Environmental risks and toxicity mechanisms of water-soluble polymers in freshwater systems

Robison-Smith, Charlotte 2025. Environmental risks and toxicity mechanisms of water-soluble polymers in freshwater systems. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Plastic pollution is now recognised as a critical global challenge within the escalating climate crisis. Plastics are a subset of a broader chemical class of synthetic polymers, which remain largely unregulated. Polymer chemicals are not required for registration within EU/UK REACH. While progress has been made to address the issue of plastic pollution, such as single-use plastic bans, more nuanced chemical management strategies are needed to sufficiently address the risks synthetic polymers pose on the environment. A significant regulatory gap concerns water-soluble polymers (WSPs). The European Union’s ban on intentionally added microplastics explicitly excludes WSPs on the basis of their water solubility and longstanding assumptions of biological inertness. However, given their widespread use and environmental persistence, WSPs are emerging as pervasive pollutants in freshwater ecosystems, yet their ecological effects remain poorly understood. WSPs are widely used across biomedical applications but also in aquaculture practices, hence understanding their biological effects are both environmentally and commercially important. This thesis presents novel laboratory studies on environmentally relevant WSP exposures in freshwater fish, examining endpoints with direct relevance to aquaculture, including growth performance, behaviour and metabolic rate. An alternative biodegradable polymer was also evaluated as a potential safer substitute, with promising results for the aquaculture industry. Standardised ecotoxicity testing (OECD) further revealed lethal effects of WSPs on a freshwater invertebrate at real-world concentrations, underscoring the need for consideration of WSPs within chemical hazard assessment frameworks. Analytical chemistry and proteomics reveal underlying mechanisms of toxicity for the WSPs tested in the exposure models, yielding evidence for both indirect (nutrient stress) and direct (neurotoxicity) toxicity mechanisms. The regulatory implications and recommendations for future work are discussed in the final chapter of this thesis. Overall, this work demonstrates WSPs represent an overlooked environmental risk for freshwater systems, highlighting the need for WSP hazard assessment to be a required within the EU Commissions emerging legislative framework on polymer registration.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Biosciences
Subjects:	Q Science > Q Science (General)
Funders:	NERC funded PhD studentship; ECORISC CDT
Date of First Compliant Deposit:	19 May 2026
Last Modified:	19 May 2026 15:22
URI:	https://orca.cardiff.ac.uk/id/eprint/187111

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