Temephos is a biocidal active substance used in insecticides to prevent larvae pools in the natural environment, which falls within the scope of Directive 98/8/EC of the European Parliament and of the Council of 16 February 1998 concerning the placing of biocidal products on the market.
This substance has been identified as a biocidal active substance existing on the European market before 14 May 2000. In this regard, it should have been covered by an assessment dossier given its inclusion in the list of products authorised for use as insecticides. However, since no manufacturer announced their intention to submit such a dossier, it had to be withdrawn from the market in the medium term.
Given the importance of temephos for French mosquito control operators and the importance of vector control, on 31 March 2006 the French Ministry of Ecology, the competent authority for implementing Directive 98/8/EC in France, submitted an application for the essential use of temephos for the purposes of treating larvae pools in the natural environment.
The essential use application dossier, compiled by the competent authorities, contains a summary of the available physicochemical, toxicological and ecotoxicological data as well as data concerning the assessment of risks, for humans and the environment, of the substance.
Afsset's expertise was called on to contribute to the constitution of this essential use application dossier for the environmental and health risk assessment section. This first involved producing a summary of the available information on the physicochemistry of the substance and its dangers for humans and the environment; a simplified assessment of the risks for workers, consumers, humans through the environment and the environment, for the use of this substance to treat larvae pools in the natural environment.
General points & contextual elements:
The potential withdrawal of temephos from the market has concerned all mosquito control operators in France. This is because only two active substances were used to control larvae pools in France: temephos and Bti (Bacillus thuringiensis israelensis). The latter was notified and could therefore stay on the market after 1 September 2006. It seems that it cannot replace temephos entirely, however. Moreover, mosquito control operators fear finding themselves with no control tools if cases of Bti resistance arise. Accordingly, temephos has been used in vector control overseas, particularly on Reunion Island, where a Chikungunya epidemic broke out in early 2006.
Article 4 b) of Commission Regulation (EC) No 2032/2003 states that Member States can apply for essential use when they believe that a non-notified active substance, which should therefore have been withdrawn from the market on 1 September 2006, is essential for reasons of health, safety or protection of the cultural heritage, or for the proper functioning of society in the absence of technically or economically viable substitutes or replacement solutions, acceptable from an environmental and health viewpoint. This derogation cannot apply beyond 2010.
This summary and assessment are based on:
i) general data, available in the literature on the substance, collected by Afsset;
ii) data particularly on the dangers of the substance and its precise methods of use, provided by mosquito control operators or manufacturers of the substance or preparations, or obtained from the temephos dossier submitted to the French Ministry of Agriculture. Regarding the dangers, an initial summary rather than an in-depth validation of the available data is needed.
Furthermore, the risk assessment involved a general assessment based, in the absence of exposure data, on generic scenarios of exposure on this type of use.
The first report of the assessment of dangers and risks associated with the use of temephos has been analysed critically by Afsset's Biocides Unit and two rapporteurs, identified through the competent CSE of Afsset. Data were compiled on the basis of information available in the general literature, obtained mainly from the US EPA on the one hand and substance use data gathered with the help of the inter-County mosquito control agreement (EID) departments in mainland France on the other. Risk assessments were conducted in accordance with the methods currently applied in Europe for processing plant protection product dossiers (Directive 91/414/EEC) and biocides (Directive 98/8/EC), by using the most appropriate exposure models available in particular. There is room for improving them though, given the time it takes to process them.
The report seeks more particularly to provide information about the physicochemical properties and dangers of the substance, exposure modelling and the main results of the risk assessments.
In terms of the physicochemical properties, we shall note that temephos is not very soluble in water and has a high octanol-water partition coefficient, helping it to adsorb on sediments and accumulate in living organisms in natural conditions; however, studies in the aquatic environment reveal that the parent compound breaks down relatively quickly (50% decomposed in 15 to 17 days). The degradation products formed through photolysis and biodegradation have not all been identified. They do not seem to have any insecticide action, however.
Like other substances from the organic phosphorated compound family, temephos is a neurotoxin by its anticholinesterasic properties, to which it also owes its insecticide action. It is fat-soluble but very rapidly broken down. Given its LD50 (lethal dose for 50% of the exposed population) in rabbits, the most sensitive species at acute toxicity (LD50 = 1,300 mg/kg), temephos is nevertheless categorised as one of the least toxic organic phosphorated compounds (LD50 > 500 mg/kg). Not all of the potential subchronic and chronic dangers of this substance are fully described in the literature, however. The data available are therefore insufficient for drawing a conclusion on the carcinogenic or mutagenic potential of the molecule. Lastly, tests examining toxicity for reproduction, although not revealing any effects, could not be validated. As a result, a NOAEL (no-observed-adverse-effect-level) of 0.3 mg/kg of body weight has been adopted to calculate risks.
Available ecotoxicological data show very high sensitivity among aquatic invertebrates (CL50-48h = 11 µg/L on daphnia) while fish seem to be 1000 times less sensitive. Moreover, the substance has a high bioaccumulation potential, compensated by rapid elimination.
With more particular regard to risk assessments, the following should be noted:
i) they are based on academic approaches using generic modelling tools (UK POEM, BBA, EUROPOEM, PHED, etc.) which are also used for approving plant protection products in the framework of Directive 91/414/EEC and based on conditions of use supplied by the EIDs only;
ii) none of these descriptions have been validated by actual measures in the environment, however;
iii) concerning risks that are potentially induced by the use of the substance by workers for vector control, all of the scenarios, except aerial applications, reveal non-conforming risks with regard to the safety margins adopted and justified in the study, irrespective of the protection means used.
iv) concerning potentially induced risks for the general population or population within the immediate vicinity of the applicator or treated zone (bystanders), the studies conducted do not in principle enable unacceptable risk scenarios to be identified. It would be worth going into these studies in more detail, however, by using more precise usage data;
v) concerning ecotoxicity, all of the studies conducted reveal a high risk both for aquatic organisms (fish, invertebrates, crustaceans, molluscs) and for non-targeted organisms further up the food chain (birds, mammals). The scenario tested for bees does not reveal a specific risk, however.
Nevertheless, beyond these academic studies which lead to the documentation of worrying potential risks associated with temephos use, the literature lacks observed and precise descriptions of impacts or the effects caused by this substance on the general or working population. The EIDs have not announced serious cases of poisoning by this product since it was first used for mosquito control either. Regarding ecosystems, we note that some studies (particularly the work of INRA in Rennes or the LIFE-ENVIRONNEMENT programme) tend to show a rapid recovery (one to three weeks) of ecosystems after exposure to temephos-based treatments and a limited impact on the structure of populations.
Following the essential use application to the European Commission:
With regard to the report submitted on 30 March 2006 by Afsset on the assessment of dangers and risks associated with temephos use and the importance of having a variety of effective products available to prevent the spread of an epidemic, particularly in areas where vector diseases are endemic, the French authorities have submitted a derogation application dossier for essential use (31 May 2006).
The conclusions of 28 November 2006 are in favour of keeping temephos on the French market until 14 May 2009 for the purposes of vector control. This authorisation for use is limited to the following four overseas départements: Guadeloupe, French Guiana, Martinique and Reunion Island.
Outside of these four départements, the marketing of temephos-based insecticide products is banned. Temephos-based product stocks held by organisations in charge of mosquito control could be used until 1 September 2007, in accordance with the order of the French Ministry of the Environment of 10 May 2007.
The European Commission is encouraging the French authorities to develop alternative solutions to temephos.
Greece, which also submitted a derogation application for the essential use of temephos on 24 March 2006, obtained an extension for the authorisation to use temephos until 1 November 2007. The application from Italy, submitted on 11 July 2006, was rejected however.