There is growing concern about the proliferation of microplastics in the aquatic environment and their impact on ecosystem functioning. At the same time the frequency of occurrence and size of harmful algal blooms is increasing globally in these ecosystems, yet we know very little about how the two interact. Microplastics in aquatic habitats become rapidly colonised by microbial biofilms, and this interface between plastic surfaces and the environment has been termed the ‘Plastisphere’. However, our understanding of microbial colonisation dynamics of marine and freshwater microplastics is limited to descriptive taxonomic studies, which have highlighted the huge diversity of bacteria (including human pathogens) that colonise the surface of plastic debris. An important area of microplastic research, that has been largely ignored, is the interactions of microplastics with algae. The enrichment of surface waters with nutrients can cause the proliferation of algal blooms, including species of toxin-producing algae and cyanobacteria, which are harmful to human health. Algal blooms are also hypothesised to provide a habitat that can protect waterborne human pathogens such as cholera. Subsequently, there is an urgent need to understand the dynamics of the relationship between algal blooms and microplastics and quantify their potential for enhancing the survival and transport of human pathogens such as cholera.
By understanding how microplastics can facilitate a multi-pollutant effect, this project will contribute to more accurate risk assessments, by integrating the effects of microplastics with harmful plastic-associated microbes. Therefore, the novelty of this project lies in exploring the processes and interactions occurring within the Plastisphere, but also by quantifying the combined risks to water quality from the synergistic effects of these three important groups of pollutants. Results from this research will provide both novel and timely data, with direct implications for stakeholders such as Defra, SEPA, EA and the NHS, and could have direct impact on policy (EU Bathing Waters Directive; EU Urban Wastewater Treatment Directive; Shellfish Protected Areas).
Key research questions:
Specifically, the large gaps in our understanding of microplastic-algal-human pathogen dynamics will be directly addressed through this studentship by focusing on the following questions:
1. Do distinct spatial and temporal patterns of microplastic-algal-pathogen associations exist in relation to seasonal environmental drivers of nutrient inputs into aquatic systems?
2. Does the presence of microplastic in eutrophic waters result in enhanced persistence of human pathogens in algal blooms through habitat, e.g. via colonisation of microplastics, and nutrient provision, e.g. from algal exudates?
3. How does microplastic pollution, together with potential shifts in the spatial and temporal variation of N and P under a changing climate impact the dynamics of algal occurrence and pathogen persistence?
4. To what extent are human pathogens associated with microplastics in algal blooms protected from environmental stressors?
Furthermore, such interactions could also have significant repercussions for environmental regulation and management if algal/microplastic populations contribute to a skewed persistence profile of faecal indicator organisms (FIOs), the microbial compliance parameter currently used by UK regulators such as the Environment Agency. Therefore, this project will also explore the risks to water quality through altered FIO dynamics associated with toxic algal blooms, and the risks to human health by comparative assessment of FIO behaviour versus that of specific pathogens, in the presence of microplastics.
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Using a combined field and laboratory-based experimental approach, this interdisciplinary project will provide the fundamental understanding necessary to refine regulatory policy, and deliver a step-change in our definition of ‘harmful algal blooms’. To ensure the impact of the science case, sampling methodology will be the same as that used by UK regulators and within projects informing environmental policy. The effect of microplastics on growth, morphology and toxicity of phytoplankton will be determined through mesocosm experiments focusing on key bloom-forming species found in inland, transitional and coastal waters. Experimental cultures will be spiked with commercially available microplastic beads and fibres (PE, PPE and PMMA) covering a wide size range. Colonisation of algae on microplastic particles (1 – 5 mm range) or the effect of particles (< 1mm) on algal physiology, e.g. C fixation or toxin production, will be quantified. To understand the effect of microplastics on algal blooms and human pathogen dynamics the student will use a range of environmental pathogen isolates, e.g. Vibrio cholerae and a lux-marked non-toxigenic environmental isolate of E. coli O157:H7, together with faecal indicator organisms such as E. coli and intestinal enterococcus. The experimental phases of this project will take 36 months to complete, with the remaining time being allocated to writing the thesis & papers for publication, attending conferences and networking with stakeholders.
Following a critical review of the literature (months: 0-4), an intensive series of laboratory experiments using replicated mesocosms will be undertaken to investigate persistence profiles and decay coefficients of human pathogens colonising microplastics in association with toxic algal blooms.
A comprehensive series of field-relevant controlled laboratory mesocosm experiments will investigate the effect of different sized microplastics and algal taxa exudates on the die-off kinetics and metabolic activity of human pathogens
Experiments will be conducted to further understand algae-microplastics-human pathogen dynamics in freshwater under a range of environmental & anthropogenic variables, e.g. climate change scenarios, eutrophication and simulated sewage release
The student will organise and lead a workshop to present the results from this project to a range of stakeholders including environmental managers and regulators, policy makers, the water industry and environmental groups. The remaining time will be spent writing up the thesis and papers for publication
The student will receive specialist training from the supervisory team at both Stirling and CEH on the safe handling of Hazard Group 2 microorganisms (including cholera) and toxin-producing micro-algae. The student will become fully embedded within the £1.85M NERC funded “Plastic Vectors Project” https://plasticvectors.stir.ac.uk/ led by Prof Richard Quilliam at the University of Stirling. This project is looking at wider issues of microbial colonisation of microplastics by pathogenic viruses and bacteria, and the student will have the opportunity to work closely with post-doctoral staff researching complementary areas, attend project group meetings and become part of the team with senior scientists and important stakeholders involved with the project. Undertaking this project will broaden the scope of the applicant’s skills base by providing specialist training in microplastic and microbial pollution, and in methods in freshwater biology and ecology.
References & further reading
Keswani A, Oliver DM, Gutierrez T, Quilliam RS. (2016). Microbial hitchhikers on marine plastic debris: human exposure risks at bathing waters and beach environments. Marine Environmental Research 118, 10-19
Rodrigues A, Oliver DM, McCarron A, Quilliam RS. (2019). Colonisation of plastic pellets (nurdles) by E. coli at public bathing beaches. Marine Pollution Bulletin 139, 376-380
Wu Y, Guo P, Zhang X, Zhang Y, Xie S, Deng J. (2019). Effect of microplastic exposure on the photosynthesis system of freshwater algae. Journal of Hazardous Materials, 374, 219-227.
Professor Richard Quilliam
Tel: 01786 467769