Pesticide transfers in a small agricultural catchment (Aurade, south west of France) during flood flows: partitioning into dissolved and particulate fractions

Abstract

Pesticide transfer dynamic is studied during 2 flood events in a small experimental catchment close to Toulouse (South West of France). 16 to 25 pesticide molecules (herbicides, fungicides) have been analysed by multi-residue technique on filtered and unfiltered waters and on bottom sediments. 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 ug/L and even higher than 1 ug/L in the unfiltered waters. In the suspended matters and in the bottom sediments, the concentrations vary respectively between 0.1-30 ug/g and 0.01 -1 ug/g according to the molecules. All the molecule concentrations increase during the flood flows and present positive relationship with the stream discharge, but hysteresis between rising and falling periods can be observed for some molecules. Pesticide concentrations in unfiltered waters are generally controlled by dissolved organic carbon (DOC) content and total suspended matter (TSM) concentration. Partitioning between dissolved and particulate (Kd) fractions is also controlled by DOC, and TSM. A good negative relationship can be established between log Kd and log Kow for 6 molecules.