Hawaii turns ocean plastic into roads to fight pollution

In Hawaii, researchers are literally paving the roads with good intentions. They have developed an innovative method to combat the island’s plastic pollution, by covering its roads with asphalt mixed with plastic waste and old fishing nets.

While plastic paving initiatives are happening in places like Missouri And Texasthe Hawaii project is the first to use marine debris. It is designed to address the islands’ unique exposure to abandoned fishing gear, tourist waste and Great Pacific Garbage Patchwhich engulfs the island chain every few years. To date, 90 tons of plastic waste have been removed from the Pacific Ocean and more than a ton of fishing nets have been placed on Hawaiian roads.

A key question is whether wear and tear on this pavement could release microplastics into the environment. Preliminary results show that the asphalt remains largely intact, the researchers reported March 22 at the American Chemical Society meeting in Atlanta.

“We are extremely concerned about the release of plastics or other chemicals into the environment,” because this can expose humans and animals to toxic plastic additives, leading to hormonal disruptions, chronic inflammation and reproductive problems, says chemist Jennifer Lynch. She directs the Marine Debris Research Center at Hawaii Pacific University in Honolulu.

The center manages the Road Nets Program in which marine biologist Mafalda de Freitas and her colleagues collect and sort marine debris and plastic picked up on beaches, selecting waste made from a durable plastic called polyethylene found in milk jugs, yogurt containers and fishing nets.

The waste and nets are sent to the mainland United States, where they are shredded and ground, then returned to an Oahu-based pavement production plant, where they are mixed with other ingredients to make asphalt. The hot mixture is loaded onto trucks and used to pave a length of road on Ewa Beach, in the southwest of the island, Lynch says.

In the first phase of research in 2022, three experimental pavement strips were laid: A section with a mixture of traditional asphalt and a rubber called styrene-butadiene-styrene, which adds durability and flexibility to the mixture; another with crushed marine waste and rubber; and a third with waste and asphalt without the rubber.

Eleven months later, researchers collected road samples to test for microplastic leaching. “We want to empirically test [leaching] before it can be expanded,” says Lynch.

The team used various methods to simulate how microplastics would normally be released into the ecosystem, such as mimicking stormwater by dumping multi-filtered and disinfected water onto the road, then testing it for individual plastic polymers and sweeping the roads to collect gravel dust to look for polymers.

There was no significant release of microplastics compared to the plastic-free road strip mixed with the asphalt, says Jeremy Axworthy, a marine biologist and laboratory director who worked on the CMDR program and presented the results at the meeting.

Researchers began a second phase of the program in 2024, with five experimental road strips. The first strip was paved with ground fishing nets and styrene-butadiene-styrene rubber. Another part was covered with plastic from consumer waste and the same rubber, and the third contained a mixture of traditional asphalt and rubber, again the experimental control. A fourth contained fishing nets but no rubber, and a fifth used plastic waste but no rubber.

The team is now using an industrial solvent called dichlorobenzene to extract plastic polymers from the mixed dust to more precisely quantify the amount released. These results are forthcoming.

Bill Buttlar, director of the Mizzou Asphalt Pavement and Innovation Lab at the University of Missouri in Columbia, says he is impressed with the program, but notes that the road performance challenges in Hawaii are different from those in the mainland United States. The tropical climate, with its heavy rains and volcanism, faces underground volatility, and when the ground is constantly moving, it can cause cracks in the roads.

“The main challenge in implementing this project is finding the right recipe with asphalt, because what works in Hawaii may be a little different than what works in the Midwest,” says Buttlar.