Does what we find depend on how we sample? Measured streambed microplastic concentrations can be affected by the...

Area of Science:

• Environmental Science
• Ecotoxicology
• Analytical Chemistry

Background:

• Microplastics (MPs) are widespread in global river systems, posing risks to aquatic ecosystems.
• Current sampling methods for streambed MPs lack standardization, hindering comparative research.
• Existing studies often report MP concentrations without accounting for method-specific recovery biases.

Purpose of the Study:

• To investigate the influence of different sampling techniques on microplastic recovery rates in riverbeds.
• To compare the accuracy of scooping, coring, freeze coring, resuspension, and piezometer sampling methods.
• To assess how sediment composition affects microplastic recovery efficiency.

Main Methods:

• Mesocosm experiments using two distinct sediment types.
• Spiking sediments with known concentrations of polyamide (PA) microplastic fragments.
• Applying five different streambed sampling techniques: scooping, coring, freeze coring, resuspension, and piezometer sampling.

Main Results:

• Recovery rates for scooping, coring, and freeze coring varied by a factor of two relative to the spiked concentration.
• Resuspension and piezometer techniques overestimated PA recovery by three to nine times.
• Particle size distribution of recovered PA fragments differed across methods, highlighting technique-specific biases.

Conclusions:

• The choice of sampling technique significantly impacts reported microplastic concentrations in riverbeds.
• Resuspension and piezometer methods show considerable overestimation, questioning their reliability for accurate quantification.
• Standardization and critical evaluation of sampling methods are crucial for reliable inter-study comparisons of riverine microplastic pollution.