IAP-26-052

Microplastics in Sustainable Drainage Systems: Fate, Retention and Ecological Impacts in Urban Blue-Green Infrastructure

Urban environments are increasingly recognised as major sources of microplastic pollution (Correia Prata et al., 2019). Tyre wear particles, synthetic fibres, road-marking degradation, packaging fragments and other anthropogenic materials are mobilised during rainfall events and transported through urban drainage networks into rivers, estuaries and coastal waters (Müller et al., 2020). While Sustainable Drainage Systems (SuDS) are widely implemented to improve water quality and reduce flood risk, their role in capturing, retaining and transforming microplastics remains poorly understood (García-Haba, et al, 2023).

Recent studies suggest that SuDS can effectively remove microplastics from stormwater runoff (Gilbreath at el., 2019; Smyth et al., 2021). However, considerable uncertainty remains regarding the long-term fate of these particles once retained within bioretention media, swales, detention basins and permeable pavements (Chen et al., 2021). In particular, little is known about accumulation rates within engineered soils, interactions with vegetation and biofilms, storage within geotextiles and filter materials, and the potential remobilisation of contaminants during extreme rainfall events.

This interdisciplinary project will investigate the occurrence, transport, and ecological implications of microplastics within urban SuDS. Combining expertise in urban hydrology, water quality, soil-sediment interactions, and microplastic pollution, the project will develop a process-based understanding of how microplastics behave within blue-green infrastructure.

The research will address four key questions:

1. How effectively do SuDS components retain microplastics?

2. Where do retained microplastics accumulate within engineered soils, vegetation and filter media?

3. How do biological and physical processes influence retention, transformation and remobilisation?

4. What are the implications for long-term SuDS management and urban water quality?

The project will provide the first comprehensive assessment of microplastic accumulation within SuDS in Scotland and will generate evidence to support future design, maintenance, and pollution management strategies. The outcomes will contribute to improved understanding of contaminant fate within nature-based solutions and enhance the role of SuDS in protecting aquatic environments from emerging pollutants.

The project will combine field investigations, laboratory analysis, and controlled experiments.
Field studies will be undertaken at a range of established urban SuDS across Scotland, potentially including bioretention systems, swales, detention basins and permeable pavement installations. Sampling campaigns will quantify microplastic concentrations in inflows and outflows and investigate accumulation within soils, sediments and vegetation.

The student will develop and apply robust analytical methods for extracting and characterising microplastics from complex environmental matrices. Methods will draw upon contemporary approaches including density separation, filtration, microscopy, and spectroscopic techniques for polymer identification. Particular emphasis will be placed on developing practical methods suitable for engineered SuDS media.

Laboratory studies will investigate:

• retention efficiencies of different SuDS media;

• vertical migration through engineered soils;

• accumulation within geotextiles and membrane layers;

• interactions between microplastics, vegetation and biofilms;

• remobilisation under simulated storm conditions.

Experimental systems may include column studies, rainfall simulation experiments, and controlled mesocosms. The project will also explore relationships between microplastic characteristics (size, shape and polymer type) and retention mechanisms. Statistical and hydrological analyses will be used to identify key controls on microplastic fate and transport.

Fieldwork and supervision will provide interdisciplinary training across environmental monitoring, urban hydrology, soil science and contaminant analysis. Collaboration between Heriot-Watt University and the University of St Andrews will enable the student to integrate engineering and environmental science perspectives.

Year 1

1. Literature review and training in microplastic sampling and analysis.

2. Identification and selection of SuDS case-study sites.

3. Development and validation of sampling and laboratory methods.

4. Initial field campaigns and baseline data collection.

5. Data analysis and refinement of research questions.

6. Completion of first-year review.

Year 2

1. Extensive field sampling across multiple SuDS types.

2. Characterisation of microplastic abundance and distribution in water, soils, sediments and vegetation.

3. Development of laboratory and mesocosm experiments.

4. Presentation of preliminary findings at national conferences.

5. Preparation of first journal manuscript.

6. Completion of second-year review.

Year 3

1. Completion of laboratory and experimental studies.

2. Investigation of retention mechanisms and remobilisation processes.

3. Integration of field and laboratory datasets.

4. Development of implications for SuDS design and management.

5. Preparation of additional journal manuscripts.

6. Completion of third-year review.

Year 3.5

1. Thesis completion and submission.

2. Final publications and dissemination activities.

3. Presentation of findings to academic, industry and policy stakeholders.

4. Preparation for viva examination.

The student will receive advanced interdisciplinary training in:

• Microplastic sampling and analysis
• Environmental monitoring
• Soil and sediment characterisation
• Urban hydrology
• Water quality assessment
• Experimental design
• Statistical analysis and data science
• Scientific writing and publication
• Research communication and stakeholder engagement

The student will also benefit from the IAPETUS training programme, including cohort development activities, transferable skills training and interdisciplinary networking opportunities.