MODELLING ENVIRONMENTAL FATE OF TiO2 NANOPARTICLES IN WATER – IMPLICATIONS FOR EMPIRICAL VALIDATION STUDIES

Other conference contribution, 2009

The potential environmental effects of nanoparticles (NPs) require interdisciplinary research to assess the risks. One part of a risk assessment concerns exposure, which builds on knowledge of the environmental fate. In this particular case the fate of TiO2 NPs in the water compartment was modelled by applying a second order kinetic rate equation and the DLVO theory. Assumptions were made regarding water parameters such as pH, salt concentration and temperature, as well as regarding particle properties such as Hamaker constant, primary particle size and point of zero charge. The effect of sedimentation was taken into account, but as one would expect the influence of sedimentation on such small particles is very small. The model was implemented in MATLAB®. Results indicate the importance of agglomeration as an important fate mechanism, and that pH and point of zero charge are important parameters with regards to agglomeration. Other parameters such as the Hamaker constant, salt concentration and temperature were shown not to have a significant effect, which is in good correlation with empirical studies. Also, we would like to see our model validated by empirical studies. Important implications then are to include a continuous inflow of NPs in the experimental setup and to work at environmentally relevant water properties. For example is the effect of natural organic matter (NOM) on the agglomeration not modelled, despite that its significance has been pointed out in many studies. This is due to a weak link between mathematical expressions and empirical data for this particular part of the model. It is of importance that this linkage is strengthened both by theoretical and empirical studies on NOM aiming at producing mathematical expressions, and empirical data, that can assist fate modelling of NPs.