Degradation of linuron in aqueous solution by the photo-Fenton reaction
Introduction
Herbicides represent the largest group of chemicals used as plant protection agents. One class of herbicides widely used in pre- and post-emergencies is represented by the substituted phenylureas.
The phenylureas are persistent herbicides. At high rates of application they are useful as total weed killers, but at low rates many can be used for selective weed control in a wide range of crops. Linuron, 3-[3,4-(dichlorophenyl)-1-methoxy-1-methylurea], one of the most important commercial ureas, has good contact activity and it may kill emergent weed seedlings [1]. In addition, linuron is a weak competitive androgen receptor antagonist in vitro, induces a positive response in the immature and adult rat Hershberger assay and suppresses androgen-dependent gene expression [2], [3], [4].
Half-life in soil ranges from 38 to 67 days for linuron [5]. Therefore, this compound has been found as contaminants in surface and ground waters [6] and microbial degradation is considered to be the primary mechanism for their dissipation from soil. Many bacterial [7] and fungal isolates [8] that are able to (partially) break down phenylureas have been reported. In general, biological methods commonly require long time for the wastewater containing linuron at high concentration. Therefore, the rapid and simple wastewater treatment of linuron is now required urgently.
A few of treatment techniques for wastewater which contains linuron has been reported by using O3/H2O2 [9], direct photolysis [10] and Fenton [11] procedures. Recent reports indicate that a combination of H2O2 and UV irradiation with Fe(II), so-called the photo-Fenton process, can significantly enhance decomposition of many refractory organic compounds. Until now, the photo-Fenton process has been applied to the degradation of pesticides [12], [13], nitrobenzene and other organics [14], chlorophenols [15], [16], [17], nitrophenols [18], dibutyl-phthalate [19], PCBs [20] and bisphenol A [21]. The acceleration for decomposition of organic compounds is believed to be in order to photolysis of iron aquacomplex, Fe(H2O)5(OH)2+ (represented hereafter by Fe(OH)2+), to provide a new importance source of OH radicals [22], [23]. Further, the photolysis of Fe(OH)2+ regenerates Fe(II) (Eqs. (1) and (2)), which means that the photo-Fenton reaction would need low Fe(II) concentration compared with the Fenton process.Fe2+ + H2O2 → Fe(OH)2+ + OHFe(OH)2+ + hν → Fe2+ + OH
Furthermore, the Fe(OH)2+ can absorb light at wavelengths up to ca. 410 nm, while TiO2 photocatalysis can use photon with wavelength close to 380 nm [24]. Therefore, the photo-Fenton process can be expected to be an efficient method for wastewater treatment and promotes the rate of degradation of various organic pollutants.
In the present study, we have investigated the degradation and mineralization of linuron in water using photo-Fenton process. The many factors, such as pH value and initial concentrations of Fe(II) and H2O2, affected on the degradation were evaluated. The progress of mineralization of linuron was monitored by total organic carbon (TOC) content and ionic chromatography. Furthermore, the photoproducts of linuron during this photocatalytic process have been identified by gas chromatography–mass spectrometry (GC–MS). The degradation pathway was proposed on the basis of intermediates formed.
Section snippets
Reagents
Linuron was purchased from Wako Pure Chemical Industries (Osaka, Japan) and was used as received (HPLC grade >99.0%). Analytical grade hydrogen peroxide solution (30%, w/w) and ferrous sulfate heptahydrate (FeSO4·7H2O) were purchased from Wako Pure Chemical Industries (Osaka, Japan) and Nacalai Tesque (Kyoto, Japan), respectively, and were used as received. All other chemicals and solvents were of the purest grade commercially available and were used without further purification. All aqueous
Effect of variables on the degradation of linuron
The time courses of the UV absorption spectra of linuron solution in the photocatalytic degradation by the photo-Fenton reaction were observed in the range of 0–60 min. The experimental conditions were: [Fe(II)]0 = 1.0 × 10−5 mol L−1, [H2O2]0 = 1.0 × 104 mol L−1, pH 3.0 and light intensity = 2.0 mW cm−2 Other conditions were described in Section 2. The UV spectrum of linuron solution before illumination presented one absorption maximum at 250 nm. The disappearance of 250 nm absorption band was observed with
Conclusions
The photodegradation of linuron in aqueous solution was investigated by the photo-Fenton treatment. The degradation rate was strongly affected by many factors, such as the pH value and the initial concentrations of H2O2 and Fe(II). Linuron achieved complete degradation after 20 min under the optimum conditions.
The disappearance of TOC was observed during the photo-Fenton process and the remaining TOC achieved 0.4 mg L−1 after 25 h (90% mineralization). The formations of chloride, nitrate and
Acknowledgment
This work is a part of projects of Satellite Venture Business Laboratory (SVBL), Mie University.
References (43)
- et al.
Effects of in utero exposure to linuron on androgendependent reproductive development in the male Crl:CD(SD)BR rat
Toxicol. Appl. Pharmacol.
(2000) - et al.
Investigation of a mechanism for Ley dig cell tumorigenesis by linuron in rats
Toxicol. Appl. Pharmacol.
(1993) - et al.
Seasonal transport of herbicides (triazines and phenylureas) in a small stream draining an agricultural basin: Mélarchez (France)
Water Res.
(1997) - et al.
Biodegradation of three substituted phenylurea herbicides (chlorotoluron, diuron, and isoproturon) by soil fungi. A comparative study
Chemosphere
(1996) - et al.
Complete oxidation of metolachlor and methyl parathion in water by the photoassisted Fenton reaction
Water Res.
(1995) - et al.
Degradation of selected pesticide active ingredients and commercial formulations in water by the photo-assisted Fenton reaction
Water Res.
(1999) - et al.
Photochemical oxidation of p-chlorophenol by UV/H2O2 and photo-Fenton process. A comparative study
Waste Manage.
(2001) - et al.
Hydrogen peroxide photolysis, Fenton reagent and photo-Fenton for the degradation of nitrophenols: a comparative study
Chemosphere
(2002) Photodegradation of di-n-butyl-ortho-phthalate in aqueous solutions
J. Phtochem. Photobiol. A: Chem.
(1992)- et al.
Degradation of bisphenol A in water by the photo-Fenton reaction
J. Photochem. Photobiol. A: Chem.
(2004)
Temperature dependence of hydroxyl radical formation in the hν/Fe3+/H2O2 and Fe3+/H2O2 systems
Chemosphere
Photocatalytic degradation of ammonia with TiO2 as photocatalyst in the laboratory and under the use of solar radiation
Chemosphere
pH effect in the photocatalytic transformation of a phenyl-urea herbicide
Chemosphere
Photocatalyzed mineralization of nitrogen-containing compounds at TiO2/H2O interfaces
J. Mol. Catal. A: Chem.
Kinetics of the chemical degradation of diuron
Chemosphere
Analytical chemistry of chlorpyrifos and diuron in aquatic ecosystems
Anal. Chim. Acta
Mineralization of aniline and 4-chlorophenol in acidic solution by ozonation catalyzed with Fe2+ and UVA light
Appl. Catal. B: Environ.
Cellular and molecular mechanisms of action of linuron: an antiandrogenic herbicide that produces reproductive malformations in male rats
Toxicol. Sci.
The Pesticide Manual
Isolation of isoproturon-degrading bacteria from treated soil via three different routes
J. Appl. Microbiol.
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