Risk assessment of pyrethroids following indoor use.

One notable form of toxicity associated with exposure to high concentrations of synthetic pyrethroids has been a cutaneous paresthesia. This strong excitatory action on the sense organs in the vertebrate skin and upper respiratory tract is characteristic of synthetic pyrethroids, whereas the cyano pyrethroids evoke more intense neuroexcitatory activities than the noncyano pyrethroids. Such facial sensations and irritative symptoms appear to be produced by direct stimulation of peripheral sensory nerve endings rather than by inflammatory mechanisms. Effects related to sensory irritation can be evoked by a wide variety of substances occurring in the indoor environment, and analysis of the etiopathological relationships presents difficult and complex medical and scientific issues. For the appropriate assessment of pyrethroids in the indoor environment, it would be helpful to have an objective laboratory assay to confirm and quantitate the degree of sensory irritation evoked by airborne pyrethroids. A bioassay was established using the nociceptive system of mice and rats to assess the extent of pyrethroid-related sensory irritation to the respiratory tract. For analysis, aerosolized Cyfluthrin was selected due to the greater potency of the alpha-cyano pyrethroids to evoke sensory irritation. Additionally, this pyrethroid was tested in a carpet-model to assess the extent to which pyrethroid-laden dust from carpets is likely to become airborne following continuous brushing. Comparative evaluations of the sensory irritation potential of aerosolized Cyfluthrin in mice and rats revealed that for assessment of the sensory irritant threshold concentration, rats appeared to be more susceptible than mice. Measurements performed repeatedly during subacute exposure to the pyrethroid (6 h/day, 5 days/week for 4 consecutive weeks) did not indicate any alteration in responsiveness, and the magnitude of changes in breathing patterns was similar to those observed following acute 1-h exposure. These findings confirm the conclusion that alpha-cyano-pyrethroids appear to act as "pure" sensory irritants and that the effects observed are non-cumulative and transient in nature. Concomitant respiratory tract inflammation and ensuing changes in susceptibility-common findings in chemical sensory irritants-did not occur. From the studies addressing the dislodgeability of pyrethroid containing dust from carpets, it is apparent that measurement of deposited dust is a poor substitute for airborne dust. Even under worst-case testing conditions (continuous brushing of the carpet for approximately 19 h in a bias-flow compartment), only a very small fraction of the pyrethroid laden dust particles charged to the carpet could be recovered airborne (0.04%/m2 per h). Thus, experimental findings support the conclusion that such agents cannot be dislodged from carpets to an extent that toxicologically significant airborne concentrations are attained. Therefore, assessment of health hazards in the indoor environment based solely on "vacuum cleaner" sampling is prone to a high level of errors and misjudgment.