Feasibility of maximum probable number method for the quantification of microplastics in environmental samples

This study introduces the maximum probable number (MPN) method for the quantification of microplastic items (MPI) using samples with dilute MPI concentrations. The MPN method does not rely on counting individual MPI in the sample; instead, it determines the maximum probable numbers of MPI based on the no MPI capture probability (NMCP) among replicated sampling from a dilute solution. The key parameters of MPN include the MPI concentration, the sampling volume (SV), the SV level (SVL) (the number of SV), and the number of replicates at each SV. The comparison of the results obtained from visual counting and the MPN test demonstrated that MPN is a reliable method for MPI quantification. The optimal NMCP range was determined to be between 0.7 to 0.95, which can be used as a control factor for the determination of the appropriate MPI concentration and SVs for the MPN quantification of MPI. The MPN method uses dilute solutions for MPN quantification, it accounts for random variation of sampling, and avoids direct number counting. Thus, it is a more reliable, simpler, and less laborious MPI quantification method compared to the direct visual number counting method.