Abstract
Pyrethroids often have greatly varying activities, depending on the route of administration (oral, dermal, or inhalation). The α-cyano-pyrethroids, in particular, have additional specific features, such as the upper respiratory tract sensory irritation potential. This mode of action can be quantified by inhalation testing only. Thus quantification of sensory irritation is considered to be one of the most important endpoints for risk assessment of α-cyano-pyrethroids in the indoor environment. Measurements were taken during acute and repeated exposure of rats to evaluate whether this endpoint is threshold concentration dependent or cumulative. To reproduce exposure scenarios resulting from worst-case pest control measures on carpets, the dislodgment of pyrethroid-laden dust particles was studied on a small-scale test model. Findings support the conclusion that α-cyano-pyrethroids may be potent sensory irritants. However, concomitant respiratory tract inflammation and ensuing changes in susceptibility—a common finding in chemical sensory irritants—were not found even after repeated high level exposures. Consequently, the activity of α-cyano-pyrethroids in equitoxic doses may differ considerably after inhalation and oral administration. The carpet dust study showed that there was no specific enrichment of pyrethroids in the total dust fraction, even after sustained, extreme mechanical loading (continuous brushing for 18 hours). The lack of correlation between absolute (milligrams pyrethroid/cubic meter of air) and relative (milligrams pyrethroid/kilogram of dust applied to the carpet) concentrations of airborne pyrethroids, as well as the low rate of dislodgment of pyrethroids from carpets, showed that sedimented house dust does not appear to be a suitable matrix to predict airborne concentrations of pyrethroids in such an environment, and therefore pyrethroid determinations in sedimented house dust (vacuum cleaner bag analyses) are considered a poor indicator for the assessment of potential inhalation exposure.