Detecting Microplastics in the Marine Environment

Plastic nurdles spread out on a table
Pre-production plastic pellet debris found in Hawaii.

Scientists from the University of Washington Tacoma and George Mason University worked to isolate and quantify microplastics in water and sediment samples and to compare laboratory protocols.

Type of Project: Research

Region: National

Project End Date: 2016

Who is involved?
Scientists from the University of Washington Tacoma and George Mason University created a manual titled “Laboratory Methods for the Analysis of Microplastics in the Marine Environment,” which outlines protocols intended to help standardize microplastic sample processing. As a follow-up study, scientists from the University of Washington Tacoma evaluated the comparability of protocols used by various labs. Both studies were supported by the NOAA Marine Debris Program through a NOAA Cooperative Institute with the Joint Institute for the Study of the Atmosphere and Ocean (JISAO).

What is the project and why is it important?
Microplastics are plastic debris pieces that are smaller than five millimeters in size. They can be found in most habitats on Earth as well as in the digestive tracts of many marine organisms and sea birds. As more research is done on this type of debris, the need for global standardization of sampling methods has been recognized. Since there is no single agreed-upon method for counting and weighing microplastics in water samples, it is difficult to compare results across studies. Although common approaches may be used, most laboratories develop their own procedures for microplastic sampling and processing based on factors such as budget, equipment availability, labor, and the specific research questions being asked. “Interlaboratory comparisons” are performed in many scientific fields, during which multiple labs are asked to analyze identical samples in order to test their ability to produce reliable and repeatable measurements; this can be a step toward the development of standardized sampling methods.

This project was composed of two parts aimed to address the standardization of microplastic sampling protocols. First, a standardized laboratory protocol was developed for isolating and quantifying microplastic debris in environmental samples. Second, an interlaboratory comparison was conducted to evaluate if protocols used by various labs for quantifying microplastics in water samples were comparable.

For the first stage of the project, researchers from the University of Washington Tacoma created a simple, cost-effective, and unbiased laboratory method to quantify microplastic debris in environmental samples. The protocol focuses on the filtration, separation, and quantification of many common microplastics. The protocol varies slightly depending on whether the sample is beach sand, bed sediment, or water, but the general procedure includes an initial sieving/separation of the sample, the removal of organic matter, a second separation, and finally drying, sorting, and weighing the sample. For more, access the full laboratory protocol.

The interlaboratory comparison was the second part of this project and to our knowledge, is the first study to compare different laboratory protocols for isolating and quantifying microplastic debris in water samples. To start, reference samples were created by adding known amounts of microplastic particles and organic matter to filtered water. These samples were then mailed to six national and international research laboratories well-versed in microplastic research. These laboratories used their own protocols to filter, isolate, and quantify the microplastic debris. Researchers reported their results to the team at the University of Washington Tacoma and comparisons were made between the known microplastic values from the reference samples and the values reported from each of the laboratories.

Results
Of the six laboratories to which microplastic samples were sent, five were able to process the samples and report results. One of those five labs reported counts but not mass, as their protocol does not allow for the determination of that value. There was high agreement in the particle counts made by each of the five labs versus the total number in the reference samples. The four laboratories that reported mass also had high overall accuracy in their mass measurements, with only an average 1.6% difference in microplastic mass compared to the reference sample.