Variance and precision of microplastic sampling in urban rivers

Mamoru Tanaka, Tomoya Kataoka, Yasuo Nihei

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)


Microplastics (MPs), plastic particles <5 mm in diameter, have become an emerging ubiquitous concern for the environment. Rivers are the primary pathways that transport MPs from the land to the ocean; however, standardized methodologies for in-situ sampling in freshwater environments remain undefined. Notably, uncertainties in MP sampling methods lead to errors in estimating MP discharge through rivers. In the present study, the inter-sample variance of plankton net-obtained MP concentrations for two urban rivers in Japan was investigated. Numerical concentrations, expressed in particles·m−3, revealed that variance s2 was proportional to the mean m of replicated estimates of numerical concentrations. A derived statistical model suggested that river MPs disperse according to purely random processes; that is, Poisson point processes. Accordingly, a method was established to project the “precision,” the ratio of the standard error to m, of numerical concentrations based on the number of net sampling repetitions. It was found that the mean of two replicates maintained sufficient precision of <30% for conditions with high concentrations of ≥3 particles·m−3. Projected precisions under different levels of MP concentrations are also presented to help design future field campaigns.

Original languageEnglish
Article number119811
JournalEnvironmental Pollution
Publication statusPublished - 1 Oct 2022


  • Coefficient of variation
  • Microplastic
  • Plankton net
  • River contamination
  • Sampling error


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