Indoor behavior and risk assessment following residual spraying of d-phenothrin and d-tetramethrin

To clarify the indoor behavior of insecticides in residual spraying equivalent to a crack and crevice treatment, an aerosol canister (containing a mixture of 0.9 g d-phenothrin and 1.1 g d-tetramethrin in a 300-mL product) was applied to a typical Japanese room under various conditions, and temporal concentrations in air and on the floor, walls, and ceiling were monitored. Air concentrations were chiefly dependent on ventilation rates but not on air circulation. During a periodic spraying, the airborne insecticides did not accumulate in the room, but the floor residues gradually increased with the number of sprayings. After cessation of spraying, however, dislodgeable residues on the floor decreased with time. The time-dependent behavior of d-phenothrin was simulated by a developed simulation model (InPest), which helped a more comprehensive understanding of the insecticide behavior. Indoor exposure levels of d-phenothrin and d-tetramethrin to room occupants were estimated with the monitored concentrations when a 2.5-min spraying was done four times over an 8-week period. The margins of safety, which were obtained by dividing the no observed effect levels by the exposure levels, were over 100 for unclothed occupants, even in a room with the windows closed.