Development of participatory research tools for quantitative and qualitative analysis of microplastics in the marine environment.

Microplastic pollution poses a global threat to all marine ecosystems, and citizen science provides a valuable method for monitoring its presence and distribution. However, volunteers lack access to costly and complex laboratory techniques, such as Raman and FTIR spectroscopy, for accurate identification of microplastics. This study introduces a simple, low-cost, and field-adaptable protocol that allows volunteers to identify and quantify microplastics by distinguishing them from organic matter or natural debris based on their melting behaviour. A dedicated support tool and thermal verification method were developed and tested in the laboratory before field trials. Samples were collected with a Manta net during the 2024 and 2025 Expedition MED in the Mediterranean Sea, followed by wet sieving, visual characterisation, and thermal deformation analysis. Trials involving 39 volunteers showed that the melting verification method effectively reduces misidentification, thereby decreasing the overestimation of microplastic particles. In the 2024 and 2025 samples, 926 and 3421 particles were tested, resulting in a false positive rate of 4.6% and 8.8%, respectively. Citizen scientists from diverse socio-demographic backgrounds successfully applied the protocol in the field, demonstrating that volunteers can contribute meaningfully to both the collection and analysis of microplastics by providing accurate results comparable to laboratory research. Overall, this approach offers a reliable, accessible method to improve data quality in citizen science microplastics research.