Factors contributing to the off-target transport of pyrethroid insecticides from urban surfaces.

Pyrethroid insecticides used in urban and suburban contexts have been found in urban creek sediments and associated with toxicity in aquatic bioassays. The objectives of this study were to evaluate the main factors contributing to the off-target transport of pyrethroid insecticides from surfaces typical of residential landscapes. Controlled rainfall simulations over concrete, bare soil, and turf plots treated individually with pyrethroid insecticides in a suspension concentrate, an emulsifiable concentrate, or a granule formulation were conducted at different rainfall intensities and different product set-time intervals. Pyrethroid mass washoff varied by several orders of magnitude between experimental treatments. Suspension concentrate product application to concrete yielded significantly greater washoff than any other treatment; granule product application to turf yielded the least washoff. Fractional losses at 10 L of runoff ranged from 25.9 to 0.011% of pyrethroid mass applied, and 10 L nominal mass losses ranged from 3970 to 0.18 µg. Mass washoff depended principally on formulation and surface type combination and, to a lesser degree, on set-time interval and rainfall intensity. Treatment effects were analyzed by ANOVA on main factors of formulation, surface type, and set time. Factor effects were not purely additive; a significant interaction between formulation and surface type was noted.

Wash off of imidacloprid and fipronil from turf and concrete surfaces using simulated rainfall.

The surface runoff of imidacloprid granular product (GR) from turf surfaces, and imidacloprid emulsifiable concentrate (EC), fipronil suspension concentrate (SC) products and fipronil byproducts from concrete surfaces was investigated during 1h rainfall simulations at 50 mm/h or 25 mm/h with product incubation times of 1.5 h, 1 d, 7 d, and 14 d. About 57.3% of the applied mass of imidacloprid, corresponding to an event mean concentration of 392.0 µg/L, was washed off from the concrete surfaces after 1.5h of incubation. After 1 d, 7 d, and 14 d of incubation on either turf or concrete surfaces, up to 5.9% of the applied mass of pesticide was removed in each of the run-off events. The maximum concentrations of pesticides were observed in the initial fraction of the runoff collected in the first rainfall event. They were 157.8, 3267.8 and 143.3 µg/L for imidacloprid GR, imidacloprid EC and fipronil SC, respectively. Imidacloprid was not persistent on concrete surfaces, with run-off concentrations below detection limits in 7d incubation experiments. The cumulative mass losses of imidacloprid from turf and fipronil from concrete had a linear relation with cumulative surface run-off depth, while cumulative mass losses of imidacloprid from concrete surfaces were better fit by a power function of the cumulative surface run-off depth. The concentrations of fipronil in the runoff from the third rainfall event at 14 d incubation time were still relatively high and ranged from 12.0 to 31.0 µg/L. A toxicity unit approach was also employed to evaluate the potential acute toxicity of fipronil and its byproducts to aquatic organisms.