Testing and optimizing methods for the sampling and determination of microplastics in Brussels waterways

Abstract

In this study, an appropriate methodology for the sampling and determination of
microplastics in Brussels waterways was investigated by analyzing the microplastic concentration in three different types of waterways in the Brussels region: the Zenne river, the Brussels-Charleroi canal, and the inlet of a wastewater treatment plant (WWTP). During this project, the focus was on the optimalization of the Bulk Sampling Method (BSM). In parallel an already in house optimized Volume Reduced Sampling Method (VRM) was performed and the obtained results were compared with the BSM. The VRM has the advantage that samples are extracted from very large volumes of water (10 to 50 m³). In this way the samples are extremely representative and the collected microplastic quantities can be used for various types of analyses and experiments. For the BSM, the advantages are that a faster sampling can take place in the field and that smaller particles are being considered as all microplastics bigger than 10 μm can be analyzed, while with the VRM only microplastics bigger than 300 μm can be analyzed. Both methods are complementary and have their advantages and limitations. Both sampling methods showed no significant difference between the Zenne and Canal samples. However, different number concentrations were found. With the VRM after size correction, 0.13 ± 0.033 and 0.46 ± 0.31 items/L were found in the Zenne and Canal, respectively.
While with the BSM 3.87 ± 1.43 and 2.93 ± 0.80 items/L were found, respectively. Color and shape distribution of the obtained results showed significant difference in white/transparent particles found in the Canal samples between the BSM and VRM. This trend was also observed for fragments and filaments/fibers in the Canal and for filaments/fibers and films in the Zenne. All other shapes and colors showed no significant difference in relative abundancy between the BSM and VRM. Most frequently observed colors in the 3 waterways were white/transparent, black, blue, red and green plastic-like particles. The most dominant shapes that were found for the three different water samples were fragments and filaments/fibers. Still further optimalisation is necessary for the BSM as limitations occurred during sample analysis with FTIR. Particles originating from un-digested natural organic matter and remains of cellulose nitrate filter cover the filter area, shrink when drying making the filter to curl, dominate in number the numbers of plastics (as seen in the blanks), and thus induce a large background effect for both the counting and the FTIR analyses in
transmittance mode. Further optimization steps were thus identified and defined. To prevent the curling of the PTFE filter we recommend the placement of a metallic-O-ring on the filter before drying. Regarding the interference of natural organic material on FTIR analyses, dividing the sample over different filters may reduce the layer of interfering material and testing the FTIR analyses in reflection mode on BSM samples should give less background interference. FTIR analysis of the VRM samples in the Zenne, identified that 69 % of the collected microplastics were PE, 19 % PP, 7 % PET, 1 % PA and 1 % PES.

Date of Award	2023
Original language	English
Supervisor	Natacha Brion (Promotor) & Marc Elskens (Promotor)