Multimodal characterisation of engineered nanomaterials in the environment
File(s)
Author(s)
Wang, Yunyang
Type
Thesis
Abstract
Engineered Nanomaterials (ENMs) are incorporated into many commercial products due to
their outstanding intrinsic properties as well as their small size. Due to the rapid growth and
wide range of applications of ENMs, particularly in personal care and cosmetics, the impact
of ENMs on the environment and human health has received much attention. ENMs used in
consumer products have a high potential to enter the environment during use and disposal. They could encounter the environment through wastewater, making it vital to investigate
their potential impact. The prevalent use of engineered titanium in consumer products, such as personal care
product additives, has spurred concerns that they could pollute freshwater ecosystems. The
first objective of this thesis was to characterise the morphology and composition of TiO2
NPs in different consumer products to appreciate which particle types should be tested in in
vitro and field studies. Consumer products of sunscreens and toothpaste were made of TiO2
NPs with various morphologies and agglomeration states within an organic matrix and
consisted of Anatase and Rutile phases. The thesis also aimed to characterise how pristine TiO2 NPs behave and age in fresh waters
under different illumination conditions (natural light vs visible light vs dark) to mimic these
highly relevant field conditions. High-resolution electron microscopy was used to visualise
the interaction of freshwater algae after exposure to TiO2 NPs that had been aged for
different time periods under these different illumination conditions. The impacts of the
phase of the Titania (Anatase vs Rutile) on their behaviour in ultrapure water and fresh river
waters were also compared. Anatase and Rutile of TiO2 NPs aggregated in ultra-pure and
river water. Both light-exposure conditions and the composition of the waters influenced the
3
agglomeration of the NPs. The aggregates of Rutile TiO2 were more significant in both
kinds of waters than in Anatase TiO2. The aggregation of TiO2 nanoparticles is more severe
in river water than in ultra-pure water. The aggregation size became massive with a longer
ageing time. In ultrapure and River water, the aggregation of TiO2 NPs was more marked
under visible light conditions, influenced by pH, photocatalysis, and humic acid (HA) in
solution. Subsequently, rutile TiO2 particles with greater aggregation were selected for the algal cell
contact experiments. We characterised how pure Rutile TiO2 NPs age in the standard
Economic Co-operation and Development-((3-(N-morpholino) propanesulfonic acid)
medium (OECD-MOPs) cell culture medium, under the influence of different light
conditions. This characterisation was used to understand how different light conditions
affect their subsequent interaction with freshwater algae in culture (to mimic the freshwater
environment). TiO2 NPs were pre-aged in an OECD medium for various periods under light
and natural light conditions and incubated with the freshwater green alga Raphidocelis
subcapitata (R. subcapitata). In the pre-ageing in the light experiment, we can see that the
aggregation phenomenon is aggravated by light. The aggregation of the nanoparticles
affected by UV light is even more severe. This resulted in larger aggregates under UV light
after incubation in the algal cells. Transmission electron microscopy (TEM) revealed that
the cell walls were wrinkled and detached. Scanning TEM with energy-dispersive X-ray
spectroscopy (EDS) compositional analysis also showed that these nanoparticles had contact
with the cell wall and were internalised into the algal cells. Extracellular polymeric
substance (EPS) was also found around the cells that could protect the algae from contact
with the TiO2 NPs. 4
CeO2 nanoparticles (NPs) are also used prevalently in consumer products, for example, as
diesel fuel additives, acting as fuel combustion catalysts to increase fuel efficiency and
reduce the emission of greenhouse gases. These materials will also encounter fresh waters in
the environment, probably as road runoff, where they can be washed into streams, rivers, and the broader ecosystem. For this reason, their behaviour in waters under different light
illumination conditions and interaction with freshwater algae was also characterised. Interestingly we found that the CeO2 dissolved in the OECD medium. Pre-ageing
experiments in cell culture media (OECD+ MOPS) revealed the effect of UV light on the
aggregation of CeO2 nanoparticles. The aggregation of nanoparticles was greater under
natural light than visible light. In contrast, experiments testing whether the CeO2 NPs
dissolved in OECD media demonstrated that CeO2 NPs dissolved more during pre-ageing
under natural light and even more when they contacted algae. In algal cultures, the CeO2
NPs accumulated around and approached the algal cells in both light conditions. The cell
structure became disrupted, and the cell wall had shed. This demonstrates that CeO2
nanoparticles have growth inhibition on cells. X-ray fluorescence (XRF) maps and X-ray
absorption near edge structure (XANES) characterised the valence of the shell layer of CeO2
NPs surrounding the algae. They showed that Ce3+ dominated the outer layer and Ce4+
dominated the core of the particles in both light conditions. Evidence was also found for the
internalisation of CeO2 nanoparticles into cells. Interestingly nanometer-sized Ce3+
particles were identified inside the algae by electron energy loss spectroscopy in the
scanning transmission electron microscope. The lattice constant of some of these
intracellular particles was identified by phase contrast electron microscopy as CePO4. This
is the first clear evidence of the internalisation of CeO2 and CePO4 nanoparticles inside
algae and their dissolution. It has important implications for their toxicity, as CePO4 is more
damaging to algae than CeO2 NPs. CePO4 prevents Ce3+ and Ce4+ from expressing
5
Superoxide dismutase and peroxidase activity, respectively. Although CePO4 acts as a
peroxidase to eliminate H2O2 instead of Ce4+, the inability to express the SOD activity of
Ce3+ leads to a greater risk of SOD toxicity. Also, the severe aggregation of nanoparticles
inside and outside the cell due to CePO4 can inhibit cell growth.
their outstanding intrinsic properties as well as their small size. Due to the rapid growth and
wide range of applications of ENMs, particularly in personal care and cosmetics, the impact
of ENMs on the environment and human health has received much attention. ENMs used in
consumer products have a high potential to enter the environment during use and disposal. They could encounter the environment through wastewater, making it vital to investigate
their potential impact. The prevalent use of engineered titanium in consumer products, such as personal care
product additives, has spurred concerns that they could pollute freshwater ecosystems. The
first objective of this thesis was to characterise the morphology and composition of TiO2
NPs in different consumer products to appreciate which particle types should be tested in in
vitro and field studies. Consumer products of sunscreens and toothpaste were made of TiO2
NPs with various morphologies and agglomeration states within an organic matrix and
consisted of Anatase and Rutile phases. The thesis also aimed to characterise how pristine TiO2 NPs behave and age in fresh waters
under different illumination conditions (natural light vs visible light vs dark) to mimic these
highly relevant field conditions. High-resolution electron microscopy was used to visualise
the interaction of freshwater algae after exposure to TiO2 NPs that had been aged for
different time periods under these different illumination conditions. The impacts of the
phase of the Titania (Anatase vs Rutile) on their behaviour in ultrapure water and fresh river
waters were also compared. Anatase and Rutile of TiO2 NPs aggregated in ultra-pure and
river water. Both light-exposure conditions and the composition of the waters influenced the
3
agglomeration of the NPs. The aggregates of Rutile TiO2 were more significant in both
kinds of waters than in Anatase TiO2. The aggregation of TiO2 nanoparticles is more severe
in river water than in ultra-pure water. The aggregation size became massive with a longer
ageing time. In ultrapure and River water, the aggregation of TiO2 NPs was more marked
under visible light conditions, influenced by pH, photocatalysis, and humic acid (HA) in
solution. Subsequently, rutile TiO2 particles with greater aggregation were selected for the algal cell
contact experiments. We characterised how pure Rutile TiO2 NPs age in the standard
Economic Co-operation and Development-((3-(N-morpholino) propanesulfonic acid)
medium (OECD-MOPs) cell culture medium, under the influence of different light
conditions. This characterisation was used to understand how different light conditions
affect their subsequent interaction with freshwater algae in culture (to mimic the freshwater
environment). TiO2 NPs were pre-aged in an OECD medium for various periods under light
and natural light conditions and incubated with the freshwater green alga Raphidocelis
subcapitata (R. subcapitata). In the pre-ageing in the light experiment, we can see that the
aggregation phenomenon is aggravated by light. The aggregation of the nanoparticles
affected by UV light is even more severe. This resulted in larger aggregates under UV light
after incubation in the algal cells. Transmission electron microscopy (TEM) revealed that
the cell walls were wrinkled and detached. Scanning TEM with energy-dispersive X-ray
spectroscopy (EDS) compositional analysis also showed that these nanoparticles had contact
with the cell wall and were internalised into the algal cells. Extracellular polymeric
substance (EPS) was also found around the cells that could protect the algae from contact
with the TiO2 NPs. 4
CeO2 nanoparticles (NPs) are also used prevalently in consumer products, for example, as
diesel fuel additives, acting as fuel combustion catalysts to increase fuel efficiency and
reduce the emission of greenhouse gases. These materials will also encounter fresh waters in
the environment, probably as road runoff, where they can be washed into streams, rivers, and the broader ecosystem. For this reason, their behaviour in waters under different light
illumination conditions and interaction with freshwater algae was also characterised. Interestingly we found that the CeO2 dissolved in the OECD medium. Pre-ageing
experiments in cell culture media (OECD+ MOPS) revealed the effect of UV light on the
aggregation of CeO2 nanoparticles. The aggregation of nanoparticles was greater under
natural light than visible light. In contrast, experiments testing whether the CeO2 NPs
dissolved in OECD media demonstrated that CeO2 NPs dissolved more during pre-ageing
under natural light and even more when they contacted algae. In algal cultures, the CeO2
NPs accumulated around and approached the algal cells in both light conditions. The cell
structure became disrupted, and the cell wall had shed. This demonstrates that CeO2
nanoparticles have growth inhibition on cells. X-ray fluorescence (XRF) maps and X-ray
absorption near edge structure (XANES) characterised the valence of the shell layer of CeO2
NPs surrounding the algae. They showed that Ce3+ dominated the outer layer and Ce4+
dominated the core of the particles in both light conditions. Evidence was also found for the
internalisation of CeO2 nanoparticles into cells. Interestingly nanometer-sized Ce3+
particles were identified inside the algae by electron energy loss spectroscopy in the
scanning transmission electron microscope. The lattice constant of some of these
intracellular particles was identified by phase contrast electron microscopy as CePO4. This
is the first clear evidence of the internalisation of CeO2 and CePO4 nanoparticles inside
algae and their dissolution. It has important implications for their toxicity, as CePO4 is more
damaging to algae than CeO2 NPs. CePO4 prevents Ce3+ and Ce4+ from expressing
5
Superoxide dismutase and peroxidase activity, respectively. Although CePO4 acts as a
peroxidase to eliminate H2O2 instead of Ce4+, the inability to express the SOD activity of
Ce3+ leads to a greater risk of SOD toxicity. Also, the severe aggregation of nanoparticles
inside and outside the cell due to CePO4 can inhibit cell growth.
Version
Open Access
Date Issued
2023-02-28
Date Awarded
01/09/2023
License URL
Advisor
Porter, Alexandra
Xie, Fang
Sponsor
Engineering and Physical Sciences Research Council
China Scholarship Council
Publisher Department
Materials
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)