Microplastics in Sediment

The newest wave of research indicates that huge quantities of plastic, especially microplastic has collected in marine sediments…whether it be in the sands of your local beach, or mud cored from the deep. But how do scientists extract these plastics in order to quantify them?

Photo: Chesapeake Bay Foundation

The process is more complex than you might think. When we sample microplastics from the water column, we filter out plastic from water. Sediment, in these cases is a nuisance, and can be problematic depending on the sample, but basic ways to filter out minor quantities of sediment are pretty reliable. But when your entire sample is mud or sand…how do you quickly, reliably and cheaply separate your samples?

The answer is density, and my understanding of it is elementary.  A high density solution is made, using various combinations of salts, depending on the study. This solution is supposed to float the plastics, that are denser then normal sea water (hence having sunk into the sediment), but less dense than this super dense solution, but sediment still sinks out. There are still challenges isolating some of the denser plastics, and researchers are working to come up with the best solution as well as standardize methods. A recent study out of the UK has claimed to do just that. The paper, published in Environmental Pollution this March has created a cheap, effective, efficient field model that can separate out plastic from sediment. This new contraption could help us more accurately measure just how much plastic is out there, and compare across sites.

Read the paper here

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