Browsing by Author "Kogan, Marcelo"
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- ItemAntibacterial Silver Nanoparticles Supported on Graphene Oxide with Reduced Cytotoxicity(2019) Angulo-Pineda, Carolina; Palma, Patricia; Bejarano, Julian; Riveros, Ana; Kogan, Marcelo; Palza, HumbertoThe effect of graphene oxide (GO) on both the antibacterial and cytotoxicity behavior of silver nanoparticles (Ag NPs) has been studied. Ag NPs supported on GO were synthesized by two methods, ex situ and in situ. These nanocomposites were characterized by transmission electron microscopy, ultraviolet-visible spectroscopy, Raman spectroscopy, and Fourier-transform infrared spectroscopy. The antibacterial activity of the nanomaterials was evaluated against Escherichia coli and Staphylococcus aureus by the disk-diffusion method and dynamic contact assays. While GO flakes showed antibacterial behavior only in the dynamic contact test, both GO-Ag NPs nanohybrids eradicated bacteria independent of the condition. Noteworthily, the high cytotoxicity of Ag NPs to human-derived cells was dramatically decreased by the GO layers in the nanocomposite. The in situ hybrid particles showed the lowest cytotoxicity without losing the strong antibacterial effect. These results demonstrate that growth of Ag NPs on GO layers could enable the development of a new family of antibacterial materials with low cytotoxicity to human cells.
- ItemPendimethalin and oxyfluorfen degradation under two irrigation conditions over four years application(TAYLOR & FRANCIS INC, 2009) Alister, Claudio A.; Gomez, Patricio A.; Rojas, Sandra; Kogan, MarceloA four-year field study was conducted to determine the effect of pluviometric conditions on pendimethalin and oxyfluorfen soil dynamics. Adsorption, dissipation and soil movement were studied in a sandy loam soil from 2003 to 2007. Pendimethalin and oxyfluorfen were applied every year on August at 1.33 and 0.75 kg ha-1, respectively. Herbicide soil concentrations were determined at 0, 10, 20, 40, 90 and 340 days after application (DAA), under two pluviometric regimens, natural rainfall and irrigated (30 mm every 15 days during the first 90 DAA). More than 74% of the herbicide applied was detected at the top 2.5 cm layer for both herbicides, and none was detected at 10 cm or deeper. Pendimethalin soil half-life ranged from 10.5 to 31.5 days, and was affected mainly by the time interval between application and the first rain event. Pendimethalin soil residues at 90 DAA fluctuated from 2.5 to 13.8% of the initial amount applied, and it decreased to 2.4 and 8.6% at 340 DAA. Oxyfluorfen was more persistent than pendimethalin as indicated by its soil half-life which ranged from 34.3 to 52.3 days, affected primarily by the rain amount at the first rainfall after application. Oxyfluorfen soil residues at 90 DAA ranged from 16.7 to 34.8% and it decreased to 3.3 and 17.9% at 340 DAA. Based on half-life values, herbicide soil residues after one year, and soil depth reached by the herbicides, we conclude that both herbicides should be considered as low risk to contaminate groundwater. However, herbicide concentration at the top 2.5 cm layer should be considered in cases where runoff or soil erosion could occur, because of the potential for surface water contamination.
- ItemResistance to Bensulfuron-Methyl in Water Plantain (Alisma plantago-aquatica) Populations from Chilean Paddy Fields(CAMBRIDGE UNIV PRESS, 2008) Figueroa, Rodrioro; Gebauer, Marlene; Fischer, Albert; Kogan, MarceloBensulfuron-methyl (BSM) has been one of the most widely used herbicides in Chilean rice fields because it controls a wide spectrum of weeds and does not require field drainage for application. However, failures of BSM to control water plantain in rice fields have been noted since 2002. We assessed BSM effects on suspected resistant (CU1 and CU2) and Susceptible (AN I) water plantain accessions collected in Chilean rice fields during 2004 and 2005. BSM rates resulting in 50% growth reduction (GR(50)) of CU2 and CU1 plants were 12- and 33-fold higher than for ANI plants, respectively. Acetolactate synthase (ALS) activity assays in vitro Suggested resistance in CU1 and CU2 was due to an ALS enzyme with reduced BSM sensitivity compared to the AN I biotype. Resistance indices (RI), or ratios of the resistant to susceptible I-50 values (BSM rate to inhibit ALS-enzyme activity by, 50%), were 266 (CU2/AN1) and > 38,462 (CU1/AN1). This agreed with in vivo ALS activity assays where RI were 224 (CU2/AN1) and > 8,533 (CU1/AN1). Resistance levels detected in whole-plant or in vivo ALS activity assays were orders of magnitude lower than those detected in in vitro ALS activity studies suggesting nontarget site mechanisms may have mitigated BSM toxicity. However, a consistent ranking of BSM sensitivity levels (AN1 > CU2 > CU1) throughout all three types of assays suggests resistance is primarily endowed by low target site sensitivity. We conclude that Susceptible and resistant water plantain biotypes coexist in Chilean paddies, and the use of integrated weed management involving herbicides with a different mode of action would be imperative to prevent further evolution of resistance to BSM and possibly cross-resistance to other ALS inhibitors. In vitro ALS-enzyme assays provided the best discrimination of resistance levels between biotypes.
- ItemSimazine transport in undisturbed soils from a vineyard at the Casablanca valley, Chile(2013) Suarez Poch, Francisco; Guzman, Edwin; Munoz, Jose E.; Bachmann, Jaime; Ortiz, Cristian; Alister, Claudio; Kogan, Marcelo
- ItemTransport of simazine in unsaturated sandy soil and predictions of its leaching under hypothetical field conditions(ELSEVIER, 2007) Suarez, Francisco; Bachmann, Jaime; Munoz, Jose F.; Ortiz, Cristian; Tyler, Scott W.; Alister, Claudio; Kogan, MarceloThe potential contamination of groundwater by herbicides is often controlled by processes in the vadose zone, through which herbicides travel before entering groundwater. In the vadose zone, both physical and chemical processes affect the fate and transport of herbicides, therefore it is important to represent these processes by mathematical models to predict contaminant movement. To simulate the movement of simazine, a herbicide commonly used in Chilean vineyards, batch and miscible displacement column experiments were performed on a disturbed sandy soil to quantify the primary parameters and processes of simazine transport. Chloride (Cl-) was used as a non-reactive tracer, and simazine as the reactive tracer. The Hydrus-1D model was used to estimate the parameters by inversion from the breakthrough curves of the columns and to evaluate the potential groundwater contamination in a sandy soil from the Casablanca Valley, Chile. The two-site, chemical non-equilibrium model was observed to best represent the experimental results of the miscible displacement experiments in laboratory soil columns. Predictions of transport under hypothetical field conditions using the same soil from the column experiments were made for 40 years by applying herbicide during the first 20 years, and then halting the application and considering different rates of groundwater recharge. For recharge rates smaller than 84 mm year(-1), the predicted concentration of simazine at a depth of I m is below the U.S. EPA's maximum contaminant levels (4 mu g L-1). After eight years of application at a groundwater recharge rate of 180 mm year I (approximately 50% of the annual rainfall), simazine was found to reach the groundwater (located at 1 m depth) at a higher concentration (more than 40 mu g L-1) than the existing guidelines in the USA and Europe. (c) 2007 Elsevier B.V.. All rights reserved.
- ItemUsing penoxsulam ALS inhibitor as a broad-spectrum herbicide in Chilean rice(2011) Kogan, Marcelo; Gomez, Patricio; Fischer, Albert; Alister, ClaudioM. Kogan, P. Gomez, A. Fischer, and C. Alister. 2011. Using penoxsulam ALS inhibitor as a broad-spectrum herbicide in Chilean rice. Cien. Inv. Agr. 38(1): 83-93. The continuously-flooded rice production system in Chile has selected highly competitive aquatic weeds selection capable of reducing paddy yields by 25 to 50%. Penoxsulam is abroad-spectrum triazolopyrimidine (ALS inhibitor) commercially introduced in Chile in 2006, where Alisma plantago aquatica hads already evolved resistance to sulfonylurea herbicides (SU). Several field trials with water seeded rice were conducted during 2003 and 2004 in Chile to determine efficacy, timing of application, spectrum of control, and control of SU-resistant A. plantago aquatic(a with the herbicide penoxsulam, either in single applications or in sequence with other herbicides. Penoxsulam was applied a) 12 days after seeding (DAS) into the water (I W), b) in postemergence after draining the water from field (ADW) at 35 DAS ore) IW followed by ADW applications of MCPA, cyhalofop, bentazon, or triclopyr. Penoxsulam was tested at 20, 30, and 40 g a.i. ha(-1). Comparisons were made with recommended rates of other IW treatments (metsulfuron, bensulfuron and cyclosulfomuron) and sequential applications of molinate (IW) followed by ADW applications of MCPA, cyhalofop, bentazon, or triclopyr. One IW penoxsulam application was sufficient to achieve broad-spectrum control: Echinochloa spp. (100% control), A.plantago-aquatica (80 to 100%), Schoenoplectus mucronatus (50 to 80%), and Cyperus difformis (80 to 100%). Rice yields in penoxsulam-treated plots were 30 to 56% higher than in the untreated controls. Yields with penoxsulam IW (all rates) were similar (P > 0.05) to those obtained using molinate (IW) followed by ADW applications of bentazon or MCPA. Although penoxsulam is an ALS inhibitor, it controlled A. plantago-aquatica resistant to metsulfuron and bensulfuron.