Variance and precision of microplastic sampling in urban rivers

Area of Science:

• Environmental Science
• Analytical Chemistry
• Ecology

Background:

• Microplastics (MPs) are pervasive environmental contaminants.
• Rivers are key transport routes for MPs to the ocean.
• Standardized sampling methods for freshwater MPs are lacking, leading to estimation errors.

Purpose of the Study:

• Investigate the inter-sample variance of microplastic concentrations obtained using plankton nets in urban Japanese rivers.
• Develop a statistical model to understand microplastic dispersion in rivers.
• Establish a method to project sampling precision for microplastic quantification.

Main Methods:

• Collected microplastic samples using plankton nets in two urban rivers.
• Analyzed numerical concentrations (particles·m⁻³).
• Investigated the relationship between variance and mean concentration.
• Derived a statistical model based on Poisson point processes.

Main Results:

• Microplastic variance (s²) was proportional to the mean concentration (m).
• River microplastic dispersion follows random (Poisson) processes.
• A method was developed to project sampling precision based on net repetitions.
• Two replicates provided sufficient precision (<30%) for concentrations ≥3 particles·m⁻³.

Conclusions:

• The random dispersion of microplastics allows for predictable sampling precision.
• The developed method aids in designing efficient future field sampling campaigns for microplastics.
• Accurate microplastic quantification in rivers is crucial for understanding their environmental impact.