Despite the many benefits of living in the “plastic age”, there are pervasive environmental and public health impacts resulting from the durability, unsustainable use and inappropriate waste management of plastics. Compared to the environmental impacts of larger plastic objects there is growing concern that micro and nanoplastics (<5mm MnP) pose an even greater threat due to direct or indirect toxicity and their pervasiveness in habitats and biota. We are still in the early stages of learning about the diversity of MnP sources and their different activation mechanisms, as well as their fate and transport through streams and rivers towards oceans. Despite many studies identifying MnP concentrations in rivers worldwide, it remains unclear how hydrological variability such as event-based meteorological forcing, seasonal and inter-annual changes or man-made alterations of flow in rivers and lakes impact storage and transport of MnP. We are soliciting presentations that aim to advance our understanding of how hydrological dynamics including seasonal inundation of the floodplain, flash-floods, regulated rivers, river-control structures, and evaporation or abstraction, among others, affect local exposures and transport of MnP. This session aims to elucidate hydrological controls of residence time, break-down and transport of MnP. To assess how these processes vary on spatial and temporal scales, we invite contributions from empirical, experimental and modelling studies. Of particular interest are studies that characterize extreme hydrological events or long-term observations. Ultimately, this session will help explain the large variability in observed concentrations, storage, and residence time of MnP during their river, lake and reservoir conduits.
Lead Organizer: Zoraida Quiñones-Rivera, Université Claude Bernard - Lyon 1 (zoraida.quinones@univ-lyon1.fr)
Co-organizers:
Björn Wissel, Université Claude Bernard - Lyon 1 (bjoern.wissel@univ-lyon1.fr)
Stefan Krause, University of Birmingham (s.krause@bham.ac.uk)
Presentations
04:30 PM
INTERACTIONS BETWEEN MICROPLASTICS AND CYANOBACTERIAL: GROWTH, TOXIN PRODUCTION, FATE AND TRANSPORT (9441)
Primary Presenter: Fuad Shatara, UW-Madison (shatara@wisc.edu)
Increases in runoff contribute to cyanobacterial harmful algal bloom (cHAB) formation by stimulating growth of cHAB causing species with nutrient and pollutant inputs. Microplastics are being detected at increasing concentrations in this runoff and downstream in lakes and surrounding watersheds. The effect of microplastics on cHAB formation, toxin production, and transport are largely unknown. To address this, we use Statistical Design of Experiments to elucidate microbe-plastic interactions in vitro with cyanobacteria obtained from a HAB events in the Great Lakes. This experiment measured the impact of differing sizes, concentrations, and UV-ageing times of polyethylene, polypropylene, and cellulose fibers on the chlorophyll-a content of Trichormus variabilis and Microcystis aeruginosa and microcystin-LR content in M. aeruginosa. The results suggest that polymer type and size decreased chlorophyll content over the course of four weeks. The trend was inverted for polypropylene polymers which underwent photooxidation prior to inoculation. Members of these microbial communities displayed adhesion to the polymers during this study. To complement these findings, we have designed a turbulence tank capable of mimicking environmental wave motion to further investigate microbial adhesion to microplastics and determine the influence of this complex formation on fate and transport. Initial testing has found that biofilms on neutrally buoyant particles causes them to sink consistently, while biofilm formation on negatively buoyant particles slows their terminal settling velocity.
04:45 PM
WHY BIOFOULING CANNOT CONTRIBUTE TO THE VERTICAL TRANSPORT OF SMALL MICROPLASTIC (8881)
Primary Presenter: Ina Benner, Memorial University of Newfoundland (ina.benner@gmail.com)
To explain the presence of buoyant microplastics like polyethylene and polypropylene in the deep-sea, the vertical transport by biofouling is one of the most referred mechanisms. Biofouling is thought to increase the density of microplastic particles to the point that they sink, but this has mostly been shown on microplastic particles of 1 mm or larger. Most microplastics in the ocean are smaller than 100 µm due to continuous fragmentation and microplastic particle abundance increases drastically with decreasing size. For a small buoyant microplastic particle to reach the deep-sea in a reasonable time, its excess density, the density difference between the particle and surrounding water, has to increase to the point that it can sink at around 10 m per day or faster. The composition of the biofilm and therefore its density as well as the thickness of the biofilm are important factors to gain the needed excess density. However, a biofilm matrix of only extracellular polymeric substances and bacteria has a lower density than seawater, in contrast to a biofilm including diatoms or large organisms like mussels or barnacles. And most marine biofilms seem to have a thickness of <15 µm on large surfaces. We argue that a small microplastic particle cannot host a biofilm community heavy and thick enough to induce an excess density large enough to enable rapid sinking or even sinking at all. Therefore, biofouling cannot be an efficient vertical transport mechanism for small microplastic.
05:00 PM
ARE MEDICAL FACEMASKS RESPONSIBLE FOR THE POLYPROPYLENE FIBERS IN PLACENTIA BAY, NEWFOUNDLAND? (8898)
Primary Presenter: Uta Passow, Memorial University Newfoundland (uta.passow@mun.ca)
In the summer of 2021, concentrations of microplastic 300 - 5000 μm ranged from 0.11 to 0.67 particles m-3 in the surface waters of Placentia Bay, Newfoundland. Transparent polypropylene (PP) fibers dominated by far, contributing 47% to total MP inventories, whereas transparent polyethylene (PE) fragments contributed 11%, blue PP fibers 6%, and white PE fragments 3%. The remaining 33% of microplastic particles consisted of a variety of fragments and fibers of different polymer compositions and colors, each individual group contributing < 3%. The clear dominance of transparent PP fibers, and the size frequency distribution of fibers, suggest a distinct input event of transparent PP fibers, overlaying the background microplastic signature. A back of the envelope estimate suggests that this signal is consistent with the accidental release of disposable medical facemasks during the COVID pandemic.
05:15 PM
Unraveling Microplastic Deposition in Rivers Through the Lens of Sedimentary Processes (8727)
Primary Presenter: Shai Arnon, Ben-Gurion University of the Negev (sarnon@bgu.ac.il)
River networks are the major pathways for microplastic (MP) transport from terrestrial environments to oceans. However, the ability to quantify the water–sediment exchange of MPs, locations of deposition, and the time scales over which burial occurs is limited and thus often our estimation of where MP deposit is biased. To fill this gap, previous work on processes that control MP deposition will be briefly reviewed, with the aim of enhancing our understanding of the dynamic interplay between flow, sediment transport, and MP deposition. In addition, results from flume experiments and a numerical model showed that the maximum deposition efficiency and deposition depth were found for sediment with high hydraulic conductivity and slow-moving stream water velocity. Also, we found that the exchange of water and particles due to sediment motion leads to burial and potentially long-term deposition of MPs that initially were not expected to enter the bed due to size exclusion. However, increasing celerity (i.e., speed of bed motion) reduces the depth of MP deposition in the streambed and reduces deposition efficiency due to resuspension. The burial of MP beneath the moving fraction of the bed provides a mechanism for long-term accumulation and may explain resuspension events characterized by high MP loads during floods. It is argued that incorporating data on MP distribution in riverbeds with fluvial geomorphological and particle transport models will improve the current evaluation of MP transport in river networks and their burial residence time distribution.
05:30 PM
THE PLASTIC UNDERGROUND – EXPLORING THE MECHANISMS CONTROLLING THE FATE AND TRANSPORT OF MICROPLASTICS IN THE SUBSURFACE (8993)
Primary Presenter: Stefan Krause, University of Birmingham, UK (s.krause@bham.ac.uk)
While there have been advances in understanding the above ground plastic cycle, there is still a substantial lack of understanding the sources and activation mechanisms of plastic pollution affecting the entry, fate, transport, transformation and impact of microplastics into soils, riverbeds, sediment and groundwater aquifers. We here present the initial outcomes of integrated field and laboratory analytical experimental approaches and mathematical modelling studies to provide mechanistic understanding of the overall magnitude as well as hot spots (and hot moments) of microplastic entry into subsurface ecosystems and their transport and transformation pathways. Our model results highlight that a large proportion (>95%) of all mismanaged plastic waste emitted since the 1950s is temporarily stored in river basins and able to enter subsurface ecosystems in the long-term. Using multi-scale modelling studies in combination with artificial river simulators (flumes) we evidence that hyporheic exchange represents a preferential input mechanism for smaller and lighter microplastics into streambed sediments and underlying groundwater ecosystems. This finding maps directly onto field experimental findings from our global monitoring programme which identified streambed distinct streambed hotspots of microplastic accumulation. Soil and streambed sediment columns were deployed to explore the controls on microplastic transport once they have entered the subsurface, highlighting that in particular intermittent, pulsed hydraulic forcing increases the potential for fast particle transport.
SS33 - Impacts of hydrological variability on microplastic fate and transport
Description
Time: 4:30 PM
Date: 29/3/2025
Room: W208