The increasing production and use of nanoparticles in consumer and industrial products and the large range of applications related to these nanomaterials raises some concerns about their potential ecological impacts in different ecosystems and their adverse effect on human health (Simonet and Valcárcel 2009; Salieri, et al. 2015; Girardello, et al. 2016a; Girardello, et al. 2016b). Nanoparticles have a high surface-to-volume ratio, which results in high reactivity potential and unique physical and chemical properties that differ from those of their respective bulk materials (Mallevre, Fernandes, and Aspray 2014; Girardello, et al. 2016a; Girardello, et al. 2016b). The nanoparticle composition and solubility, and interaction modes with biological systems are highlighted as main factors for risk assessment of metal oxide nanoparticles (Wang, et al. 2010; Wu, et al. 2010).
Zinc oxide nanoparticles (ZnO-NP) have a large application field, including wastewater treatment (Anjum, et al. 2016), molecular biology (Navaei-Nigjeh, et al. 2018), cosmetics (Katz, Dewan, and Bronaugh 2015; Lu, et al. 2015; Khezri, Saeedi, and Maleki Dizaj 2018), sunscreen lotions (Lu, et al. 2018), as an additive (Nanthagopal, et al. 2017), in food industry (Venkatasubbu, et al. 2016), paints (Shi, et al. 2013) and construction materials (Hossain, et al. 2014; Schaumann, et al. 2015). Such widespread and expanding production and use of ZnO-NP increases the potential for their release to the environment, causing ecotoxicological problems (Jovanović and Palić 2012). The exposure of aquatic animals to nanoparticles and their aggregates is a major concern, due to the potential harmful effects that may occur. Moreover, the nanoparticles bioavailability and uptake into cells and organisms may be affected by their association with naturally occurring colloids in aquatic systems, altering the nanoparticles behavior in this environmental compartment (Moore 2006).
The aquatic system has a variety of organisms and, once nanoparticles are into the organisms compartment, it may result in additional toxic effects, deregulate cell metabolism and generate reactive oxygen species (ROS) with effects that are related to concentration and period of exposure (Azqueta and Dusinska 2015; Marisa, et al. 2015). ROS can reason serious damage to biomolecules as lipids and proteins and deplete enzymatic defenses such as superoxide dismutase (Sod) and catalase (Cat). Non-enzymatic protein-bound sulfhydryl groups are also affected by ROS exposition (Katsumiti, et al. 2014). Nanoparticles can cause alteration in redox metabolism, modifying markers related to biomolecules oxidation (Iummato, et al. 2013; Girardello, et al. 2016a; Girardello, et al. 2016b). Furthermore, enzymatic antioxidant defenses are shown to change in different aquatic organisms (Hao, Wang, and Xing 2009; Canesi, et al. 2010; Zhu, Zhou, and Cai 2011; Faria, et al. 2014).
Ecotoxicity of ZnO-NP is related to their physical-chemical characteristics such as solubilization and photoreactivity, as well as the tested species. ZnO has photocatalytic properties and contribute to ROS generation. It is believed that solubilized Zn2+ may contribute to cytotoxicity of these nanoparticles (Ma, Williams, and Diamond 2013). In the study of exposure of the freshwater mussel Dreissena polymorpha to ZnO-NP, the oxidative stress of these bivalves showed to be increased after exposition to the nanomaterial. Zn toxicity could be influenced by both solubilized or non-solubilized Zn complexes in freshwater mussels (Gagné, et al. 2019). However, toxicity studies on aquatic invertebrates exposed to ZnO-NP are very limited and its molecular mechanisms related to nanomaterial exposition should be further investigated.
Bivalve mollusks are sensitive to nanoparticles toxicity and may be internalized by endocytosis mechanisms (Canesi, et al. 2012; Barmo, et al. 2013; Canesi, et al. 2014; Girardello, et al. 2016a; Girardello, et al. 2016b). Mussels are filter feeders and stationary organisms and, for this reason, are largely used as biomonitors for environmental perturbations (Villela, et al. 2007; Villela, et al. 2013) and nanoparticles toxicity assessment (Girardello, et al. 2016a; Girardello, et al. 2016b). Furthermore, the ability of bivalves to bioaccumulate toxic compounds in their body determines its role in the transfer of environmental pollutants to higher trophic levels (Hunt, et al. 2003).
Golden mussel (Limnoperna fortunei) is an exotic organism from Asia, that lives in freshwater compartments and has been used for biomonitoring of environmental conditions (Mariano, et al. 2006; Iummato, et al. 2013; Villela, et al. 2013; Girardello, et al. 2016a; Girardello, et al. 2016b). L. fortunei are widely distributed in Rio Grande do Sul, the southernmost state of Brazil, and can be collected during the entire year, which makes this organism an adequate tool for biomonitoring nanoparticles and an excellent candidate to a sentinel organism (Mariano, et al. 2006; Villela, et al. 2006; Villela, et al. 2007; Villela, et al. 2013; Girardello, et al. 2016a; Girardello, et al. 2016b). Ecotoxicological effect models using L. fortunei exposed to nanoparticles were validated in previous studies from our group (Girardello, et al. 2016a; Girardello, et al. 2016b).
Although there has been an increasing number of studies on nanoparticles toxicity, comprehensive knowledge on the impact of ZnO-NP on aquatic organisms is still not clear. In this sense, this study aims to evaluate the oxidative effects and DNA damage and modulation of enzymatic and non-enzymatic defenses in L. fortunei.