There is much less floating plastic at sea than can be expected. This is known as the mystery of the disappeared plastic. Where is that plastic? The degradation process now described goes some way to answering that question.
Reducing the plastic soup
Researchers associated with the Royal Netherlands Institute for Sea Research (NIOZ) exposed different types of plastic to ultraviolet (UV) rays. In their research published in the scientific journal Marine Pollution Bulletin, they estimate that 1.7% of the visible microplastics are broken down. In less than 44.4 years this amounts to half of the floating plastic. Much plastic has entered the ocean since the 1950s. We should have lost most of this plastic soup because of this mechanism. We should have lost 7% to 22% of the all the floating plastic in the ocean.
Invisible nanoplastics
Almost a quarter (22%) of all the floating plastic should have disappeared under the impact of the UV light. But the researchers point out that some of that disappeared plastic would consist of invisible nanoplastics that have unforeseen negative effects on sea life and ecosystems. The press release also states that some would be substances that could ‘Potentially … be broken down further by bacteria’. The wording suggests that no research has been carried out on whether the bacteria work in the middle of the ocean.
Other relevant mechanisms
There are other relevant mechanisms too. One is the sunlight that never reaches the plastic.
- Of all the plastic that enters the ocean, only a small percentage floats. This means that sunlight does not reach the plastic that suspends in the water column or lies on the seabed.
- Floating plastic sinks after a while as the accumulation of things like algae make it heavier. Another scientific article published in Environment Science and Technology last year concluded that since 2000, the number of microplastics at the bottom of the Mediterranean Sea has tripled, and that microplastics embedded in sediments do not break down.
Plastic disappears in other ways too. Waves and wind can push some of the microplastics and nanoplastics out of the water and into the air. It is then carried by the wind and deposited somewhere on land.
These are interesting pieces of research, but the question is whether that knowledge is useful. The plastic soup will never disappear. The only thing that will really help is to produce and use less plastic.
