Effect of concentration and competition between different fungicide residues on the adsorption efficiency of activated vegetal fibres for treatment of wine

Abstract

Vineyards are strongly exposed to fungal diseases, attacks from insects and competition with weeds. Most treatments used on grape vines contain synthetic active substances, which may be transferred to the wine. Such pesticides have a negative image because many active substances are potential health hazards. A specific oenological treatment allowing the reduction of pesticide residues in wine based on activated vegetable fibres (AVF) is under examination by the International Organisation for Vine and Wine. This technique works efficiently and alters the wine only little (Lempereur et al. 2014). The purpose of this study was to investigate the difference in adsorption efficiency of the active substances most used by Swiss winegrowers. Furthermore, effects of concentration and competition between the different active substances in the adsorption efficiency of AVF were investigated. The concentration and competition trials were carried out using white wine without pesticides allowing to artificially spike six active substances. The investigation of the concentration effect led to the Freundlich isotherms allowing the calculation of the adsorption capacities of Fenpropidin k = 1816μg/g fiber and Fluopyram k = 556μg/g of fibre. This showed that the rate of reduction of these active substances is not related to the initial concentration, but remains stable over the tested range. The results of the competition trial indicate no interaction between different active substances present in a solution for the absorption by AVF. Indeed, it was not possible to show significant differences between the reduction rate of pesticides in a wine containing a cocktail of six active substances and wines containing only one of the active substances. Our results also confirm that the reduction rate depends on the active substance. Among the tested substances, there are three different efficiency classes: Mandipropamid, Cyprodinil and Fenpropidin with reduction rates between 80-100%, Fludioxonil and Fluopyram with rates between 50-80% and Iprovalicarb with a rate under 50%. This classification confirms the results of previous pre-industrial trials (Lempereur et al. 2014), except for Fenpropidin and Fluopyram that were never tested before. These experiments show the potential of AVF for active substances untested so far such as Fluopyram and Fenpropidin. Trials are currently under way to compare the efficiency of AVF between laboratory and pre-industrial conditions and to investigate the sensory impact on the wine, particularly the perception threshold of the AVF and their impact on the colloidal balance of the wine.