In Denmark, only pesticides from the group of synthetic pyrethroids are currently used to control bedbugs. The synthetic pyrethroids are stable compounds, so relatively slow degradation is expected under normal conditions. At the same time, decreased sensitivity to pyrethroids among bedbugs has been found in many countries. This means that treatment must often be repeated, leading to the risk of accumulation and increased exposure of the residents.
The purpose of this study was to document whether in practice there is a risk of accumulation of pyrethroids through bedbug control programs and at the same time to elucidate the extent to which the residents are exposed to pyrethroids.
In general, most pyrethroid was found in dust samples. The most extreme case was 7,5 mg deltamethrin + 3 mg lambda-cyhalothrin + 46,5 mg permethrin in the dust sample from vacuuming one treated room. Thus, in a bioassay with insecticide sensitive flies, it was found that up to 189 days after a treatment, these died when exposed to the floor. It was not possible to see any clear correlation between the amount of pyrethroid present in the environment and the amount of pyrethroid metabolite present in the urine samples. This was interpreted to indicate that the behaviour of the residents has a great influence on the extent to which they are exposed to pyrethroid.
In the second part of the study a number of residents were followed during a period of treatment for bedbugs. The same samples were collected, but in addition blood samples were also taken. Again, there was quite a large variation in the amount of pyrethroid found and no clear correlation was seen between the amount of pyrethroid and the time since the last treatment. In most cases, the levels were still high on the last day of collection and therefore it was considered very likely that pyrethroid accumulation can be achieved by repeated treatments, Here, too, it was not possible to find any clear correlation between the amount of pyrethroid in the environment and the amount of pyrethroid metabolite in the urine. Some residents had obviously been exposed to large amounts of pyrethroid, as seen by the amount of metabolites in the urine. As in the first part, the behaviour of the residents in the dwelling is likely to have a great impact on how much they are exposed. It was only possible to find one pyrethroid metabolite in the blood samples and it was not possible to see any clear correlation with the other measured parameters.