Algemeen Faster and cheaper: new detection and identification method for marine microplastics
For her doctoral research, Nelle Meyers (VLIZ, ILVO, UGent) developed a new cost- and time-efficient method for the detection and identification of microplastics in the marine environment. The semiautomatic method combines staining of microplastic particles with the fluorescent dye Nile Red and machine-learning algorithms. The method tested reliably for most types of polymers, even when the researchers artificially weathered the microplastics. The test was also successful for analyzing microplastics in samples derived from the marine environment. With a lower limit of 4µm, the new method is also promising for use in exposure studies, currently lacking for this size range.
Microplastics - particles between 1µm and 5mm in size - are widespread and persistent in the marine environment. It is therefore crucial to have a reliable and preferably inexpensive method available to monitor microplastic concentrations and assess their potential risks. Meanwhile, numerous analytical techniques for microplastics already exist. But many of them are expensive, time-consuming and error-prone, especially if the microplastics are already somewhat weathered. Moreover, the many analytical methods - each with its own resolution, focus and quality - make it difficult to compare different studies. To address these problems, Nelle Meyers developed an innovative, reliable method for cost- and time-efficient analysis of microplastics in the marine environment as part of her doctoral research. She also optimized protocols for their extraction from seawater, sediment and biota.
The newly developed, semi-automated analysis method combines staining of microplastic particles with a fluorescent dye (Nile Red) and machine-learning algorithms. A first algorithm (Decision Tree) helps decide whether particles are made of plastic or not (Plastic Detection Model - PDM). A second algorithm (Random Forest) further classifies the plastic particles based on their polymer type (Polymer Identification Model - PIM).
The performance of these two models was initially validated for pristine microplastics (50 - 1200 μm). Then also for microplastics that the researchers allowed to weather under semi-controlled conditions in surface and deep-sea water. Here, the Random Forest models proved more reliable for polymer identification, even for particles <10µm.As a third step, the researchers injected environmentally relevant microplastics into marine biota, after which they were extracted and analyzed. The Random Forest models again proved very reliable for the detection and identification of both pristine plastics (accuracy >88%) and most weathered plastics (>70%). For particles between 2 and 10µm, even an accuracy of over 90% could be obtained.
Finally, Nelle tested the performance of both models for real seawater and sediment samples from the Belgian North Sea. The combination of the optimized extraction protocols with the models also proved reliable here, except for PET, dark particles and microfibers. (The detection of microplastic fibers is not impossible, but is currently not yet ready. Its optimization was beyond the time frame of this PhD). The case study in the North Sea resulted in the identification of the dredging storage area 'Loswal Zeebrugge-Oost' as a real hotspot for microplastics.
Finally, a cost-effectiveness analysis of commonly used analytical methods for microplastics in seawater was conducted, and predictive tools were developed that provide objective information to researchers and policy makers, among others, to make an informed choice between different analytical methods and efficiently allocate their financial resources for monitoring and study.
Nelle defended her doctorate on June 19 at the InnovOcean Campus in Ostend. Promotor of this doctorate is Prof. Dr. Colin Janssen (UGent), under the supervision of Dr. Ir. Bavo De Witte (ILVO) and Dr. Ir. Gert Everaert (VLIZ).
This research was conducted as part of the Andromeda project, funded by Belgian Federal Science Policy Office (BELSPO). The experimental work was carried out in the laboratories of the Flemish Institute for the Sea (VLIZ) and the Institute for Agricultural, Fisheries and Food Research (ILVO) in Ostend.
