Session 1: Microplastics - detection, transport and impacts for environmental and human health

In the environment, plastics interact with microorganisms which quickly colonizes their surfaces and form biofilms. These biofilms are referred to as the plastisphere which is distinct from the surrounding microbiome and may harbor organisms with the potential for plastic degradation. Currently, most research is focused on the characterization of the plastisphere based on polymer types and the isolation of putative plastic degrading strains. However, little is known about how these organisms interact within the plastisphere in environmentally relevant conditions. This study aims to address this shortcoming at a very fundamental level by deciphering the possible microbial interactions which are prevalent in the plastisphere. Here we show that Cyanobacteria may play a pivotal role in the establishment and sustenance of the plastisphere. A total of 137 different plastic samples were collected from around the coasts of Singapore and their plastisphere was characterized using 16S and 18S rRNA gene amplicon sequencing. Based on the sequencing results, we constructed ecological networks for all collected plastics irrespective of their polymer types and sampling location to identify conserved associations in the plastisphere. The networks show that the plastisphere may provide a niche for enhanced interkingdom interactions facilitated by different cyanobacterial species such as Schizothrix_LEGE_07164, Phormidesmis_ANT.LACV5.1 and Synechococcus_PCC-7336. These interactions are strongly enriched on the plastics compared to the surrounding seawater and sediments. While cyanobacteria may not be directly involved in plastic degradation, they may heavily influence the process of plastisphere formation in the marine environment. Clearly understanding the factors involved in plastisphere selection and formation will provide greater control and the possibility of engineering sustainable solutions for the inclusion of biological processes in plastic recycling and resource recovery.

Organic waste products (e.g. composts, green waste, manure, sewage sludge…) are a relevant substitute to chemical-based fertilisers, providing organic matter to the soils and participating to the circular economy. However, recent scientific papers suggest that plastics may end up in the environment as a result of the application of organic fertilisers (Weithmann et al., 2018). Indeed, organic soil improvers could act like a sink of microplastics (MP), such as packaging residues or agricultural plastics. There are currently standards and laws to ensure the quality of organic fertilisers and to limit the occurrence of inert components, but these are very recent and do not cover small microplastics (less than 2 mm). In order to assess the level of contamination, as well as to identify the polymers involved, a national unprecedent 3-year project was set up. The objectives are many: to determine the matrices acting as sources of MP, to study the diversity and origins of these MP, to estimate the annual flows to agricultural land. Within this framework, the IRDL laboratory (Institut de Recherche Dupuy de Lôme) is responsible for setting up and validating a MP extraction protocol applicable to 21 different complex matrices. At the same time, our team must ensure the integrity of extracted polymers (especially biodegradable ones). Validation tests show no particle loss or clear signs of degradation. Once the method was validated, 83 samples from as many sites in France were processed, of which more than half have already been chemically analysed by Fourier-transform infrared spectroscopy (FTIR). Unpublished results and preliminary recommendations following the tests will be presented and discussed. For the moment, first data indicate contamination of all matrices, at widely varying concentrations. Also, the most represented polymers are those the most commonly found in the environment. These overall results will allow us to identify action levers to limit microplastic pollution in organic fertilisers. 

Oceanic and coastal fronts are well-documented as accumulators of microplastic debris; however the impact of estuarine fronts and their associated secondary flows on microplastic concentrations are less well-known. An investigation into the dynamics of microplastic behaviour within estuarine systems will allow for a greater understanding of plastic retention and exportation to coastal and offshore environments. This study combines high resolution modelling of estuarine processes with realistically parameterized microplastic particles to determine local exposure levels, residence times and temporal variability.

We present a validated, three-dimensional, D-Flow Flexible mesh (D-Flow FM) model of a well-mixed estuary (Conwy Estuary, Wales, UK), demonstrating the regular development of an axial convergent front following high tide. A Lagrangian particle tracking model has been applied to simulate the behaviour of microplastic in these frontal systems and analyse how this behaviour may change as a response to various river discharge levels and tidal phases. The results of the ocean model and Lagrangian particle tracking model will be presented.

Understanding how estuarine fronts impact microplastic concentration and dispersal within estuaries will increase the accuracy of modelling and in-situ estuarine microplastic studies alike, helping to quantify the contribution of well-mixed estuaries to regional and global microplastic budgets, and bridging the gap between terrestrial and marine environments.

Plastic pollution has become a pressing environmental issue because the rate of disposable plastic manufacture has overcome our ability to process and recycle it efficiently. Once released to freshwater and seawater, ultraviolet (UV) exposure and mechanical abrasion can delaminate and degrade specific plastics, triggering their fragmentation into small plastic-debris and microplastics (MPs). Likewise, Zinc oxide (ZnO) engineered nanomaterials (ENMs) are at the forefront of application-driven nanotechnology because of their advantageous properties, raising concerns about their potential impact as pollutants following their inevitable release into the environment (i.e., ZnO-based sunscreens to avoid direct sun radiation).

The aim of this work is to understand the influence of MPs as vectors for binding ZnO ENMs under relevant environmental conditions. The ENMs can experience both spatial (i.e., aggregation, adsorption) and spectral (i.e., chemical speciation) modifications that can lead to different effects, ultimately affecting their eco-toxicity and hazardousness. Studying how these ENMs transform when aged in freshwater and seawater and their potential adsorption to MPs at the nanoscale, are key for determining their fate and behaviour.

Here, the MPs/ENMs interaction was investigated by: 1) scanning electron microscopy to confirm the ZnO adsorption to polystyrene MPs, 2) X-ray fluorescence and differential phase contrast imaging to unveil the morphology of the ZnO ENMs at the point of adsorption, and 3) multi-energy X-ray absorption near edge structure (XANES) spectroscopy to gain information about the intermediate Zn-species generated during incubation in environmentally relevant scenarios.

Mixtures of incipient Zn-sulfide (kinetically favoured) and Zn-phosphate in the more accessible sites (thermodynamically preferred) were observed by XANES. In addition, "real life" matrices (including the leaching of commercial sunscreens and cleanser exfoliating products) were evaluated to identify the dynamics of MPs/ENMs naturally released from these commercial products, also showing similar Zn-speciation changes after their ageing and incubation.

It is precisely the complexity of studying MPs interaction with co-contaminants at the point of exposure, which makes difficult to extrapolate conclusions widely applicable. We propose to shed some light into this topic, by studying the polystyrene microplastic ability to sorb aged ZnO nanomaterials at the nanoscale, in relevant freshwater and seawater scenarios.

Microplastics (MPs) are recognized as a ubiquitous environmental contaminant that has contaminated our food and water resources and raised significant concerns for public health. Here we investigated the effect of High-Density Polyethylene Microplastic (HDPE-MPs) 10µm to 30µm size beads on the survival and growth of Eastern Oyster (Crassostrea virginica) Larva. The experiments were conducted at the oyster hatchery of Morgan State University Patuxent Environmental and Aquatic Research Laboratory during the summer of 2022. The cohort of larvae (9 to 11 days after spawning) was randomly divided into four groups with a density of 2,500 to 5,000 larvae/L. Two groups were exposed to MPs at the level of 10 mg/L while the other two groups serve as a control for the experiment. The growth and survival of the larva were monitored twice a week for 2 Weeks. The preliminary results showed no significant difference in larval survival rate between the two treatments. However, the proportion of the larvae that were ready for metamorphosis in the MP’s treated group is significantly lowered than in the control group. We concluded that even though MPs did not influence the survival of the larva but could significantly slow the growth of the larvae. This research provided us insights on how MPs could influence the development of oyster larvae and consequential restoration of the Eastern Oyster reef at the Chesapeake Bay.

Water and wastewater treatment plants process large volumes of influent liquid and at the same time, also discharges large volume of treated effluent into the environment. With the increase in the presence of microplastics found in these treatment plants[1], there are serious concerns as these treatment plants provide drinking water for people and discharge large volume of effluents either into the environment or used as agriculture irrigation. Most water and wastewater treatment plants contain membrane filtration systems that are susceptible to fouling by particulates such as nano/microplastics[1]. Therefore, in order to improve operation of treatment plants and separation of nano/microplastic separation using membranes, a better understanding of nano/microplastics fouling on membrane filtration systems is important. This presentation will show using microplastics sourced from a commercial facial scrub (i) how microplastics can easily fragment into nanoplastics[2] (ii) fouling of ultrafiltration membranes by nano/microplastics[3] and (iii) possible mitigation of the fouling via chemical surface treatment of membranes using plasma technology [4] coupled with physical air scouring [5].

References

[1] M. Enfrin, L.F. Dumée, J. Lee, Nano/microplastics in water and wastewater treatment processes–origin, impact and potential solutions, Water Res., 161 (2019) 621-638.

[2] M. Enfrin, J. Lee, Y. Gibert, F. Basheer, L. Kong, L.F. Dumée, Release of hazardous nanoplastic contaminants due to microplastics fragmentation under shear stress forces, J. Hazard. Mater., 384 (2020) 121393.

[3] M. Enfrin, J. Lee, P. Le-Clech, L.F. Dumée, Kinetic and mechanistic aspects of ultrafiltration membrane fouling by nano-and microplastics, J. Membr. Sci., 601 (2020) 117890.

[4] M. Enfrin, J. Wang, A. Merenda, L.F. Dumée, J. Lee, Mitigation of membrane fouling by nano/microplastic