Ecotoxicological research was rapidly developing due to the pollution of the environment induced by the rapid industrial development (Anne Kahru, Henri-Charles Dubourguier., 2010). Three key elements of nanoparticles toxicity screening strategies have been outlined by Oberdörster et al. (2005a): (i) physicochemical characterization (size, surface area, shape, solubility, and aggregation), elucidation of biological effects involving (ii) in vitro and (iii) in vivo studies. These three key elements were formulated mainly from the point of view of potential effects of nanoparticles on humans. There are clear tendencies of development of both, terrestrial and aquatic ecotoxicology through the movement of traditional ecotoxicology into toxicogenomics (Spurgeon et al., 2008). The most toxic nanoparticles for nematodes and algae were nano ZnO (Anne Kahru, Henri-Charles Dubourguier., 2010). For bacteria, fish and ciliates the most toxic was C60 fullerene and for the crustaceans, nano Ag. It is well known that at nanosize range, the properties of materials vary considerably from bulk materials of the same composition, mostly due to the increased specific surface area and reactivity, which may lead to amplified bioavailability and toxicity (Nel et al., 2006). Indeed, NPs of CuO were up to 50-fold more toxic than particles of bulk CuO towards crustaceans (Heinlaan et al., 2008), algae (Aruoja et al., 2009), protozoa (Mortimer et al., 2010) and yeast (Kasemets et al., 2009). TiO2 and Al2O3 NPs were about twice more toxic than their respective bulk formulations towards nematodes (Wang et al., 2009).

For hazard assessment of NPs quantitative nano ecotoxicological data are required. Currently, assessing the safety of synthetic NPs has become a worldwide issue. The ecotoxicological research on NPs is also supported and promoted by EC science policy. Despite of a growing understanding that synthetic NPs should be evaluated for their potential environmental hazard prior their use in products and subsequent inevitable release into the environment, there are currently few data on the toxicity of nanomaterials to environmentally relevant species, limiting the quantitative risk assessment of NPs. Indeed, nanotoxicology research started in the early 1990s as shown by the first few scientific papers recorded in Web of Science of Thomson Scientific (formerly known as Thomson ISI) and this research was remarkably supported by the earlier studies concerning (pulmonary) effects of ultrafine particles (Oberdörster et al., 2005b). Ecotoxicological tests were mostly developed for aquatic test organisms and water-soluble chemical compounds. Aquatic toxicity testing of nanoparticles is a challenge. However, whatever the evident route of exposure and the mechanisms of toxicity, bioavailability remains a key factor for the hazard valuation of synthetic NPs. Bioavailability is an active model that considers physical, chemical, and biological processes of contaminant exposure and dose, it incorporates concepts of environmental chemistry and ecotoxicology, fate, integrating contaminant concentration, and an organism's behavior in the given environment. Bioavailability of nanoparticles depends on the: (i) on nanoparticle-organism contact environment, (ii) physicochemical properties of the particles (aggregation, solubility), (iii) on the target organism (particle-ingesting or not) (Anne Kahru, Henri-Charles Dubourguier., 2010).

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Author is pursuing M.phil/PhD in environment science from Central university of Gujarat