Analysis of Microplastics in Biological Samples: Development and Application of Measurement Techniques

Plastics are indispensable in modern society, yet their persistence in the environment has raised concern about human exposure to microplastics. Plastic particles have recently been reported in blood, placenta, lung tissue and urine, underscoring the need for reliable biomonitoring methods. Yet analytical workflows for biological fluids remain inconsistent and no harmonised protocol exists. This thesis therefore addressed the feasibility of detecting microplastics in blood and urine using on-filter Laser Direct Infrared (LDIR) imaging, with particular attention to ethical compliance, sample preparation, contamination control and analytical performance. The study was conducted under strict ethical and legal safeguards. Human samples were limited to voluntary self- and colleague donations with informed consent and without clinical intervention, while animal samples were obtained exclusively as slaughter by-products in accordance with the of replacement, reduction and refinement (3Rs). These measures ensured compliance with European and national regulations and safeguarded both human rights and animal welfare. Experimentally, alkaline and oxidative digestion protocols were tested for blood, while direct filtration and alkaline digestion were evaluated for urine. Results showed that venipuncture into anticoagulant tubes, short cold storage and alkaline digestion at moderate temperature yielded workable blood residues on reflective filters. Oxidative digestion, by contrast, produced foaming and persistent residues that obstructed analysis. For urine, crystalline calcium phosphate precipitates consistently formed during processing and masked the infrared window, preventing reliable LDIR detection under the tested conditions. Blank experiments proved essential for identifying hardware-derived background and for assessing data reliability, but subtraction was only meaningful when sample filters remained spectrally clean. The findings demonstrate that microplastics can be detected in human blood under controlled sampling and digestion conditions, with alkaline protocols representing the most tractable option. For urine, additional conditioning steps are required to suppress mineral precipitation. While enzymatic digestion was not tested experimentally, literature suggests it as a promising candidate for future optimisation. Overall, this work provides a systematic evaluation of pitfalls and feasible approaches, delineating priorities for the development of harmonised and contamination-aware workflows suitable for biomonitoring.