Since the 80’s, there has been an increase in the amount of plastics entering our oceans. However, when researchers tried to map out the ocean garbage, they found a smaller amount than they expected. On a study published on 30th June in the journal Proceedings of The National Academy of Sciences, researchers said that "These studies suggest that surface waters are not the final destination for buoyant plastic debris in the ocean." Where then could this plastic be going? Plastics that get into the ocean often get broken down by waves and the sun into small particles of about 1 centimeter or less. Scientists therefore expected to find many tiny pieces of around 1 millimeter or less, but most samples taken didn't have them. They are not sure as to where the plastic is disappearing to, but they have some theories on the same:
1. Shore deposition
One of the theories is that the plastics could be washed ashore.
The theory however is problematic since it’s unlikely that smaller things alone only would wash ashore. “A selective washing ashore of the millimeter-sized fragments trapped in central areas of the open ocean is unlikely,” the report says.
2. Nanofragmentation
This is the theory that the small pieces of plastics could be undergoing degradation continuously hence making them smaller and undetectable.
The problem with this theory however is that, the sun contributes to the degradation of the plastics and although this continually happens, no reason yet has been found to show that degradation has increased since the 80’s. Plastics would only be broken down further if planktons or some sort of bacteria evolved to do it, or did it naturally. In fact, research has been done to back this up: “Recent scanning electron micrographs of the surface of microplastic particles showed indications that oceanic bacterial populations may be contributing to their degradation, potentially intervening in the fragmentation dynamics.”
3. Biofouling
There are some non-parasitic plants that grow on other plants and oceanic epiphytes could be latching on the plastic as it floats. This could lead to the plastics sinking since as the organisms continue accumulating on the plastic, they make it heavy.
This could be possible except for the fact that, previous studies done show that when a plastic with a plant growing on it sinks in the ocean, the parasitic plant dies and falls off. This causes the plastic to pop back up.
4. Ingestion
The scientists consider this the most likely scenario. The ocean has tiny animals known as Zooplankton that are the size of the missing plastic. Fish that feed on these animals may mistake the plastics for food. These fish live in depths of between 200 and 1000 feet deep and migrate to the surface when they need to feed and this is where the plastic is. According to the researchers, if the plastics are consumed, they can stay in the fish’s stomach for a day or an year. They get ingested and removed as poop that sinks quickly. “The plastic fragments ingested by small fish can be transferred to larger predators, sink with the bodies of dead fish, or be defecated. Gut content of mesopelagic fish is evacuated as long viscous feces that assume spheroid shapes while sinking at high velocities (around 1,000 m⋅d−1). Hence, microplastic fragments could also reach the bottom via defecation, a proposition that requires further quantitative testing.”
The answer to where these plastics are disappearing to could lie maybe in a combination of these four scenarios. If we ever want to clean up our oceans, we have to find the reason plastics are disappearing fast.
What scenario do you think is causing the plastic disappearance in our oceans?
