Effects of temperature and water content on degradation of isoproturon in three soil profiles

• Published in: Chemosphere (Oxford) Vol. 64; no. 7; pp. 1053 - 1061
• Main Authors: Alletto, Lionel, Coquet, Yves, Benoit, Pierre, Bergheaud, Valérie
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.08.2006; Elsevier
• Subjects: agricultural soils; Agronomy. Soil science and plant productions; Applied sciences; biodegradation; Biodegradation, Environmental; Biological and medical sciences; Biological and physicochemical properties of pollutants. Interaction in the soil; Clay content; clay fraction; Degradation half-life; Degradation pathway; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; environmental fate; Environmental Sciences; Exact sciences and technology; France; Fundamental and applied biological sciences. Psychology; Global Changes; half life; herbicide residues; Herbicides - metabolism; isoproturon; Kinetics; Mineralization; Phenylurea Compounds - metabolism; Polar metabolites; Pollution; Pollution, environment geology; Soil - analysis; Soil and sediments pollution; Soil and water pollution; Soil Microbiology; Soil Pollutants - metabolism; soil profiles; Soil science; soil temperature; soil water content; soil water potential; subsoil; Temperature; topsoil; Water - analysis; Water availability; France; Europe; Clay content; Polar metabolites; Water availability; Mineralization; Degradation pathway; Degradation half-life; Microbial activity; Metabolite; Temperature effect; Environmental factor; Metabolic pathway; Soil pollution; Luvisols; Selfpurification; Risk assessment; Ureas; Organic compounds; Ground water; Biodegradation; Cambisols; Pollutant behavior; Soil moisture; Isoproturon; Pesticides; Agricultural soil; Herbicide; Water pollution; Degradation product; TENEUR EN EAU DU SOL; WATER AVAILABILITY; DEGRADATION HALF-LIFE; CLAY CONTENT; DEGRADATION PATHWAY; MINERALIZATION; POLAR METABOLITES
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2005.12.004

The phenylurea herbicide isoproturon, 3-(4-isopropylphenyl)-1,1-dimethylurea (IPU), is widely used to control pre- and post-emergence of grass and broad-leaved weeds in cereal crops. Its degradation in soils is a key process for assessing its leaching risk to groundwater resources. The degradation properties of various samples from surface and subsurface soil (down to 1 m depth) of a heterogeneous agricultural field were studied using 14C-IPU. Laboratory incubations were carried out at 22 and 10 °C and at water contents 90% and 50% of the estimated water holding capacity (eWHC) corresponding to water potentials between −56 kPa and −660 MPa. Degradation was found to be more sensitive to water content variations than to temperature variations in the ranges that we used. For surface layers, at 10 and 22 °C, the degradation half-life increased by a factor 10 and 15, respectively, when water content decreased from 90% to 50% eWHC. Under optimal degradation conditions (i.e. 22 °C and 90% eWHC), 3-(4-isopropylphenyl)-1-methylurea (MDIPU) was the main metabolite in surface samples. At subsurface depths, IPU half-lives were larger than 100 d, IPU was the main compound after 92 d of incubation and the main metabolite was an unidentified polar metabolite. These results suggest a metabolic pathway involving hydroxylations for subsurface materials. IPU degradation was largely affected by water availability in both surface and subsurface horizons. Clay content seemed to play a major role in degradation processes in subsurface soil by determining through sorption IPU availability in soil solution and/or by limiting water availability for microorganisms.