Degradation of primisulfuron by a combination of chemical and microbiological processes

Microbial degradation of the herbicide primisulfuron was investigated using enrichment cultures from contaminated soils and 20 axenic cultures. At neutral pH, no disappearance of the herbicide was detected either in the enrichment cultures or in the growth media of the axenic microbial cultures. During the growth of some of the microbial strains, however, the pH of the medium dropped below 6, resulting in the hydrolysis of primisulfuron. The rate of primisulfuron hydrolysis was clearly pH dependent; primisulfuron was more persistent in neutral or weakly basic solutions than in acidic solutions. After hydrolysis of the herbicide, four products were observed. These were identified as methyl 2-(aminosulfonyl)benzoate, 2-amino-4,6-(difluoromethoxy)pyrimidine, 2-N-[[[[[4, 6-bis(difluoromethoxy)-2-pyrimidinyl]amino]carbonyl]amino]sulfonyl ]be nzoic acid, and 2-(aminosulfonyl)benzoic acid. After hydrolysis, it was found that the fungus Phanerochaete chrysosporium mineralized 27 and 24% of (14)C-phenyl- and (14)C-pyrimidine-labeled products, respectively, after 24 days of incubation. Similarly, Trametes versicolor mineralized 13 and 11% of (14)C-phenyl- and (14)C-pyrimidine-labeled hydrolysis products, respectively. In addition, primisulfuron in a hydrolytically stable solution, at pH 7. 0, was rapidly decomposed after ultraviolet irradiation, and two photolysis products were isolated [methylbenzoate and 4, 6-(difluoromethoxy)pyrimidin-2-ylurea]. When (14)C-phenyl-labeled primisulfuron was exposed to photolysis for 24 h, 32% of the initial radioactivity was recovered as (14)CO(2), whereas no (14)CO(2) was detected if the herbicide was labeled at the (14)C-pyrimidine position. Mineralization of (14)C-pyrimidine-labeled products of photolyzed primisulfuron by P. chrysosporium was approximately 25% after 24 days. These results clearly indicate that hydrolysis and photolysis of primisulfuron facilitated microbial degradation.     

Adsorption and desorption of triasulfuron by soil

The adsorption and desorption of the herbicide triasulfuron [2-(2-chloroethoxy)-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide] by three soils, soil organic matter (H(+) and Ca(2+)-saturated), and an amorphous iron oxide were studied. Adsorption isotherms conformed to the Freundlich equation. It was found that pH is the main factor influencing the adsorption in all of the systems. Indeed, the adsorption on soils was negatively correlated with pH. The highest level of adsorption was measured on soils with low pH and high organic carbon content. Moreover, it was found that humic acid is more effective in the adsorption compared with calcium humate (the pH values of the suspensions being 3.5 and 6, respectively). Experiments on amorphous iron oxide confirmed the pH dependence. Desorption was hysteretic on soils having high organic carbon content.     

Calcium chloride washing of calcareous sediment from a freshwater canal: effect on the removal of potentially toxic elements and water aggregate stability

Journal of Soils and Sediments - Canal dredging and shaping produce considerable amounts of sediments whose reuse on- and off-site depends on their pollution level. This study explores the...     

Photodegradation of herbicide triasulfuron

Triasulfuron was degraded in aqueous solution by ultraviolet irradiation to yield 2-chloroethoxybenzene and (4-methoxy-6-methyl-1,3,5-triazin-2-yl)urea. The reaction followed first-order kinetics. In sunlight, the reaction was slower and afforded these two photoproducts together with 2-amino-4-methoxy-6-methyltriazine and 2-(2-chloroethoxy)benzenesulfonamide. The latter compounds arise from hydrolytic cleavage of the sulfonylurea bridge of triasulfuron because of the acidity of the reaction medium due to the loss of sulfur dioxide. A mechanism which accounts for the formation of the photoproducts is proposed. © 1999 Society of Chemical Industry     

Effect of undesalted dissolved organic matter from composts on persistence, adsorption, and mobility of cyhalofop herbicide in soils

The effect of undesalted dissolved organic matter (DOM) extracted from composts on the degradation, adsorption, and mobility of cyhalofop herbicide in soils was studied. A paddy-field sediment poor in organic matter (OM), an OM-rich forest soil, and DOM from agroindustrial or municipal waste compost were used. DOM increased the cyhalofop-acid but not the cyhalofop-butyl solubility in water. The degradation of cyhalofop-butyl in the sediment was slow, giving cyhalofop-acid as the only metabolite, whereas in forest soil, the process was faster, and three byproducts were detected. Soil pretreatment with DOM did not modify the degradation pattern but only reduced the adsorption of cyhalofop-butyl by soil, whereas it increased the adsorption of cyhalofop-acid. Among the cationic components of DOM solutions, the potassium ion seems to be related to the increased adsorption of the cyhalofop-acid in both OM-poor and OM-rich soils, yielding reversible complexes with the former and favoring hydrophobic interactions with the latter.     

Hydrolysis and adsorption of cyhalofop-butyl and cyhalofop-acid on soil colloids

A study was undertaken to investigate the stability of cyhalofop-butyl (2 R)-2-[4-(4-cyano-2-fluorophenoxy)phenoxy]butylpropanoate (CyB), an aryloxyphenoxy-propionic herbicide, at different pH values. The hydrolysis of CyB was faster in nonsterile than in sterile water. In sterile medium, CyB degraded only to (2 R)-2-[4-(4-cyano-2-fluorophenoxy)phenoxy]propanoic acid (CyA), whereas in nonsterile water, also the metabolites (2 R)-2-[4-(4-carbamoyl-2-fluorophenoxy)phenoxy]propanoic acid (CyAA) and (2 R)-2-[4-(4-carboxyl-2-fluorophenoxy)phenoxy]propanoic acid (CyD) were detected. The adsorption of CyB onto clays, iron oxide, and dissolved organic matter (DOM), using a batch equilibrium method, was also studied. A lipophilic bond is responsible for CyB adsorption on DOM. CyB was adsorbed on Fe(III)- and Ca-clays through hydrogen bonding between the carbonyl oxygen and water surrounding the exchangeable cations. In the interlayer of K-clay, CyB was hydrolyzed to CyA, which remained adsorbed therein as a monomer. The acid CyA was adsorbed only by the Fe-oxide through complexation. The CyA-Fe-oxide complex was stable and did not undergo degradation.