Risk assessment of the use of deltamethrin on bednets for the prevention of malaria.

Risk assessments covering the use of the pyrethroid, deltamethrin, on bednets for the prevention of malaria have been conducted The toxicity of deltamethrin in humans and animals is reviewed following both dermal and oral exposure. The no-adverse-effect level (NOEL) for exposure via the dermal route was 1000 mg/kg body weight/day. From this an acceptable exposure level (AEL) of 10 mg/kg body weight/day has been derived. The NOEL for exposure via the oral route was 1 mg/kg body weight/day, with exposures above this causing neurotoxic effects in animals. This NOEL has been used to derive margins of safety compared with predicted exposures. While direct skin contact does not seem to cause systemic toxicity in humans, it can cause burning, numbness and tingling of the skin, which is a local effect. This too is taken into account in the risk assessments. The risk assessments cover those treating bednets, on an intermittent or regular basis, the washing of treated nets, sleeping under treated nets (infants, children and adults). Worst case scenarios for each of these situations show that dermal exposures are low (one-tenth or less of the AEL) and the margins of safety for systemic exposure derived from oral data are acceptable, ranging from 10 to 3300. The benefits of the use of treated bednets in reducing morbidity and mortality from malaria are considerable and it can be concluded that the risk:benefit ratio is very favourable.