Hazard identification and risk assessment of pyrethroids in the indoor environment

Household insecticide products raise several important considerations concerning safety. These are related to the use of insecticides by untrained individuals, the difficulty of controlling the use of these products once purchased by the consumer and the potential exposure of the very young and very old, possibly with or without pre-existing pulmonary disease. Exposure to pyrethroids contained in mats or vaporizers, being slow release systems, have particular potential for long-term low-level exposure whilst for foggers, spray-cans or sprayed formulations the short-term high-level exposures may be of more concern. According to the volatility of the active ingredient contained in the household insecticide, its persistence in a non-inhalable matrix, i.e. sedimented house dust, may be short or long for highly volatile or low volatile active ingredients, respectively. On the other hand, the potential of exposure is apparently just reciprocal. This demonstrates that the extent and duration of exposure may be highly product-specific. Accordingly, the extent of exposure has to be accounted for and for risk assessment both concentration-dependent (e.g. sensory irritation) as well as concentration x time (= dose) related effects have to be considered and addressed in adequate bioassays. The issue as to whether pyrethroids adhering to house dust is of concern has been addressed in a model study using carpets treated with pyrethroids. This study has demonstrated that the total mass of pyrethroid applied to the carpet and that brushed off within an 18-h period is too small to be of any relevance for risk assessment. Therefore, assessment of health hazards in the indoor environment based simply on methodologies of emptying the household vacuum cleaner and analysing its content, which addresses contamination only, rather than examination of the actual airborne concentration, including other relevant airborne materials, is prone to tremendous errors and misjudgments. Due to the many substances potentially present in house dust and indoor air, e.g. bioaerosols originating from animals, pests and microorganisms, volatile organic substances (VOCs) or metals, prudent expert judgment is needed to assess the relevance of analytical findings. The complex indoor exposure scenario makes it especially difficult to causally relate clinical and epidemiological findings to arbitrarily selected indicator substances contained in a matrix not readily available to inhalation exposure.