutaneous ivermectin. Our purpose is to encourage pharmacokinetic and pharmacodynamic studies to establish this route of administration in the future as an alternative for those patients who have a high risk of therapeutic failure with the oral route.

La estrongiloidiasis es una enfermedad causada por el nematodo Strongyloides stercoralis, endémico en las regiones rurales de los países tropicales y subtropicales. Los pacientes inmunosuprimidos tienen un mayor riesgo de infección con este parásito y pueden terminar desarrollando un síndrome de hiperinfección que conlleva un alto riesgo de muerte. En el tratamiento se utiliza la ivermectina, pero, ni en Colombia ni en el mundo, existe una presentación parenteral del medicamento para uso en humanos, lo cual es un problema en aquellos pacientes que puedan tener comprometida la absorción intestinal, como es el caso de aquellos con obstrucciones intestinales. Se reporta el caso de un síndrome de hiperinfección por S. stercoralis en Colombia tratado con ivermectina subcutánea; la idea al presentarlo es incentivar los estudios de farmacocinética y farmacodinamia que analicen esta vía de administración como alternativa para el tratamiento de pacientes con riesgo de fracaso terapéutico con la vía oral.

Ivermectina subcutánea en el tratamiento de un síndrome de hiperinfección por Strongyloides stercoralis / Subcutaneous ivermectin for the treatment of the hyperinfection syndrome by Strongyloides stercoralis

La estrongiloidiasis es una enfermedad causada por el nematodo Strongyloides stercoralis, endémico en las regiones rurales de los países tropicales y subtropicales. Los pacientes inmunosuprimidos tienen un mayor riesgo de infección con este parásito y pueden terminar desarrollando un síndrome de hiperinfección que conlleva un alto riesgo de muerte. En el tratamiento se utiliza la ivermectina, pero, ni en Colombia ni en el mundo, existe una presentación parenteral del medicamento para uso en humanos, lo cual es un problema en aquellos pacientes que puedan tener comprometida la absorción intestinal, como es el caso de aquellos con obstrucciones intestinales. Se reporta el caso de un síndrome de hiperinfección por S. stercoralis en Colombia tratado con ivermectina subcutánea; la idea al presentarlo es incentivar los estudios de farmacocinética y farmacodinamia que analicen esta vía de administración como alternativa para el tratamiento de pacientes con riesgo de fracaso terapéutico con la vía oral.

Strongyloidiasis is a disease caused by the nematode Strongyloides stercoralis that is endemic in rural regions in tropical and subtropical countries. Immunosuppressed patients have an increased risk of infection by this parasite and are at risk of developing a hyperinfection syndrome which involves a higher risk of death. The syndrome is treated with ivermectin, however, there is no parenteral presentation of this medication for human use in Colombia or the world, which is an important problem in patients who have compromised enteral absorption, for instance, those with intestinal obstructions. We present a case of hyperinfection syndrome by Strongyloides stercoralis in Colombia, which was treated with subcutaneous ivermectin. Our purpose is to encourage pharmacokinetic and pharmacodynamic studies to establish this route of administration in the future as an alternative for those patients who have a high risk of therapeutic failure with the oral route.

Bisphenol A and other phenols in human placenta from children with cryptorchidism or hypospadias.

Embryo-foetal exposure to low doses of endocrine disrupting chemicals (EDCs) has been related to reproductive tract diseases in experimental animals but not convincingly in human populations. The aim of this case-control study was to explore the relationship between exposure to non-persistent EDCs during pregnancy and male genital development. Exposure to bisphenol-A (BPA), benzophenones (BPs) [BP-1, BP-2, BP-3, BP-6, BP-8 and 4-hydroxybenzophenone (4-OH-BP),] and parabens (PBs) [methyl-, ethyl-, propyl- and butyl-PB] was analyzed by means of ultra-high performance liquid chromatography-tandem mass spectrometry in placenta samples from a subsample of 28 cases and 51 healthy controls nested in a cohort of newborns recruited between 2000 and 2002. The multivariable regression analyses indicated a statistically significant association between exposure to BPA and propyl-PB and the risk of malformations [adjusted odd ratio (95% CIs) in the third tertile of exposure: 7.2 (1.5-35.5) and 6.4 (1.2-35.5) for BPA and propyl-PB, respectively].

Sensitive determination of parabens in human urine and serum using methacrylate monoliths and reversed-phase capillary liquid chromatography-mass spectrometry.

A method for the determination of parabens in human urine and serum by capillary liquid chromatography (cLC) with UV-Vis and mass spectrometry (MS) detection using methacrylate ester-based monolithic columns has been developed. The influence of composition of polymerization mixture was studied. The optimum monolith was obtained with butyl methacrylate monomer at 60/40% (wt/wt) butyl methacrylate/ethylene dimethacrylate ratio and 50wt% porogens (composed of 36wt% of 1,4-butanediol, 54wt% 1-propanol and 10wt% water). Baseline resolution of analytes was achieved through a mobile phase of acetonitrile/water in gradient elution mode. Additionally, dispersive liquid-liquid microextraction (DLLME) was combined with both cLC-UV-Vis and cLC-MS to achieve the determination of parabens in human urine and serum samples with very low limits of detection. Satisfactory intra- and inter-day repeatabilities were obtained in UV-Vis and MS detection, although the latter provided lower detection limits (up to 300-fold) than the UV-Vis detection. Recoveries for the target analytes from spiked biological samples ranged from 95.2% to 106.7%. The proposed methodology for the ultra-low determination of parabens in human urine and serum samples is simple and fast, the consumption of reagents is very low, and very small samples can be analyzed.

Multiclass method for the determination of quinolones and ß-lactams, in raw cow milk using dispersive liquid-liquid microextraction and ultra high performance liquid chromatography-tandem mass spectrometry.

An analytical method based on a sample treatment by dispersive liquid-liquid microextraction (DLLME) followed by ultra high performance liquid chromatography-tandem mass spectrometry analysis (UHPLC-MS/MS) for the determination of 17 quinolones and 14 ß-lactams (penicillins and cephalosporins) in raw cow milk, was validated according to the European Commission guidelines as cited in the Decision 2002/657/EC. The extraction efficiency of the DLLME depends on several parameters such as the nature and volumes of extractant and dispersive solvents, pH, concentration of salt, shaking time and time of centrifugation. These variables were accurately optimized using multivariate optimization strategies. A Plackett-Burman design to select the most influential parameters and a Doehlert design to obtain the optimum conditions have been applied. Two different pH values were used for the extraction of compounds (pH 3 for acidic quinolones and ß-lactams and pH 8 for amphoteric quinolones). The method was validated using matrix-matched standard calibration followed by a recovery assay with spiked samples. The limits of quantification found ranged from 0.3 ng g(-1) for amoxicillin to 6.6 ng g(-1) for ciprofloxacin, and the precision was lower than 15% in all cases as is required by the European Regulation. The decision limits (CCα) ranged between 4.1 and 104.8 ng g(-1), while detection capabilities (CCß) from 4.2 to 109.7 ng g(-1). These values were very close to the corresponding maximum residue limits (MLRs) for the studied antibiotics. Recoveries between 72 and 110% were also obtained. Finally, in order to evaluate the applicability of the method, 28 raw cow milk samples were analysed and it was observed that 28% of the samples were positive. However, only 11% were considered non-compliant with the current EU legislation (Commission Regulation 37/2010), due to some milk samples corresponded to treated cows with these antibiotics.

Stir-membrane solid-liquid-liquid microextraction for the determination of parabens in human breast milk samples by ultra high performance liquid chromatography-tandem mass spectrometry.

In this article, stir-membrane solid-liquid-liquid microextraction (SM-SLLME) is tailored for the analysis of solid matrices and it has been evaluated for the determination of parabens in l breast milk samples. A three-phase microextraction mode was used for the extraction of the target compounds taking advantage of their acid-base properties. The unit allows the simultaneous extraction of the target compounds from the solid sample to an organic media and the subsequent transference of the analytes to an aqueous acceptor phase. The method includes the identification and quantification of the analytes by ultra high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). All the variables involved in the extraction procedure have been accurately studied and optimized. The analytes were detected and quantified using a triple quadrupole mass spectrometer (QqQ). The selection of two specific fragmentation transitions for each compound allowed simultaneous quantification and identification. The method has been analytically characterized on the basis of its linearity, sensitivity and precision. Limits of detection ranged from 0.1 to 0.2ngmL(-1) with precision better than 8%, (expressed as relative standard deviation). Relative recoveries were in the range from 91 to 106% which demonstrated the applicability of the stir-membrane solid-liquid-liquid microextraction for the proposed analytical problem. Moreover, the method has been satisfactorily applied for the determination of parabens in lyophilized breast milk samples from 10 randomly selected individuals.

Sorption and desorption of alcohol sulfate surfactants in an agricultural soil.

Alcohol sulfates are one of the most important types of commercial anionic surfactants and may pose serious environmental problems. The present study examines the sorption behavior of alcohol sulfates in an agricultural soil using a batch reactor and column experiments. Kinetics and equilibrium isotherms of the sorption and desorption processes of the following alcohol sulfate homologues have been determined: AS-C12, AS-C14, AS-C16 , and AS-C18. Sorption and desorption occurred rapidly, and equilibrium was achieved in approximately 1 h. The sorbed mass percentages were 35.1% AS-C12 , 67.2% AS-C14 , and 100% for both AS-C16 and AS-C18. A pseudo-first-order kinetic model provided an adequate fit of data. Sorption and desorption equilibrium data were fitted into 1) a linear model, with r(2) values in the ranges 0.712 to 0.988 and 0.736 to 0.983, respectively, and 2) a Freundlich model, with r(2) values in the ranges 0.956 to 0.991 and 0.891 to 0.981, respectively. Continuous-flow experiments in soil columns were carried out to obtain the breakthrough curves for each compound. The present study provides basic theoretical concepts and key parameters for developing mathematical models that simulate the migration of alcohol sulfate into agricultural soils.

Environmental monitoring of alcohol sulfates and alcohol ethoxysulfates in marine sediments.

The study describes the environmental monitoring of anionic surfactants-alcohol sulfates (AS) and alcohol ethoxysulfates (AES)-in marine sediments. Concentration values were obtained after pressurised liquid extraction (PLE) and liquid chromatography-tandem mass spectrometry analysis (LC-MS/MS). Samples were collected from a range of wastewater discharge points along the coast of the provinces of Huelva, Málaga, Granada and Almería. Urban, agricultural and industrial wastewaters are discharged at the selected 38 sampling sites. Principal component analysis was carried out in order to evaluate the distribution and behaviour of these compounds in these coastal environments. Evaluation of the data revealed that the behaviour and sources of AS and AES in marine sediments are different, and that the distribution of AES depends on the length of the alkyl chain, while the number of ethoxylated units is not relevant. Additionally, the 38 sampling sites can be grouped into only two types of outfalls according to their AS distribution. The concentration of compounds in sediment samples ranged from 7.52 to 13.50 mg kg(-1) for AS, from 3.04 to 10.68 mg kg(-1) for AES-C12Ex and from 3.83 to 11.56 mg kg(-1) for AES-C14Ex.

Quantification, chemical and biological characterization of the saponosides material from Sida cordifolia L. (escobilla) / Cuantificación, caracterización química y biológica del contenido saponósido de Sida cordifolia L. (escobilla)

Introduction: Sida cordifolia L. (Malvaceae) is a weed about which not much is known in Colombia. This plant is used in folk medicine to treat oral mucosa, blennorrhea, asthma and bronchitis.In Brazil it finds application as an anti-inflammatory,while in Colombia its "baba" is used for treating hair loss, constipation and internal fever, among other ailments. Objectives: to quantify the saponoside content and evaluate its antioxidant and antifungal functionality. Methods: we prepared organic, aqueous and hydroalcoholic extracts from the aerial section of the plant. The saponoside material was quantified by the DNS and p-anisaldehyde methods. The most concentrated extracts were selected for antioxidant and antifungal assays. Results: it was found that Sida cordifolia, collected in Ibague-Colombia, is a good source of saponins with diverse chemical structures, mainly of steroidal nature, some of which may be hecogenin, diosgenin or a homologue. Conclusions: these factors may contribute, at least in part, to the antioxidant and antifungal functionality of Sida cordifolia L., but this capacity may be modified if these saponins act independently or together with some other metabolites of the plant such as tannins, flavonoids steroids, and alkaloids among others.

Introducción: Sida cordifolia L. (Malvaceae) es una hierba de la cual se tiene un conocimiento limitado en Colombia. Se utiliza en la medicina popular para el tratamiento de la mucosa oral, la blenorragia, el asma y la bronquitis. En Brasil encuentra aplicación como antiinflamatorio, mientras que en Colombia su "baba" se utiliza para tratar la pérdida del cabello, el estreñimiento, y la fiebre interna, entre otros padecimientos. Objetivos: cuantificar el contenido saponósido y evaluar sus propiedades antioxidantes y funcionalidad antifúngica. Métodos: se prepararon extractos orgánicos, acuosos e hidroalcohólicos de la parte aérea de la planta. El material de saponósidos se cuantificó por los métodos del DNS (dinitrosalicylic acid reagent) y de p-anisaldehído. Los extractos más concentrados se seleccionaron para los ensayos antioxidante y antifúngico. Resultados: estos mostraron que Sida cordifolia, colectada en Ibague-Colombia, es una buena fuente de saponinas con diversas estructuras químicas, principalmente de naturaleza esteroidal, algunas de las cuales pueden ser hecogenina, diosgenina o un homólogo. Conclusiones: estos factores pueden contribuir, al menos en parte, en la funcionalidad antioxidante y antifúngica de Sida cordifolia L., pero su capacidad se puede modificar si esas saponinas actúan de forma independiente o en conjunto con otros metabolitos de la planta, como taninos, esteroides flavonoides, alcaloides, entre otros.

Environmental monitoring study of linear alkylbenzene sulfonates and insoluble soap in Spanish sewage sludge samples.

In this work we present a monitoring study of linear alkylbenzene sulfonates (LAS) and insoluble soap performed on Spanish sewage sludge samples. This work focuses on finding statistical relations between LAS concentrations and insoluble soap in sewage sludge samples and variables related to wastewater treatment plants such as water hardness, population and treatment type. It is worth to mention that 38 samples, collected from different Spanish regions, were studied. The statistical tool we used was Principal Component Analysis (PC), in order to reduce the number of response variables. The analysis of variance (ANOVA) test and a non-parametric test such as the Kruskal-Wallis test were also studied through the estimation of the p-value (probability of obtaining a test statistic at least as extreme as the one that was actually observed, assuming that the null hypothesis is true) in order to study possible relations between the concentration of both analytes and the rest of variables. We also compared LAS and insoluble soap behaviors. In addition, the results obtained for LAS (mean value) were compared with the limit value proposed by the future Directive entitled "Working Document on Sludge". According to the results, the mean obtained for soap and LAS was 26.49 g kg(-1) and 6.15 g kg(-1) respectively. It is worth noting that LAS mean was significantly higher than the limit value (2.6 g kg(-1)). In addition, LAS and soap concentrations depend largely on water hardness. However, only LAS concentration depends on treatment type.

Matrix effect study in the determination of linear alkylbenzene sulfonates in sewage sludge samples.

We propose a study of the matrix effect in the determination of linear alkylbenzene sulfonates (LAS) in sewage sludge samples. First, a rapid, selective and sensitive method is proposed. The method involves two stages: the extraction of the compound from the samples and analysis by liquid chromatography with fluorescence detection (LC-FLD). Three different techniques of extraction (microwave-assisted extraction, Soxhlet, and ultrasounds) were compared, and microwave-assisted extraction was selected as the best suited for our purpose. Microwave-assisted extraction allows reducing the extraction time (25 min compared with 12 h for conventional Soxhlet extraction) and solvent waste (25 ml of methanol compared with 200 ml for Soxhlet or more than 50 ml for the ultrasonic procedure). Absence of matrix effect was evaluated with two standards (2ØC(8:0) and 2ØC(16:0) ) that are not commercial; therefore, neither of them was detected in sewage sludge samples and they showed similar environmental behavior (adsorption and precipitation) to LAS (C(11:0) -C(13.0) ), which allow us to evaluate the matrix effect. Validation was carried out by a recovery assay, and the method was applied to samples from different sources; therefore, they had different compositions.

Determination of insoluble soap in agricultural soil and sewage sludge samples by liquid chromatography with ultraviolet detection.

We have developed a new analytical procedure for determining insoluble Ca and Mg fatty acid salts (soaps) in agricultural soil and sewage sludge samples. The number of analytical methodologies that focus in the determination of insoluble soap salts in different environmental compartments is very limited. In this work, we propose a methodology that involves a sample clean-up step with petroleum ether to remove soluble salts and a conversion of Ca and Mg insoluble salts into soluble potassium salts using tripotassium ethylenediaminetetraacetate salt and potassium carbonate, followed by the extraction of analytes from the samples using microwave-assisted extraction with methanol. An improved esterification procedure using 2,4-dibromoacetophenone before the liquid chromatography with ultraviolet detection analysis also has been developed. The absence of matrix effect was demonstrated with two fatty acid Ca salts that are not commercial and are never detected in natural samples (C13:0 and C17:0). Therefore, it was possible to evaluate the matrix effect because both standards have similar environmental behavior (adsorption and precipitation) to commercial soaps (C10:0) to C18:0). We also studied the effect of the different variables on the clean-up, the conversion of Ca soap, and the extraction and derivatization procedures. The quantification limits found ranged from 0.4 to 0.8 mg/kg. The proposed method was satisfactorily applied for the development of a study on soap behavior in agricultural soil and sewage sludge samples.

Mobility and fate of carbetamide in an agricultural soil.

The objective of this work is to gain a better understanding of the fate of carbetamide, as a representative herbicide, after its soil application. To reach this goal, batch and column laboratory experiments were performed and a transport model was proposed consistent with these results. Then field-scale experiments were carried out for two years and the results compared with those that would be obtained from the transport model, once the degradation terms were introduced. All this is done for four different scenarios: first, considering that the soil is under its natural condition; second, the soil is amended with organic carbon by the addition of stabilized sewage sludge; third, considering that the percolating aqueous phase contains a significant quantity of surfactant [Linear Alkyl Benzene Sulfonate, (LAS)]; and fourth, the scenario in which the sewage sludge and the surfactant are present simultaneously. The Freundlich model yields a good fit to the data of the sorption isotherms obtained from batch equilibrium experiments, but the isotherms are close to linear. The batch sorption/desorption kinetic data together with the column and field results indicate that the retention kinetics are quite fast and local equilibrium can be assumed for the description of the sorption phenomenon. Results also prove that carbetamide is moderately retained in the original soil with a mean value of the partition coefficient of carbetamide about 0.46 (L kg(-1)). When the soil is amended with sewage sludge, this coefficient is somewhat lower, about 0.40 (L kg(-1)). A further decrease is observed 0.32 L kg(-1)) when the surfactant (LAS) at critical micelle concentration (CMC) is used. The two-region model yields a good reproduction of the results of carbetamide mobility in the soil, both at the laboratory scale and at the field scale.