Off-site transport of pesticides in dissolved and particulate forms from two land uses in the Mt. Lofty Ranges, South Australia

The form in which pesticides are transported off-site can have implications for their bioavailability, ecotoxicological impact and the effectiveness of any management strategies implemented to minimise their movement. We have investigated the form in which nine pesticides (carbaryl, fenarimol, azinphos methyl, penconazole, pirimicarb, chlorpyrifos, propiconazole, procymidone and bupirimate) were transported in surface water from an apple and cherry orchard in the Mt. Lofty Ranges, South Australia, over three years. The majority of pesticides monitored were found to move off-site in the dissolved (<1.2 μm) phase. Only propiconazole moved off-site predominantly (70–90%) by colloidal transport in association with particulate (>1.2 μm) material. Chlorpyrifos was detected in surface drainage water for several months and the predominant phase in which it moved varied between events in a year and during an event. The effectiveness of pesticide physicochemical properties as surrogates for predicting mode of transport of pesticides, in this region was determined by regression of average proportion (%) of each pesticide in the dissolved phase for each event against the relevant physicochemical parameters. There was no relationship between average proportion in the dissolved phase (<1.2 μm) and any of the pesticide characteristics considered. This suggests that off-site transport of pesticides is governed by complex biological and hydrological interactions and the use of simple physicochemical properties as surrogates for predicting offsite transport may not be applicable. These results have implications for the effectiveness of management strategies, including buffer strips and sedimentation ponds, to minimise transport and suggest that, unless adequate residency time is available for sorption of the pesticides, these strategies may have limited use for minimising the transport of the pesticides used in the two land uses studied here. This study has highlighted the importance of understanding the mode of transport of pesticides for informing the choice of management strategies to minimise potential offsite transport of pesticides under different field conditions.

► The form in which nine insecticides and fungicides were transported off-site was studied.
► The majority of the pesticides were transported in the dissolved (<1.2 μm) phase irrespective of hydrology.
► Propiconazole moved predominantly (70–90%) in association with particulate (>1.2 μm) phase.
► There was no relationship between the average proportion in the dissolved (<1.2 μm) phase and any pesticide physico-chemical property.