In a fish-eat-fish world, microplastic is a perplexing problem. These puny plastic particles are consumed by small fish, which are then eaten by larger fish—passing the pollutant up the food chain, eventually to humans.
Scientists know that many microplastics come from the massive modern use of plastic packaging, which breaks down into the small specks swallowed at sea. One source not previously considered is synthetic rope used by many maritime vessels, including fishing boats.
Turns out, it contributes a “substantial amount of microplastic contamination” to the environment, report researchers with the International Marine Litter Research Unit at University of Plymouth in England. Published in the peer-reviewed journal Science of the Total Environment, a new study shows that aging ropes and nets made from plastics are a significant source of this pollution, reports Ben Coxworth of New Atlas.
Researchers discovered that new and one-year-old synthetic ropes can release around 20 microplastic fragments for every yard hauled in the ocean—and that number climbs exponentially with older equipment. Two-year-old ropes emit 720 fragments per yard while ten-year-old tethers can shed 760 units per yard, reports Technology Networks.
According to the report, fishing vessels use around 220 yards of rope during a typical haul. Based on a conservative 50-yard line, researchers estimate that new rope can release up to 2,000 microplastic fragments each time while old rope could reach levels of 40,000 units.
“For centuries, most everyday items including rope and netting used in the maritime industry was produced using natural resources,” says study co-author Richard Thompson, a professor at the University of Plymouth, in a statement. “However, the large-scale increase in plastic production since the 1950s has resulted in plastics progressively replacing their natural counterparts. The durability of plastic has however resulted in a major environmental challenge once items reach the end of their lifetime or, as in this study, when they shed microplastics.”
For the study, researchers conducted lab-based simulations and field experiments. Estimates were based on hauling a 5.5-pound weight on a 50-yard rope. Lead scientist Imogen Napper, a postdoctoral researcher at the university, cautioned that these figures are considerably less than what would be used on real fishing vessels.
“Most maritime activities would be hauling much heavier loads, creating more friction and potentially more fragments,” she says in a statement. “It highlights the pressing need for standards on rope maintenance, replacement and recycling in the maritime industry. However, it also shows the importance of continued innovation in synthetic rope design with the specific aim to reduce microplastic emissions.”
Researchers used the United Kingdom fishing fleet of about 4,500 active vessels as a basis for this study. Based on that total, they estimate that 326 million to 17 billion microplastic pieces could be entering the ocean annually from just this source, according to a University of Plymouth press release.
“Greater appreciation of the issues within wider society are starting to make a difference,” Thompson concludes in the statement. “However, this study emphasizes a previously unquantified yet substantive source of microplastics and reinforces the level of collaboration required to achieve lasting and positive change.”