Generation of macro- and microplastic databases by high-throughput FTIR analysis with microplate readers.

FTIR spectral identification is today's gold standard analytical procedure for plastic pollution material characterization. High-throughput FTIR techniques have been advanced for small microplastics (10-500 µm) but less so for large microplastics (500-5 mm) and macroplastics (> 5 mm). These larger plastics are typically analyzed using ATR, which is highly manual and can sometimes destroy particles of interest. Furthermore, spectral libraries are often inadequate due to the limited variety of reference materials and spectral collection modes, resulting from expensive spectral data collection. We advance a new high-throughput technique to remedy these problems using FTIR microplate readers for measuring large particles (> 500 µm). We created a new reference database of over 6000 spectra for transmission, ATR, and reflection spectral collection modes with over 600 plastic, organic, and mineral reference materials relevant to plastic pollution research. We also streamline future analysis in microplate readers by creating a new particle holder for transmission measurements using off-the-shelf parts and fabricating a nonplastic 96-well microplate for storing particles. We determined that particles should be presented to microplate readers as thin as possible due to thick particles causing poor-quality spectra and identifications. We validated the new database using Open Specy and demonstrated that additional transmission and reflection spectra reference data were needed in spectral libraries.

Comparison of two rapid automated analysis tools for large FTIR microplastic datasets.

One of the biggest issues in microplastic (MP, plastic items <5 mm) research is the lack of standardisation and harmonisation in all fields, reaching from sampling methodology to sample purification, analytical methods and data analysis. This hampers comparability as well as reproducibility among studies. Concerning chemical analysis of MPs, Fourier-transform infrared (FTIR) spectroscocopy is one of the most powerful tools. Here, focal plane array (FPA) based micro-FTIR (µFTIR) imaging allows for rapid measurement and identification without manual preselection of putative MP and therefore enables large sample throughputs with high spatial resolution. The resulting huge datasets necessitate automated algorithms for data analysis in a reasonable time frame. Although solutions are available, little is known about the comparability or the level of reliability of their output. For the first time, within our study, we compare two well-established and frequently applied data analysis algorithms in regard to results in abundance, polymer composition and size distributions of MP (11-500 µm) derived from selected environmental water samples: (a) the siMPle analysis tool (systematic identification of MicroPlastics in the environment) in combination with MPAPP (MicroPlastic Automated Particle/fibre analysis Pipeline) and (b) the BPF (Bayreuth Particle Finder). The results of our comparison show an overall good accordance but also indicate discrepancies concerning certain polymer types/clusters as well as the smallest MP size classes. Our study further demonstrates that a detailed comparison of MP algorithms is an essential prerequisite for a better comparability of MP data.

Microplastics in two German wastewater treatment plants: Year-long effluent analysis with FTIR and Py-GC/MS.

Microplastics (MP) have been recorded in various environments around the globe. For a better understanding of distribution patterns and for providing a basis for risk assessments, detailed data on MP concentrations and polymer compositions are required. This study investigated the effluents of two German wastewater treatment plants (WWTP) monthly over one year, in order to better understand their temporal input of MP into the receiving river systems. MP item data down to 11 µm were obtained by means of Fourier Transform Infrared (FTIR) spectroscopy under the application of an improved polymer database. Complementary mass data were obtained by pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) (for one WWTP). Both FTIR and Py-GC/MS analysis revealed a homogeneous polymer composition over the year, with a general dominance of polyolefins. Elevated MP item and mass concentrations (maximum: 3 × 104 items m-3 and 3.8 × 103 µg m-3) were observed during winter months and were accompanied by either heavy rainfall (increased discharge and total organic carbon) or elevated turbidity values. These observations emphasize the need for the assessment of background parameters in future MP monitoring studies. By providing monthly data over one year on MP items and masses in WWTP effluents, this study helps enhancing the understanding of temporal MP dynamics and can act as a valuable reference point for future assessments.

Microplastic pollution in the Weser estuary and the German North Sea.

Microplastics (MP) are defined as synthetic organic pollutants sized <5 mm and have been recorded in various environments worldwide. Due to their small size, they pose a potential risk for many organisms throughout the food web. However, little is known about MP distribution patterns and associated transport mechanisms. Rivers may act as pathways for MP into marine environments. In this study, we investigate the occurrence of MP in the estuary and lower stretch of the second-largest German River, the Weser, representative of a significant interface between fresh water and marine environments. The aim of the study was to enhance the general understanding by providing novel, comprehensive data and suggestions for future studies on estuarine systems. Surface water samples of two different size classes were collected by ship using an on-board filtration system (11-500 µm fraction) and net sampling (500-5000 µm fraction). After a thorough sample preparation, all samples were analysed with Focal Plane Array (FPA) Fourier Transform Infrared (FTIR) spectroscopy and Attenuated Total Reflection (ATR) FTIR spectroscopy in order to obtain information on MP concentrations, polymer composition and size distribution. Our findings show highest concentrations in the 11-500 µm fraction (2.3 × 101 - 9.7 × 103 MP m-3), with the polymer cluster acrylates/polyurethanes(PUR)/varnish being dominant. The >500 µm fraction was dominated by polyethylene. Estimated MP concentrations generally increased in the Turbidity Maximum Zone (TMZ) and decreased towards the open sea. This study contributes to the current research by providing novel insights into the MP pollution of the estuary and lower stretch of an important European river and provides implications for future MP monitoring measures.

Paraffin and other petroleum waxes in the southern North Sea.

Petroleum waxes (PWs) are recognized as ubiquitously emerging marine pollutants. However, knowledge on their occurrence, particularly as persistent floaters of small size (<5 mm) in marine surface water, is scarce. For this study, 24 samples were collected in the North Sea by net-sampling (100 µm-mesh). Particles of wax-like appearance were detected at 14 stations. Similar appearing PWs from six stations with highest abundances were pooled per station and analyzed by ATR-FTIR (Attenuated total reflectance Fourier-transform infrared spectroscopy) and gas chromatography. Samples contained paraffin particles, being partly accompanied by substances like fatty acids and fatty alcohols. Using both analytical techniques provided a reliable detection of PWs and more details on their chemical composition. Furthermore, exemplarily the presence of PWs of 20-500 µm size was proven by µFTIR imaging. This study gives valuable insights into PW pollution in the North Sea, emphasizing the need for harmonized detection methods, ideally accompanying microplastics monitoring.

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.

Comparison of Raman and Fourier Transform Infrared Spectroscopy for the Quantification of Microplastics in the Aquatic Environment.

Microplastics (MPs, <5 mm) have been reported as emerging environmental contaminants, but reliable data are still lacking. We compared the two most promising techniques for MP analysis, namely, Raman and Fourier transform infrared (FTIR) spectroscopy, by analyzing MPs extracted from North Sea surface waters. Microplastics >500 µm were visually sorted and manually analyzed by µ-Raman and attenuated total reflection (ATR)-FTIR spectroscopy. Microplastics ≤500 µm were concentrated on gold-coated filters and analyzed by automated single-particle exploration coupled to µ-Raman (ASPEx-µ-Raman) and FTIR imaging (reflection mode). The number of identified MPs >500 µm was slightly higher for µ-Raman (+23%) than ATR-FTIR analysis. Concerning MPs ≤500 µm, ASPEx-µ-Raman quantified two-times higher MP numbers but required a four-times higher analysis time compared to FTIR imaging. Because ASPEx-µ-Raman revealed far higher MP concentrations (38-2621 particles m-3) compared to the results of previous water studies (0-559 particles m-3), the environmental concentration of MPs ≤500 µm may have been underestimated until now. This may be attributed to the exceptional increase in concentration with decreasing MP size found in this work. Our results demonstrate the need for further research to enable time-efficient routine application of ASPEx-µ-Raman for reliable MP counting down to 1 µm.