The increasing amount of plastic wastes in the ocean does not only seem to kill larger animals in the ocean like whales but also affects and even kill one of the sources of oxygen in the world: the bacteria Prochorococcus. The toxic materials being leached into the seawater constrain the growth and photosynthetic activity of the said bacteria which is responsible for the 20% of the oxygen we breathe and carbon capture.
Prochorococcus is a cyanobacterium found in the ocean and just like plants it makes its own food by undergoing photosynthesis, taking in carbon dioxide and releasing oxygen. The scientist had found out that the said bacteria are not only taking in carbon but also plastic toxins which leached into the water and is known as leachates.
Researchers conducted their study by growing Prochorococcus in an artificial seawater base containing different amount of plastics and comparing it with a control of Prochorococcus grow in untainted artificial sea water. Base on the result, as the concentration of leachate, increases the bacteria's cells don't grow hence causing death. "When the plastics leachates increase in concentration, you see that the cells don't grow as well, and in fact, at the highest concentrations they are dying," said Lisa Moore of Macquarie University in Australia, a co-author on the paper.
Furthermore, it also affects the bacteria's photosynthetic activity which they tested at different concentration using equipment that looks at the intensity of the cell's fluorescence. "We saw parallels to what we saw with the growth: a decrease in photosynthetic efficiency and, in fact, a pretty dramatic decrease with the higher concentrations," Moore said. The obtained result was confirmed by another experiment they conducted, wherein they looked at the genes of the bacterial population to see whether they were being expressed more or less in the leachates presence. The result showed that a large portion of it was observed to be expressed less and is associated with photosynthesis and therefore verifies the results in the first experiment.
Even though the study shows significant results, it is not relevant enough to be endorse given the fact that the work was done in the laboratory hence the amount or concentration of artificial seawater was controlled. "That's a limitation, trying to equate what concentrations we did in the lab versus what's in the oceans," said Moore. "So what we were at least trying to estimate in the article were the number of particles that are found in the ocean, relative to the number of cells that are found in the ocean" she added.
"We know plastic is bad. This paper shows it can negatively affect one of the most abundant photosynthetic organisms on Earth, but we don't know if the concentrations of these chemicals ever get this high in the ocean" says Luiz Rocha, curator of fishes at the California Academy of Sciences.
It was also pointed by Allen Burton, University of Michigan eco-toxicologist that much of the concern now is not the microplastics which might have less effect in the ocean but rather macroplastics that greatly affects and end up usually in the stomach of sea creatures. "I'm the first to say our problem with plastics is the macroplastics. We all know how horrible the impacts have been with so many species due to macroplastics. Microplastics, not so much. Leachates, probably less" says Allen.
As of now, plastic pollution may not appear to be the bigger problem, reasons may be because first; less knowledge about its major effect in the environment, second, it is a new science that is needed to be explored and lastly the great concern with climate change.
"Everyone acknowledges we need more research, but the sky isn't falling because of leachates or microplastics," says Burton.
