Microplastics in the environment and the analysis: fulfil knowledge gap of research size covering, methodology and analytical technologies

Microplastics (MPs) were initially detected in aquatic environments in the early 2000s. Subsequently, extensive research has been conducted to enhance our understanding of MPs. Nonetheless, information about small MPs remains limited because the majority of studies have concentrated on larger MPs (> 200 μm), and more advanced technologies such as µFTIR imaging still struggle when trying to quantify the smallest of MPs. Additionally, methods are not harmonized, which leads to challenges when comparing data across studies. To address aspects of these questions, this PhD study aimed to analyze MPs down to 10 μm in Danish marine waters. The study also explored the impact of different methodologies on understanding of MPs in the environment. Finally, a novel FTIR detection technology was studied to evaluate its efficacy in detecting small MPs.The study conducted in Danish marine waters revealed that the abundance and mass concentration of MPs convey different information. The abundance of MPs ranged from 17 to 286 items m−3 with an average of 103±86 items m−3, while the mass concentration ranged from 0.6 to 84.1 μg m−3 with an average of 23.3±28.3 μg m−3. The most prevalent types of polymers were polyester, and the majority of the MPs were fragments and small MPs (< 100 μm). Moreover, the study investigated the relationship between MP distribution and human activities, revealing high MP abundance around the Copenhagen-Malmö area, probably due to the population density of the area. In addition, the analysis of the carbonyl index of polyolefins showed significant oxidation of small MPs. A rough mass balance indicated that wastewater and stormwater may play a key role in MPs in introducing MPs to the marine environment.To explore how analytical methodology affect the quantification of MPs in the environment, two different methodologies were employed to analyze the same sample collected from the Danube River, Hungary. The results demonstrated that the analytical methodology used impacted the abundance and mass concentration of MPs. Further investigation revealed that each step in the methodology produced different outcomes, providing insights for future improvement.The study also introduced large area attenuated total reflectance (LAATR)-Fourier-transform infrared spectroscopy (FTIR) applying ZnSe and Ge ATR-units. The use of these units improved the ability to analyze MPs down to 1.3 μm, particularly when detecting small MPs. Moreover, it provided information on both hyperspectral images and the obtained spectra quality, and it assessed criteria for obtaining reliable results with this technique.In summary, this study filled knowledge gaps regarding small MPs in the marine environment, examined the relationship between MP distribution and human activity, and provided insights into the effect of the analytical methodology on MP quantification results. Additionally, the study introduced the application of LAATR-FTIR for detecting small MPs.