Behavior of nursery-box-applied fipronil and its sulfone metabolite in rice paddy fields

Simulating the fate and transport of nursery‐box‐applied pesticide in rice paddy fields

“…The RZ compartment was estimated to be 5 cm deep and to occupy 5% of the total rice paddy field area. Fipronil was applied as a conventional‐release granular formulation during both BT and AS applications, whereas imidacloprid was applied as a controlled‐release granular formulation as an AS treatment and as a conventional‐release granular formulation during the BT treatment . As previously mentioned, the insecticides were applied immediately before the transplanting of rice seedlings during the BT treatment, whereas rice seeds and insecticides were broadcast over the basal soil layer of about 1 cm and then covered by a topsoil layer of approximately 1 cm during the AS treatment .…”

“…Fipronil was applied as a conventional‐release granular formulation during both BT and AS applications, whereas imidacloprid was applied as a controlled‐release granular formulation as an AS treatment and as a conventional‐release granular formulation during the BT treatment . As previously mentioned, the insecticides were applied immediately before the transplanting of rice seedlings during the BT treatment, whereas rice seeds and insecticides were broadcast over the basal soil layer of about 1 cm and then covered by a topsoil layer of approximately 1 cm during the AS treatment . Water balances were monitored on a daily basis over the duration of 35 days, whereas fipronil and imidacloprid concentrations in the PW and PSL were analysed at 1, 3, 5, 7, 14, 21, 28 and 35 days after transplanting the rice in the field …”

“…The granular pesticide was applied to the AS‐treated NB 14 days before transplanting. The losses of granular pesticide through degradation or run‐off from the bottom of the NBs during the 14 days prior to the transplanting were not significant for the BT‐ and AS‐treated NBs for either fipronil or imidacloprid ( t ‐test, α = 0.05) . As the initial concentrations of fipronil and imidacloprid in the soil of the NBs for BT and AS treatments can be considered to be the same as during the time of transplanting, the PCPF‐NB simulations start immediately after rice transplanting.…”

“…Soil samples were collected at 0, 1, 7, 14, 28, 42 and 70 days after the initial spike of pesticides on the 7 November 2013. All details regarding the procedures for chemical analyses can be found elsewhere …”

“…During the BT treatment, pesticide granules are broadcast over rice seedlings in NBs immediately before transplanting. In contrast, during the AS treatment, pesticide granules are sandwiched together with the rice seeds in soil, or incorporated with the soil during the rice sowing in the NB approximately 14 days before transplanting …”