Support the news

Those Plastic Stats Are Trash. No One Knows How Long It Takes For Your Dunks Cup To Biodegrade

In this Aug. 13, 2015, file photo, a plastic bottle lies among other debris washed ashore on the Indian Ocean beach in Uswetakeiyawa, north of Colombo, Sri Lanka. (Gemunu Amarasinghe/AP)

If you chuck a Styrofoam cup or a plastic bottle into the woods or the ocean — not that you would ever do such a thing — how long before it disintegrates? Fifty years? 500? Forever?

Turns out, there appears to be no scientific evidence for any of those estimates. That’s what two scientists at the Woods Hole Oceanographic Institution found out when they investigated the various "environmental lifetimes" of plastics reported in widely-used infographics.

The scientists, Collin Ward and Christopher Reddy, looked at 57 different infographics published by government agencies, nonprofits, academic institutions and other groups, from 13 countries and in four languages.

"When we hunted down and checked every one of these values for how long a piece of plastic may live, from 57 different posters and infographics, we could not find a citable or credible source that supported those graphics. Not one," Reddy says. "We were astonished."

Their results were published in the Proceedings of the National Academies of Sciences in June.

"When we hunted down and checked every one of these values for how long a piece of plastic may live, from 57 different posters and infographics, we could not find a citable or credible source that supported those graphics. Not one."

The scientists began their investigation as an outgrowth of their own lab work — both Ward and Reddy are chemists who study how plastics break down in the environment. It's an important question, says Reddy, because emerging evidence indicates that different types of plastic may break down much faster or slower under different environmental conditions — if they are in sunlight or darkness, for instance, or exposed to certain types of bacteria.

Ward wanted to check his lab findings against existing data, but couldn't find any. What he found instead were posters and infographics offering a wide range of estimates.

"The numbers are all over the place," Reddy says. "You know, a Styrofoam cup is 50 years to thousands of years."

Some of the posters and infographics cited a source — often the National Oceanic and Atmospheric Administration (NOAA) — but many did not. The lack of data puzzled the scientists, so they performed a literature search, enlisted the help of a research librarian, and reached out to program directors at NOAA to track down the science behind the numbers. They found none.

"I'm really impressed at how far they dug to try to find the basis of some of these claims," says Kara Lavender Law, a research professor of oceanography at the Sea Education Association, and an expert on plastic pollution in the ocean. Law says she thinks the infographics were a well-intentioned effort at public communication.

"We want people to think about what it means if a piece of plastic is sitting on the street, or on the beach, or in the ocean, and how it's really likely that it's going to be there a very long time," Law says. "But we now need to try to do some real science to get good numbers on that."

Both Law and Reddy emphasize the lack of data is not a license to pollute – scientists have found plastic in the ocean that’s decades old, so we know it can last a long time. Humans dump an estimated 4.8 to 12.7 million metric tons of plastic into the ocean each year, and scientists have raised concerns about the health effects of microplastics in the sea and air.

Plastic particles and filaments collected in a 1995 Atlantic Ocean tow. (Robin Lubbock/WBUR)

But Reddy says that dealing with plastic pollution will mean getting some hard numbers on how long it sticks around in different environments, what makes it disintegrate, and what it actually becomes when it breaks down.

This paper is "not a free pass for people to throw plastic out the door," Reddy says. "It's just moving the field forward so that we can make the most well-informed decisions."

More from WBUR