Analysis of small microplastics in coastal surface water samples of the subtropical island of Okinawa, Japan

Marine plastic debris is a widely recognized environmental issue. By employing an optical micro-Raman tweezers setup, we have identified the composition of particles trapped in marine aggregates collected from the coastal surface waters around the subtropical island of Okinawa, Japan. This chemical identification of small microplas- tics at the single-particle level contributes to extending our knowledge of plastic pollution in the ocean around a Blue Zone region.

Detection of microplastics from water is crucial for various reasons, such as food safety monitoring, monitoring of the fate and transport of microplastics, and development of preventive measures for their occurrence. Currently, microplastics are detected by isolating them using filtration, separation by centrifugation, or membrane filtration, subsequently followed by analysis using well-established analytical methods, such as Raman spectroscopy. However, due to their variability in shape, color, size, and density, isolation using the conventional methods mentioned above is cumbersome and time-consuming. In this work, we show a surface-nanodroplet-decorated microfluidic device for isolation and analysis of small microplastics (diameter of 10 μm) from water. Surface nanodroplets are able to capture nearby microplastics as water flows through the microfluidic device. Using a model microplastic solution, we show that microplastics of various sizes and types can be captured and visualized by using optical and fluorescence microscopy. More importantly, as the surface nanodroplets are pinned on the microfluidic channel, the captured microplastics can also be analyzed using a Raman spectroscope, which enables both physical (i.e., size and shape) and chemical (i.e., type) characterization of microplastics at a single-particle level. The technique shown here can be used as a simple, fast, and economical detection method for small microplastics.

Microplastic (MP) pollution in the aquatic environment has become a problem of growing concern due to potential adverse effects on aquatic organisms and ecosystems. While MP transport and fate in marine systems has been researched to quite some extent relatively little is known about the transport mechanisms of MP particles in terrestrial surface waters and in saturated porous media like in groundwater or the hyporheic zone (HZ). We investigated the transport and fate of small (1, 3 and 10 μm diameter) polystyrene MP particles in a rippled, sandy stream bed (D50 = 1.04 mm) using CFD simulations calibrated to a set of flume experiments. A novel detection system for fluorescent MP particles (Boos et al. 2021) was used to track and quantify particle movement in the turbulent open water and in the hyporheic sediments in the laboratory flume following a pulse injection of MP particles into the surface water compartment. A new, integrated CFD simulation scheme within the OpenFOAM suite of CFD solvers was implemented for the flume system for a seamless simulation of water flow and particle transport in the open water and in the hyporheic sediments (Dichgans et al. 2023). Additionally we simulated the transport and fate of a range of “virtual” particles in the open water for different channel geometries using a Lagrangian approach. Simulations show that 1 μm MP particles are transported through the HZ like a solute, following the typical hyporheic flow cells below the bedforms. Transport and particle progression through the HZ could be adequately described with an advection-dispersion equation. Larger 10 µm MP particles instead showed retarded transport through the HZ, while retardation increased with travel distance in the sediments. Our results indicate that advective pumping across the streambed interface can transport very small MP particles through the HZ, while larger particles are increasingly retained. Distinct flow structures in the open water are found to be decisive for the fate of MP particles in the river channel.

Marine plastic debris is a global environmental problem. Surveys have shown that <5 mm plastic particles, known as microplastics, are significantly more abundant in surface seawater and on shorelines than larger plastic particles are. Nevertheless, quantification of microplastics in the environment is hampered by a lack of adequate high-throughput methods for distinguishing and quantifying smaller size fractions (<1 mm), and this has probably resulted in an underestimation of actual microplastic concentrations. Here we present a protocol that allows high-throughput detection and automated quantification of small microplastic particles (20-1000 μm) using the dye Nile red, fluorescence microscopy, and image analysis software. This protocol has proven to be highly effective in the quantification of small polyethylene, polypropylene, polystyrene, and nylon-6 particles, which frequently occur in the water column. Our preliminary results from sea surface tows show a power-law increase in small microplastics (i.e., <1 mm) with a decreasing particle size. Hence, our data help to resolve speculation about the "apparent" loss of this fraction from surface waters. We consider that this method presents a step change in the ability to detect small microplastics by substituting the subjectivity of human visual sorting with a sensitive and semiautomated procedure.

Despite the significant progress in the detection of nano and small microplastics, the detection of such particles still faces problems caused by the limitations of current detection methods and instruments. Herein, we present the optical methods for detection of sub 20 μm microplastics. We introduce optical methods for the analysis of individual microplastics and the fabrication of a substrate using plasmonic particles to detect plastic nanoparticles. We summarize recent experimental activities involving the construction of portable Raman tweezers that can be used for optical trapping and analysis of microplastics with size from a few hundred nanometers to lower tens of micrometers. Optical trapping is complemented by another optical manipulation method: nanoimprinting of plasmonic nanoparticles that enables create the “active” aggregates that can be used for Surface Enhanced Raman Spectroscopy (SERS) detection in microfluidic circuits and as plasmon-enhanced thermoplasmonic concentrators for nanoscale particulate matter such as nanoplastics. The principle of nanoimprinting is based on the dominance of the scattering force (compared to the gradient force) for plasmonic particles, this force pushes the particles in the direction of propagation of the light beam. This phenomenon enables the preparation of an aggregate comprising of plasmonic particles that can serve as a substrate for SERS and as a source of the temperature gradient that is able to attract dielectric nanoparticles. In both cases, enhanced sensitivity is demonstrated, allowing the detection of nanoplastics/molecules of size/concentration orders of magnitude lower than what can be achieved by Raman spectroscopy. This study demonstrates that the combination of two optical manipulation techniques with Raman spectroscopy is capable of filling the technological gap in the detection of plastic particles ranging in size from a few tens of nanometers to 20 micrometers. This is an ideal solution for the detection of very small microplastics, which currently lacks a suitable technology.

Plastic is a widely used material in our daily lives. Microplastic pollution has also generated worldwide concern due to its distribution in the environment, and its potential threat to human and animal health. Due to the complexity of sampling and extracting plastics from the marine environment, existing studies have largely focused on mesoplastics, macroplastics, and large microplastics. Having accurate methods for quantifying the abundance of small microplastics in seawater is key for defining the extent of the problem they pose. In this work, we propose a non-invasive method to analyze sub-20 μm plastics in seawater around the subtropical island of Okinawa through optical tweezers micro-Raman spectroscopy. Our results show the dominance of low-density polyethylene with highest concentrations in areas with large-scale anthropogenic activities. This study provides evidence on the presence of microplastics in ocean around a blue zone region.

Microplastics (MPs) are universally present in the ecosystem and pose great threats to the environment and living organisms. Research studies have shown that small MPs (<50 μm in diameter) are especially toxic and account for more than half of all MPs collected in the Atlantic Ocean. Nevertheless, current methods for the detection and analysis of MPs are incapable of achieving rapid and in situ analysis of small MPs in the biota to ultimately enable the study of their biological effects. In this work, we report a method that allows rapid in situ identification and spatial mapping of small MPs directly from paramecia with high accuracy by acquiring chemical composition information using secondary-ion mass spectrometry (SIMS) imaging. Specifically, six types of common MPs (polymethyl methacrylate, polyvinyl chloride, polypropylene, polyethylene terephthalate, polyglycidyl methacrylate, and polyamide 6) with a diameter of 1-50 μm were simultaneously imaged with high chemical specificity at a spatial resolution of 700 nm. In situ spatial mapping of a group of MPs ingested by paramecia was performed using SIMS fragments specific to the plastic composition with no sample pretreatment, revealing the aggregation of MPs in paramecia after ingestion. Compared with existing methods, one additional advantage of the developed method is that the MPs and the organism can be analyzed in the same experimental workflow to record their fingerprint spectra, acquiring biochemical information to evaluate MP fate, toxicity, and the MP-biota interaction.

Validation of sample preparation methods for small microplastics (≤10 µm) in wastewater effluents

The paper considers the seasonal dynamics of the content of microplastic particles with a size from 0.5 to 5 mm in the sands of the surf zone of the Vistula Spit (the Baltic Sea). Microplastic particles are classified by size and color. The results are compared with the data for the Curonian Spit. It is concluded that the level of contamination with small microplastics (0.5–2 mm) of the sands of the swash zone can be used as a "background" value for the entire region and during all seasons of the year. The current level of sand contamination in the wave swash zone in the South-Eastern Baltic by small microplastic particles (0.5–2 mm) is 30–60 pieces per kg of dry weight throughout the year, while more than 90% are fibers.

<scp>ASLO</scp> 2020 Award Winners

Volatile organic compounds in open ocean and coastal surface waters

Marine biodiversity plays a vital role in ecosystem resilience and stability against climate change and alien species invasions, among others. This also plays a role in the provision of ecosystem services and functions that benefits humans. However due to anthropogenic activities and population increase, marine biodiversity have been affected most. We conducted a review using open-sourced journals on the effects of nutrient enrichment, sedimentation, heavy metals and plastic pollution in the marine environment and its implications on marine biodiversity. Lethal and sub-lethal effects were observed in different organisms that could affect marine biodiversity directly or indirectly. Direct effects include mortality of organisms while indirect effects include habitat degradation or alteration, a simplified food web, increase alien species invasion and reduced fitness of organisms. Human land use change, coastal construction activities, untreated sewage discharges, pesticides, mine tailings, uncollected, unsegregated and improperly dumped garbages and unabated garbage dumping at sea have been found to negatively influence marine biodiversity. In the Philippines, very few studies have been conducted with regards to marine pollution, especially on marine plastic debris, and even fewer studies have been made that tackles the effect of these stressors at an ecosystem level. Furthermore, this review has identified direct and indirect effects of pollution stressors on marine organisms which include: mortality and reduced fitness, vulnerability to disease or sickness,-habitat degradation, and food web simplification. Keywords - Ecology, nutrient enrichment, sedimentation, plastic, biodiversity, literature review, pollution, Philippines

Thermogravimetric analysis and kinetic study of marine plastic litter

Sub-sampling strategies for analysis of small (<20 µm) microplastics in water.

Separation and removal of microplastic pollution from aquatic environments as a global environmental issue is classified as one of the major concerns in both water and wastewater treatment plants. Microplastics as polymeric particles less than 5 mm in at least one dimension are found with different shapes, chemical compositions, and sizes in soil, water, and sediments. Conventional treatment methods for organic separation have shown high removal efficiency for microplastics, while the separation of small microplastic particles, mainly less than 100 µm, in wastewater treatment plants is particularly challenging. This review aims to review the principle and application of different physical and chemical methods for the separation and removal of microplastic particles from aquatic environments, especially in water treatments process, with emphasis on some alternative and emerging separation methods. Advantages and disadvantages of conventional separation techniques such as clarification, sedimentation, floatation, activated sludge, sieving, filtration, and density separation are discussed. The advanced separation methods can be integrated with conventional techniques or utilize as a separate step for separating small microplastic particles. These advanced microplastic separation methods include membrane bioreactor, magnetic separation, micromachines, and degradation-based methods such as electrocatalysis, photocatalysis, biodegradation, and thermal degradation.