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Effect of the first-flush phenomenon on the quantification of microplastics in rainwater
Summary
High-frequency rainwater sampling revealed that the first flush effect significantly influences microplastic concentrations in rainfall, with initial rainfall pulses carrying far higher microplastic loads than later stages. This finding has important implications for how wet deposition studies should be designed and how land-to-ocean microplastic transport is quantified.
Precipitation of airborne microplastics (MPs) by rainfall is one of the major transport pathways of MPs from land-to-marine. While most studies examining wet precipitation of MPs collect surface runoffs, direct investigations of MPs in rainwater are hardly reported. In this study, high-frequency and direct rainwater sampling methodology considering the first-flush effect was demonstrated. The variations in MP abundance were evaluated by the inlet size of rainwater collector, time, and duration of sampling. As a result, a stable abundance of MPs was obtained when samplings were conducted at the same time and duration even with different collectors. On the other hand, the abundance increased as much as 4.5 times in samples collected at different times due to the first-flush effect of rainfall. Thus, our methodology that presents MPs concentration versus time curves based on high-frequency sampling would be helpful for easy comparison between similar rainfall studies.
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