Most things we hear about ocean plastic are depressing, but here’s a welcome ray of good news from the Journal of Hazardous Materials. When scientists floated sterile plastic fragments in sterile water and placed them in a solar simulator system that mimicked the effects of sun shining down on plastic in the sea, they found…
Sunlight can remove plastic from the sea surface. There was less plastic after two months in the solar simulator than there was at the beginning of the experiment.
The type of plastic influences how rapidly microplastics photo-degrade. Several types of plastic particles were used in this experiment. Expanded polystyrene (to-go containers for example) broke down most quickly. Scientists estimated that polystyrene would completely degrade in about 2.8 years. Polypropylene (bottle caps, some bottles) were estimated to completely decompose in 4.3 years. Polyethylene (laundry detergent jugs and many other products) was the slowest to degrade. This plastic was estimated to take 33 years to decompose.
Microplastics dissolve at the sea surface due to sunlight-driven photochemistry. The plastic used in this experiment was carefully sterilized and then put in sterile water before being exposed to simulated sunlight. There is evidence that some bacteria are able to slowly break down plastic but the loss of plastic in this study is due to sunlight.
Dissolved organic carbon (DOC) is produced as microplastics photo-dissolve in sunlight. DOC is produced when dead organic matter decomposes. DOC is taken up by microorganisms and then enters marine food webs. The amount of DOC produced from the dissolution of plastic is very small compared to DOC already cycling through the ocean.
Photo-produced dissolved organic carbon impacts marine bacteria. In all but one sample, the dissolved organic carbon formed by the dissolution of plastic was readily taken up by marine bacteria. In one sample bacterial growth was inhibited.
We have a good idea of how much plastic enters the oceans and where it is coming from. What has puzzled researchers for years is what happens to plastic after it leaks into the ocean. Only a small percentage of plastic that enters the ocean can be accounted for. This study indicates that some of the missing plastic has been converted into DOC and has entered the marine food web.
This is promising news, but there are still many questions about the fate and effects of plastic waste in the ocean. What was it that inhibited microbial growth in one sample? What happens to denser plastics, like PET water and soda bottles, that sink to the bottom of the sea and are not exposed to the sun’s dissolving rays? And how do we keep plastic out of the ocean in the first place? BlueTube can help with that. Grab a bag from the BlueTube at your shore. Pick up plastic trash and throw it away before it reaches the ocean. Reuse your plastic bags by adding them to a BlueTube so others can collect plastic and keep it out of the ocean too.