It is commonly reported that it takes 450-years for a common plastic bottle to decompose in the ocean. No more, no less, 450. A quick search online returns ample evidence for this. Skipping over the problems of giving such an exact figure instead of a range, where does this figure come from?
The figure is relatively 'famous' in its popularity in mainstream media. See The Longest Live Stream Ever from the WWF that highlights the acceptance of the figure.
It can be found in other places too, many of which I consider to be reputable, and often conducting fact checks themselves. However, cited sources have not been verified, merely copied from the previous instance of the figure being used.
So let's have a dig ...
The Wikipedia article on Marine Debris has the below image in the section on Mitigation note the source: Data from NOAA.
For reference, NOAA is the National Oceanic and Atmospheric Administration (USA).
The website Statista has an article titled Plastic Can Take 500 Years To Bio-Degrade In The Ocean with the same figure and NOAA attributed once again, plus the Woods Hole Sea Grant. Thankfully, they also had the thoughtfulness to state that the exact time will vary by product type and marine conditions, good job!
OurWorldinData have a page titled FAQs on Plastic, and in the section How long does it take plastics to break down? we see the same figure, and the same source, with the addition of the US National Park Service and the Mote Marine lab.
Under the Sources tab for the image they link to their source from the New Hampshire Department of Environmental Services. The link is dead, all that appears is "Page Not Found". I contacted OurWorldinData regarding this issue but they did not get back to me. Their sources remained unchanged as of October 2022.
I also reached out to NHDoES, who did respond, stating:
"New Hampshire Department of Environmental Services has no records responsive to your request. The fact sheet which once existed at the web link you provided has been retired by the Department and we no longer maintain, control, or possess the document. We partner with the Blue Ocean Society (blueoceansociety.org) and refer you to their resources to assist with your research. Also, you may find helpful information on our website at https://www.des.nh.gov/water/healthy-swimming/clean-beaches or the University of New Hampshire Sea Grant College Program at https://seagrant.unh.edu."
Unfortunately the further links were not helpful and returned no evidence for the figure.
Returning to NOAA and the Woods Hole Sea Grant (of the Woods Hole Oceanographic Institution or WHOI) a poster can be found online, the weblink is still active and working as of October 2022. The sources are somewhat self-citing, but there is also a link to the designer, LianneDunn.com, on first search the website was last copyright in 2012, though it now returns a 404.
I reached out the the Woods Hole Oceanographic Institute and NOAA to help me understand where the figure came from, what is the scientific basis?
I was contacted by Collin Ward (Assistant Scientist), Jeffrey Brodeur (Communications and Outrearch Specialist), and Matt Charette, Senior Scientist and Director of the Woods Hole Sea Grant. Below are the replies in chronological order.
From Jeffrey:
"Thanks for reaching out about our poster, for which there are several versions as you have found through your online research. The degradation values originated from a poster created by the South Carolina Department of Health and Environmental Control as part of a NOAA funded project. These numbers have also been attributed to a 2005 poster from the Mote Marine Lab, as it appears you’ve discovered as well.
In recent years, we have strived to stay away from using decomposition rates for marine debris items, especially plastics. There are many types of plastics that all have different chemical compositions, molecular weights, and additives. The decomposition rates of plastics can vary based on these factors and environmental conditions, and it is possible that they never fully go away."
From Collin:
"The oldest references I found date back to a 1993 Mote Marine Lab poster sold in the gift shop and designed by volunteers. The items on their poster (the one's discussed in the PNAS piece) are different than those on this poster. I suspect the volunteers may have been motivated by this graphic (or one's like it at the time), but I still can't figure out where they got their data from. I've talked to lots of retired librarians at Mote Marine Lab. They have no records of data being generated on this topic in their archives. It's kind of a wild story.. "
From Matt:
"As Jeffrey stated, a poster was developed many years ago as part of an educational initiative on marine debris. We since learned that much of the decomposition rate data was not based on peer-reviewed science. While we no longer endorse its use or distribute paper copies of the poster, it lives online in various places (difficult to remove - but we can certainly do so for the version you found on one of our servers)."
As of October 2022, the WHOI weblink is still active. Similar investigation by Collin Ward and team on such figures was publised in June 2020. Chris Reddy (also of WHOI) states in the linked article:
"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."
In such a case, the degradant products of (micro)plastics will of course not be found.
To summarise:
The organisation strives to stay away from decomposition rates due to the complexity of the topic,
The oldest references they had found do not match and it could not be determined how they gathered the data,
No records exist of the data,
It is not based on peer-reviewed science.
This leaves the figure wildly open to speculation as to its validity. In fact, Jennifer Kennedy, Executive Director of the Blue Ocean Society for Marine Conservation got back to me about this issue to:
"Thanks for your inquiry. I believe we used to have that statistic on our web page, but took it down after not finding a great reference for it ourselves. So I don’t have a good answer for you, I’m sorry! I’m CC’ing my colleague at Woods Hole Sea Grant, Jeffrey Brodeur. They published a poster with this information several years ago, I’m not sure if he might provide a more reliable source for you. Please let me know if you do find out!"
Unfortunately, I have not found out and at this rate I do not believe I will. Regardless, I did continue searching and found the 450-year figure cropped up elsewhere. Specifically in A-Way with Waste. A Waste Management Curriculum for Schools (2nd ed.) from July 1985, written by Todd Peterson and others, published by the Washington State Department of Ecology Litter Control & Recycling Program. To correctly cite, as per textual guidance:
"This material borrowed from A-Way With Waste curriculum guide. A
program of the Washington State Department of Ecology."
Here is an image excerpt from the text entitled Enduring Litter.
Note the source, the Book of Lists 2. This refers to The People's Almanac Presents The Book of Lists #2 by Irving Wallace, David Wallechinsky, Amy Wallace, Sylvia Wallace, published November 1981 by Bantam books. I bought the book and here is the source:
I'd like to specifically highlight here the recognition that degradation varies on a great many factors but also these are:
"calculated estimates based on average degradation environments."
This raises a number of questions:
Where are the calculations?
How were they calculated?
What are the average environments?
What are the average degradation environments?
How were they averaged?
Unfortunately Irving Wallace, Amy Wallace, Sylvia Wallace have all passed, but David Wallechinsky is still alive. I contacted the publisher and David (via their website: allgov.com) but no-one got back to me.
The trail went cold. It seems this figure has been living in perpetuity unsourced and will likely remain so.
Now ...
It's all well and good to bring the 450-year figure into disrepute, but what's the point? Does it matter if it takes 451-years, or 449? No. Absolutely not. The point is not that it does not matter that we are littering the oceans with our waste, because that matters deeply. The lack of scientific credibility, however, to such common claims made in the media and the pervasiveness they can have on societal thought and beliefs is of concern. Tackling such issues becomes a convoluted web of inaccuracies that diminish our ability to target a problem adequately if we are using poor data. Or, perhaps more worryingly if using the correct data, to convince the general public of this if they believe something else. Issues with waste management and disposal will stick with us for a long time and, in my opinion, ultimately a systemic change is the only way to fix it.
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