title: Penetration of herbicides to groundwater in an unconfined chalk aquifer following normal soil applications.
abstract: The persistence and penetration of the herbicides isoproturon and chlorotoluron in an unconfined chalk aquifer has been monitored over a 4-year period through soil sampling, shallow coring and groundwater monitoring. Chlorotoluron was applied on plots as a marker compound, having never been used previously on that, or surrounding fields. The fieldsite had a 5 degree slope with soil depths of 0.5 to 1.5 m and a water table between 20 and 5 m from the soil surface. Where the water table was deepest (9-20 m below surface (mbs)) little or no positive herbicide detections were made. However, where the water table was at only 4-5 mbs, a regular pesticide signal of around 0.1 microg/l for isoproturon and chlorotoluron could be distinguished. Over the winter recharge period automatic borehole samplers revealed a series of short-lived peaks of isoproturon and chlorotoluron reaching up to 0.8 microg/l. This is consistent with a preferential flow mechanism operating at this particular part of the field. Such peaks were occurring over 2 years after the last application of these compounds. Shallow coring failed to uncover any significant pesticide pulse moving through the deep unsaturated zone matrix at the fieldsite.
authors.affiliation: Centre for Ecology and Hydrology, Wallingford, Oxon, UK. a.johnson@mail.nwl.ac.uk
authors.forename: A C
authors.initials: AC
authors.lastname: Johnson
authors.forename: T J
authors.initials: TJ
authors.lastname: Besien
authors.forename: C L
authors.initials: CL
authors.lastname: Bhardwaj
authors.forename: A
authors.initials: A
authors.lastname: Dixon
authors.forename: D C
authors.initials: DC
authors.lastname: Gooddy
authors.forename: A H
authors.initials: AH
authors.lastname: Haria
authors.forename: C
authors.initials: C
authors.lastname: White
mesh_terms: D004784:Environmental Monitoring; D006540:Herbicides / Q000032:analysis*; D008782:Methylurea Compounds / Q000032:analysis*; D010671:Phenylurea Compounds / Q000032:analysis*; D012621:Seasons; D012987:Soil; D012989:Soil Pollutants / Q000032:analysis*; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D006540:Herbicides; D008782:Methylurea Compounds; D010671:Phenylurea Compounds; D012987:Soil; D012989:Soil Pollutants; D014874:Water Pollutants, Chemical; C028904:isoproturon; C007033:chlortoluron