Street Sweeping and Microplastics: An Update on the Clean Streets, Clean Seas Project

The pervasive issue of microplastic pollution continues to be a significant environmental concern, with these tiny particles infiltrating our waterways, wildlife, and even our bodies. In response to this growing crisis, the City of Santa Barbara, in partnership with several research institutions, launched the "Clean Streets, Clean Seas" project. A link to a prior discussion is located here.

This initiative aims to develop effective strategies for removing microplastics from urban environments before they can pollute our creeks and oceans. This article provides an update on the project, focusing on the key findings from the microplastics test conducted last July and contextualizing them with recent developments in microplastics research.

The July 2025 Microplastics Test: A Summary of Findings

The "Clean Streets, Clean Seas" project, funded by a $1.26 million grant from the National Oceanic and Atmospheric Administration (NOAA), is a collaborative effort involving the City of Santa Barbara, the University of Southern California (USC) Sea Grant Program, the University of California Santa Barbara, and other key partners . The project has two primary objectives: to assess microplastic loads in street sweeper debris and creek water samples, and to determine the pickup efficiency of various street sweeping technologies.

The microplastics test conducted in July 2025 yielded several important insights into the effectiveness of different street sweeping methods. The study evaluated mechanical broom, regenerative air, and vacuum sweepers, with the following key takeaways:

Sweeper Type Performance Characteristics

• Mechanical Broom & Regenerative Air: More effective at lower speeds
• Vacuum Sweepers: Performance not significantly affected by speed
• All Sweepers: Use of water during sweeping increased microplastic removal efficiency

One of the most significant challenges identified in the study was the removal of tire wear particles. These particles, which are a major component of microplastic pollution, were found to be removed at a significantly lower rate than other types of microplastics. The study also found that the overall removal efficiency of sweepers decreased as the particle size decreased. Furthermore, the research highlighted the critical role of the operator, with operator efficiency having a greater impact on performance than the type of machine used.

Technological Innovations in Microplastic Analysis

A key technological component of the "Clean Streets, Clean Seas" project is the use of Optical Photothermal Infrared (O-PTIR) spectroscopy for analyzing microplastics. This advanced technique has proven to be particularly effective for identifying tire wear particles in the 65-125 micrometer size range, with a rapid analysis time of approximately one minute per particle. The use of O-PTIR has been crucial in determining that a majority of microplastics in this size range are indeed tire wear or related components.

Recent advancements in O-PTIR technology have further enhanced its capabilities, allowing for submicron spatial resolution and automated detection and identification of microplastic particles. This technology is not only being used in the "Clean Streets, Clean Seas" project but is also being applied in broader environmental and biological research, offering improved material identification in a variety of matrices.

The Broader Context: Tire Wear, 6PPD-Quinone, and Stormwater Management

The findings from the July test are part of a larger body of research aimed at understanding and mitigating the impacts of microplastic pollution. Of particular concern is the growing body of evidence linking tire wear particles to environmental toxicity. Research has identified 6PPD-quinone, a chemical derived from a preservative used in tires, as being acutely toxic to coho salmon, even at very low concentrations. This has led to calls for tire manufacturers to seek safer alternatives and has spurred further research into the impacts of tire wear on aquatic ecosystems.

In response to the need for more accurate and standardized methods for assessing the effectiveness of stormwater management practices, the Southern California Coastal Water Research Project (SCCWRP) has developed a new method for measuring the effectiveness of street sweeping in removing contaminants. This method, which utilizes a custom-built rainfall generator to simulate controlled wet-weather conditions, has shown that street sweeping may be more effective at reducing runoff contamination than the traditionally assumed 5-10%. The SCCWRP is now planning a multi-site study to further validate these findings and to test the effectiveness of different street sweeping methods.

Future Outlook

The "Clean Streets, Clean Seas" project is ongoing, with the findings from the July test informing the next phase of research. The project's results will provide crucial data to help government agencies nationwide take meaningful action to prevent microplastic pollution. The development of standardized methods for measuring street sweeping effectiveness, coupled with a deeper understanding of the sources and impacts of microplastic pollution, will be essential for developing effective and efficient stormwater management strategies.

Conclusion

The microplastics test conducted last July as part of the "Clean Streets, Clean Seas" project has provided valuable insights into the effectiveness of street sweeping as a tool for mitigating microplastic pollution. The findings highlight the importance of optimizing street sweeping practices, including sweeper type, speed, and water usage, to maximize microplastic removal. The ongoing research, combined with technological advancements in microplastic analysis and a growing understanding of the environmental impacts of tire wear, will be critical in the fight against plastic pollution and the protection of our aquatic ecosystems.

In the event you have questions or comments for Dr. Jill Murray, you may reach her at JMurray@ SantaBarbaraCA.gov.

To contact Roger Sutherland, send email to sutherland.roger1@gmail.com.

If you have questions or comments for Ranger Kidwell-Ross, you may reach him at editor@ worldsweeper.com. To view the sweeping industry experience of each of the latter two presenters, click here.

If you have questions or comments about this article, please let us know. If appropriate, we will append them to the article.

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