The increasing use of nanoparticles will inevitably result in their release into the aquatic environment and thereby cause the exposure of living organisms. Due to their larger surface area, high ratio of particle number to mass, enhanced chemical reactivity, and potential for easier penetration of cells, nanoparticles may be more toxic than larger particles of the same substance. Some researchers have been showing some relations between nanoparticles and certain diseases. However, the doses, surface shapes, material toxicity and persistence of nanoparticles may all be factors in determining harmful biological effects. In order to better evaluate their risks, potential exposure route of nanoparticles has to be taken into consideration as well. Finally, a brief summary of techniques for nanoparticle removal in waters and wastewaters is presented, but it seems that no treatment can absolutely protect the public from exposure to a large-scale dissemination of nanomaterials. (C) 2013 Published by Elsevier B.V.