Holistic Approach to Water Quality: Biotic and Abiotic Contaminations in Water

Abstract

Effectively addressing water contamination requires a comprehensive approach that considers both biological and chemical contaminants, highlighting their interconnected impact and presents an accurate picture of the real environmental conditions. Microplastics (MP), per- and polyfluoroalkyl substances (PFAS) and antibiotic-resistant bacteria (ARB) coexist in real-world environments. These stressors are considered emerging waterborne contaminants. The interaction between MP/PFAS and ARB may synergistically impact several endpoints, potentially exacerbating environmental risks and posing significant challenges to water management systems and human health. This thesis is structured into two primary sections. The first part focuses on chemical contamination (MP and PFAS) in water systems, investigating their toxicological impact on Daphnia magna, a sentinel species for assessing ecological health due to its sensitivity to water quality changes. The second part investigates drinking water contamination from a microbiological perspective with a focus on ARB, providing a comprehensive analysis of water quality concerns. Research on environmentally relevant concentrations of MP/PFAS, their combined effects, and their interactions within ecosystems remains limited. A chronic toxicity exposure test was conducted on two genotypes of Daphnia magna with different exposure histories to chemicals (naive and experienced). The experimental setup mimicked natural environmental conditions to investigate Daphnia’s ecotoxicological response to the individual and combined effects of MP, PFOA and PFOS. This study enhances our understanding of the mechanisms of toxicity triggered by these environmental stressors and their impact on Daphnia’s life history traits and overall fitness throughout its life cycle. It was discovered that the stressors negatively affected the plasticity in both genotypes. However, the naive genotype exhibited greater tolerance to chemical stressors than the experienced genotype. The interactions between these chemicals were also investigated. Prior to chronic exposure, a proof-of-concept study was conducted to optimise the experimental design using Daphnia magna to assess the ingestion, retention and egestion rates of four common MP both in the presence and absence of algae as a food source. This groundwork prepared the study for chronic exposure and helped validate key techniques, such as MP characterisation, their concentration, dispersal methods, refining the choice of one MP and ensuring that the study is well-designed and methodologically accurate. Despite the significance of ARB as emerging biological contaminants, comparatively little research has focused on their presence, diversity, and concentration within household drinking water systems compared to clinical or wastewater systems. Research into the isolation, characterisation and identification of ARB from household drinking systems addresses a critical gap in understanding how these bacteria persist and proliferate in domestic environments. In the next phase of this thesis, the presence, prevalence, and diversity of ARB were investigated in three sites (showerheads, bathroom taps and kitchen taps) within 30 residences. This study provides valuable insight into the link between environmental ARB contamination in community settings and the quality of treated wastewater. This knowledge enhances our understanding of their environmental and public health implications, supports the development of effective mitigation strategies, and promotes increased public awareness of antimicrobial resistance. This thesis emphasises the need to incorporate realistic environmental conditions to accurately represent natural processes and better understand the impacts and interactions of these contaminants on the environment and humans, inspiring further research in this critical field.