Subsurface tile drainage loss of modern pesticides: field experiment results

The concentration and loss of two herbicides (bentazone and MCPA), two fungicides (fenpropimorph and propiconazole) and two insecticides (dimethoate and pirimicarb) were measured in tile drainage water from a 2,813 m² experimental grass field from May to August 2001. Three different pesticides were applied to the field and subsequently a rainfall of 10 mm was simulated during the first experiment and 16 mm during the second experiment. Bromide was applied as a conservative tracer in the first experiment and the concentration of bromide and suspended sediment was also measured in tile drainage water. In the first experiment, maximum concentrations of bentazone, fenpropimorph and dimethoate in drainage water were 5.8 μg l^-1, 0.33 μg l^-1 and 2.29 μg l^-1, respectively. In the second experiment, maximum concentrations for MCPA, propiconazole and pirimicarb were 3.6 μg l^-1, 0.065 μg l^-1, 2.3 μg l^-1, respectively. The loss:applied ratio was highest for bentazone (0.088%) and declined in the order of dimethoate (0.057%), pirimicarb (0.050%), propiconazole (0.0031%) and fenpropimorph (0.00042%). Exposure of the macroinvertebrate species Gammarus pulex to pesticides in the drainage water during the second experiment (exposure time: 7 hours) showed significant mortality/inactivity as compared to an upstream and downstream control.