Determining the Degradation of Microplastics in Canal Water project

Hello everyone :)
     So this semester I worked on a project with Cathy and Melissa where we collected canal water and put microplastics in it to see whether the bacteria already present in the canal water was eating away or somehow degrading microplastics naturally. The set up for our experiment was basically a tank full of canal water with some added dirt that was found near the canal. In the tank, 6 tea pods with 90 punches of plastic each were placed. The six plastic types that we used were:

• Plastic 1: PET or Polyethylene Terephthalate
• One of the most commonly used plastics. Can be found in most water bottles and several forms of packaging. Recyclable but should not be reused due to increased risk of bacterial growth.
• Plastic #2: HDPE or High-Density Polyethylene
• Used to make milk jugs, detergent containers, grocery bags, and toys. Recyclable but only about 30-35% of HDPE plastic used in America gets recycled each year, so it’s wise to use as little as possible.
• Plastic #3: PVC or Polyvinyl Chloride
• Used to make cooking oil bottles, clear plastic wrapping, teething rings, and computer cables. Due to its impenetrable material it is also used for window frames. Only less than 1% of this plastic is recycled, because it contains many toxins.
• Plastic #4: LDPE or Low-Density Polyethylene
• Used to make dry cleaner bags, squeezable bottles, and plastic bags to pack bread. Considered the safest because it does not contain many toxins; however, it is not commonly recycled.
• Plastic #5: PP or Polypropylene
• Used to make disposable diapers, plastic bottle tops, straws, and more. It is a recycled material, but only 3% is currently being recycled in the US.
• Plastic #6: PS or Polystyrene
• Commonly known to make disposable Styrofoam cups, take-out containers for food, and egg cartons. Due to this type of plastic not being widely accepted for recycling, 35% of U.S. landfill is accounted towards Polystyrene.

Each month, we would collect 10 pieces of plastic and plate them. The plates were Pseudomonas Isolation Agar (PIA) plates and two plates with 5 punches each were designated for each plastic every month. We decided that since Pseudomonas are commonly found in soil and water, it would be easier and more likely to find in the canal water. Once the plastics were plated, we would incubate them for about 24 hours and then perform tests on them to identify what bacteria could possibly be growing on the plates. The tests that were performed on the plastics were:

• Oxidase test
• Gram staining
• Growth on Macconkey plates

     In addition to the tests that we performed, we also sanitized and weighed the microplastics so that we could see if there was any decrease in mass over the months. From December to March, we did see some decrease in the masses of certain plastics. However, not all of them had a decrease. We though this could have been due to a sanitation error, possibly. Maybe we did not sanitize some plastics properly and there could be residues that were taken into account. 

     However, it is also important to point out that the experiment only lasted for a few months. My partners and I concluded that we would need more time to continue the experiment and see better results. It is not very realistic to expect much change in the masses of the microplastics even if they were being degraded. If we were able to continue it for a year like we ideally planned, the changes might be more drastic. 

     Though we were not able to really tell if the plastics were being degraded, we were able to obtain a good estimate of what bacteria we were growing on our plastics. In order to know for sure, we would need to perform a DNA test, in case they turn out to be a bacteria that has similar characteristics to Pseudomonas. But from what we obtained, all the tests we performed were positively correlated with the characteristics of Pseudomonas.