Sorption, degradation and transport phenomena of alcohol ethoxysulfates in agricultural soils. Laboratory studies.

In the present work, laboratory studies were conducted in order to determine and model the sorption, degradation and transport processes of alcohol ethoxysulfates (AES), one of the most important groups of anionic surfactants. Adsorption/desorption isotherms were obtained for several structurally related AES ethoxymers (homologue AES-C12En with n = 0-10 ethoxymer units and homologue AES-C14En with n = 0-7 ethoxymer units) using a batch equilibrium method. Data were fitted to a linear and a Freundlich isotherm models. Additionally, experiments in continuous-flow soil columns were also carried out and the breakthrough curves observed for each compound were studied. Breakthrough curves were used to determine the fundamental parameters of the transport model (hydrodynamic dispersion coefficient, degradation rate constant and adsorption/desorption isotherm slope), that is the main phenomena that take place simultaneously when AES move through agricultural soil. When the results obtained for the AES ethoxymers are combined, they reveal a clear and consistent trend towards a sorption increase with the number of ethoxylated units and with the length of the alkyl chain that opens the possibility to estimate the values of the transport parameters for other structurally related ethoxymers.

Wide-range and accurate modeling of linear alkylbenzene sulfonate (LAS) adsorption/desorption on agricultural soil.

In this paper, rigorous data and adequate models about linear alkylbenzene sulfonate (LAS) adsorption/desorption on agricultural soil are presented, contributing with a substantial improvement over available adsorption works. The kinetics of the adsorption/desorption phenomenon and the adsorption/desorption equilibrium isotherms were determined through batch studies for total LAS amount and also for each homologue series: C10, C11, C12 and C13. The proposed multiple pseudo-first order kinetic model provides the best fit to the kinetic data, indicating the presence of two adsorption/desorption processes in the general phenomenon. Equilibrium adsorption and desorption data have been properly fitted by a model consisting of a Langmuir plus quadratic term, which provides a good integrated description of the experimental data over a wide range of concentrations. At low concentrations, the Langmuir term explains the adsorption of LAS on soil sites which are highly selective of the n-alkyl groups and cover a very small fraction of the soil surface area, whereas the quadratic term describes adsorption on the much larger part of the soil surface and on LAS retained at moderate to high concentrations. Since adsorption/desorption phenomenon plays a major role in the LAS behavior in soils, relevant conclusions can be drawn from the obtained results.

Evaluation of Linear Alkylbenzene Sulfonate (LAS) behaviour in agricultural soil through laboratory continuous studies.

The behaviour of Linear Alkylbenzene Sulfonate (LAS) in agricultural soil is investigated in the laboratory using continuous-flow soil column studies in order to simultaneously analyze the three main underlying phenomena (adsorption/desorption, degradation and transport). The continuous-flow soil column experiments generated the breakthrough curves for each LAS homologue, C10, C11, C12 and C13, and by adding them up, for total LAS, from which the relevant retention, degradation and transport parameters could be estimated, after proposing adequate models. Several transport equations were considered, including the degradation of the sorbate in solution and its retention by soil, under equilibrium and non-equilibrium conditions between the sorbent and the sorbate. In general, the results obtained for the estimates of those parameters that were common to the various models studied (such as the isotherm slope, first order degradation rate coefficient and the hydrodynamic dispersion coefficient) were rather consistent, meaning that mass transfer limitations are not playing a major role in the experiments. These three parameters increase with the length of the LAS homologue chain. The study will provide the underlying conceptual framework and fundamental parameters to understand, simulate and predict the environmental behaviour of LAS compounds in agricultural soils.

[Evaluation of the analgesic effectiveness of ketorolac in intravenous regional anesthesia induced by lidocaine]. / Evaluación de la eficacia analgésica del ketorolaco en la anestesia regional intravenosa inducida con lidocaína.

OBJECTIVES: Intravenous regional anesthesia (i.v.r.) is a safe, effective technique for surgery on the upper extremities, but it provides no postoperative analgesia. The aim of this study was to evaluate the analgesic efficacy of ketorolac during and after surgery with i.v.r. induced by lidocaine. PATIENTS AND METHODS: A double blind, placebo-controlled clinical trial. Twenty-six patients undergoing elective surgery on the upper extremities under i.v.r. were studied. In the anteroom of the operating theater, an anesthesiologist prepared the anesthetic solution to be administered from two syringes. One contained 3 mg/kg of 0.5% lidocaine (0.6 ml/kg). The second syringe (2 ml) contained 1 ml of 0.9% saline solution for the control group or 1 ml with 30 mg of ketorolac for the treatment group. A second anesthesiologist received the patient in the operating theater and used the syringes provided to induce the blockade. After releasing the pneumatic tourniquets we assessed the appearance of postoperative pain on a visual analog scale over the first 24 hours. The dats were compared using parametric (Student t test) and non parametric tests (Mann-Whitney U test and Fisher's exact test). RESULTS: No significant differences in the characteristics or hemodynamic parameters analyzed were found between the two groups. Nor did we find any differences in analgesia during surgery. Ten of the 13 patients (77%) in the control group required analgesia within the first two hours, whereas none of the patients in the treatment group required analgesia during that time (p < 0.0001). There were no statistically significant differences between the two groups in the total amount administered altogether, both during and after surgery. No local or systemic side effects were observed.