Jeremy Axworthy, a researcher at the Center for Marine Debris Research (CMDR) at Hawaiʻi Pacific University, presented the findings at the spring meeting of the American Chemical Society (ACS).

"This work investigates whether it's responsible to use recycled plastics in Hawaii's roads," shares Axworthy. "By reusing plastic waste that is already in Hawaii, we can reduce the environmental and economic impacts of transporting waste plastics from the islands, incinerating it or dumping it in Hawaii's overflowing landfills."

Why Hawaii Is Testing Recycled Plastic Roads

Since 2020, most roads in Hawaii have been built using polymer-modified asphalt (PMA), which is designed to improve strength and durability. Compared with conventional asphalt, PMA is more flexible and better able to resist cracking, rutting, and water damage, making it well suited to Hawaii's tropical climate.

To make PMA, pellets of styrene-butadiene-styrene (SBS; a type of copolymer) are melted into a sticky petroleum-based asphalt binder. That binder is then mixed with heated aggregates (rocks and sand), coating the material before it is laid as pavement.

Researchers wondered whether some of the virgin polymer could be replaced with discarded plastics. They also wanted to know whether roads made with recycled plastics would perform well and whether they might release microplastics or other chemicals into the environment. Those questions led the Hawaii Department of Transportation (HDOT) to partner with environmental chemist Jennifer Lynch, director of CMDR and leader of the research team.

Recycling Fishing Nets Into Asphalt

HDOT asked Lynch's team to tackle two key tasks. The first was to supply abandoned fishing nets collected from Hawaii's waters for use in experimental recycled plastic asphalt.

"Foreign plastic derelict fishing gear is the largest contributor of Hawaii's marine debris problem," shares Lynch. "To date, CMDR's Bounty Project, which pays a financial reward to licensed commercial fishers for marine debris removal, has removed 84 tons of large, derelict fishing gear from the Pacific Ocean."

The second goal was to determine whether pavement made with recycled plastic released more microplastics than standard SBS-modified asphalt.

"CMDR's laboratory is equipped with state-of-the-art chemical instrumentation for quantifying and characterizing microplastics in environmental samples," explains Lynch. "This capability is incredibly unique and impactful, especially when coupled to our marine debris-removal project and our mission to recycle the debris into long-term, locally necessary infrastructure products."

After a U.S. company processed the recovered plastics into materials suitable for asphalt production, HDOT moved the project into the real world. A local paving company resurfaced sections of a residential street on Oahu using three different asphalt mixtures: one with standard SBS, one containing recycled polyethylene from Honolulu's residential recycling program, and one made with polyethylene recovered from discarded fishing nets.

About 11 months later, Lynch's team returned to collect road dust from each section so they could measure any microplastic released into the surrounding environment.

Measuring Microplastic Shedding

The scientists separated different types of polymers from the road dust, including microplastics, larger plastic fragments, and tire rubber. They then used pyrolysis gas chromatography-mass spectrometry (Py-GC-MS) to determine where the materials came from. The analysis identified styrene and butadiene from standard PMA, polyethylene from recycled plastic and fishing net pavements, and isoprene and butadiene rubber from vehicle tires.

Early findings showed that pavement containing recycled polyethylene did not release more polymers than conventional SBS pavement. The same pattern appeared in laboratory performance testing and in simulated stormwater collected from the experimental road sections.

Although researchers detected microplastic-sized particles, only a very small number were identified as polyethylene, regardless of which pavement type they came from. The researchers believe this is because the plastic becomes blended into the asphalt binder. As the road wears over time, the particles that break away are made up of rock, asphalt binder, and polymer together rather than plastic by itself.

The team is also comparing polymer release from the pavement with the amount of tire material found in road dust.

"In our initial Py-GC-MS data," continues Lynch, "we saw tire wear swamps the signal of polyethylene by orders of magnitude, like gigantic peaks! We had to search the weeds of the chromatogram to find signs of polyethylene."

A Possible New Future for Plastic Waste

More testing is still needed to evaluate how well these recycled plastic roads hold up over the long term. Even so, the researchers believe the approach could eventually reduce both landfill waste and marine debris across Hawaii.

"Some people think plastic recycling is a hoax -- that it doesn't work; it's too challenging," Lynch shares. "But this work demonstrates that recycling can work when society prioritizes sustainability."

The research was funded by the Hawaii Department of Transportation.

Meeting

ACS Spring 2026

Title

Harvesting ocean plastics to pave hawaiian roads: Evaluation of microplastic and plastic additive release from asphalt incorporating recycled plastic from various waste streams

Abstract

Polymer modified asphalt (PMA) is used to increase strength and durability of roads. In Hawaii, PMA is typically produced using the virgin co-polymer styrene-butadiene-styrene (SBS). Recycled plastics, such as high-density polyethylene (HDPE), may also be added to asphalt serving to sequester plastic waste. In the state of Hawaii, derelict fishing gear (DFG) is a significant problem, yet it is also a source of HDPE that can be used in recycling. However, asphalt performance and the consequences of adding recycled polymers to asphalt are not well understood. In collaboration with the Hawaii Department of Transportation (HDOT) and the University of Hawaii (UH), the Center for Marine Debris Research (CMDR) are testing the feasibility of using recycled HDPE in asphalt by quantifying microplastics and plastic additives release from roads paved with asphalts made from different combinations of virgin and recycled polymers. The specific asphalt combinations being tested are: SBS (Control-PMA), DFG with and without SBS (DFG-PMA and DFG-neat), Local Waste recycled HDPE with and without SBS (LW-PMA and LW-neat), and Commercially Available, post-industrial recycled HDPE with and without SBS (CA-PMA and CA-neat). Microplastic and plastic additive release under laboratory conditions were performed using a Hamburg Wheel Tracker Test (HWTT) with water sample analyses. Field trials were conducted on a residential road on the island of Oahu, Hawaii. Road dust was swept and analyzed for microplastics by direct analysis and solvent extraction to separate bound plastic from asphalt and plastic additives by water extraction. Microplastic samples utilized pyrolysis gas chromatography mass spectrometry for analysis. Plastic additives are subjected to solid phase extraction with analysis by gas chromatography mass spectrometry. Results produced using these novel analytical methods provide guidance on the use of recycled plastics over virgin plastics in roadways. Moreover, results of this study may provide a viable end of life fate for plastic marine debris, leading to cleaner and healthier oceans.