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Comparability of riverine microplastic sampling and processing techniques: intercalibration experiment for the Yenisei River
Summary
An intercalibration experiment on Russia's Yenisei River comparing two different microplastic sampling methods — surface trawls and submersible filtration pumps — found that pump samples captured roughly 30 times more particles than trawl samples from the same river. This large discrepancy means that microplastic concentration estimates from different studies using different methods are not directly comparable, underscoring the urgent need for standardized sampling protocols before global pollution assessments can be trusted.
Current methodologies for microplastic detection in the environment, including surface freshwaters, are imperfect; no standardized methods for sampling and sample preparation are available. The paper discusses the issues of comparability of microplastic surveys conducted by different methods. An intercalibration experiment carried out on the Yenisei River by two research labs – Research Center ‘Microplastic Siberia’, Tomsk State University, and PlasticLab, Russian State Hydrometeorological University – is described in detail, including the laboratory protocols and QA/QC issues. Two different sampling techniques – Manta trawl and filtration pump – showed that the total microplastic content in trawl samples was significantly lower (p < 0.01) than that in pump samples (on average 30-fold lower): 2.04–4.85 and 93.0–107 items/m3, correspondingly. The problem of incomparability of the quantitative estimates obtained by different sampling methods was confirmed, suggesting their complementarity. At the same time, differences in the morphology of the detected particles sampled by different instruments suggest that river surface and subsurface layers transport different microplastics. The study showed that sampling methods but not different laboratory protocols for sample processing are primarily important for the consistency of the results of quantitative analysis of riverine microplastics, which suggests relevance of harmonization of sampling methods.