Buoyancy Technique

When we were at WHOI I came up with the idea of using water to see if the plastics would float.  I then learned from them that if i added a substantial amount of salt to the water, it would increase the buoyancy of the plastic.

To make sure my floating technique worked, we put it to the test. First we added 6 cups of water and tested the >5 mm and <5 mm- >1 mm size plastics.

The >5 mm plastics floated with no problem.  

> 5 mm
Sample SW5.1

One sample of < 5 mm - >1 mm plastics floated right away.  

< 5 mm- >1 mm
Sample SW1

However, the second <5 mm - >1 mm sample sunk.  

Sample MB1

We are not positive this sample is plastic.  We decided to put it to the test, so we added ½ cup of salt to the water. The two pieces of plastic started to hover slightly above the bottom of the container, but they didn't float to the top. We then added another ½ cup of salt to the water and the plastics rose a little more.  The coarse salt wasn't really dissolving so we decided to leave it overnight to see what happened. When we looked at it the next day, the plastics were at the top of the water!  

Floating sample

With further testing, this might prove to be a helpful strategy to use when looking for micro-plastics.