Pesticide volatilization from plants : experimental approach and modelling

Abstract : The agricultural activity presents the main source of the atmospheric contamination by pesticides. The occurrence of pesticides in the atmosphere concerns the research community due to their potential impacts on population and ecosystems. The volatilization from plants is higher and faster than the volatilization from soil. However, this transfer pathway is difficult to assess with few available models. The lack of knowledge on pesticide volatilization from plants is essentially linked to the complex interactions between processes occurring at the leaf surface and competing with volatilization, such as leaf penetration and photodegradation. A laboratory volatilization chamber was developed in order to study simultaneously the processes of volatilization and leaf penetration of 3 fungicides (epoxyconazole, chlorothalonil and fenpropidine) applied on wheat leaves. These experimentations allowed a refined description of leaf penetration process using a well-defined sequential extraction procedure of leaves. Leaf penetration coefficients, which are necessary to modelling the pesticide fate in plants, were calculated. Moreover relationships between physicochemical properties of pesticides and processes regulating their distribution on and in plant leaves were identified. The experimental study on the photodegradation process consisted in irradiating wax films using simulated solarlight. The results showed that for experimental conditions and pesticides chosen in our study, photodegradation seems to have played a minor role as dissipation process.The soil-vegetation-atmosphere exchange model SURFATM was adapted for pesticides using an approach inspired from the parameterization developed in the PEARL model. The originality of this model resides in its mechanistic description of the micro-meteorological conditions inside the canopy. As a first step the SURFATM-Pesticides model describes leaf penetration and photodegradation processes using empirical coefficients. Then a distribution of pesticide residues in the different compartments of the leaf surface was identified based on the experimental results. This approach allowed the quantification of pesticide fraction on the leaf surface available for volatilization. The combination of this compartmental approach and the identified relationships between physicochemical properties of pesticides and the leaf penetration process improves the genericity of the model. Moreover, the effect of the pesticide formulation in the commercial preparations was integrated in the model via empirical coefficients allowing a better simulation of the volatilization fluxes in the case of systemic pesticides. Comparison of model results and experimental measurements collected from two datasets showed satisfactory results. Once the contribution of soil volatilization has been activated, the SURFATM-Pesticides model will allow us to predict the overall pesticide volatilization at the field scale.
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Nebila Lichiheb. Pesticide volatilization from plants : experimental approach and modelling. Ecology, environment. AgroParisTech, 2014. English. ⟨NNT : 2014AGPT0047⟩. ⟨tel-01160239⟩

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