HOUSEHOLD INSECTICIDES - EVALUATION AND ASSESSMENT OF INHALATION TOXICITY - A WORKSHOP SUMMARY

Particularly in tropical countries household insecticides are used on a day-by-day basis to control mosquitoes, other crawling and flying in sects to prevent the spread of vector-borne diseases. The products use d most often are spray-cans, oil-sprays, mosquito coils as well as slo w-release vaporising systems such as mars and liquid vaporiser. The ex tent and duration of exposure of humans is highly dependent on the typ e of product used. The objective of this workshop was to analyse the n ecessity and feasibility of inhalation studies with household insectic ides taking into account the specific constrains associated with each type of end-use product. The standardisation of inhalation studies wit h regard to the generation of test atmospheres, mode and duration of e xposure, and selection of adequate toxicological endpoints were addres sed. Due to the complex nature of exposure atmospheres generated by so me household insecticides, viz. mosquito coils, it is scientifically c hallenging to characterise the pathomechanism of most concern, since i rritant combustion gases, volatile and semi-volatile organic substance s, particulates (soot), condensation aerosols and re-condensed substan ces onto particulates may act independently, synergistically or mixtur e specific. It has been concluded that for the comparative safety eval uation and risk assessment of indoor insecticide end-use products gene rally recognised guidance for harmonised inhalation testing is require d: 1) For high-dose release products, such as spray-cans, acute inhala tion testing appears to be most relevant. 2) For low-dose, slow-releas e devices, subchronic inhalation studies of 13-weeks, duration of expo sure 6 hours/day for 5 consecutive days per week, should be performed on rats preferably with the end-use product. A dose-range finding stud y of 2-weeks duration, daily exposure, should be available for the jus tification of dose selection and to demonstrate that the findings of 5 days/week exposure is not different from that utilising a daily expos ure. 3) In certain instances, inhalation testing of shorter duration, for example 2 or 4 weeks, may be appropriate if the inhalation toxicit y of the basic formula has already been characterised or the major con stituents contained in the formulation have been examined in extant st udies. The duration of study should also depend on actual use and expo sure pattern, the accumulation potential and the mode of action of the ingredients of concern. 4) Particularly for mosquito coil smokes, the possible physico-chemical interactions of particulates, potentially i rritant water soluble or nonsoluble vapours and aerosol or vapours of the active ingredient(s) are virtually impossible to predict without a ppropriate inhalation testing. 5) Physiological measurements may be us eful for the detection and quantification of the respiratory tract sen sory irritation potency. Biochemical endpoints in lung lavage and conv entional histopathology of the lungs and extrathoracic airways are con sidered to be important. 6) It has been agreed that the nose-only expo sure technique provides the most cost-effective and controlled means t o expose small laboratory animals to well defined atmospheres as long as the limitations of this technique are taken into account.