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A Model for Linking the Effects of Parathion in Soil to its Degradation and Bioavailability Kinetics

^a Institut National de la Recherche Agronomique (INRA), CSE Bat. Sol, Site Agroparc, 84914 Avignon cedex 09, France
^b Département "Environnement et Agronomie", Institut National de la Recherche Agronomique (INRA), Bat. CSE-Sol, Site Agroparc, 84914 Avignon cedex 09, France
^c Institut National Agronomique de Paris-Grignon, EGC-sol, BP: 01, 78850 Thiverval-Grignon, France

View larger version (11K): [in a new window]   Fig. 1. Schematic representation of the model (S for the pesticide and M for the metabolite; k1, k2, k3, k4 and km1, km2, km3, km4 are kinetic coefficients of sorption of parathion and paraoxon, respectively).

View larger version (20K): [in a new window]   Fig. 2. Measured (symbols) and simulated (continuous lines) water potentials at different depths in a soil column.

View larger version (41K): [in a new window]   Fig. 3. Parathion and metabolites as percentage of radioactivity (by layer) in the soluble phase and in the weakly sorbed phase 5 and 19 d after the beginning of incubation in two soil columns in the top 5 cm.

View larger version (20K): [in a new window]   Fig. 4. Depth profiles of measured (symbols) and predicted (continuous lines) (parathion + metabolites) concentration profiles (a) 5 and (b) 19 d after the beginning of incubation in two soil columns. Error bars are not presented because they are less than 0.0008 (x10–6 g g–1 of soil) and not visible.

View larger version (24K): [in a new window]   Fig. 5. Times series of measured (symbols) and predicted (continuous lines) concentrations for parathion (a, c) and its metabolite (b, d) in the layers 0 to 0.01 and 0.03 to 0.04 m during the 19 d of the experiment. For metabolite concentrations, the experimental points correspond to the total (paraoxon + p-nitrophenol) concentration.

View larger version (20K): [in a new window]   Fig. 6. (a) Rainfall, (b) water potential, and (c) soil temperature versus time in an 11-mo simulation. The continuous lines correspond to the model predictions and the symbols correspond to the measurements performed during the experiment.

View larger version (20K): [in a new window]   Fig. 7. Predicted (parathion + metabolites) concentration profiles (a) 1 and (b) 11 mo after the application of parathion.

View larger version (26K): [in a new window]   Fig. 8. Predicted concentrations for parathion and paraoxon at two depths, during an 11-mo simulation.

View larger version (16K): [in a new window]   Fig. 9. Product (concentration of parathion and paraoxon x time of application) during (a) a 19-d experiment and (b) 11 mo of simulation at different depths. The horizontal line indicates the EC50 value (effective concentration that inhibits the mobility of 50% nematodes) for the nematode Caenorhabditis elegans.