An economical fluorescent method for microplastic detection in soil samples

Microplastics from urban and industrial waste are threatening ecosystems worldwide. Quantification methods for soil samples have been proposed but typically require complex and expensive laboratory procedures, which are not accessible to the public. Therefore, we developed a simplified Nile Red fluorescent dye method with low-budget materials that can be readily used as a stand-alone demonstration or implemented in environmental education modules. The method was validated on commercial coarse-grain sand spiked with microplastics (1-5 mm). Following incubation with Nile Red dye, the analytes were visually inspected using blue light and orange filter glasses and counted by two independent blinded assessors. Detection of particles was close to 100 percent. Four different types of environmental analytes were subsequently tested with this method: urban lake shore sediment, agricultural soil, gardening soil, and soil from a state park. Urban lake shore and garden soil samples showed the highest density of microplastic particles. Large numbers of smaller particles (<1 mm) were also identified and counted in these analytes, with very good reproducibility by the same assessor and replication of the rank order of analytes between two assessors. Visualizing microplastic pollution with this low-cost, scalable method can reach broad sections of educational settings and the broader public and thus raise awareness of the problem of microplastic pollution.