Hawaii mixed recycled fishing nets into an Oahu road; 11 months later, researchers found no more polyethylene microplastics than in regular asphalt

Shipping waste off Hawaiʻi's islands is expensive, local landfills are running out of room, and Pacific currents keep depositing tons of derelict fishing gear onto the shoreline. Researchers at Hawaiʻi Pacific University tested whether washed-up plastic could be melted into asphalt and returned about 11 months later to test whether the road was shedding microplastics back into the environment.Derelict fishing gear becomes Hawaiʻi's largest marine debris problemJennifer Lynch, director of CMDR at Hawaiʻi Pacific University, says most debris in Hawaiian waters consists of fishing nets and fishing lines that drift in from elsewhere. Hawaiʻi has been adopting polymer-modified asphalt since around 2020 for its improved resistance to cracking, rutting and water damage in the state's tropical climate. That pavement is normally made by melting a virgin plastic copolymer into the asphalt binder before it is mixed with heated rock and sand.However, the Hawaiʻi Department of Transportation wondered if some of that virgin plastic could be replaced by recycled plastic, such as the abandoned fishing equipment that was being washed ashore on the beaches of the island state. The agency asked Lynch's group to supply fishing nets for the asphalt mix and to determine whether the asphalt would shed more microplastics than regular asphalt.CMDR's Bounty Project removes tons of fishing gear from the Pacific CMDR has implemented an initiative known as the Bounty Program, whereby commercial licensed fishermen are rewarded for retrieving lost fishing equipment, according to Hawaiʻi Pacific University’s announcement of the project. As of the study's presentation in March 2026, Hawaiʻi Pacific University reported the initiative had retrieved 84 tons of large fishing equipment from the Pacific. Science News separately reported a running total closer to 90 metric tons of plastic trash pulled from the ocean by that point, a discrepancy the two sources do not reconcile, and which may reflect a difference between short tons and metric tons rather than a factual error.After the nets and plastic collected through the Bounty Program were processed for use in asphalt, the Hawaiʻi Department of Transportation moved the experimental mixtures onto a real road. The local construction firm poured pavement of a residential road on the island of Oahu using various mixtures of asphalt: the control sample using regular copolymer, a mixture using recycled polyethylene gathered from recycling bins in Honolulu and a mixture using recycled polyethylene from fishing nets.Researchers return after 11 months to sample road dust for microplastics Instead of testing the pavement in the laboratory and calling it done, Lynch’s group let the road lie under normal traffic first. Around 11 months into the study, the researchers routinely swept up the road dust found in segments of asphalt pavement to see if the wear and tear had released microplastics into the dirt. In the laboratory, the dust was processed to extract different types of polymer material, including microplastics, larger plastic fragments and tire-wear rubber.The team was able to infer which source the polymers came from using pyrolysis gas chromatography mass spectrometry. The researchers traced styrene and butadiene to the standard pavement, polyethylene to the plastic-waste and fishing-net mixes, and isoprene and butadiene rubber to tire wear.Tire wear swamps the polyethylene signal in the test results The recycled polyethylene pavement did not lose more plastic than the control pavement in lab wear tests or in stormwater runoff samples. In the dust, microplastic-sized particles appeared no matter which pavement mix was tested, but very few of those particles were identified as polyethylene. The recycled plastic is melted directly into the asphalt binder, which means that anything that ultimately breaks loose can be a fused mass of rock, binder and polymer, rather than loose plastic. Lynch says it’s a difference from other additive technologies.The researchers initially had difficulty isolating the companion signal from the tire-wear noise. According to Lynch, the readings showed huge peaks, indicating that tire wear overwhelmed the polyethylene signal by orders of magnitude. The team had to pick through the chromatogram readings to see if they could find any signal from the recycled plastic at all.According to the American Chemical Society's press release on the study, more work is needed on long‑term durability. Researchers say conclusions do not answer every question about how the pavement holds up over years of use. But for a state running out of places to put its plastic waste, an 11-month road test that sheds no more microplastic than ordinary asphalt is a promising start.Catch the latest World News and Live updates. Download the TOI app.