Characterization of aggregation and dissolution rate constants of metal oxide nanoparticles in freshwater archetypes

The assessment of the potential impacts posed by the production, use and application of ENPs (engineered nanoparticles) is an imperative to well evaluate their real benefit. Although, the ENPs offer environmental benefits, for example with their application in soil/water remediation, concerns on their potential environmental impact are on debate. Despite the NPs are already released into environment, the evaluation of the environmental exposure is still far to be reached due to the lack of knowledge in the field of risk assessment. The assessment of the environmental exposure needs the knowledge of the environmental behavior of the NPs in the environment media (for example freshwater, air, soil, etc.). In the last couple of years, framework to assess the exposure or risk assessment of NPs has been developed. There are evidences that the ambient chemistry parameters influence the fate processes and the toxicity of the NPs. Focusing on the freshwater compartment, physical-chemical parameters such as pH, natural organic matter (NOM), ionic strength are directly involved on the processes of dissolution and aggregation. Whereas the processes of aggregation and dissolution has been referred as important key factors in the field of nano (eco) toxicity. In fact, studies evidenced that the aggregation process leads adhesion of the NPs (ex. TiO2) to the body of the organism (Daphnia magna) and influencing the mobility (Baun et al. 2010; Dabrunz et al. 2012 ). As well, the dissolution of metallic nanoparticle ( ZnO ) could influence the toxicity aggregates .These researches highlight that the bioavailable forms is strictly related to the environmental chemical condition. In line with current understanding is that nanoparticles form colloids in freshwater. Praetorius et al. (2012) have developed a fate model for describing nanoparticle river behavior by modeling aggregation using relationships established for colloids, and considering NP-specific processes such as dissolution and aggregation. The applicability of the model of Praetorius et al. 2012 was demonstrated for n-TiO2 emitted to the river of Rhine. Their model requires input parameters specific for the river of interest, such as ionic composition and pH, and is therefore well suited for site-specific assessments, such as ERA. In this study, Praetorius et al. 2012 model will be applied on 12 set of water-types in European Union (EU) (Ghandy et al. 2010 ). The model will be applied on n-TiO2 and n-ZnO to calculate freshwater- and nanoparticle-specific aggregation and dissolution rate constants. The evaluation of the aggregation and dissolution rate constants in several freshwater archetypes is aiming to evaluate the dominating fate processes. Moreover the results will permit to explore the effect of variability in freshwater chemistry and to improve the knowledge on the NPs behavior in freshwater. The calculation of aggregation and dissolution rate will be improved in USEtox model to calculate the fate factor for metallic nanoparticles.