title: Long-term experiments to investigate irreversibility in sorption of pesticides to soil.
abstract: Experiments investigated irreversibility in pesticide sorption to soil. Sorption behaviour under abiotic conditions was quantified for chlorotoluron, prometryn and hexaconazole in three soils over periods of up to 274 days. An isotope-exchange procedure was used whereby sorption of (12)C- and (14)C-pesticide isotopes in shaken suspensions of three soils (56-168 days shaking) was followed by substitution of the isotopes in the liquid phase and a 14-day exchange phase. This was followed by forced isotope exchange where the sorbed (14)C material was exchanged by adding an excess of non-radiolabelled compound. Experiments were concluded with solvent extraction and soil combustion to determine remaining radioactivity. Under conditions of continuous shaking, the pesticide-soil systems took around four months to approach sorption equilibrium, resulting in strong asymmetry between the profiles of exchange for isotopes of all three compounds. Physically entrapped residues were released back into solution under the steep concentration gradient of forced isotope exchange and small amounts of radioactivity were still being released at the termination of the experiment. The profiles of exchange did not deviate markedly from ideal behaviour based on the assumption that sorption is fully reversible. Whilst the timescales for release of sorbed residues back into solution were very long, soil combustion at study termination only yielded <1-2% of applied radioactivity; this confirms that sorption processes under abiotic soil conditions were overwhelmingly reversible for this set of compounds and soils.
authors.affiliation: Environment Department, University of York, Heslington, York, YO10 5DD, UK; Food and Environment Research Agency (FERA), Sand Hutton, York, YO41 1LZ, UK; Syngenta Ltd, Jealott's Hill International Research Station, Bracknell, Berkshire, RG42 6EY, UK. Electronic address: laura.suddaby@tsgeconsulting.com.
authors.forename: L A
authors.initials: LA
authors.lastname: Suddaby
authors.affiliation: Food and Environment Research Agency (FERA), Sand Hutton, York, YO41 1LZ, UK. Electronic address: sabine.beulke@enviresearch.com.
authors.forename: S
authors.initials: S
authors.lastname: Beulke
authors.affiliation: Food and Environment Research Agency (FERA), Sand Hutton, York, YO41 1LZ, UK. Electronic address: wendy.vanbeinum@enviresearch.com.
authors.forename: W
authors.initials: W
authors.lastname: van Beinum
authors.affiliation: Syngenta Ltd, Jealott's Hill International Research Station, Bracknell, Berkshire, RG42 6EY, UK. Electronic address: robin.oliver@syngenta.com.
authors.forename: R G
authors.initials: RG
authors.lastname: Oliver
authors.affiliation: Syngenta Ltd, Jealott's Hill International Research Station, Bracknell, Berkshire, RG42 6EY, UK. Electronic address: sui.kuet@syngenta.com.
authors.forename: S
authors.initials: S
authors.lastname: Kuet
authors.affiliation: Environment Department, University of York, Heslington, York, YO10 5DD, UK. Electronic address: colin.brown@york.ac.uk.
authors.forename: C D
authors.initials: CD
authors.lastname: Brown
mesh_terms: D000327:Adsorption; D008956:Models, Chemical; D010575:Pesticides / Q000032:analysis / Q000737:chemistry*; D010671:Phenylurea Compounds; D011400:Prometryne; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis / Q000737:chemistry*
chemical_list: D010575:Pesticides; D010671:Phenylurea Compounds; D012987:Soil; D012989:Soil Pollutants; D011400:Prometryne; C007033:chlortoluron
keywords: Bound residue; Desorption; Irreversible sorption; Non-extractable residue; Pesticide; Sorption