Experimental release and exposure studies for quantitative and qualitative risk assessment of nanoforms

Abstract

Humankind emits huge amounts of artificial and engineered nanoparticles into the environmental atmosphere. One contributing factor is the emission of ultrafine particles from combustion processes. The second contributing factor is the release of aerosolized engineered nanoforms (NFs) from nano-enabled products (NEPs) that are used in daily life, such as cosmetics, sports products, cement or other construction materials and polymeric composites by processes such as abrasion, weathering or incineration. In the year 2010, the world health organization (WHO) classified the soot particles from combustion processes as carcinogenic. Similarly, pristine NFs and released aerosols from NEPs that contain NFs can induce adverse health effects. Size and chemical composition have been found to be determining factors for the toxicity of pristine NFs and aerosols containing NF fragments. Consequently, detailed knowledge of the morphology and chemical composition of the released particles is very important. A comprehensive risk assessment of released particles requires considering NF release and exposure through the entire life cycle of a NEP or a NF, starting from manufacturing, over use to end-of-life treatment, but also the accurate and complete characterization of a sufficient number of aerosols and NFs. An efficient risk assessment of multiple NFs and NEPs can be done via grouping and read-across of NFs or NEPs with similar hazard profiles; the approach of the European project GRACIOUS, to which this thesis contributed a small part by exploring the release and the exposure for various NFs and aerosols. There are data on the physico-chemical properties of generated aerosols and released NFs and the exposure to these particles, but they are in most cases not quantitative. Consequently, this thesis aimed at a quantitative evaluation of aerosol release, the development of precise and fast approaches for the quantification of the released NFs in the generated aerosols and an accurate assessment of the inhalation exposure to aerosols in the nano size range. Important factors for the adverse effects of an aerosol were studied. The investigated factors were the concentration of generated aerosols, the released NF fraction (fraction of freestanding and protruding NFs in an aerosol), the morphology (shape and size) of the aerosol particles, the chemical composition of the aerosols, the lung deposited aerosol concentration, the lung deposited aerosol fraction, the influence of considered concentration metric (number, surface area or mass) on the lung deposition and the fact whether such a concentration metric (i.e. the lung deposited surface area) can be accurately determined. Novel quantitative and qualitative data on aerosol and NF release and exposure were generated, which facilitate together with literature data and novel results from other project partners the grouping and read-across approach. Abrasion and combustion experiments were conducted to simulate aerosol and NF release from NEPs during use and end-of-life treatment. In addition, lung deposition of combustion-generated particles and multi-walled carbon nanotubes (MWCNTs) was simulated for exposure evaluation and filtration of MWCNTs was assessed. 4 In chapter 2, abrasion-induced release of graphene-related materials (GRMs) from epoxy-composites was evaluated using qualitative (scanning electron microscopy coupled to an energy-dispersive X-ray, SEM-EDX), semi-quantitative (Raman) and quantitative (inductively coupled plasma-optical emission spectroscopy, ICP-OES) methods. The released GRM fraction was linked to the physical-chemical properties of the GRM, the interaction with the matrix material, the interlayer bonding strength in-between the GRM layers and the characteristics of the composite. 18 to 92 % of the embedded pristine GRMs were released depending on the size and the chemical composition of the GRM particles. Bigger size of the GRM and higher oxygen content on the GRM`s surface led to higher released GRM fractions. Aerosol release from the combustion of polymeric composites with CuPhthalocyanine NFs, applied paint on wood and paper, with Fe2O3 and/or silica SiO2 NFs was studied (chapter 3). The released aerosol concentration was evaluated via FMPS (fast mobility particle sizer) and APS (aerodynamic particle sizer) and aerosol number emission factors (nefs) were calculated. The chemical composition of the aerosols was investigated via SEM-EDX. The concentrations of the Cu, Fe and Si signature elements of the embedded NFs in the aerosol were investigated via inductively coupled plasma-mass-spectrometry (ICP-MS). The generated aerosols showed modified size compared to the pristine NFs and gained their chemical composition mainly from the matrix and only to a minor fraction from the pristine NF. Since the nefs in the FMPS size range were specific for each type of NEP, we conclude that NEPs could be categorized according to their potential to release aerosols when they are burnt. Exposure to aerosols from the most widely spread combustion processes and in ambient air was studied via calculating their lung deposition by using the Multiple Path Particle Dosimetry (MPPD) model. The relationship between the deposited particle fraction and size distribution was established in chapter 4. The results revealed that the lung deposition fraction depended on the diameter of the mode of a aerosol size distribution. It was higher for human beings than for animals. The lung deposition fractions that were calculated based on number were slightly higher than those that were calculated based on surface area or mass. Nevertheless, the dependence on the considered metric (number, surface area or mass) was not strong. Inhalation exposure of single standing airborne multi-walled carbon nanotubes (MWCNTs) and CNT agglomerates was evaluated, by assessing their filtration and deposition in the deep lung using calculation models (appendix, section A4.). Previous models were revised and models for realistic CNT mixtures in the air were developed using mixing states of CNT agglomerates and single standing CNTs. The results revealed that filtration, inhalation and deposition were influenced by the agglomeration of the CNTs. The calculated lung deposition for the realistic CNT mixtures and CNT agglomerates showed much higher deposition rates than that for single standing CNTs under a variety of flow conditions. 5 In chapter 5, the effective particle dose in the lung was calculated based on the lung deposited surface area (LDSA), which was determined by combining the lung deposition curves of the MPPD model and the geometric surface area of the particles. It was verified if the application range of nanoparticle surface area monitor (NSAM), which was developed based on the ICRP-model, could be extended to the MPPD model. Deposited concentrations in the alveolar and trachea-bronchial regions were calculated and model-specific calibration factors on the LDSA were developed. It turned out that despite small errors the application range of NSAM could be extended to other lung deposition models. The generated data serve to enhance the understanding of release and exposure mechanisms, explain the influences of the most important factors for the adverse effects of the generated aerosols with NF contents and allow the assessment of the effects of these aerosols on environmental health and safety (EHS). The generated quantification data support the hypotheses for grouping and read-across of NFs of the European GRACIOUS project and were added to the release library of the GRACIOUS project.