RISK ASSESSMENT OF PYRETHROIDS FOLLOWING INDOOR USE

One notable form of toxicity associated with exposure to high concentr ations of synthetic pyrethroids has been a cutaneous paresthesia. This strong excitatory action on the sense organs in the vertebrate skin a nd upper respiratory tract is characteristic of synthetic pyrethroids, whereas the cyano pyrethroids evoke more intense neuroexcitatory acti vities than the noncyano pyrethroids. Such facial sensations and irrit ative symptoms appear to be produced by direct stimulation of peripher al sensory nerve endings rather than by inflammatory mechanisms. Effec ts related to sensory irritation can be evoked by a wide variety of su bstances occurring in the indoor environment, and analysis of the etio pathological relationships presents difficult and complex medical and scientific issues. For the appropriate assessment of pyrethroids in th e indoor environment, it would be helpful to have an objective laborat ory assay to confirm and quantitate the degree of sensory irritation e voked by airborne pyrethroids. A bioassay was established using the no ciceptive system of mice and rats to assess the extent of pyrethroid-r elated sensory irritation to the respiratory tract. For analysis, aero solized Cyfluthrin was selected due to the greater potency of the alph a-cyano pyrethroids to evoke sensory irritation. Additionally, this py rethroid was tested in a carpet-model to assess the extent to which py rethroid-laden dust from carpets is likely to become airborne followin g continuous brushing. Comparative evaluations of the sensory irritati on potential of aerosolized Cyfluthrin in mice and rats revealed that for assessment of the sensory irritant threshold concentration, rats a ppeared to be more susceptible than mice. Measurements performed repea tedly during subacute exposure to the pyrethroid (6 h/day, 5 days/week for 4 consecutive weeks) did not indicate any alteration in responsiv eness, and the magnitude of changes in breathing patterns was similar to those observed following acute l-h exposure. These findings confirm the conclusion that cr-cyano-pyrethroids appear to act as ''pure'' se nsory irritants and that the effects observed are non-cumulative and t ransient in nature. Concomitant respiratory tract inflammation and ens uing changes in susceptibility-common findings in chemical sensory irr itants-did not occur. From the studies addressing the dislodgeability of pyrethroid containing dust from carpets, it is apparent that measur ement of deposited dust is a poor substitute for airborne dust. Even u nder 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%/m(2) per h). Thus, experimental fin dings support the conclusion that such agents cannot be dislodged from carpets to an extent that toxicologically significant airborne concen trations are attained. Therefore, assessment of health hazards in the indoor environment based solely on ''vacuum cleaner'' sampling is pron e to a high level of errors and misjudgment.