//
you're reading...

Pollution

Are biodegradable plastics too good to be true? Here’s what actually happens to them in the ocean

Reviewing: Lott, Christian, et al. “Half-life of biodegradable plastics in the marine environment depends on material, habitat, and climate zone.” Frontiers in Marine Science 8 (2021): 426. https://doi.org/10.3389/fmars.2021.662074

 

“Biodegradable plastics are better for the environment!” You might have heard this a lot, but is this true?

Biodegradable plastic is a type of plastic designed to be broken down completely into water and compost by microbes. And they are becoming a popular alternative to regular plastic .Throwing away a biodegradable food container or a coffee cup into your trash feels almost comforting – they will break down quickly and won’t stay forever in the environment, right? What is not widely marketed is that biodegradable plastic can only be disintegrated under the “right” conditions. These plastics actually need to be in the right temperature, humidity and oxygen level for bacteria to feed on them. Would the ocean be considered the “right” environment for biodegradable plastic to be degraded? A group of scientists decided to answer this question by testing how long biodegradable plastic last in different parts of the ocean.

A vegetable container made of biodegradable plastic (Wikimedia Commons)

A biodegradable plastic cup made from corn starch (Flickr)

 

 

 

 

 

 

 

 

 

Putting biodegradable and regular plastic in the ocean

Lott and colleagues compared how quickly biodegradable plastic broke down relative to regular plastic, by comparing a biodegradable plastic material (polyhydroxybutyrate) to two other common plastic materials (polybutylene sebacate and polybutylene sebacate co-terephthalate) in three different ocean environments – beach, seafloor and open water.

For the “beach test”, the team filled huge 60-liter plastic bins with sediments from a beach at Island of Elba, Italy. They then put film made from either biodegradable or regular plastic on top, and put the bins in the ocean. The “seafloor test” was conducted in both the Mediterranean (Tuscan Archipelago, Italy) and Southeast Asia (Sahaong Bay, Indonesia), where plastic films were put on a flat panel fixed to the seafloor. Finally, the “open water test” took place at the Mediterranean Sea, where plastic samples were attached to an anchored frame at a depth of 20 meters.

To determine how much plastic was degraded in the different ocean conditions, the scientists measured how much the total plastic film area decreased. They then put these measurements into a statistical model to calculate the half-life of plastic (the time that it had taken for the plastic film to lose half of its area). Why half the area? Comparing the half-life of different plastic materials is better than comparing how much plastic was left after the experiment, because plastic does not break down at the same speed over time. Let’s say a piece of plastic in the ocean completely breaks down and disappears after 100 days. It is very unlikely that a hundredth of plastic disappeared every day. Instead, plastic may disappear more quickly over the first 50 days, when microbes are starting to break it down and feed on it, but as the more easily degradable material gets consumed first by microbes, the remaining piece will take longer to disappear.

Left: “beach test” setting, where plastic films were on top of sand-filled bins and put in a rack on the Island of Elba; center: “open water test” setting, where plastic films were put on a rack at 20m-deep water in the Mediterranean sea; right: “seafloor test” setting, where plastic films were fixed to the sandy seafloor on both the Mediterranean Sea and Southeast Asia (Lott et al. 2021)

Biodegradable plastic breaks down faster than plastic, but still takes a long time to break down

The test results showed that biodegradable plastic films degrade faster than regular plastic films on the beach and at the seafloor. The half-life of biodegradable plastic film on the beach was 14 months, which was much shorter than the two types of plastic (23 and 40 months each). Similarly, the half-life of biodegradable plastic at the seafloor of the Mediterranean Sea was 22 months, again much shorter than regular plastic (27 and 47 months each). In contrast, the half-lives of biodegradable plastic and the two other plastic types at the seafloor in Southeast Asia were 2, 7 and 4 months. Because microbes that break down plastic are much more active at higher temperatures, they degraded plastic faster in the tropical waters in Southeast Asia (28.5°C) than in the Mediterranean Sea (17.5°C).

However, both biodegradable and regular plastic films barely broke down at all in the open Mediterranean waters, even though the scientists monitored them for almost 2 years. Because there isn’t much microbial activity going on in the open waters, even biodegradable plastic didn’t break down over 2 years.

Plastic litter on the beach (Flickr)

Takeaway? Biodegradable plastic may not be “biodegradable”.

Even though biodegradable plastic breaks down faster than plastic, it will still stay in the environment for a long time. The term “biodegradable” can be quite misleading, because the biodegradability of plastic depends so much more on which environment it is in. So the next time you buy a biodegradable plastic bag, consider how really “biodegradable” and “environmental-friendly” that bag is.

 

 

 

Discussion

No comments yet.

Post a Comment

Instagram

  • by oceanbites 2 months ago
    Happy Earth Day! Take some time today to do something for the planet and appreciate the ocean, which covers 71% of the Earth’s surface.  #EarthDay   #OceanAppreciation   #Oceanbites   #CoastalVibes   #CoastalRI 
  • by oceanbites 3 months ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 4 months ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 5 months ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 7 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 8 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 9 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 9 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 9 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 10 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 11 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 11 months ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
WP2Social Auto Publish Powered By : XYZScripts.com