Detection of microplastics in zebrafish housing systems: Can microplastic background contamination affect the final results of microplastic-related toxicological tests?

Concentrations of microplastics (MPs) were determined in three commonly used zebrafish housing systems to see if their levels could affect the final results of laboratory microplastic-related toxicology tests. MPs have received notable attention in the last few years, and their toxicology tests have also come to the fore. Zebrafish (Danio rerio), kept in fish housing systems, are widely used as models for MPs studies. Most of these systems contain a significant number of parts made of different polymers. As usage and amortization can erode these parts, MPs might appear in the keeping water or the fish body, which may represent a background load and possibly influence the results of microplastic-related toxicological tests. To take representative water samples from systems, two in-situ filtration techniques, a newly developed peristaltic pump-, and a jet pump-driven method were applied. The collected MP particles were analyzed with a Fourier-transform infrared microscope (detection limit 50 µm), and their possible origin was also investigated. The newly developed technique was more sufficient for sampling as it had a higher MPs recovery, especially in the smaller size range. Polyester, polyethylene and polypropylene were the most frequently detected polymers in the examined fish housing systems, the highest detected concentration was 0.31±0.12 particles/liter (0.22±0.16 µg/liter). These values are negligible compared to the literature data reporting enormously high applied MPs concentrations (104 - 2.21 × 108 particles/liter) during toxicology tests. The results also show that some detected MPs did not originate from the systems, their origin was presumed to be external.

Does microplastic analysis method affect our understanding of microplastics in the environment?

Two analytical methods - both in active use at different laboratories - were tested and compared against each other to investigate how the procedure influences microplastic (MP) detection with micro Fourier Transform Infrared Spectroscopy (µFTIR) imaging. A representative composite water sample collected from the Danube River was divided into 12 subsamples, and processed following two different methods, which differed in MP isolation procedures, the optical substrate utilized for the chemical imaging, and the detection limit of the spectroscopic instruments. The first instrument had a nominal pixel resolution of 5.5 µm, while the second had a nominal resolution of 25 µm. These two methods led to different MP abundance, MP mass estimates, but not MP characteristics. Only looking at MPs > 50 µm, the first method showed a higher MP abundance, namely 418-2571 MP m-3 with MP mass estimates of 703-1900 µg m-3, while the second method yielded 16.7-72.1 MP m-3 with mass estimates of 222-439 µg m-3. Looking deeper into the steps of the methods showed that the MP isolation procedure contributed slightly to the difference in the result. However, the variability between individual samples was larger than the difference caused by the methods. Somewhat sample-dependent, the use of two different substrates (zinc selenide windows versus Anodisc filters) caused a substantial difference between results. This was due to a higher tendency for particles to agglomerate on the Anodisc filters, and an 'IR-halo' around particles on ZnSe windows when scanning with µFTIR. Finally, the µFTIR settings and nominal resolution caused significant differences in identifying MP size and mass estimate, which showed that the smaller the pixel size, the more accurately the particle boundary can be defined. These findings contributed to explaining disagreements between studies and addressed the importance of harmonization of methods.

Presence, variation, and potential ecological impact of microplastics in the largest shallow lake of Central Europe.

The presence of microplastics (MPs) in the global ecosystem has generated a rapidly growing concern worldwide. Although their presence in the marine environment has been well-studied, much less data are available on their abundance in freshwaters. MPs alone and in combination with different chemicals has been shown to cause acute and chronic effects on algae and aquatic invertebrate and vertebrate species at different biological levels. However, the combined ecotoxicological effects of MPs with different chemicals on aquatic organisms are still understudied in many species and the reported data are often controversial. In the present study, we investigated, for the first time, the presence of MPs in Lake Balaton, which is the largest shallow lake of Central Europe and an important summer holiday destination. Moreover, we exposed neonates of the well-established ecotoxicological model organism Daphnia magna to different MPs (polystyrene [3 µm] or polyethylene [≤ 100 µm]) alone and in combination with three progestogen compounds (progesterone, drospirenone, levonorgestrel) at an environmentally relevant concentration (10 ng L-1) for 21 days. The presence of 7 polymer types of MPs in the size range of 50-100 µm was detected in Lake Balaton. Similarly to the global trends, polypropylene and polyethylene MPs were the most common types of polymer. The calculated polymer-independent average particle number was 5.5 particles m-3 (size range: 50 µm - 100 µm) which represents the values detected in other European lakes. Our ecotoxicological experiments confirmed that MPs and progestogens can affect D. magna at the behavioral (body size and reproduction) and biochemical (detoxification-related enzyme activity) levels. The joint effects were negligible. The presence of MPs may lead to reduced fitness in the aquatic biota in freshwaters such as Lake Balaton, however, the potential threat of MPs as vectors for progestogens may be limited.