The lifetime of plastic is misrepresented and not well understood

Plastic pollution is a global crisis that has been well-documented, and one of the biggest concerns is how long plastics persist in the environment. However, a new study suggests that we do not know nearly enough about the lifetime of plastics to sufficiently address the issue. 

Collin Ward is a marine chemist at the Woods Hole Oceanographic Institution (WHOI) and a member of the Microplastics Catalyst Program, a long-term research program on plastics in the ocean. He explained that getting a true read on how long it takes for plastic to break down in the environment is tricky business.

“Plastics are everywhere, but one of the most pressing questions is how long plastics last in the environment,” said Ward. “The environmental and human health risks associated with something that lasts one year in the environment, versus the same thing that lasts 500 years, are completely different.”

It is critical to understand more about the lifetime of plastics to support better consumer choices, to help experts assess associated health risks, and to inform legislators and new policies.

Ward collaborated with WHOI marine chemist Chris Reddy to analyze nearly 60 relevant documents from a variety of sources, including governmental agencies, non-profits, textbooks, and social media sites. The experts found that there was little consistency in the lifetime estimates of the most common plastic products, like plastic bags.

“The estimates being reported to the general public and legislators vary widely,” said Ward. “In some cases, they vary from one year to hundreds of years to forever.”

There were also some lifetime estimates that seemed to be too similar. Of particular interest, Ward noted, were the estimates for how long fishing line lasts in the ocean. He said that 37 different documents reported that fishing line has a lifetime of 600 years.

“Every single one said 600 years, it was incredible. I’m being a little tongue-in-cheek here, but we’re all more likely to win the lottery than 37 independent science studies arriving at the same answer of 600 years for fishing line to degrade in the environment.”

Furthermore, Ward could not find evidence that a single estimate was backed by a scientific study. Instead, the research was either funded or conducted by the agencies that published the documents. 

“The reality is that what the public and legislators know about the environmental persistence of plastic goods is often not based on solid science, despite the need for reliable information to form the foundation for a great many decisions, large and small,” wrote the study authors.

Last year, Ward and his team conducted a study which showed that polystyrene, which is widely used in a variety of products, may degrade in decades when exposed to sunlight. Prior to the study, it was believed that polystyrene persisted for thousands of years. 

The researchers used mass spectometry to investigate how environmental factors such as sunlight affect the chemical breakdown of the polystyrene, which is the first type of plastic found in the coastal ocean by WHOI scientists nearly fifty years ago.

According to Reddy, one of the biggest misconceptions surrounding the fate of plastics in the environment is that they simply break down into smaller bits that hang around forever.

“This is the narrative we see all the time in the press and social media, and it’s not a complete picture,” said Reddy. “But through our own research and collaborating with others, we’ve determined that in addition to plastics breaking down into smaller fragments, they also degrade partially into different chemicals, and they break down completely into CO2.” 

The chemical form of plastic would be overlooked in ocean surveys searching for missing plastics.

Chelsea Rochman, a biologist at the University of Toronto, noted that understanding the various forms of plastic degradation will be key to solving one of the enduring mysteries of plastic pollution: more than 99 percent of the plastic that should be detected in the ocean is missing.

“Researchers are beginning to talk about the global plastic cycle. A key part of this will be understanding the persistence of plastics in nature. We know they break down into smaller and smaller pieces, but truly understanding mechanisms and transformation products are key parts of the puzzle,” said says Rochman.

The WHOI analysis highlights the need for public information to be supported by scientific evidence.

“The question of environmental persistence of plastics is not going to be easy to answer,” said Ward. “But by bringing transparency to this environmental issue, we will help improve the quality of information available to all stakeholders – consumers, scientists, and legislators – to make informed, sustainable decisions.”

The study is published in the journal Proceedings of the National Academy of Sciences.

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By Chrissy Sexton, Earth.com Staff Writer