A systematic literature search identified publications relevant to repeated (94 papers) and mixture exposure (152 papers) of aquatic organisms. Limited data are available on pulsed exposure of pesticides and reports on repeated pulse or fluctuating exposures are even rarer. Although there has been recognition of the need for more realistic testing scenarios these lack a systematic approach. Among the reports on pesticide mixtures most of the plant studies evaluated interactions between mixtures of herbicides or fungicides / algicides. A small number of reports evaluated the effects on invertebrates of mixtures of pesticides with the same mode of action and these showed additive toxicity. More studies in invertebrates assessed interactions between pesticides with different modes of action including herbicide/ insecticide combinations some of which showed toxicity greater than additive. The majority of studies in fish have investigated the toxicity of insecticide mixtures. The toxicity of most combinations was at most additive, with a small number antagonistic. A small number of papers reported mixture effects of pesticides in amphibians; more than additive effects were observed with atrazine combinations. Simple models can be used to determine the additive toxicity of pesticide mixtures based on concentration addition or independent action. More complex models to determine the scale of synergy are species-and dose-dependent and rely on an understanding of the interactions involved. Further work is required to develop a greater understanding of the species, dose and time dependence of exposure to pesticide mixtures in which more complex interactions occur. In the interim, in the majority of cases the increase in toxicity is no greater than 3 fold when compared to additive, the deviation from additivity decreases with the increasing number of components in the mixture, and where no known interactions have been reported this may be an appropriate factor to include in risk assessments. KEY WORDSPulsed, mixtures, pesticides, aquatic organisms, synergism, additive effects DISCLAIMERThe present document has been produced and adopted by the bodies identified above as author(s). This task has been carried out exclusively by the author(s) in the context of a contract between the European Food Safety Authority and the author(s), awarded following a tender procedure. The present document is published complying with the transparency principle to which the Authority is subject. It may not be considered as an output adopted by the Authority. The European food Safety Authority reserves its rights, view and position as regards the issues addressed and the conclusions reached in the present document, without prejudice to the rights of the authors 1 Question No EFSA-Q-2011-00786. Repeated and Multiple Stress in Aquatic OrganismsSupporting publications 2012:EN-347 2The present document has been produced and adopted by the bodies identified above as author(s). This task has been carried out exclusively by the author(s) in the...

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