Maria J. Calderon

Organosmectites as sorbent and carrier of the herbicide bentazone

Sorption isotherms of bentazone on diverse organoclays (OCls) were measured at aqueous concentrations from 25 to 1500 microM. Sorption on organophilic OCls, OCls with large quaternary alkylammonium groups, i.e. hexadecyltrimethylammonium (AHDT) and dioctadecyldimethylammonium (ADOD), were compared to that on sorptive OCls, which have large primary alkylammonium (octadecylammonium, AC18) and small quaternary alkylammonium (phenyltrimethylammonium, PTA) groups. The organophilic OCls showed much higher sorption (AHDT Kd = 682-1789; ADOD Kd = 838-1728) than the sorptive OCls (AC18 Kd = 38-40; PTA Kd = 0), suggesting hydrophobic bentazone-organocation interactions as the main mechanism responsible for sorption. The incubation of the two organophilic OCls with soil contaminated with bentazone showed that availability of the herbicide decreased almost instantaneously from 124 microg g(-1) to 1 microg g(-1). Bentazone sorbed on the OCl, and thus immobilized, was partially extractable with CaCl2/methanol solution suggesting its potential bioavailability. Two OCls, with high and low sorptions, were assayed as herbicide carriers by preparing bentazone-OCl complexes and monitoring their herbicide release in water and soil-water suspensions. These bentazone-OCl complexes released 20-80% of their bentazone content, depending of the sorbent capacity and the bentazone-OCl interaction. Results of this work show that by varying the sorptive properties of OCls, they can be used to immobilize pesticide in a contaminated soil and to protect soil and water by using OCl as pesticide carriers in slow release formulations.

Epidemiology of chronic disease related to arsenic in Argentina: A systematic review.

Four million people in Argentina are exposed to arsenic contamination from drinking waters of several center-northern provinces. A systematic review to examine the geographical distribution of arsenic-related diseases in Argentina was conducted, searching electronic databases and gray literature up to November 2013. Key informants were also contacted. Of the 430 references identified, 47 (mostly cross-sectional and ecological designs) referred to arsenic concentration in water and its relationship with the incidence and mortality of cancer, dermatological diseases and genetic disorders. A high percentage of the water samples had arsenic concentrations above the WHO threshold value of 10μg/L, especially in the province of Buenos Aires. The median prevalence of arsenicosis was 2.6% in exposed areas. The proportion of skin cancer in patients with arsenicosis reached 88% in case-series from the Buenos Aires province. We found higher incidence rate ratios per 100μg/L increment in inorganic arsenic concentration for colorectal, lung, breast, prostate and skin cancer, for both genders. Liver and skin cancer mortality risk ratios were higher in regions with medium/high concentrations than in those with low concentrations. The relative risk of mortality by skin cancer associated to arsenic exposure in the province of Buenos Aires ranged from 2.5 to 5.2. In the north of this province, high levels of arsenic in drinking water were reported; however, removal interventions were scarcely documented. Arsenic contamination in Argentina is associated with an increased risk of serious chronic diseases, including cancer, showing the need for adequate and timely actions.

Hexazinone and simazine dissipation in forestry field nurseries.

Hexazinone and simazine field dissipation was studied in two different soils from Spain (Toledo and Burgos), devoted to forest nurseries for Pinus nigra. Laboratory experiments (adsorption-desorption isotherms, leaching experiment and degradation study) were carried out to determine possible mechanisms of dissipation. Higher adsorption was observed for hexazinone in Toledo (KfT = 0.69) compare to in Burgos soil (KfB = 0.20) probably due to the higher organic matter (OM) content of Toledo soil. No differences in adsorption were obtained for simazine in both soils (KfT = 1.27; KfB = 1.34). In every case, adsorption was higher for simazine than for hexazinone, in both soils. The total recovery of hexazinone in the leachates from handpacked soil columns was higher in Burgos (100%) than in Toledo (80%), because of the larger adsorption of hexazinone in this last soil. No differences in simazine leaching between both soils were found, although the total amount of pesticide recovered in leachates (40% in the two soils) was lower for simazine than for hexazinone. Finally, lower degradation was found in Burgos (t1/2 = 91 d) vs Toledo (t1/2 = 47 d), directly related with the high OM content of Toledo. No half-life was calculated for simazine in Toledo because no changes in herbicide soil content were observed during the period of time studied. In the case of Burgos, the half-life for simazine was 50 days. The field residues study showed larger persistence of simazine than hexazinone mainly due to the higher adsorption and lower mobility of simazine in the two soils. The lower persistence of hexazinone in Toledo soil than in Burgos soil is related to the larger rainfall occurred in this soil besides the higher degradation of this herbicide observed in Toledo soil. The much lower temperature in Burgos than in Toledo soil during winter contribute to the higher persistence of the two herbicides in Burgos soil.

Fenuron sorption on homoionic natural and modified smectites.

Abstract The adsorption isotherms of fenuron (l, l‐dimethyl‐3‐phenylurea) on three smectites (SWy and SAz montmorillonites and SH hectorite) differing in their layer charge (SH<SWy<SAz) and saturated with several inorganic and organic cations were determined. The isotherms and sorption parameters from Freundlich equation indicate low adsorptivity on inorganic clays, but medium sorption in organoclays (OCls). Fenuron adsorption on homoionic smectites increases with decreasing layer charge and hydratation power of the inorganic exchangeable cation (except Fe3+), indicating that fenuron adsorbs as neutral molecule on uncharged siloxane surface by hydrophobic bonding, with some contribution of polar bond (fenuron C=O group and water associated to exchangeable cation). In the case of Fe3+‐saturated smectite fenuron protonation, provided by the interlayer acidic environment, promotes further sorption of fenuron as cationic form. The sorption on organoclays is enhanced via hydrophobic interaction with organocations, which is favoured for high layer charge and basal spacing and organocation saturation close to CEC. Quaternary alkylamonium is more efficient in high layer charge smectite, whereas primary alkylammonium is more efficient in medium charge smectite. The low values of the maximum sorption obtained with homoionic inorganic and organic smectites (100 and 5000 μmol/Kg) represent one fenuron molecule for each 2000–200 exchange sites and indicate that fenuron sorption is mainly associated to the outer exchange sites. This low adsorptivity of fenuron, as consequence of its high water affinity (high water solubility) would suggest high mobility of fenuron in natural soil and water systems.

Orbital differentiation and the role of orbital ordering in the magnetic state of Fe superconductors

We analyze the metallic (pi,0) antiferromagnetic state of a five-orbital model for iron superconductors. We find that with increasing interactions the system does not evolve trivially from the pure itinerant to the pure localized regime. Instead we find a region with a strong orbital differentiation between xy and yz, which are half-filled gapped states at the Fermi level, and itinerant zx, 3z^2-r^2 and x^2-y^2. We argue that orbital ordering between yz and zx orbitals arises as a consequence of the interplay of the exchange energy in the antiferromagnetic x direction and the kinetic energy gained by the itinerant orbitals along the ferromagnetic y direction with an overall dominance of the kinetic energy gain. We indicate that iron superconductors are close to the boundary between the itinerant and the orbital differentiated regimes and that it could be possible to cross this boundary with doping.

An exchange-coupled donor molecule in silicon.

We present a combined experimental-theoretical demonstration of the energy spectrum and exchange coupling of an isolated donor pair in a silicon nanotransistor. The molecular hybridization of the atomic orbitals leads to an enhancement of the one- and two-electron binding energies and charging energy with respect to the single donor case, a desirable feature for quantum electronic devices. Our hydrogen molecule-like model based on a multivalley central-cell corrected effective mass theory incorporating a full configuration interaction treatment of the 2-electron spectrum matches the measured data for an arsenic diatomic molecule with interatomic distance R = 2.3 ± 0.5 nm.

Herbicide monitoring in soil, runoff waters and sediments in an olive orchard

Occurrences of surface water contamination by herbicides in areas where olive orchards are established reveal a need to understand soil processes affecting herbicide fate at field scale for this popular Mediterranean crop. A monitoring study with two herbicides (terbuthylazine and oxyfluorfen) in the first 2cm of soil, runoff waters, and sediments, was carried out after under natural rainfall conditions following winter herbicide application. At the end of the 107day field experiment, no residues of the soil applied terbuthylazine were recovered, whereas 42% of the oxyfluorfen applied remained in the top soil. Very low levels of both herbicides were measured in runoff waters; however, concentrations were slightly higher for terbuthylazine (0.53% of applied) than for oxyfluorfen (0.03% of applied), relating to their respective water solubilities. Congruent with soil residue data, 38.15% of the applied oxyfluorfen was found in runoff-sediment, compared to only 0.46% for terbuthylazine. Accordingly, the herbicide soil distribution coefficients measured within runoff field tanks was much greater for oxyfluorfen (Kd=3098) than for terbuthylazine (Kd=1.57). The herbicide oxyfluorfen is co-transported with sediment in runoff, remaining trapped and/or adsorbed to soil particle aggregates, due in part to its low water solubility. In contrast, terbuthylazine soil dissipation may be associated more so with leaching processes, favored by its high water solubility, low sorption, and slow degradation. By comparing these two herbicides, our results reaffirm the importance of herbicide physico-chemical properties in dictating their behavior in soil and also suggest that herbicides with low solubility, as seen in the case oxyfluorfen, remain susceptible to offsite transport associated with sediments.

Correlation, doping, and interband effects on the optical conductivity of iron superconductors

Electronic interactions in multiorbital systems lead to non-trivial features in the optical spectrum. In iron superconductors the Drude weight is strongly suppressed with hole-doping. We discuss why the common association of the renormalization of the Drude weight with that of the kinetic energy, used in single band systems, does not hold in multi-orbital systems. This applies even in a Fermi liquid description when each orbital is renormalized dierently, as it happens in iron superconductors. We estimate the contribution of interband transitions at low energies. We show that this contribution is strongly enhanced by interactions and dominates the coherent part of the spectral weight in hole-doped samples at frequencies currently used to determine the Drude weight.

Seasonal terbuthylazine monitoring in olive groves under conventional tillage

During the last two decades there have been several herbicide pollution episodes of both surface and groundwater in areas where olive groves are established. These episodes always coincided with rainy periods. Understanding the evolution of herbicides in this type of plantation depending on the season of application is critical, especially when conventional tillage is used. Field monitoring of terbuthylazine in the first 2 cm of soil and in runoff water and sediment yield was carried out after winter and spring soil applications. Soil disappearance of terbuthylazine was associated with the first important rainfall event in both seasons (41 mm in spring and 30 mm in winter). At the end of the experiment (85 days and 103 mm rain in spring, and 107 days and 148 mm in winter), no terbuthylazine soil residues were found in winter, whereas 15% of terbuthylazine applied remained in spring. A higher percentage of the applied terbuthylazine in runoff water was recovered in winter (0.53%) than in spring (0.16%). However, no differences in terbuthylazine residues in sediment yields were observed (0.45% in spring and 0.46% winter). These data suggest that the dissipation of terbuthylazine from soil is related not only to the runoff process but also to other processes like leaching, which are more relevant at the end of the winter season.During the last two decades there have been several herbicide pollution episodes of both surface and groundwater in areas where olive groves are established. These episodes always coincided with rainy periods. Understanding the evolution of herbicides in this type of plantation depending on the season of application is critical, especially when conventional tillage is used. Field monitoring of terbuthylazine in the first 2 cm of soil and in runoff water and sediment yield was carried out after winter and spring soil applications. Soil disappearance of terbuthylazine was associated with the first important rainfall event in both seasons (41 mm in spring and 30 mm in winter). At the end of the experiment (85 days and 103 mm rain in spring, and 107 days and 148 mm in winter), no terbuthylazine soil residues were found in winter, whereas 15% of terbuthylazine applied remained in spring. A higher percentage of the applied terbuthylazine in runoff water was recovered in winter (0.53%) than in spring (0.16%). However, no differences in terbuthylazine residues in sediment yields were observed (0.45% in spring and 0.46% winter). These data suggest that the dissipation of terbuthylazine from soil is related not only to the runoff process but also to other processes like leaching, which are more relevant at the end of the winter season.

Reparación Endovascular para Aneurisma de Aorta: Revisión Panorámica sobre su evidencia en el mundo y su aplicación en Latinoamérica

BACKGROUND Aortic aneurysm (AA) is a pathology with high morbidity and mortality. The management can be expectant, surgical, or through endovascular repair (EVAR). In Latin America the incidence of AA has increased and the analysis of therapeutic options, especially if they are expensive, is fundamental. OBJECTIVE To analyze available evidence on the effectiveness, safety and coverage policies of the EVAR. METHODOLOGY Panoramic review in the main bibliographical bases (MEDLINE, LILACS, EMBASE, Cochrane Library, DARE) and generic internet searchers, main health technology assessment (HTA) agencies and health insurance companies. Systematic reviews (SR), clinical practice guidelines (CPG), HTA and coverage policies, followed by the identification of primary studies published after the SR search date were included. A search of studies published until November 2015 in English and Spanish was carried out. RESULTS 311 references were recovered, from which seven SRs were selected, one clinical study and 15 CPGs, consensus or coverage policies and ETS. CONCLUSIONS For abdominal AA, high quality evidence showed no differences inlong-term survival with the use of EVAR compared to conventional surgery, but lower early mortality was observed (OR = 0.33, 95% CI 0.20 -0.55). EVAR was associated with a greater need for re-intervention. In the case of other types of AA, further evidence is still required to establish the benefit of EVAR. The CPGs, consensus, HTAs and coverage policies identified, mostly consider open surgery as the treatment of choice, reserving the EVAR for patients with high surgical risk for conventional surgery in the presence of favorable anatomy.