Flood event impact on pesticide transfer in a small agricultural catchment (Montoussé at Auradé, south west France)

Abstract

In this paper, pesticide transfer dynamic is studied during two flood events in a small experimental catchment close to Toulouse (south west France). Thirteen pesticide molecules (herbicides, fungicides) have been analysed by multi-residue technique on filtered and unfiltered waters. The results show very high pesticide concentrations in the different fractions compared to low flow periods and to the data collected by the French institutional networks in charge of the pesticide river water pollution survey. Several molecules present concentration higher than 0.1 µg L⁻¹ and even higher than 1 µg L⁻¹ in the unfiltered waters. In the suspended matters the concentrations vary respectively between 0.1 and 30 µg g⁻¹ according to the molecules and can represent 40 to 90% of the total concentration for low soluble molecules. All the molecule concentrations and fluxes increase during the flood flows and have positive relationships with the stream discharge, but hysteresis between rising and falling periods can be observed for some molecules. Pesticide concentrations in unfiltered waters and partitioning between dissolved and particulate fractions (K_d = [diss]/[part]) are controlled by dissolved organic carbon and total suspended matter. A good negative relationship can be established between log K_d and log K_ow for 6 molecules.

Keywords:

• fungicide
• herbicide
• stream waters
• filtered waters
• unfiltered waters
• suspended matters
• dissolved organic carbon
• hysteresis
• partition coefficient

Acknowledgements

This study was supported by CPER (Midi-Pyrénées region) and FEDER (European Commission) funds within the framework of IMAQUE (IMpact des Activités agricoles sur Qualité des Eaux, des sols, des sédiments et des milieux aquatiques) project (ECOBAG research network). Many thanks to the Association des Agriculteurs d’Auradé (AAA), to GPN Agriculture/TOTAL and to the CESBIO laboratory (CNRS-University of Toulouse-CNES) for their cooperation. Lobat Taghavi benefits from a PhD fellowship from Karoon Khozistan Compagny (Iran).