Multi-temporal surveys for microplastic particles enabled by a novel and fast application of SWIR imaging spectroscopy – Study of an urban watercourse traversing the city of Berlin, Germany

Abstract

Following the widespread assumption that a majority of ubiquitous marine microplastic particles originate from land-based sources, recent studies identify rivers as important pathways for microplastic particles (MPP) to the oceans. Yet a detailed understanding of the underlying processes and dominant sources is difficult to obtain with the existing accurate but extremely time-consuming methods available for the identification of MPP. Thus in the presented study, a novel approach applying short-wave infrared imaging spectroscopy for the quick and semi-automated identification of MPP is applied in combination with a multitemporal survey concept. Volume-reduced surface water samples were taken from transects at ten points along a major watercourse running through the South of Berlin, Germany, on six dates. After laboratory treatment, the samples were filtered onto glass fiber filters, scanned with an imaging spectrometer and analyzed by image processing. The presented method allows to count MPP, classify the plastic types and determine particle sizes. At the present stage of development particles larger than 450 μm in diameter can be identified and a visual validation showed that the results are reliable after a subsequent visual final check of certain typical error types. Therefore, the method has the potential to accelerate microplastic identification by complementing FTIR and Raman microspectroscopy. Technical advancements (e.g. new lens) will allow lower detection limits and a higher grade of automatization in the near future. The resulting microplastic concentrations in the water samples are discussed in a spatio-temporal context with respect to the influence (i) of urban areas, (ii) of effluents of three major Berlin wastewater treatment plants discharging into the canal and (iii) of precipitation events. Microplastic concentrations were higher downstream of the urban area and after precipitation. An increase in microplastic concentrations was discernible for the wastewater treatment plant located furthest upstream though not for the other two.

Microplastic Concentrations in Raw and Drinking Water in the Sinos River, Southern Brazil

“…In the lower areas of the basin, the amount of particle input generated in urban areas is reflected by the increase of mean particle concentration. Tibbets et al [14] found major microplastic concentrations downstream from urban areas of Birmingham (UK) in the river sediment, as did Schmidt et al [42] in the water of an urban stream crossing Berlin (Germany). However, no direct relation between population density and particle concentration is evident.…”

Contributions of Fourier transform infrared spectroscopy in microplastic pollution research: A review

“…Moreover, training the classifier can increase the analysis speed substantially when dealing with large datasets of FTIR spectra. For example, automated identification methods were tested based on hierarchical cluster analysis (Primpke et al, 2018), shortwave infrared imaging (Schmidt et al, 2018), identification of the most relevant bands (Renner et al, 2017;Renner, Nellessen, et al, 2019), random decision forest method (Hufnagl et al, 2019), modified chemometric identification concept (Renner, Sauerbier, et al, 2019), machine learning method (Kedzierski et al, 2019), Python based lFTIR mapping (Renner et al, 2020) and Hybrid fusion method (Chabuka & Kalivas, 2020). The analysis of FTIR spectra is time-consuming as often it is needed to compare the spectra one by one with the reference spectra.…”

Small Microplastic Sampling in Water: Development of an Encapsulated Filtration Device

“…Bongo nets, WP-2 nets, as well as special constructions for layered profiling have been applied alike [5][6][7][8]. Single or staggered open sieve constructions, as well as encapsulated flow-through filtration devices are approaches that have been utilised by other studies [9][10][11]. Additionally, sampling of MP has been accomplished by means of density separation in continuous flow centrifuges used in suspended matter analysis [12].…”