AbstractTrials have been carried out in order to determine the concentrations of dichlorvos that occur in the air of houses when “VAPONA”“VAPONA” is a Shell trade mark.strips are placed under conditions of normal domestic use. The ten trials were conducted in the U.K., Australia and France in the years 1967 to 1970. Two trials were also carried out in the U.K. with a shorter, slightly thicker product 6.5 in strip (16.5 cm) of the same basic formulation.Samples of air were taken at regular intervals throughout the 3 or 4 month period of each trial and the samples were analysed for dichlorvos by an enzyme inhibition – ΔpH method.The results from more than 3000 samples of air showed that the great majority of values (97.2) were 0.1 μg dichlorvos per litre of air or less. Values ranged from less than 0.01 μg/1 to 0.24 μg/l, the higher concentrations being associated with houses closed because of the absence of the householders or with several strips in place in the house, or both.In each trial the dichlorvos concentration in the air rose rapidly and then fell exponentially. In temperate area trials, the concentration was at its highest 1 to 2 weeks after placing the strips, the geometric mean of all the values at this time being 0.04 μg/1 and 3 months after placement the mean concentration was 0.01 μg/1.In the two trials with the 6.5 in (16.5 cm) product, concentrations in air were in one of these no different and in the other slightly lower than from the 10 in (25.4 cm) strip, the rate of decline of the concentrations of dichlorvos being the same in both trials.Observation strongly suggests that ventilation is the most important factor in determining the level of dichlorvos in the air of a room. In the trials in Brisbane, Australia, where houses are constructed to allow a flow of air and where doors and windows are open day and night, concentrations of dichlorvos were low initially and quickly fell below the limit of determination.The effect of increased ambient temperature is to increase the rate of emission of dichlorvos from the strip. However, in general, it seems that the increased ventilation associated with higher temperatures outweighed the increased rate of emission of insecticide since concentrations in air tended to fall with increasing temperature.Some rooms, especially kitchens, are smaller than the volume recommended for placement of strips (30 m3per strip). However, statistical analysis of the results shows that initial concentrations in kitchens are no higher than in other rooms, and that the rate of decline of concentrations in kitchens is significantly higher than
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