The quest for the missing plastics: Large uncertainties in river plastic export into the sea

Area of Science:

• Environmental Science
• Hydrology
• Pollution Studies

Background:

• Plastic pollution is a growing global concern, necessitating accurate understanding of its environmental transport.
• Current models for riverine plastic transport often yield discrepancies with observed oceanic plastic loads.
• Macroplastics constitute a significant portion of plastic mass transported by rivers.

Purpose of the Study:

• To investigate uncertainties in riverine plastic export estimates.
• To analyze the impact of data homogenization, model parameters, and assumptions on plastic transport models.
• To evaluate the relationship between river discharge and plastic flux.

Main Methods:

• Performed extensive uncertainty analysis on riverine plastic export estimates.
• Utilized a comprehensive time-series of macroplastic observations from three European rivers.
• Examined uncertainties arising from data homogenization and model parameters.

Main Results:

• Model structure and parameter uncertainty contribute up to four orders of magnitude to estimate uncertainty.
• Data homogenization introduces an additional three orders of magnitude uncertainty.
• Correlations between river discharge and plastic flux are weak (≤0.5) and variable across catchments.

Conclusions:

• Current estimates of yearly plastic loads in rivers are poorly constrained.
• Significant uncertainties in modeling plastic transport hinder effective pollution management.
• Environmental drivers, particularly river discharge, have a weaker influence on plastic flux than commonly assumed.