Tanare C.R. Ferreira

A comparative study of the electrochemical oxidation of the herbicide tebuthiuron using boron-doped diamond electrodes.

The thiadiazolylurea derivative tebuthiuron (TBH) is commonly used as an herbicide even though it is highly toxic to humans. While various processes have been proposed for the removal of organic contaminants of this type from wastewater, electrochemical degradation has shown particular promise. The aim of the present study was to investigate the electrochemical degradation of TBH using anodes comprising boron-doped (5000 and 30,000 ppm) diamond (BDD) films deposited onto Ti substrates operated at current densities in the range 10-200 mA cm(-2). Both anodes removed TBH following a similar pseudo first-order reaction kinetics with k(app) close to 3.2 × 10(-2) min(-1). The maximum mineralization efficiency obtained was 80%. High-pressure liquid chromatography with UV-VIS detection established that both anodes degraded TBH via similar intermediates. Ion chromatography revealed that increasing concentrations of nitrate ions (up to 0.9 ppm) were formed with increasing current density, while the formation of nitrite ions was observed with both anodes at current densities ≥ 150 mA cm(-2). The BDD film prepared at the lower doping level (5000 ppm) was more efficient in degrading TBH than its more highly doped counterpart. This unexpected finding may be explained in terms of the quantity of impurities incorporated into the diamond lattice during chemical vapor deposition.

Photo-Fenton degradation of the insecticide esfenvalerate in aqueous medium using a recirculation flow-through UV photoreactor

The aim of the study was to evaluate the efficiencies of photo-Fenton (Fe(2+)) and (Fe(3+)) processes in the degradation of high-concentrations of esfenvalerate (in the form of aqueous emulsion of a commercial formulation) using a recirculation flow-through photoreactor irradiated with UV light from a 15 W lamp (254 nm emission peak). The results obtained using a basic photo-Fenton (Fe(2+)) reaction (esfenvalerate 17 mg L(-1); ferrous sulphate 1 mM; hydrogen peroxide 25 mM; pH 2.5) were compared with those acquired when ferrioxalate (1, 3 or 5 mM) served as the iron source. Degradation of the active component of the commercial formulation was significantly greater, and the rate of oxidation more rapid, using a photo-Fenton (Fe(3+)) process compared with its Fe(2+) counterpart. The most efficient degradation of the insecticide (75% in 180 min) was achieved with a reaction mixture containing 5mM ferrioxalate. However, under the same experimental conditions, degradation of pure esfenvalerate preceded much faster (99% in 60 min) and was 100% complete within 180 min reaction time.

Simultaneous Degradation of Diuron and Hexazinone Herbicides by Photo-Fenton: Assessment of Concentrations of H2O2 and Fe2+ by the Response Surface Methodology

Abstract Pesticides are often reported in aquatic environments contamination as being a result of soil leaching and improper disposal of agricultural packages. Advanced oxidation processes have been studied as alternatives to treat such compounds in aqueous media. The aim of this study was to determine the best concentrations of H2O2 and Fe2+ that achieved the most efficient simultaneous degradation of hexazinone and diuron. The central composite design (CCD) and response surface method (RSM) were applied to evaluate and optimize the interactive effects of H2O2 and Fe2+. The dosages of H2O2 and Fe2+ used in the photo-Fenton degradation of an aqueous solution of hexazinone and diuron ranged from 0.09 to 29.1 mmol L-1 and 0.01 to 0.92 mmol L-1, respectively. The response surface revealed low concentrations of H2O2 and Fe2+ to the ideal degradation. These photo-Fenton conditions promoted 100% degradation of hexazinone and diuron and 76% of mineralization in only 30 minutes.

Simultaneous degradation of hexazinone and diuron herbicides by H2O2/UV and toxicity assessment

Diuron (DR) and hexazinone (HX) are potent herbicides worldwide consolidated in agricultural practices. In Brazil, their mixed formulation has been intensively applied to cultures of sugar cane crops. However, when detected in agricultural watersheds, these compounds are potentially toxic to aquatic organisms and may be potentially carcinogenic. Advanced oxidation processes (AOP) is an alternative treatment of DR/HX in aqueous environment. In this study, we evaluate the H2O2/UV simultaneous degradation and photolysis process of DR/HX using central composite design. The HX and DR initial concentrations were close to 7 and 20 mg L-1, respectively. In the system, the planning showed that the H2O2 concentration has bigger influence than pH. The optimum degradation conditions (7 mmol L-1 of H2O2 and pH 2.8) provide a total organic carbon removing of 96.4% while the photolysis process only 17.2%. Since neither of the herbicides were detected after 2 min of reaction, it was not possible to differ kinetics degradation process of DR and HX during the process. After the treatment, the toxicity was tested using Vibrio fischeri bioluminescent bacteria and showed a decrease when H2O2/UV is applied. Degradation H2O2/UV was successfully employed, showing excellent performance due to increased mineralization.

Fate of Enrofloxacin in Lake Sediment: Biodegradation, Transformation Product Identification, and Ecotoxicological Implications

ABSTRACT Various pharmaceutical drugs are being detected in different environmental compartments such as surface waters, groundwater, and sediment; a major concern since they are biologically active substances which can interfere with biological systems affecting the native biota. Among these drugs, antimicrobials are especially worrisome mainly due to the development of bacterial resistance. The aims of this study were to investigate if enrofloxacin, an emergent antibiotic pollutant, could be biodegraded in lake sediment, identify its break down products and to determine if these products have antimicrobial properties or are toxic. Three biodegradation products were identified and the antibiotic susceptibility assay proved that the products formed did not display antibiotic effects. Ecotoxicity testing with green algae suggested that the degradation products do not cause adverse effects statistically. However, it is suggested that further investigations are needed to identify the mechanism of degradation and the microbes involved.

Screening of By-Products of Esfenvalerate in Aqueous Medium Using SBSE Probe Desorption GC-IT-MS Technique

The pyrethroids, their metabolites and by-products have been recognized as toxic to environment and human health. Despite several studies about esfenvalerate toxicity and its detection in water and sediments, information about its degradation products is still scanty. In this work, esfenvalerate degradation products were obtained by chemical oxidation with hydrogen peroxide and their structure was elucidated using a procedure known as stir bar sorptive extraction (SBSE) probe desorption gas chromatography-ion trap mass spectrometry (GC-IT-MS) analysis. This procedure consists of the thermal desorption of analytes extracted from a SBSE stir bar introduced by a probe into a gas chromatograph (GC) coupled to an ion trap mass spectrometry (IT-MS) system. Based on IT-MS data, a degradation pathway of esfenvalerate is proposed with ten products of chemical oxidation of esfenvalerate that are fully identified. Among these compounds, 3-phenoxybenzoic acid and 3-phenoxybenzaldehyde were detected, reported as being environmental metabolites of some pyrethroids, with endocrine-disrupting activity.