Assessing the impact of micro-plastics on river ecosystem DOM fingerprints

Overview

Plastic debris in waters represent a major contemporary environmental problem affecting numerous aquatic fauna (Eriksen et al., 2014). However, the impact on plastics at the micro-scale remains largely unknown. Microplastics (MPs; typically, smaller than 5 mm) ultimately derived from land can leach a variety of organic substances into surrounding waters with recent estimates suggesting that marine environments globally receive up to 23,400 MT of dissolved organic carbon (DOC) per year. Much of this is bioavailable (Romera-Castillo et al., 2018) but it remains unclear how this additional carbon pool impacts ecosystem function. MP-derived DOC in freshwater environments also has the potential to impact microbial food webs with the addition that chlorination-based water-treatment technologies can create potentially harmful trihalomethanes in drinking water (Lee et al., 2020).

The coastal margin, squeezed between the land and the sea, receives plastic pollution from both of these domains. Vietnam’s 3260 km coastline stretches across 28 coastal provinces, supporting rural livelihoods engaged in coastal tourism, small- and large-scale fishing and aquaculture industries, the latter particularly focused around the Mekong Delta. Vietnam is crossed by several large transboundary river systems, and, as a result, plastic pollution within the water system is derived not only from Vietnam, but also from countries and watersheds up-stream; the outcome is a total discharge into the aquatic system estimated at 270-735 thousand tonnes of plastic waste per annum (Ritchie & Roser 2020).
This PhD project will investigate DOC leachate potential from a variety of MP sources of the Red and Mekong Rivers currently investigated as part of the UKRI GCRF Living Delta’s Hub and a UKRI GCRF funded project investigating the sources, sinks and solutions for the plastic issues in Vietnam. This project will map unique DOM fingerprint signatures novel geochemical approaches (see methodology) with a virtual-globe imaging platform in Google Earth to provide an ecosystem services-based river assessment of MP derived DOC (Large & Gilvear, 2015; Keele et al., 2019). A key focus will be to develop empirical relationships between plastic source and type with DOC composition and ecosystem response (e.g. McGowan et al., 2012) using next generation geochemical and isotopic analytical approaches (e.g. Huber et al., 2011; Pereira et al., 2014) in controlled laboratory and field-based experiments. A secondary focus will examine and ascertain the disinfection biproduct formation potential from DOM leached plastics for safe drinking water supply (e.g. Finkbeiner et al., 2020). This PhD utilises the current expertise and profiles of the supervisory team in Vietnam as part of two major ongoing research projects with a unique and fundamental need to address the role of an as yet unconstrained impact of plastics on the aquatic carbon cycle.

Methodology

The project will focus on identifying key DOC pools using the latest liquid chromatography organic carbon and nitrogen detection systems (LC-OCD-OND; Huber et al., 2011) and and Elementer LC-irMS to explore DOC transformations under changing environmental conditions using the climate-controlled facilities at the Lyell Centre (www.lyellcentre.ac.uk). Newcastle University will support the student to construct a new model to explore geographical relationships between DOC compositional pools of the Red and Mekong Rivers using the empirical relationships established at the Lyell Centre and Vietnamese field sites, combined with plastic particle data provided by Vietnamese partners through an existing project. The new model will interogate MPs and DOC relationships with ecosystem function (pigment biomarkers) in a geographical context to build a systematic approach for future environmental based impact assessments.

Project Timeline

Year 1

• Carry out literature review
• Construct initial Google Earth model at Newcastle University
• Meet all supervisors to finalise PhD objectives and plan fieldwork for Year 2
• Identify training needs to complete ongoing workplan
• Receive training in relevant analytical methods
• Set up initial climate-controlled laboratory experiments

Year 2

• Analyse the results on Year 1 climate-controlled experiments
• Complete Vietnam fieldwork with support from overseas partners
• Continue new experiments for MP-DOC transformations with THM potential
• Meet supervisors to assess progress and plan for Year 3.
• Input new results into conceptual MP-DOC model
• Present results at national conference

Year 3

• Participate in additional fieldwork if necessary
• Complete outstanding experiments
• Make substantial progress towards thesis preparation and define a detailed timeline to ensure completion with 3.5 years
• Present results at international conference
• Prepare first publication

Year 3.5

• Complete and submit thesis
• Prepare additional data for publication

Training
& Skills

The supervisors will provide full training in their individual expertise areas, enabling the student to combine current best practice and develop the skills necessary to advance this science. Supervision will be provided jointly by Heriot-Watt (RP) and Newcastle (AL) universities, with additional support in ecosystem function biomarker approaches at Nottingham Univeristy (SM/VP). Directly relevant training will be provided by all institutes to equip the student with the skills necessary for all aspects of the project. IAPETUS fosters a strong sense of “community” that encourages students to organise a range of activities (e.g. annual conference) and identify additional training needs to be addressed via tailored opportunities. The student will have opportunities for additional training at the partner institution. The student should develop strong collaborations that will potentially benefit post-PhD career opportunities.

References & further reading

Eriksen M., L.C. Lebreton, H.S. Carson, M. Thiel, C.J. Moore, J.C. Borerro, F. Galgani, P.G. Ryan, J. Reisser (2014) Plastic pollution in the world’s oceans: more than 5 trillion plastic pieces weighing over 250,000 tons afloat at sea, PloS One, e111913

Finkbeiner, P., G. Moore, R. Pereira, B. Jefferson and P. Jarvis (2020). “The combined influence of hydrophobicity, charge and molecular weight on natural organic matter removal by ion exchange and coagulation.” Chemosphere 238: 124633.

Huber, S. A., A. Balz, M. Abert and W. Pronk (2011). “Characterisation of aquatic humic and non-humic matter with size-exclusion chromatography – organic carbon detection – organic nitrogen detection (LC-OCD-OND).” Water Research 45(2): 879-885.

Keele, V., D. Gilvear, A. Large, A. Tree and P. Boon (2019). “A new method for assessing river ecosystem services and its application to rivers in Scotland with and without nature conservation designations.” River Research and Applications 35(8): 1338-1358.
Large, A. R. G. and D. J. Gilvear (2015). “UsingGoogle Earth, A Virtual-Globe Imaging Platform, for Ecosystem Services-Based River Assessment.” River Research and Applications 31(4): 406-421.

Lee, Y. K., C. Romera-Castillo, S. Hong and J. Hur (2020). “Characteristics of microplastic polymer-derived dissolved organic matter and its potential as a disinfection byproduct precursor.” Water Research 175: 115678.

Pereira, R., C. I. Bovolo, R. G. M. Spencer, P. J. Hernes, E. Tipping, A. Vieth-Hillebrand, N. Pedentchouk, N. A. Chappell, G. Parkin and T. Wagner (2014). “Mobilization of optically invisible dissolved organic matter in response to rainstorm events in a tropical forest headwater river.” Geophysical Research Letters 41(4): 1202-1208.

Ritchie & Roser 2020 https://ourworldindata.org/plastic-pollution

Romera-Castillo, C., Pinto, M., Langer, T.M. et al. Dissolved organic carbon leaching from plastics stimulates microbial activity in the ocean. Nat Commun 9, 1430 (2018).

McGowan, S., P. Barker, E. Y. Haworth, P. R. Leavitt, S. C. Maberly, and J. Pates. 2012. Humans and climate as drivers of algal community change in Windermere since 1850. Freshwat. Biol. 57: 260-277.

Further Information

Dr Ryan Pereira,
The Lyell Centre, Institute of Life and Earth Sciences, School of Energy, Geoscience and Society, Heriot Watt University, EH14 4AS.
Email: r.pereira@hw.ac.uk
Telephone: 0131 451 3537

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