Toxicity evaluation of new engineered nanomaterials in model organisms

Abstract

According to the definition adopted by European Commission in 2011 a nanomaterial (NM) is a natural, incidental or manufactured material containing particles, in an unbound state or as an aggregate or as an agglomerate and where, for 50% or more of the particles in the number size distribution, one or more external dimensions is in the size range 1 nm-100 nm (European Commission, 2011/696/EU). NM exhibit peculiar characteristics (e.g. small size, large surface area to mass ratio, shape, surface charge, reactive surface groups, state of agglomeration) that confer them properties substantially different from those of the bulk particles of the same composition. Due to their widespread use in the consumer and industrial products, NMs can be released into the environment and it has been raised concern of the scientists about this question (Royal Society and the Royal Academy of Engineering, 2004). The effects that NMs have on aquatic organisms depend on their characteristics influenced by environmental parameters. NMs enter the aquatic organisms mainly through the epithelial surfaces (such as gills, skin) or direct ingestion (Moore, 2006). After crossing the cell membrane, NMs may be stored in vesicles, mitochondria and additional organelles within epithelial cells. They may generate reactive oxygen species, oxidative stress, cytotoxicity, apoptosis and necrosis (Oberdörster et al., 2005). Ecotoxicological tests of NMs should first consider the behaviour of NMs in the aquatic environment and the conditions that may influence aggregation state. For example, some NMs are almost impossible to disperse in water by physical methods such as sonication or stirring and may require the use of a dispersing agent. The choice of dispersant is problematic since some of the best dispersants from a chemistry point of view are also toxic to organisms. The potential for NMs to cause oxidative injury in fish and invertebrates remains controversial. Bar-Ilan et al., 2009 showed that silver nanoparticles (AgNPs) induced almost 100% mortality in larvae of Danio rerio after acute exposure and a variety of embryonic morphological malformations were observed. A study showed that gold nanoparticles (AuNPs) are non toxic at the employed concentrations and do not cause obvious abnormalities in developing zebrafish embryos (Asharani et al., 2010). Zhu et al. (2009) observed effects on mortality and immobility on D. magna in the case of titanium nanoparticles (TiO2NPs) nanoparticles smaller than 20 nm. Currently there is a lack of knowledge about long-term risks and potential mechanisms of toxicity of NMs; the industrial-scale application of engineered nanomaterials in many areas of daily life raises the question of the security of these systems because the nanodimensions are able to overcome natural barriers, resulting in potential biological damage. The main aim of this Ph.D. Thesis was the evaluation of the potential toxic effects of several NMs on aquatic organisms used as models considering their increasing use in the product market. Short and long-term ecotoxicological assays developed, searching for specific biomarkers of exposure by immunohistochemistry, western blotting and gene expression analysis.