Light as a feather and seemingly ubiquitous, plastic drinking straws tip the scales as environmental villains — clogging landfills, choking marine life and lasting for years.
In the face of local restrictions on single-use plastic items, some companies are manufacturing straws marketed as biodegradable and environmentally friendly.
But are they really?
The life cycle of a ‘green’ straw
Northeastern University researcher Bryan James and colleagues at the Woods Hole Oceanographic Institution on Cape Cod put 13 drinking straws made from paper, bioplastics, oyster shell fillers and other materials to the test.
“The study looked into how circular, sustainable and persistent they were,” says James, an assistant professor of chemical engineering.
“An example of a non-circular material would be one made using oil and disposed of in landfill, removing the material from being used again,” he says, such as traditional polypropylene straws that may persist for years.
Bryan James assistant professor of chemical and engineering, found straws with oyster shell and agave fiber fillers also contained polluting polypropylene. Photo by Matthew Modoono/Northeastern University
What the team found may surprise you.
Not only did James and his colleagues discover evidence of “green washing,” it turned out a straw originally derived from captured methane, a potent greenhouse gas, had the least impact on the environment.
“It was the lightest and made out of a marine degradable material that had the thinnest wall,” James says.
An earth-friendly straw derived from a greenhouse gas
It was a classic example of circularity in action, he says.
Producing the straw required taking the pollutant methane, a gas with 28 times the global warming potential as carbon dioxide, out of the atmosphere by capturing it at the source of human-based activity, such as landfill emissions.
Microbes that feed on methane then produce the bioplastic material (polyhydroxyalkanoates or PHAs) that make up the drinking straw, which can be composted, being food for microbes in the soil, completing the circle, James says.
The methane-derived straw also biodegraded more rapidly than many other straws in the testing phase at WHOI’s Environmental Systems Laboratory on Cape Cod.
Bryan James, assistant professor of chemical engineering, says paper straws take 10 to 100 times more water to produce than drinking straws made out of bioplastics. Photo by Matthew Modoono/Northeastern University
The seawater flow test
That’s where the 13 different straws were exposed to a continuous flow of seawater from nearby Martha’s Vineyard Sound to see how long they persisted.
The straws are cut into one-inch sections and threaded onto cords that sway in specially built tubs.
“Seawater is pumped over the samples 24/7,” says Collin Ward, an associate scientist at WHOI who collaborated on the paper. At different time points, researchers fish out the samples to examine them for signs of degradation.
Unlike traditional biodegradation tests, which rely on putting samples in bottles, the continuous flow system designed by James and his colleagues at WHOI is designed to mimic a natural marine environment.
When the only food source in a long-term bottle incubation is the plastic sample, starving microbes might feast on the sample at a faster rate than they would in flowing seawater with more nutrients.
“Our dynamic testing system affords realistic estimates of the lifetime of a consumer good in the ocean,” Ward says. It also provides critical information needed to design straws for maximum degradability or to draft regulations to restrict the proliferation of imperishable straws.
Not-so ‘green’ drinking straws
As quickly as the methane-derived straw was able to biodegrade, paper straws are faster to break down, James says. But they have similar estimated lifetimes of one to two years because the paper straw used more material than the methane-derived straw.
He says the scientific team — made up of engineers and environmental scientists — gave the paper product a lower score when it came to sustainability because paper takes 10 to 100 times more water to produce than bioplastics.
“As freshwater resources become more limited, either regionally or globally, it becomes another impact that needs to be considered,” James says.
The researchers also found that straws advertised as nature-based due to fillers such as oyster shells or agave fibers contained a polypropylene material that did not degrade, he says.
Some straws are colored green or an earthy brown tone designed to suit a green sensibility, James says.
But while many drinking straws are certified as compostable and claim to be biodegradable, “few present evidence for their degradation in the marine environment where they are ubiquitous pollution,” the researchers say.
If you have to use a disposable drinking straw, pick the lightest one made from bioplastic and dispose of it appropriately in the compost heap, James says.
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