Plastic litter in macrophyte system: environmental fate and ecological implications

Project Information

SCRAP

Grant agreement ID: 101029198

DOI

10.3030/101029198

Project closed

EC signature date 17 March 2021

Start date 1 September 2022

End date 30 April 2025

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 191 852,16

EU contribution

€ 191 852,16

Coordinated by

STOCKHOLMS UNIVERSITET
Sweden

Periodic Reporting for period 1 - SCRAP (Plastic litter in macrophyte system: environmental fate and ecological implications)

Reporting period: 2022-09-01 to 2024-08-31

Summary of the context and overall objectives of the project

Coastal macrophyte act as dynamic sinks and secondary sources of marine litter, yet managers have lacked quantitative data on the magnitude and consequences of this trapping process; our project therefore set out to (i) track the fate of plastics in seaweed beds, (ii) evaluate whether plastic particles and additive leachates impair algal physiology, and (iii) establish whether such stress propagates to higher-level ecosystem functions such as trophic transfer. Comprehensive field surveys combined with 1 km-resolution Lagrangian modelling revealed that within 30 days roughly 34 % of algal-associated plastics are re-exported to the pelagic food web while 51% are sequestered in adjacent sediments. Leachate bioassays showed hormetic growth stimulation but chlorophyll suppression at environmentally realistic concentrations. A derived EC50 for the ORAC (oxygen-radical absorbance capacity) endpoint was 5–10 µg L⁻¹ for TDCPP (one of the leachates tested). Multiple stressors experiment revealed that orgnaic pollutants such as polyaromatic hydrocarbons as the dominant driver of photosystem-II inhibition, whole microplastics and turbulence acting synergistically. The project developed a multi-endpoint macrophyte toxicity assay (growth, chlorophyll, ORAC) now constitute an early-warning toolkit already adopted by the host laboratory. Baseline surveys of nutrient stoichiometry, extracellular-enzyme activity and litter decomposition seeded five follow-on grant proposals that will scale the work to ecosystem level. Collectively, the project delivers the first empirical export–burial coefficients for seaweed-mediated plastic fluxes, validated bioassays for regulatory monitoring, and open-access SOPs and scripts that HELCOM and UNEP will consider to integrate into regional and global plastic-litter assessments, thereby enabling evidence-based nature-based solutions and reinforcing the EU zero-pollution agenda.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

All planned tasks were excecuated, including WP1 on plastic fluxes in seaweed beds, WP2 on algal physiological responses, and WP3 on ecosystem-function pilots by field surveys, controlled-flume trials. An enzymatic + Fenton digestion protocol applied to 50 macroalgae samples, coupled with 1 km-resolution 30-day Lagrangian particle tracking, showed that 34 ± 8 % of canopy-retained plastics are exported pelagically while 51 ± 10 % settle in local sediments. Leachate assays on Ceramium tenuicorne exposed to polyethylene and TDCPP (7 d) revealed hormetic growth yet chlorophyll suppression, with ORAC emerging as a sensitive biomarker. A fully factorial flume experiment (microplastics × PAHs × turbulence) identified PAHs as the main driver of −18 % ΦPSII, with microplastic-induced resuspension amplifying oxidative stress (+41 % ORAC). Baseline C:N:P stoichiometry, extracellular-enzyme activity and litter decomposition data from beach wrack at four sites seeded five grant proposals for post-fellowship scaling. Key outcomes include the first export/burial coefficients for algal-associated plastics, a validated multi-endpoint macrophyte toxicity battery (growth + chlorophyll + ORAC), and a partial least-squares structural-equation (PLS-SEM) toolkit (image 1) for disentangling direct chemical from indirect physical stressors. Numeric flux factors, SOPs and R scripts have been transferred and under discussion within HELCOM working groups for integration into Descriptor 10 metrics and the Global Marine-Litter Assessment. Dissemination includes one peer-reviewed article, two under review, a CRC-Press chapter, presentations at SETAC-Europe, Baltic Sea Day and Stockholm Research Day, media outreach (Sveriges Radio), European Researchers’ Night activities, and supervision of one post-doc, one MSc and seven Erasmus students plus a 1.5-month scientific exchange; collectively delivering protocols, data and early-warning biomarkers used by regulators, academics and industry.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Previous estimates of plastic fluxes in seaweed beds were mostly inferred from open-water data. By combining our own field measurements with fine-scale particle-tracking, we derived the site-based coefficients: roughly one-third of trapped plastics are released back to the water column and a little over half become buried in nearby sediments within a month. Practical advance incldue (i) a 92 %-efficient extraction that recovers polymers from seaweed samples; (ii) a multi-endpoint macrophyte bioassay (growth, chlorophyll and ORAC) sensitive to sub-lethal stress at environmentally realistic concentrations; and (iii) use of PLS-SEM modelling to separate direct chemical effects from those linked to abrasion or turbidity.

A harmonised dataset that bundles canopy-scale plastic-flux coefficients, leachate-response curves and flume outputs will accompany three to four peer-reviewed papers due in 2025 (multi-stressor flume, leachate study and two algal-toxicology manuscripts). These export-and-burial factors, together with ORAC-based early-warning biomarkers, will submit to HELCOM Descriptor-10 and UNEP marine-litter teams preparing the next indicator update. A multi-endpoint macrophyte assay that is about 40 % quicker and cheaper than LC-MS-only screens, is in inter-laboratory validation; its open-licensed extraction SOP and R pipeline allow blue-tech SMEs to build plug-and-play monitoring kits.. Ongoing media features, school workshops and the training of one post-doc, one MSc and seven Erasmus students sustain public momentum and expand Europe’s talent pool, keeping the project aligned with the EU Green Deal’s zero-pollution target and Sustainable Development Goal 14.

partial least square structural equation modelling to delinearate multiple stressors incl. plastics