Contributions to Emission, Exposure and Risk Assessment of Nanomaterials

Doctoral thesis, 2012

In recent years, synthetic nanomaterials have begun to be produced and used in increasingly larger volumes. These materials may cause new or increased risks to the environment, but no harmonized methods for structured assessment of their environmental risks exist. The main aim of this thesis is to contribute to the development of emission and exposure assessment methods, and thus also risk assessment methods, for nanomaterials. The second aim is to apply developed methods to specific nanomaterials. The nanomaterials assessed were titanium dioxide nanoparticles, silver nanoparticles, and graphene. Starting from the two methods of risk assessment of chemicals and substance flow analysis, three different methods were outlined. The first method is called particle flow analysis, and can be used to assess current and future potential particle number-based emissions of nanoparticles. The second method is an exposure model for nanoparticles based on colloidal stability. This method can be used to derive particle number-based predicted environmental concentrations of nanoparticles. The third method is exposure modeling of nanomaterials based on partitioning factors, a method that can be used to derive mass-based predicted environmental concentrations. By applying the particle flow analysis method, it was shown that antibacterial clothing is a large source of particle number-based emissions of silver nanoparticles, and could become an even larger source. Applying the same method to titanium dioxide nanoparticles showed that both the currently highest, and potentially also the future highest, particle number-based emissions come from sunscreen. By applying the exposure method based on partitioning factors, it was shown that if the silver content of antibacterial clothing is as high as some measurements have indicated, there is considerable risk of high silver levels in wastewater treatment sludge and in agricultural land if the sludge is applied as fertilizer. A review of risk-related properties of graphene showed that the risk-related data is very scarce, but what is available gives reason for concern in relation to high potential emissions, high persistence, hydrophobicity, and considerable toxicity. The developed methods, case study results, and some reflections and suggestions for future research together constitute contributions to emission assessment, exposure assessment, and risk assessment of nanomaterials.