From sieve to microscope: An efficient technique for sample transfer in the process of microplastics' quantification.

In the field of microplastics' quantification, efficient and reproducible methodology is still needed. Procedures of sample fractionation and transfer are often insufficiently reported, although fractionating a sample in similarly sized particles is a crucial prerequisite for the subsequent detection and identification process. At the same time, fractionation is error-prone as particles can be lost during transfer between different vessels. This article presents a four-step technique of sample preparation and microscopic examination, suited for different kind of environmental samples (e.g., water, sediment, soil): The sample is size-fractionated in a sieve cascade (I), rinsed from the sieve and vacuum-filtrated onto a filter (II), rinsed from the filter into a glass petri dish with a low amount of water (III), and examined under the microscope in wet or dry condition (IV). The technique manages on standard laboratory equipment and is reliable for fragments > 300 µm: In a validation experiment with polypropylene, the average recovery was 94 ± 13.5% (arithmetic mean ± standard deviation) and 100% (median), respectively.•Reliable sample transfer after wet-sieving.•Concentration of the pretreated sample in a very small amount of water.•Usage of transmitted light in microscopy.

Exploring the potential of photoluminescence spectroscopy in combination with Nile Red staining for microplastic detection.

The significant amount of plastic litter in the form of microplastics (size <5 mm) is garnering attention owing to its potential threat to marine life. Reliable, cost- and time-efficient analysis methods for monitoring microplastic abundance globally are still missing. Several studies proposed a fast detection method by binding the solvatochromic dye Nile Red on the surface of microplastics and using fluorescence microscopy for their detection. All the staining approaches reported so far differ in terms of Nile Red concentration, solvents, and staining procedure. Here, we compare the staining protocols published prior to 2019 and propose an optimized staining protocol. Furthermore, we explore the potential of Nile Red staining in combination with photoluminescence spectroscopy to identify the polymer type and to distinguish plastics from non-plastics.

Exploring the Potential of Time-Resolved Photoluminescence Spectroscopy for the Detection of Plastics.

Accurate data on microplastic occurrence in aquatic and terrestrial ecosystems are a basic requirement for microplastic risk assessment and management. Existing analysis techniques like Raman spectroscopy and Fourier transform infrared (FT-IR) spectroscopy imaging are still time-consuming and depend on laborious sample preparation. Therefore, we investigate the potential of time-resolved photoluminescence spectroscopy as an alternative technique to identify plastic materials, and, for the first time determine the photoluminescence lifetime of a series of polymers and several non-plastic samples typically found in a marine environment. The obtained photoluminescence lifetimes can be used to distinguish between plastic and natural materials. Furthermore, they allow us to identify distinct types of plastics. Therefore, the described approach has the potential to identify materials either as a stand-alone technique or for pre-characterization of sample materials for otherwise time-consuming analytical methods such as Raman spectroscopy or FT-IR spectroscopy.

Spatial distribution of microplastics in sediments and surface waters of the southern North Sea.

Microplastic pollution within the marine environment is of pressing concern globally. Accordingly, spatial monitoring of microplastic concentrations, composition and size distribution may help to identify sources and entry pathways, and hence allow initiating focused mitigation. Spatial distribution patterns of microplastics were investigated in two compartments of the southern North Sea by collecting sublittoral sediment and surface water samples from 24 stations. Large microplastics (500-5000 µm) were detected visually and identified using attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopy. The remaining sample was digested enzymatically, concentrated onto filters and analyzed for small microplastics (11-500 µm) using Focal Plane Array (FPA) FTIR imaging. Microplastics were detected in all samples with concentrations ranging between 2.8 and 1188.8 particles kg-1 for sediments and 0.1-245.4 particles m-3 for surface waters. On average 98% of microplastics were <100 µm in sediments and 86% in surface waters. The most prevalent polymer types in both compartments were polypropylene, acrylates/polyurethane/varnish, and polyamide. However, polymer composition differed significantly between sediment and surface water samples as well as between the Frisian Islands and the English Channel sites. These results show that microplastics are not evenly distributed, in neither location nor size, which is illuminating regarding the development of monitoring protocols.

Evidence for mutual allocation of social attention through interactive signaling in a mormyrid weakly electric fish.

Mormyrid weakly electric fish produce electric organ discharges (EODs) for active electrolocation and electrocommunication. These pulses are emitted with variable interdischarge intervals (IDIs) resulting in temporal discharge patterns and interactive signaling episodes with nearby conspecifics. However, unequivocal assignment of interactive signaling to a specific behavioral context has proven to be challenging. Using an ethorobotical approach, we confronted single individuals of weakly electric Mormyrus rume proboscirostris with a mobile fish robot capable of interacting both physically, on arbitrary trajectories, as well as electrically, by generating echo responses through playback of species-specific EODs, thus synchronizing signals with the fish. Interactive signaling by the fish was more pronounced in response to a dynamic echo playback generated by the robot than in response to playback of static random IDI sequences. Such synchronizations were particularly strong at a distance corresponding to the outer limit of active electrolocation, and when fish oriented toward the fish replica. We therefore argue that interactive signaling through echoing of a conspecific's EODs provides a simple mechanism by which weakly electric fish can specifically address nearby individuals during electrocommunication. Echoing may thus enable mormyrids to mutually allocate social attention and constitute a foundation for complex social behavior and relatively advanced cognitive abilities in a basal vertebrate lineage.