Raman microspectroscopic identification of microplastic particles in freshwater bivalves (Unio pictorum) exposed to sewage treatment plant effluents under different exposure scenarios.

We investigated the uptake of microplastic (MP, <5 mm) particles by using freshwater bivalves (Unio pictorum) as biological samplers in the environment. They were exposed either directly to the biologically purified sewage of a North Bavarian sewage treatment plant (STP) or placed in a small river up- and downstream of the wastewater discharge for 28 days and 6 months, respectively. A control group was maintained in a pond. After acid digestion, the soft tissue was analyzed for MP particles by means of Raman microspectroscopy (RM, over 3000 particles individually measured), which allows for identification and quantification of particles down to 1 µm. Only in the bivalve collective exposed to STP effluents MP was found, however a very small amount (maximum of nine MP particles in the bivalve sample exposed for 6 months). In the bivalves up- and downstream of the wastewater discharge and in control organisms from a pond, no microplastic was identified. The amount of microplastic particles was small in absolute terms and small in relative terms (ca. 1:100 (6 months) and below 1:1000 (28 days)) as hundreds of particles per sample were analyzed which turned out to be non-plastic. Including the results for the river, this indicates a rather low MP contamination level for organisms in close vicinity to a sewage treatment plant.

Variation in plastic abundance at different lake beach zones - A case study.

Plastic particles in marine and freshwater environments span from macroscopic to microscopic size classes. Each may have a different impact on individuals, populations and ecosystems, but still the wide variety of methods used in beach sediment sampling inhibit comparisons among studies and therefore hampers a risk assessment. A large portion of the uncertainties is due to differing sampling strategies. By quantifying the alongshore distribution of macro- and microplastic particles within five beaches of Lake Garda, we aim to shed light on the accumulation behavior of microplastic particles at an exemplary lake which might give indications for potential sampling zones. The identification of plastic at the single particle level with a spatial resolution down to 1µm was performed by Raman microspectroscopy. Given the time consuming approach we reduced the number of samples in the field but increased the spatial area where a single sample was taken, by utilizing a transect approach in combination with sediment cores (5cm depth). The study revealed that, in comparison to the water line and the high-water line, the drift line of all five beaches always contained plastic particles. Since the drift line accumulate particulate matter on a relatively distinct zone, it will enable a comparable sampling of microplastic particles. The applied sampling approach provided a representative method for quantifying microplastic down to 1µm on a shore consisting of pebbles and sand. Hence, as first step towards a harmonization of beach sediment sampling we suggest to perform sampling at the drift line, although further methodological improvements are still necessary.

Stable-isotope Raman microspectroscopy for the analysis of soil organic matter.

We examined the potential of stable-isotope Raman microspectroscopy (SIRM) for the evaluation of differently enriched 13C-labeled humic acids as model substances for soil organic matter (SOM). The SOM itself can be linked to the soil water holding capacity. Therefore, artificial humic acids (HA) with known isotopic compositions were synthesized and analyzed by means of SIRM. By performing a pregraphitization, a suitable analysis method was developed to cope with the high fluorescence background. Results were verified against isotope ratio mass spectrometry (IRMS). The limit of quantification was 2.1 × 10-1 13C/C tot for the total region and 3.2 × 10-2 13C/C tot for a linear correlation up to 0.25 13C/C tot. Complementary nanoscale secondary ion mass spectrometry (NanoSIMS) analysis indicated small-scale heterogeneity within the dry sample material, even though-owing to sample topography and occurring matrix effects-obtained values deviated in magnitude from those of IRMS and SIRM. Our study shows that SIRM is well-suited for the analysis of stable isotope-labeled HA. This method requires no specific sample preparation and can provide information with a spatial resolution in the micrometer range. Graphical abstract Analysis of the isotopic composition of humic acids by Raman microspectroscopy in combination with isotope ratio mass spectrometry and nanoscale secondary ion mass spectrometry.

Microplastic in Aquatic Ecosystems.

The contamination of marine and freshwater ecosystems with plastic, and especially with microplastic (MP), is a global ecological problem of increasing scientific concern. This has stimulated a great deal of research on the occurrence of MP, interaction of MP with chemical pollutants, the uptake of MP by aquatic organisms, and the resulting (negative) impact of MP. Herein, we review the major issues of MP in aquatic environments, with the principal aims 1) to characterize the methods applied for MP analysis (including sampling, processing, identification and quantification), indicate the most reliable techniques, and discuss the required further improvements; 2) to estimate the abundance of MP in marine/freshwater ecosystems and clarify the problems that hamper the comparability of such results; and 3) to summarize the existing literature on the uptake of MP by living organisms. Finally, we identify knowledge gaps, suggest possible strategies to assess environmental risks arising from MP, and discuss prospects to minimize MP abundance in aquatic ecosystems.

Pigments and plastic in limnetic ecosystems: A qualitative and quantitative study on microparticles of different size classes.

Recently, macroplastic (>5 mm) and especially microplastic (<5 mm) particles have been reported as emerging contaminants in marine and limnetic ecosystems. Their coloration is gained by the addition of pigments to the polymer blend which is the major component of the respective product. However, color is also a feature of paint and coatings whereby the pigment is the major component. Once abraded from a surface, paint particles may enter the environment via similar pathways as microplastic particles. So far no detailed studies of microplastic particles (pigmented and non-pigmented) as well as paint particles have been performed focusing on very small microparticles (1-50 µm), in either marine or limnetic ecosystems. Using Raman microspectroscopy with a spatial resolution down to 1 µm, we report a remarkable increase in the occurrence of (pigmented) microplastic particles below 500 µm. Among those, most particles were found at a size of ∼130 µm in a freshwater ecosystem (subalpine Lake Garda, Italy). Moreover, our qualitative and quantitative analyses revealed that the number of paint microparticles significantly increased below the size range of 50 µm due to their brittleness (the smallest detected paint particle had a size of 4 µm). Inductively coupled plasma mass spectrometry measurements showed that both colored particles found in nature as well as virgin particles contain a high variety of metals such as cadmium, lead and copper. These additives may elicit adverse effects in biota ingesting these microparticles, thus paints and associated compounds may act as formerly overlooked contaminants in freshwater ecosystems.