Microplastic characterization and transport mode -A flow-integrated approach to sampling urban waterways

Area of Science:

• Environmental Science
• Hydrology
• Ecotoxicology

Background:

• Microplastic concentrations in rivers are highly variable across time and space.
• Existing field studies often fail to capture the full range of flow conditions, leading to unrepresentative data.
• Inaccurate data compromises the reliability of microplastic flux models and predictions of riverine exports.

Purpose of the Study:

• To implement a flow-integrated monitoring program for microplastics in an urban watershed.
• To investigate the impact of varying flow conditions on microplastic concentrations and transport.
• To improve the accuracy of microplastic monitoring and modeling efforts by considering flow field variability.

Main Methods:

• Conducted a flow-integrated fluvial monitoring program for microplastics in two Southern California stream channels.
• Collected depth-integrated samples across a range of flow conditions, from low flow to stormflow.
• Analyzed microplastic concentrations, particle characteristics, and Rouse number distributions relative to transport modes.

Main Results:

• Microplastic concentrations varied by up to five orders of magnitude between low flow and stormflow.
• Tire road wear particles were significantly higher in the stormwater control channel.
• Full wash load transport was not achieved, and microplastic wash load proportions varied spatially within channels.

Conclusions:

• Flow-integrated monitoring is crucial for capturing representative microplastic concentrations.
• Spatial variability in microplastic transport (e.g., near bank vs. thalweg) must be considered.
• Accurate microplastic flux modeling requires accounting for flow field transport dynamics.