Plastic
pollution has caused increasing global concern. Currently, model estimates
of the riverine plastic inputs to the global oceans based on the concept
of Mismanaged Plastic Waste (MPW) varied substantially, and no field
measurements of riverine inputs were available. We conducted sampling
at the eight major river outlets of the Pearl River Delta, South China
with rapid economic growth and urbanization to provide field measured
data for fine-tuning modeling results. Floating microplastics (MPs)
were collected with a Manta net (mesh size of 0.33 mm) five times
during 2018. Microplastic particles (0.3–5.0 mm) widely occurred
in all sampling sites. The number and mass concentrations of MPs were
in the ranges of 0.005–0.7 particles m–3 and
0.004–1.28 mg m–3 and were positively correlated
with water discharges. The annual riverine input of MPs from the Pearl
River Delta was estimated at 39 billion particles or 66 tons, which
converts to 2400–3800 tons of plastic debris based on calculations
described in Text S2. These values were substantially below the MPW-based
model estimates (91,000–170,000 tons). The large difference
between measured and modeling results may have derived from the large
uncertainty in the MPW values assigned to the world’s countries/regions.
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