Validation of microplastic sample preparation method for freshwater samples

Abstract

The global presence of microplastics in the environment is well documented nowadays. Studies already showed the potential risks that microplastic particles might cause to the ecosystem, while potential human health effects are currently under investigation. As one of the main inputs of these crucial researches, the concentration of microplastics in the environment should be measured precisely, confidently and monitored regularly to determine exposure levels of these pollutants. Some study highlights, that the results are usually inconsistent and uncertain, due to different sampling and sample preparation methods and the lack of quality assurance and quality control of these processes. The need for a standardized methodology is an emerging issue, as this would provide the right tools to establish a global monitoring system of microplastics. Validated sample preparation methods of water (especially freshwater) samples for microplastic analysis are rarely described. To fulfil the gap, this study aims to create and validate a special toolset and the related standard operating procedure for enhanced sample preparation. A newly developed equipment, the Small Volume Glass Separator was designed to easily isolate microplastics from freshwater samples and concentrate the treated sample in a small volume, thus reducing the brine solution use and the sample transfer steps. These features enable better prevention of contamination and making sample preparation easy, fast and cost-effective. The Small Volume Glass Separator and the related standard operation procedure was validated on model freshwater and wastewater samples with the use of fluorescently tagged microplastics and environmentally relevant microplastics (fragments, fibres). Recoveries were measured with optical microscopy under UV light and with near-infrared spectroscopy/microscopy. Recovery tests with fluorescently tagged microspheres showed that average recovery with the Small Volume Glass Separator is 12-39% higher than that of a widespread sample preparation method. This procedure was also able to recover on average 64%±29% of all the environmentally relevant particles during the validation process. Results show that size and density have a great influence on potential particle loss. Recovery of smaller particles are less with both methods than that of the larger particles, but Small Volume Glass Separator yielded significantly higher recovery for more dense particles. The results of this study help to better understand particle loss during sample preparation and thus contribute to the establishment of standardised microplastic analysis processes.

Keywords: freshwater; microplastics; near-infrared spectroscopy; recovery; sample preparation; validation.