Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Nanomaterials are used in a wide spectrum of applications, including nanowires that are objects with at least one of its dimensions in the range of 1 to 100nm. Recently, a new type of silver vanadate nanowire decorated with silver nanoparticles (SVSN-LQES1) with promising antimicrobial activity against different pathogenic bacteria was described. The objective of the present study was to evaluate the role of silver and vanadium release in the acute toxicity of this material using Daphnia similis. To verify the effect of the presence of the nanowires in the test solution, tests were performed before and after filtration. Total silver release to the testing media was determined using the method of inductively coupled plasma atomic emission spectroscopy (ICP-AES). Silver vanadate nanowires decorated with silver nanoparticles (SVSN-LQES1) are acutely toxic to D. similis. The release of silver from the nanomaterial trapped in the gut along with the silver released to the test media seems to be responsible for the observed toxicity. Although toxic to Daphnia, vanadium does not contribute to the toxicity of SVSN-LQES1. The observed increase in lipid droplets appears to be related to the exposure of the organisms to the nanomaterials, but the significance of this response needs further investigation. Environ. Toxicol. Chem. 2013;32:908912. (c) 2013 SETAC324908912Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)FAPESP [2008/57974-9]