The fate and impacts of microplastics in freshwater systems

It has been estimated there are between 5 and 50 trillion plastic particles on the surface of the ocean. Microplastics are typically defined as particles <5mm in size. They can travel thousands of miles in both marine and freshwater systems. As such they are widely distributed in rivers, lakes, seas and the ocean. Ingestion of microplastics has been recorded in over 100 aquatic organisms, from zooplankton upwards in size. A diverse variety of pollutants, including metals, can adsorb onto microplastics, while substances of concern are widely used in plastics manufacturing. Thus, the impacts of aquatic plastic litter are presumed to be widespread and insidious.

As the majority of previous research has investigated plastic litter in the ocean, its fate and impacts in freshwater systems remain largely unknown. While the ocean is an obvious destination for microplastics, an unknown proportion are also present in river sediments and freshwater systems. This project will advance our scientific knowledge of the subject by investigating the following topics:

1. Development of robust experimental methods for isolation and identification of plastics in freshwater systems

Method development with start with published methods for the analysis of plastic particles in wastewater and seawater, which typically involve the following components: density separation, filtration, sieving, centrifugation, visual examination, chemical oxidation, enzymatic oxidation, staining and specific polymer identification (e.g. with Raman or Fourier transform infrared (FTIR) spectroscopy). By initially testing synthetic samples, before moving onto authentic freshwater samples (surface waters, river sediments, groundwater), the project will validate the efficacy of selected isolation and detection steps. Importantly the ability to spike and recover plastic particles from environmental samples, i.e. to determine the recovery of the analytical method, will be determined.

2. Occurrence and fate of microplastics in freshwater systems

Using the previously developed and validated method, microplastics will be identified and quantified in freshwater. These will include samples taken from the Thames river (surface samples and sediments), before riverbank filtration, in groundwater wells following riverbank filtration, and following groundwater treatment processes. This will build upon existing relationships with Affinity Water and a previous project, which assessed how a shallow aquifer riverbank filtration system impacted water quality (Ascott et al., 2016). Hence, the project will determine the amount of microplastics which are transported from river water to groundwater, accumulate in river sediments, and are removed by riverbank filtration and during water treatment.

3. Uptake and leaching of hazardous pollutants to and from plastic particles

Selected particles from part 2 of the project will be subjected to additional analyses. Metals will be detected using inductively coupled plasma mass spectrometry (ICP-MS) and organic pollutants, for example, pesticides and plasticisers, targeted using gas chromatography with mass spectrometry (GC-MS). By comparing amounts of pollutants from plastic particles isolated from freshwater, the project will evaluate how environmental processing (e.g. biofilm formation, photochemical oxidation) affects concentrations of pollutants as plastic litter moves between different environmental compartments. 

Reference

M.J. Ascott, D.J. Lapworth, D.C. Gooddy, R.C. Sage, I. Karapanos. Science of the Total Environment (2016), 554–555, 89–101.

Candidates should hold a first or upper-second class Bachelor’s degree and a Master’s degree at distinction level (or equivalent experience/qualifications) in an appropriate discipline.

NERC studentships are open to all UK citizens, and other European Union students who have lived in the UK for the past three years. Other students may also be eligible if they have an established relevant connection with the UK.

Space Environment and Protection Group, Surrey Space Centre. The project is run in combination with the NERC Centre for Ecology and Hydrology (CEH), Met Office and University of Bristol.

The student will be based at the University of Surrey but will undertake a placement (6 months) with the NERC Centre for Ecology and Hydrology which runs the COSMOS-UK network. Time will also be spent with the UK Met Office to understand the space weather user requirements.