title: Spatial variability in herbicide degradation in the subsurface environment of a groundwater protection zone.
abstract: The aim of this study was to investigate the spatial variability in degradation and mineralization of atrazine and isoproturon in subsurface samples taken from sandy loam soils overlying gravel terraces which form part of a groundwater protection zone. Percussion drilling was used to obtain samples from 11 boreholes (maximum depth 3 m). Unlabelled atrazine or isoproturon, and ring-14C-labelled atrazine or isoproturon were added to samples, incubated at 25 degrees C for up to 16 weeks, and analyzed for the residual herbicide or [14C]carbon dioxide. All samples showed the potential to degrade these herbicides, although the percentage degradation decreased by a factor of 2-3 from the surface soil to a depth of 3 m. This was associated with a decrease in organic matter content, but there was no change in the potential to mineralize acetate, indicating that specific changes in the catabolic ability of the microbial population occurred with depth. The capacity of samples to mineralize atrazine and isoproturon to carbon dioxide decreased markedly with depth, with no mineralization potential observed at a depth of 80 cm.
authors.affiliation: Department of Soil Science, University of Reading, Whiteknights, PO Box 233, Reading RG6 6DW, UK. m.wood@reading.ac.uk
authors.forename: Martin
authors.initials: M
authors.lastname: Wood
authors.forename: Salah
authors.initials: S
authors.lastname: Issa
authors.forename: Miriam
authors.initials: M
authors.lastname: Albuquerque
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Johnson
mesh_terms: D000085:Acetates / Q000378:metabolism; D001280:Atrazine / Q000737:chemistry / Q000378:metabolism; D001419:Bacteria / Q000254:growth & development; D002245:Carbon Dioxide / Q000138:chemical synthesis; D002250:Carbon Radioisotopes; D005618:Fresh Water / Q000032:analysis*; D006540:Herbicides / Q000737:chemistry / Q000378:metabolism*; D008782:Methylurea Compounds / Q000737:chemistry / Q000378:metabolism; D008903:Minerals / Q000138:chemical synthesis; D010671:Phenylurea Compounds; D012822:Silicon Dioxide / Q000032:analysis; D012987:Soil / Q000032:analysis*; D012988:Soil Microbiology; D013997:Time Factors; D014227:Triazines / Q000737:chemistry / Q000378:metabolism
chemical_list: D000085:Acetates; D002250:Carbon Radioisotopes; D006540:Herbicides; D008782:Methylurea Compounds; D008903:Minerals; D010671:Phenylurea Compounds; D012987:Soil; D014227:Triazines; D002245:Carbon Dioxide; C028904:isoproturon; D012822:Silicon Dioxide; D001280:Atrazine