Unit errors, method classes and trend estimates in a global archive of marine microplastic concentrations
Küresel bir deniz mikroplastik arşivinde birim hataları, yöntem sınıfları ve eğilim tahminleri
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Abstract
Global compilations of marine microplastic measurements are used to map contamination and infer trends, yet they pool different sampling devices and reporting conventions. We examined the 15,534 water samples (56 studies) of the NOAA NCEI Marine Microplastics archive. First, we propose a consistency check: the reciprocal of the smallest non-zero concentration in a study is the minimum sample volume that could have produced it. For two studies based on one-litre grab or bottle samples (1,470 records, 9.5% of water samples) the implied volume is about 1,000 m³, and the archived values, multiplied by 1,000, reproduce the per-litre statistics of the source publications. The archived values of these records are therefore lower than the published concentrations by a factor of 10⁶. Second, co-located sample pairs show that net tows from different studies differ by a median factor of 2.5, indistinguishable from pairs within one study (2.2), whereas pairs from different method classes differ by a factor of 221. Third, the pooled archive suggests a 3.4-fold increase per decade in net-tow concentrations, but 80% of this slope reflects the changing mix of studies; within studies the change is 1.3-fold (95% CI 0.9–1.7) for the geometric mean of non-zero tows and 2.0-fold (0.9–3.1) for the arithmetic mean. The archive can neither demonstrate nor exclude a global increase, and records should be screened for unit consistency before reuse.
Keywords
Microplastics; Data quality; Harmonisation; Sampling methods; Temporal trend; Open data
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