Plastics were first popularised in the mid-twentieth century and have since become an integral part of our everyday lives. The versatility of plastics means that they can be moulded into almost any shape or size and have a range of uses. They can be dyed many colours, made to be waterproof and are generally very durable. However, this also means that they do not break down very easily once used, resulting in the accumulation of plastic debris within the environment. As they are slowly weathered over time, they produce ‘microplastic’ particles (plastic particles less than 5 mm in size), which have been found in a range of habitats and organisms around the world.

Why study salt marshes?

Urban river estuaries are recognised as key microplastic transport corridors, connecting terrestrial sources of microplastics to marine sinks. Coastal intertidal zones (salt marshes and mudflats) are known to accumulate many different anthropogenic pollutants, but their role in the accumulation and transport of microplastics remains understudied. In a collaboration between BGS and the University of Nottingham, my PhD project aims to understand how salt marshes along the Thames estuary (England, UK) store and interact with microplastics, explaining the key processes that control their accumulation and release. This insight will provide a more holistic view of microplastic particles’ behaviour and their migration through estuary corridors.

The fieldtrip

For the project to meet its aims, Dr Chris Vane (BGS) and I undertook a fieldtrip to the Thames estuary in June 2022. We visited two salt marshes: Rainham Marsh on the northern shore in Essex and Swanscombe Marsh on the southern shore in Kent. The trip proved to be very successful and we got incredibly lucky with some sunny weather too!

We needed a transect of samples running perpendicular to the shoreline and across each vegetation zone at each salt marsh, so we could explore the relationship between different salt marsh conditions and the microplastic distribution. By coring to a depth of 50 cm, we also hoped that we could capture a temporal record of microplastics for these marshes. The cores may show that microplastics are not stored within sediment layers at all; rather, particles could be retained in the active surface layer of sediment, or they may be stored for shorter temporal periods.  

We successfully obtained a total of eight 50 cm cores, as well as a number of salt marsh surface samples that will be used to further investigate microplastic variation spatially across the marshes. The samples obtained on this fieldtrip will complement those taken during a previous fieldtrip in February 2022, which sampled sites in the more urban, London regions of the Thames and its tributaries.

Studying the samples

Back in the laboratory, the cores have been separated into 10 cm sections and freeze-dried to preserve any temporal variation in microplastic abundance. I will now process them using a series of steps to quantify the microplastic particles within each sample. In time, the data collected during this project will make it possible to understand the role of salt marshes in the storage and transfer of microplastics within estuary corridors.

About the author

Megan Trusler is a PhD student at Nottingham University, studying salt marshes along the Thames estuary and how they interact with microplastics.

Given that microplastics are now ubiquitous within our environment, the issues associated with this persistent anthropogenic pollutant are of global concern. It is widely acknowledged that plastic polymers are slow to degrade in the environment and can persist over long timescales, so it is particularly important to identify microplastic fate transport pathways.

Urban estuaries are known to be key plastic-transport corridors and coastal, intertidal zones, such as salt marshes and mudflats, are already recognised as accumulators of many different anthropogenic pollutants. Intertidal zones are therefore likely to play an important role in the accumulation of microplastics, but they remain understudied.

The project

My PhD project aims to develop understanding of how salt marshes store and interact with plastics, explaining the key processes that control their accumulation and release. This has the potential to aid management efforts, including the use of salt marshes as nature-based solutions that reduce the flow of microplastics into the marine environment. Working with Dr Sarah Cook and Dr Barry Lomax from the University of Nottingham (UoN), as well as Dr Christopher Vane from BGS, a mixture of natural and reclaimed salt marsh sites across the River Thames will be used to explore controls on spatial and temporal microplastic abundances.

A series of sediment cores will be extracted and analysed using a number of techniques, including microplastic density separation, Fourier-transform infrared spectroscopy (FTIR) and Rock-Eval pyrolysis. These techniques will be used to develop a microplastic accumulation record, comparing downcore variations in composition and abundance.

Microplastics could then have potential use as a novel geochronological tool, reflecting changes in anthropogenic activity and possibly climate events. The role of vegetation in the trapping of microplastics and subsequent degradation will also be analysed, as will the possible relationship between sediment size and microplastic entrapment.

There remains much to be understood about the processes that facilitate the decay of plastics, enabling the transition to microplastics from larger macroplastics. A degradation experiment was recently set up at UoN Sutton Bonington campus that will follow the degradation of plastic coffee cup lids under different environmental conditions for the next five years. Treatments will compare the effect of sunlight, shading and exposure to air and soil, as well as the difference in degradation rates between biodegradable and conventional plastic types. Samples of the polymers will be analysed monthly, with the resulting data documenting their decay and highlighting the key processes involved in releasing secondary microplastics (microplastics derived from larger plastics) into the environment.

About the author

Megan Trusler is a graduate of the University of Birmingham (BSc geography) and Loughborough University (MSc environmental monitoring, research and management). She was Chair of the Birmingham University Conservation Volunteers 2019–2020 and received a joint part studentship from the JBA Trust, the British Hydrological Societyand the Environment Agency to complete her masters.

Megan is now a biosciences PhD student at the University of Nottingham and BGS, investigating microplastics in River Thames salt marshes. Her interests lie in understanding the impacts of anthropogenic activity, focusing on the fate and management of pollutants in aquatic ecosystems. The pursuit of this led her to the study of plastic accumulation in the environment.

Outside of research, she enjoys hiking, live music, doing puzzles and spending time with friends.