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Relevant academic research and scientific papers

Diuron degradation in irradiated, heterogeneous iron/oxalate systems: The rate-determining step

The purpose of this study was to examine the various factors that control the kinetics of diuron degradation in irradiated, aerated suspensions containing goethite (α-FeOOH) and oxalate, in the following denoted as heterogeneous photo-Fenton systems. In t

Degradation products of a phenylurea herbicide, diuron: Synthesis, ecotoxicity, and biotransformation

The degradation products of diuron (photoproducts and metabolites), already described in the literature, were synthesized in order to carry out further investigations. Their ecotoxicity was determined using the standardized Microtox test, and most of the derivatives presented a nontarget toxicity higher than that of diuron. Therefore, the biotransformation of these compounds was tested with four fungal strains and a bacterial strain, which were known to be efficient for diuron transformation. With the exception of the 3,4-dichlorophenylurea, all the degradation products underwent other transformations with most of the strains tested, but no mineralization was observed. For many of them, the biodegradation compound for which the toxicity was important was 3,4-dichlorophenylurea. This study underlines the importance of knowing the nature of the degradation products, which has to be kept in mind while analyzing natural water samples or soil samples.

Degradation of diuron photoinduced by iron(III) in aqueous solution

The degradation of diuron photoinduced by iron(III) in aqueous solution has been investigated with different iron(III) species (monomeric species Fe(OH)2+, dimeric species Fe2(OH)2/4+ and water-soluble oligomeric species) under monochromatic excitation at 365 nm and under sunlight. The rate of degradation depends on the concentration in Fe(OH)2+, the most reactive species in terms of ·OH radical formation. The major photoproduct is 3-(3,4-dichlorophenyl)-1-formyl-1-methylurea which represents more than 60% of diuron disappearance. The mechanism only involves the attack by ·OH radicals arising from iron(III) excited species. The half-lives of diuron when submitted to such a process in the environment were estimated to be 1-2 h and a few days according to the concentration of Fe(OH)2+ (respectively 70% and 10% of total iron(III) concentration).

Photolysis of diuron

The major photoproducts observed in the photolysis of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] (2) in aqueous solution resulted from a heterolytic substitution of chlorine by OH (photohydrolysis) A wavelength effect was observed: at 254 nm the formation of 3-(4-chloro-3-hydroxyphenyl)-1,1-dimethylurea (3) accounted for more than 90% of the conversion, whereas when the solution was irradiated in 'black light' (85% of photons emitted at 365 nm, about 7% at 334 nm), the major photoproduct was 3-(3-chloro-4-hydroxyphenyl) -1,1-dimethylurea (4). The presence of methanol favoured the photoreduction into 3-(3-chlorophenyl)- 1, 1 -dimethylurea (5). Completely different reactions were observed when 2 was irradiated in dry aerobic conditions on silica. They resulted from elimination or oxidation of methyl groups. The main photoproducts initially formed were 3-(3,4-dichlorophenyl)-l-methyl urea (6) and 3-(3,4-dichlorophenyl)-l-formyl-l-methylurea (7). In the second stage (6) was transformed into (3,4-dichlorophenyl)-urea (8) and 3-(3,4-dichlorophenyl)-1-formylurea (9); some other minor products such as monuron (1) were also identified. The formation rate of 6 and 7 was much slower on clay (montmorillonite or kaolin) than on silica. In contrast with products 6 and 8, the formation of 7 and 9 needed the presence of oxygen: they did not appear when diuron was irradiated in deoxygenated C2Cl3F3 . It can be concluded that the photolysis of diuron is highly dependent on the conditions of irradiation.