Sampling, Sorting, and Characterizing Microplastics in Aquatic Environments with High Suspended Sediment Loads and Large Floating Debris

This method will help researchers quantify microplastic loads in rivers, which often contain high sediment loads, as they are a major source of plastic debris to the ocean. The main advantage of this technique is that it enables filtering and sorting of microplastics and water samples with high sediment loads at sizes not typically included in previous studies. To begin rinse the filtration device and nylon mesh sieves three times with deionized water.

Then place the mesh sieves into each union joint, with the pour sizes decreasing from top to bottom. To prevent leaks seal each joint tightly. Next wet a mixed cellulose ester membrane filter with deionized water.

While the filter is still damp fold it into a cone. Then place a stainless steel mesh basket into the last union joint. Carefully place the folded membrane filter into the basket.

Fold the lip of the filter over the edge of the joint. Next place a mesh sieve on top of the membrane filter in the last union joint. Ensure that all of the union joints are sealed tightly.

Then attach the hose form the top of the filtering flask to the base of the filtration device. Turn on the vacuum pump, ensuring that the pressure does not exceed 127 milliliters of mercury. Using a 500 milliliter graduated cylinder measure the total volume of the sample.

Next record the volume of the sample and transfer it to the filtration device. To empty the filtering flask turn off the pump and detach the two hoses from the flask. Then empty the flask into a waste container.

To continue the filtration cycle reattach the hoses and turn on the pump. Once the entire sample has been filtered use deionized water to rinse the sample container and graduated cylinder three times. After each rinse filter the deionized water used to rinse the container and graduated cylinder.

Using deionized water rinse the walls of the filtration device three times. Then turn off the vacuum pump, and use a deionized water wash bottle to rinse the edges of the union joint. Turn the pump off and use forceps to remove the mesh sieve from the union joint.

Place the sieve in a covered Petri Dish and dry it at 60 degrees celsius for 24 hours. Repeat this process for each union joint. Then turn the vacuum pump on and rinse the edges of a membrane filter using a deionized water wash bottle.

Wash the particulates at the edges of the filter into the center, and ensure that all of the water passes through the filter. Next use forceps to remove and unfold the membrane filter. Place the filter in a foil envelope and dry at 60 degrees celsius for 24 hours.

First examine the membrane filter under a stereo microscope. Suspected plastics will not have cellular structure. The fibers will have equal thickness throughout, and the particles will not appear shiny.

Remove suspected plastics from the filter and place them into a collection vial containing 70%ethanol. Record the color and shape of each suspected plastic. For nylon mesh sieves stored in Petri Dishes after all suspected plastics have been removed from the filter examine the lid and bottom of the Petri Dish for additional suspected plastics.

To validate this protocol three samples from Oso Bay were spiked with 10 blue polyethylene particles and 50 green nylon fibers. On average, 100%of the polyethylene particles and 92%of the nylon fibers were recovered from the samples. The loss of fibers may be due to a small amount of sample loss during filtration or incorrect identification.

Once mastered multiple filtration apparatus can be run simultaneously with samples taking less than two hours each to filter. Sample sorting times under the microscope however are sample specific. While attempting this procedure it’s important to remember to account for potential contamination using lab equipment and field blanks for each step in the process.

Following this procedure other methods like Fourier Transform Infrared Spectroscopy can be used to verify material properties. With its development this technique enables researchers studying environmental contaminates to explore microplastic pollution and waterways with high suspended sediment loads, as well as floating and submerged debris.