Adulticide substitutes
|
With no vaccine or etiological treatment, the main means of controlling the chikungunya epidemic, which swept through Reunion Island, is vector control. Measures must be taken to reduce the density of the Aedes albopictus vector. |
 |
The first adulticide treatments on Reunion Island were conducted using fenitrothion-based products. However, given the concern over the health effects and impact on ecosystems that fenitrothion may have, and pending the results of Afsset’s work, the public authorities decided to replace it with deltamethrine from February 2006. A solicited request was therefore sent to Afsset on 10 February 2006, on the comparative assessment of the effectiveness and associated risks of the use of adulticide products for vector control. The solicited request involved two tasks: 
the comparative assessment of the effectiveness and risks of fenitrothion and deltamethrin to begin with; then the identification and comparative assessment of potential substitutes.
After consulting the French Ministries of Health and Ecology, CEHTRA and the IRD and on the basis of the IRD’s bibliographic work, naled and pyrethrum were selected for their predicted effectiveness and toxicological profile, favourable in principle.
Working method:
The risks associated with the use of these insecticides were assessed on the basis of firstly European regulatory assessment diagrams used for plant protection products and biocides and secondly reviews published by official assessor bodies. It concerns the production of a review of the information available on the physicochemistry of substances and their dangers for humans and the environment and a brief assessment of the risks for workers, consumers, humans through the environment and the environment, for the use of these substances as a larvicide on Reunion Island. Their effectiveness was assessed using bibliographic data and, given the emergency context, the assessment was simplified to allow for a swift response.
This review and assessment were based on: general data, available in the literature, on the substances and their dangers, which were collected by Afsset; Data on the precise methods for use, provided by mosquito control operators or manufacturers of the substance or preparations; An estimation of exposure levels, with no real measures, based on generic exposure scenarios related to this type of use. Developed initially for use in continental Europe, their appropriateness for vector control on Reunion Island is uncertain. 
Concerning their effectiveness:
Naled belongs to the same chemical family of organic phosphorated compounds as fenitrothion. Some cases of resistance have been observed. It is used at the dose of 22.4 g/ha.
Pyrethrum belongs to the chemical family of natural pyrethrums, similar to that of deltamethrine (synthetic pyrethrinoids). To date, cases of resistance associated with pyrethrum have been rare, due mainly to the nature of the substance (mixture of 6 active isomers). It is used at the dose of 5 to 10 g/ha.
Concerning their toxicological properties:
Naled is toxic by cutaneous route, harmful if inhaled, irritant for the skin, and very irritant for the eyes. Moreover, it breaks down into dichlorvos, classed 2B (possible carcinogen for humans) by the International Agency for Research on Cancer (IARC).
Pyrethrum is hardly toxic by cutaneous route, not irritant for the skin or eyes and not sensitising. Moreover, it is not mutagenic, not toxic for reproduction and not teratogenic. However, carcinogenic effects have been observed by oral route in animals, but these effects cannot be transposed to humans. Minimal neurotoxic effects have also been observed in animals by oral route. Lastly, cases of sensitisation (eczema, asthma) have been observed in the occupational environment.
Concerning their physicochemical properties and their behaviour in the environment:
Neither pyrethrum nor naled are very soluble in water.
Naled breaks down very quickly in all types of environment. Pyrethrum also breaks down quickly, particularly in light.
Pyrethrum has a strong affinity for organic matter, which indicates a very strong tendency to retention in the soil and a high adsorption on suspended particles in water. Naled has a low affinity for organic matter, however.
Pyrethrum has a very high bioaccumulation potential, which indicates a potential risk of bioaccumulation in the food chain. Naled has a low biocaccumulation potential.
Naled is volatile and pyrethrum moderately volatile.
Concerning their ecotoxicological properties:
Naled and pyrethrum are very toxic for aquatic organisms.
Naled is toxic for birds and mammals and pyrethrum is slightly toxic for birds and toxic for mammals. Because of their insecticide nature, both substances are very toxic for bees.
Concerning risks for humans:
The exposure levels determined outside of this research raise worrying risks associated with the use of naled for applicators and for the general population in the vicinity of treated areas. The risk associated with pyrethrum exposure while it is being applied is acceptable for operators and people in the vicinity only when certain recommendations of use are complied with.
Concerning risks for the environment:
Exposure levels determined during this work result in worrying risks associated with the use of naled and pyrethrum for the ecosystems studied. The specific risks for local ecosystems on Reunion Island could not be assessed, however.
In conclusion, pyrethrum proves to be a promising substitute because of the low occurrence of resistances and its acceptable risks for humans and the environment. Naled does not seem to be a satisfactory substitute, however, given its risks for humans.
More information:
Chikungunya epidemic on Reunion Island 
In France, bathing is the most common recreational activity carried out in water. Not requiring any specific level of fitness and enjoyed by most people, it is recommended to everyone as a source of benefits, particularly for children.
>> Read more
