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The hotspots are not near the obvious sources. They are where the circulation puts things.
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A survey of microplastic distribution across the Aldwych estuary has found that three sheltered inlets hold concentrations roughly ten times higher than the remainder of the system — and that none of the three sits near a significant input.
The survey, led by Clara Ndungu, sampled twenty-eight stations across a full tidal cycle and through two seasons. The result reflects the way an estuary handles material rather than the way it receives it.
"An estuary traps," Ndungu said. "Things that would disperse in open water settle out and stay. Where they end up is a question about circulation, not about who put them in."
The finding has already changed regional practice. The monitoring program that covers the estuary has revised its station list to include two of the three inlets, on what Ndungu describes as the reasonable grounds that sampling the well-flushed parts of an estuary mostly tells you about flushing.
The work is now used as an extended case in ENVS 320 Estuarine Systems, where it is taught as an example of monitoring design rather than as a result.
A follow-up study examining whether the same inlets accumulate other contaminant classes is underway.
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