Due to Hawaii’s economic and logistical challenges in recycling plastic waste, such as marine debris lingering in its ocean waters, researchers have been pioneering a method for recycling this waste (e.g. derelict fishing nets, discarded fishing gear, tourist waste, the Great Pacific Garbage Patch, and residential plastic trash) by covering roads with an asphalt-plastic mix. While places such as Missouri and Texas have both already introduced plastic-paving initiatives, Hawaii is the first to use marine debris in the effort. Already, more than 90 tons of plastic trash have been removed from the Pacific Ocean, with more than a metric ton of fishing nets alone being repurposed in this endeavor.
To move forward with plans, the Hawaii Department of Transportation (HDOT) reached out to environmental chemist Jennifer Lynch (director at the Center for Marine Debris Research or CMDR) with two requests: provide derelict fishing nets to be recycled in these modified pavements, and measure potential microplastic shedding from said pavements in comparison to roads modified with SBS (a type of copolymer) that had been mostly used since 2020 to increase strength and durability in the tropical climate.
In fact, one of the key questions in the introduction of these new roads was whether their wear and tear would shed microplastics into the environment, especially concerning the chance of exposing humans and animals to toxic plastic additives that may lead to several health drawbacks, such as hormone disruption, chronic inflammation, and reproductive problems. According to Lynch, “CMDR’s laboratory is equipped with state-of-the-art chemical instrumentation for quantifying and characterizing microplastics in environmental samples,” which has been put to full use during initial testing. Preliminary results have been promising, with the asphalt remaining largely intact, according to researchers who reported on March 22 at the American Chemical Society meeting in Atlanta.
The first phase of this research began in 2022, when three experimental pavement strips were laid: one of traditional asphalt and SBS, one of marine waste and rubber, and one of marine waste and asphalt without rubber. After 11 months, samples were collected and tested for microplastic leaching through a variety of ways simulating how microplastics are normally released into the ecosystem, revealing no significant microplastic release compared to the strip without plastic mixed in, according to marine biologist Jeremy Axworthy, a lab manager who worked on the program for CMDR. In fact, it was determined that polymers shed by tires far surpassed those from the pavement itself.
The second phase began in 2024, where five experimental strips were tested: one with ground fishing nets and SBS, one with plastic from consumer trash and SBS, one with traditional asphalt and SBS (the control), one with fishing nets and no SBS, and one with plastic waste and no SBS. This time, the team made use of an industrial solvent called dichlorobenzene in order to extract polymers from the mixed dust to more accurately quantify the release of microplastics from the roads. These results are still to come, as Lynch would say at the end of March, “we don’t have any findings yet from the road that contains the fishing nets,” though he recounted the promising results from phase one so far.
When reflecting on current progress, Lynch described how “some people think plastic recycling is a hoax — that it doesn’t work; it’s too challenging…But this work demonstrates that recycling can work when society prioritizes sustainability.”
