Nebila LICHIHEB Pesticide Behaviour in Soils, Water and Air 2-4 September 2013 York, UK

Transcription

1 Development and validation of a mechanistic pesticide emission model at the field scale: toward a tool for evaluating the sources of atmospheric contamination by pesticides Nebila LICHIHEB Nebila.Lichiheb@grignon.inra.fr Bedos C., Personne E., Benoit P., Bouhlel J., Bergheaud V., Fanucci O., Trivella A., Richard C., Barriuso E. UMR INRA-AgroParisTech Environnement et Grandes Cultures UMR CNRS, Institut de chimie de Clermont-Ferrand Pesticide Behaviour in Soils, Water and Air 2-4 September 2013 York, UK

2 Volatilization from plants Total pesticide volatilization Volatilization from soils Drift Deposition Wind erosion Run-off Surface processes of pesticides after their application to plants and soil The volatilization may represent a major emission pathway : several tens of percentage of the application dose (Bedos et al., 2002) 2/17

3 The volatilization from plants is faster and 5-13 times higher than volatilization from the soil (Rudel, 1997) The estimation of this transfer pathway remains problematic: poor understanding of processes occurring at the leaf surface Photodegradation Wash-off Leaf penetration lack of experimental data The complex interactions between agronomic and environmental : the use of modeling 3/17

4 Objective The development of a mechanistic pesticide emission model at the field scale in order to: Describe the processes occurring at the leaf surface and competing with volatilization Estimate pesticide volatilization at the field scale Outline of the presentation (1) of the pesticide volatilization process from plants: Adaptation of a resistive model (2) to study: The volatilization and leaf penetration processes The photodegradation process 4/17

5 Description of the pesticide volatilization process from plants using the SURFATM model (Personne et al., 2009) Inputs - Meteorological data - Plant and soil properties Inputs - Physico-chemical properties of pesticides - Application dose - Time of application Energy budget model (Choudhury and Monteith, 1988) Surface temperature Pollutant exchange model (Nemitz et al., 2000) Outputs - Energy balance - Surface temperature (soil, leaf) - Pesticide volatilization flux 5/17

6 Adaptation of the SURFATM model to pesticides A biophysical model based on the concept of resistances (article submitted) Atmosphere x a Parameterization inspired from PEARL model Leaf R a R bc x c Stomatal R s x i Cuticular = 0 R c F c 1 R bc Volatilization Canopy flux from boundary canopy layer resistance x c x x i i eff Pesticide concentration in the canopy x ieff Psat RT Pesticide concentration available for volatilization x T M i Q(t) Soil R 2 Q( t) Q( t 1 ) ( F c ( K pen K deg ) Q( t 1 )) t Soil x soil x i the air pesticide concentration just above the leaves, Q(t) the areic mass of pesticide on the plants at time t, λ the reference areic mass of pesticide on the plants (Leistra and Wolters, 2004) 6/17

7 SURFATM-Pesticides Mechanistic description of volatilization process Empirical description of processes at the leaf surface Integration of empirical coefficients of leaf penetration (K pen ) and photodegradation (K deg ) Measured experimentally Leistra (2005) classification Five main classes of leaf penetration rate - Very fast penetration: K pen = 17d -1 - Fast penetration: K pen = 3.3 d -1 - Moderate penetration: K pen = 0.69 d -1 - Slow penetration: K pen = 0.14 d -1 - Very slow penetration: K pen = 0.03 d -1 Five main classes of photodegradation rate - Very fast photodegradation: K deg = 17d -1 - Fast photodegradation: K deg = 3.3 d -1 - Moderate photodegradation: K deg = 0.69 d -1 - Slow photodegradation: K deg = 0.14 d -1 - Very slow photodegradation: K deg = 0.03 d -1 7/17

8 Comparison of simulated and experimental data at the field scale (Bedos et al., 2010) chlorothalonil fenpropidin K pen = 0.14 d -1, K deg = 0.23 d-1 (Leistra and Van den Berg, 2007) K pen + K deg = 20 d -1 (Leistra, 2005) - Volatilization fluxes of chlorothalonil were satisfactory simulated - Model can't describe volatilization flux of fenpropidin: the empirical coefficients used for competing process are inadequate? How to describe competing processes in a mechanistic way? 8/17

9 Experimental set-up in laboratory allowing the study of volatilization and leaf penetration processes Temperature inside: C Dark: without photodegradation 3 wheat leaves in chamber C-labelled fungicides: epoxiconazole chlorothalonil fenpropidin (applied as pure substance and formulated product) Duration: 1, 3, 6 and 24h - Leaf and PUF extractions => suitable solvents - Samples => a liquid scintillation counter 9/17

10 Working assumption: quantification of four extracted fractions on and in plant leaves (Leistra, 2005; Rashott et al., 2001; Riederer and Muller, 2006) 10/17

11 Plant material - Wheat leaves sampled from plants cultivated in the field Pesticide application procedure Winter wheat Premio - Application of 60 µl per leaf (30 droplets of 2 µl) - The dose covered homogenously all the leaf surface (electronic Eppendorf micropipette) Electronic micropipette 11/17

12 Extraction of leaves - Water washable fraction: rinsing with 20 ml of Milli-Q water during 60 s - Fraction adsorbed on leaf surface: soaking in 20 ml of ethanol during 60 s - Fraction penetrated into cuticular waxes: soaking in 20 ml of hexane during 60 s - Fraction of bound residues: combustion of leaves Extraction of PUF - Five successive extractions with 20 ml of ethanol - Manual shaking for 1 min - Squeezing for 1 min using a metal spatula 12/17

13 Extracted radioactivity Introduction Distribution kinetic of the different fractions of epoxiconazole applied on wheat leaves Pure epoxiconazole Formulated epoxiconazole Fraction penetrated into foliar cells Fraction penetrated into cuticular waxes Fraction adsorbed on leaf surface Water washable fraction Volatilised fraction Time after application (h) Low temporal evolution of the different fractions Time after application (h) Gradual decrease in the water washable fraction compensated by an increase of the fraction of bound residues 24h after application only 3.4 % had volatilized: low volatile fungicide 52.2% of epoxiconazole had penetrated into plant leaves: effect of formulation 13/17 Pure epoxiconazole: K pen = 0.18 d -1, Formulated epoxiconazole: K pen = 0.48 d -1

14 Relations between competing processes and physico-chemical properties of pesticides Fraction adsorbed on leaf surface Fraction penetrated into foliar cells Epoxiconazole Epoxiconazole Fenpropidin Chlorothalonil Fenpropidin Effect of formulation Formulations Pure products Chlorothalonil Log (Kow) Water solubility (mg/l) Pure products: pesticide adsorption on leaf surface tends to increase with increasing lipophilicity of the compound Formulated products: the formulation promotes the penetration into plant leaves => the availability of the product on leaf surface Pesticide penetration into foliar cells tends to increase with increasing water solubility of the compound Penetration via the aqueous route occurs for compounds with high water solubility 14/17

15 Experiments allowing the study of the photodegradation process Preparation of thin paraffin wax films to represent the waxy upper layer of leaves Application of the pesticide solution as pure substance and formulated product Evaporation of the solvent using a drying device For pesticides studied photodegradation seems to have played a minor role Irradiation of the samples using a simulated solar light (Suntest) Rinsing of the wax films using suitable solvent and analysis of the samples by HPLC 15/17

16 Conclusions - The adaptation of SURFATM to pesticides: successful development of a processbased model to simulate pesticide volatilization from plants. - The new experimental system: the study of the behavior of pesticides applied on the leaf surface and the description of the effect of formulation => recovery rates of % of the applied radioactivity. - The adopted working assumption for the extraction procedure of leaves is proving successful: a refined description of leaf penetration process. - Further analysis of the relationships between competing processes and physicochemical properties of pesticides : a generic parameterization of processes occurring at the leaf surface. - Evaluation of the model with available datasets and comparison with other models (eg: PEARL model). - Analysis of the contribution of soil volatilization to the global volatilization by a modelling approach: coupling SURFATM-Volt air 16/17

17 Thank you for your attention Acknowledments ECHAP project founded by the French Ministry of Environment (Pest- 2011/02/10-11) Soil team of UMR EGC (INRA-Grignon, France) Laboratory of photochemistry (Clermont-Ferrand, France) Alterra Laboratory (Wageningen, Pays Bas) Syngenta 17/17