Analysing the role of surface aging on the impact of microplastic pollution in soil matrices
Creators: name: Savage, Dom
Publisher: name: Lancaster University
Year: 2024

description: Plastics are modern-day super materials, capable of being tailored to
 virtually every material application imaginable. However, their low cost,
 resilient nature, and meteoric rise into prolific production has
 contributed significantly to their widespread pollution of the
 environment. In recent years citizens
 
 and scientists alike have recognised this as an emerging ecological and
 environmental crisis, and as such keen concern has followed, and
 significant interest to understand and address this crisis has emerged.
 
 
 Once present in the environment plastics present a number of novel
 hazards. Whilst they are resilient to complete mineralisation, they
 readily break down and fragment into smaller particles known as
 microplastics and nanoplastics. These tiny particles are promptly
 dispersed throughout the natural world, making their retrieval and cleanup
 all but impossible. As a result, understanding what happens
 
 to these materials as they age within the environment, and assessing what
 impact they will have, is essential. This study is naturally an uphill
 battle for a number of reasons: these materials are highly diverse, owing
 to their ability to be synthesised readily from a wide variety of monomers
 in a wide variety of arrangements, their ability to be further adapted
 with chemical additives, and their uncontrolled degradation in
 environmental matrices which changes their properties further still.
 
 
 Because of this, existing research has often focused on the use of
 so-called ‘pristine’ materials; outof-the-factory polymers which are easy
 to obtain, characterise, and categorise. However, whilst this approach is
 a sensible first step, it leaves a lot of critical understanding out of
 the picture. More recently,
 
 research has progressed to test hypotheses with ‘aged’ materials, as they
 are more representative of pollution found in the environment. There are a
 number of common methods for approaching this, but they have their own
 limitations, and are generally quite slow, making rapid progress on this
 issue challenging. In very recent studies, new potential tools have been
 discussed to evaluate hypotheses
 
 related to material aging on much faster timescales, such as the use of
 plasmas.
 
 
 In this thesis, plasma degradation was pioneered as a proxy for
 environmental aging in microplastics research. Plasma surface treatment is
 not a new technology, and indeed polymers have been routinely exposed to
 plasma in other fields of research to achieve a variety of outcomes.
 However, its application
 
 as a potential aging method to rapidly simulate environmental
 photodegradation is all but missing. Herein an in-depth analysis and
 optimisation of plasma degradation for this application was made, with
 recommendations for sensible implementation of this technique. Overall, it
 was deemed a rapid
 
 alternative method that can significantly accelerate the pace of
 aging-focused studies, whilst remaining a plausible abstraction of
 photodegradation within appropriately designed methodologies. This
 technique was demonstrated to have enormous potential in its application
 to microplastics research.
 
 The optimised aging protocol was then carried forth into two research
 chapters: the first an analysis of environmental sorption dynamics of
 common soil nutrients to aged plastic surfaces, using XPS as a method to
 determine surface adhesion. Results indicated material-specific and
 aging-specific sorption occurs, however it was concluded that further
 research was needed to ascertain if nutrient
 
 immobilisation is a real concern. The second was a soil incubation study,
 investigating the impact that the environmental aging of microplastic
 pollution will have on soil health. These results concluded that even in a
 low (but representative) concentration of 0.25% w/w microplastics have a
 small but
 
 notable and significant impact on soil health, with some treatments being
 able to influence phosphorus and ammonium availability, affect soil
 aggregation, as well as alter pH and EC values within the soil. There was
 evidence of aging-specific variation, however these data indicated
 material-specific features
 
 were more relevant. These studies demonstrated that plasma surface
 treatment can be used as an effective and sensible aging protocol for
 microplastics research in the environment.