The Behaviour of Pyrethroids Indoors: A Model Study

Abstract Pest control agents containing three different formulations of the pyrethroids permethrin and deltamethrin and/or pyrethrines and the synergist piperonyl butoxide were applied in a model house simulating indoor pest control. The concentrations of the agents were monitored in the gas phase, on suspended particles, house dust and on furniture surfaces over a period of 24 months. Permethrin and deltamethrin were detected only in the gas phase immediately after application of the agents. High concentrations of deltamethrin (˜2 μg/m³) and permethrin (˜40 μg/m³) were found on suspended particles directly after application. This concentration decreased rapidly within two days (deltamethrin ˜5 ng/m³, permethrin −100 ng/m³) but much more slowly during the following 24 months. In house dust, deltamethrin was observed with initial concentrations of ˜50 mg/kg and permethrin at initial concentrations of 150–800 mg/ kg (depending on the formulation). The concentration levels of both compounds decreased by a factor of ˜10 within the first 12 months but remained almost constant thereafter. Decontamination of the rooms using a commercially available household cleanser has little effect on the pyrethroid concentration found on suspended particles, but leads to a substantial reduction of the contamination level in house dust and on furniture surfaces.