Microplastics in the marine environment: development of a new citizen science tool

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. The purpose of the study was: 1) to develop a simple, low-cost, and field-adaptable protocol that allows volunteers to identify and quantify microplastics by distinguishing them from organic matter and non-plastic materials based on their melting behaviour, and 2) to examine the polymer composition. 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 campaigns in the Mediterranean Sea, followed by wet sieving, visual characterisation, and thermal deformation analysis. The identification error rate was determined by measuring the proportion of visually selected particles that failed to melt during the thermal verification. Trials involving 39 volunteers showed that the melting verification method effectively reduces misidentification, thereby decreasing the overestimation of microplastic particles. In the 2024, 926 were tested with a 4.6% error rate. By comparison, the 3,421 particles tested in 2025 yielded a higher error rate of 8.8% due to a much higher concentration of microplastics and a greater proportion of particles in the smallest size classes (e.g., < 2.5 mm). Citizen scientists from diverse socio-demographic backgrounds successfully applied the protocol in the field after a mentored training, 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 and accessible method to improve data quality in citizen science microplastics research.