The Pursuit of an Optimal Method for Microplastics Identification

insights from industryDr. Jennifer LynchResearch BiologistNational Institute of Standards and Technology

In this interview, Rui Chen, Senior Manager of the Applications group of the Spectroscopy business at Thermo Fisher Scientific, talks to Dr. Jennifer Lynch, Research Biologist of the Chemical Science Division at the National Institute of Standards and Technology and co-director of the center for Marine debris research at Hawaii Pacific University, about how an FTIR microscope can be used to identify microplastics.

Can you tell us about how you get your sample into your lab, what the typical workflow is, and what you use the FTIR -iS5 spectrometer for?

In this answer, I will refer to our mesoplastics and megaplastics workflow.

We start by visiting a beach to monitor the effectiveness of a particular single-use plastic ban. For instance, there is now an expanded polystyrene foam ban for all carry-out and take out food, whether from a grocery store, food truck, or restaurant. We tracked the amount of expanded polystyrene foam on the beaches before and after the ban took place to see if it had made any difference.

I will describe a typical selection of incredibly common plastic pieces collected from Kailua Beach. It takes five minutes or less to manage this sort of piece selection.

We also have a weathering index that we have named the Breakneck Weathering Index. Kayla Breakneck, our lab manager, is a past student who came up with the idea of identifying square fracturing when looking at a piece’s surface weathering. If the sample exhibits severe square fracturing, it is a “code three”. If it is a fresh piece, the zip tie in this collection, which still has a sheen and no square fracturing, would be a “code one”. We make visual assessments of the weathering code.

We also note whether a piece is a fishing line, net, or rope. There are different categories, and we typically use fragments, foams, or sheets if it is a very thin film of plastic. For example, a plastic bag would be categorized as a sheet. Other categories such as line and pellet are categorized and kept separately. Unlike many other labs, we identify whole items such as a bottle cap or a cigarette filter.

We use collaborative online data collection software so that everyone does not have to be in the same place. Therefore, the data is collected in real-time.

The next step is to put them on the FTIR. With some fragments, the plastic can shatter as the FTIR is tightened. Fortunately, when that happens, it leaves a little bit of the powder underneath the force gauge, so we can still collect an excellent spectrum.

Polyethylene makes up around 70% of the samples that we analyze. The polyethylene spectrum is a very common one to see and easily recognized.

We are trained to look for individual peaks. However, we do not look for tiny peaks or analyze every single spectrum in detail. If there is a noisy peak, we rerun the sample. If one pops up as unknown and we cannot quickly figure out what it is from the top 10 common polymers, we will run it through a library and try to figure it out in more detail. That is our standard laboratory workflow.

We then have all the data analysis to complete. At this point, our spreadsheet has around 10,000 pieces and rows of information. Different colors, polymers, and whole items are pulled into pie charts to determine the debris sources.

What kind of sample do you use the FTIR microscope for?

Once we get back into the lab, the samples that are placed on the FTIR microscope are Hawaiian beach sand microplastics samples. We would also like to carry out more fish, sea turtle, and seabird gut analysis at the micro-level. Most of what we have analyzed so far has been larger than one millimeter. However, we want to look at the microplastic size range in more depth. Right now, we have proposals to get funding to look at fish stomachs.

We also have a proposal to look at microplastics and sediment cores, primarily through the cores' depths. This can then tell you when the microplastics first settled on the sand. With radiocarbon dating, we can match each layer of the sediment core up to the date that we know that sediment was laid down, and then we can look back in time.

In another project, JRC is running a drinking water study in our laboratory. The samples are sitting in my refrigerator, waiting for me to come back in. I will use the iN10 MX FTIR Imaging Microscope on the drinking water they have provided with microplastic standards. I will try to separate the plastics before analyzing them on the FTIR microscope through chemical image mapping on the filter. This is the first sample that will be going through the microscope.

The second sample set going through the microscope is for a project that we have been doing at James Campbell National Wildlife Refuge, looking at the Hawaiian beaches in places where there are no people but lines and lines of trash wash in every day.

If you look at the sand, you can see the microplastic particles. Our preliminary data suggest that the Hawaiian Islands have the worst microplastic pollution in the world. To prove that, we need this kind of FTIR microscope tool to show that those particles are microplastics and not beach sand. If they are one millimeter or more, our eyes are pretty good at distinguishing them, but when you get down to the 250-micrometer level, our eyes are not very good at picking out the plastics from the sand. We need the FTIR microscope to confirm what we are seeing and determine the particles' chemical composition. This is what we are doing on the Hawaiian beach sand.

This project was spearheaded by one of our University of Hawaii undergraduate students, Ray Aivazian. Our research center is at Hawaii Pacific University, but we open our doors to students from any university. We do not want walls and barriers to this - we want the brightest, most interested, passionate minds to join us.

Aivazian engineered a buoyancy separator device. It is essentially a wheelbarrow with a recirculating pump. He puts water into the wheelbarrow with a tray of beach sand, and it floats the plastic up out of the sand. It then pours over the side of the tray into the wheelbarrow. We then scoop that up using a bucket strainer of 25 micrometers and take that material into the lab.

Aivazian has designed the Trash Time Machine (TTM). This puts the floating material into a pot of water. A vacuum then pulls all the air bubbles out of both the plastic and plant material pores. Once you release the vacuum, the plant matter sinks to the bottom, and the plastics remain floating at the top.

It is a fantastic concept. Ray is an exceptional student who is a retired combat engineer from the Marine Corps. Combat engineers work in the trenches, designing what they need right there at the moment to get a job done – there are high stakes. Ray found himself retired from the Marine Corps and sitting on the Hawaiian beaches, shaking his head about what is happening there.

He engineered a way to obtain plastic efficiently and leave the plant matter back on the beach as we do not want to remove those nutrients from the beach. These nutrients are essential for the ecosystem.

His collaboration with the FTIR microscope and me is exactly what we need to get this study done and prove that his engineered tool works very well on Hawaiian beaches. We are currently in the middle of that study.

We see the materials in eight different size classes. We are in the process of doing all the larger sizes by hand, and once we go back to work, we will be diving into the 500-micrometer, 250-micrometer, 125-micrometer, 63-micrometer, and 25-micrometer classes.

Why is sample prep and standardization so significant in your work, and where is it currently at?

I find it incredibly frustrating that we are not all using the same method. If we could use the same methods and standardize those methods, we could compare concentrations and polymer composition more easily across the world by combining these studies and carrying out meta-analyses.

In 2018, I carried out a meta-analysis on the plastics that sea turtles are ingesting. You could see the frustration in my writing. It was insane that I could not do anything with these 130 papers because they all did something different. They were apples and oranges. I tried to find the best way to turn them all into apples, but many assumptions had to be made to do that.

However, there is another side to this: when I stepped into my lab, I thought about the optimal method. I do not believe we have found it yet. The problem is that we are all tinkering and still trying to find the best method for separating plastics of digesta, sediment, and sand.

I think it is really common, and I fall into this category too, for scientists to look around their lab shelves and say, "I have this chemical on the shelf. I am going to use this because it is right here, I can use it right now, and it costs me nothing extra." But maybe that chemical is not the most optimal. Then that publication goes out, and other labs start to replicate it, even though it is not optimal.

I am trying to take a step back and look at what everyone is doing to find a more optimal method. I am a scientist, and I am skeptical until I do that. My lab is pretty new, so I have not had a ton of experience in this yet.

One thing that we have been doing is collaborating with a master’s student named Jenna Carr. She took the different methods that labs have published and attempted to separate plastics from biological tissue such as animals' guts. Jenna takes the Holman 13 polymers that we find in Hawaii that we want to look at in our samples and places them into the chemicals that the scientists have been using.

There is no single method published so far that does not destroy one of those 13 polymers, which tells me that we are not yet at a place where we can assign an optimal standardized method, although we all want it very badly. There is still a lot of work to do, and our number one problem for making progress is funding.

I have great things to say about Thermo Fisher and all the people we have collaborated with. It seems that everyone is genuinely interested, cares, and is making a difference in a new scientific field and struggling to get started. We are excited to get back to normal and get some concrete data.

**Certain commercial equipment, instruments, or materials are identified in this interview to specify adequately the experimental procedure. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose

About Dr. Jennifer Lynch

Dr. Jennifer M. Lynch’s research interests are to improve the quality of measurements in the field of marine environmental toxicology and chemistry.  She has performed organic analytical chemistry research for the National Institute of Standards and Technology since 2003.  In 2019 she became the Co-Director of the Hawaii Pacific University (HPU) Center for Marine Debris Research (CMDR). Dr. Lynch is motivated to study pollution exposure and effects in the ocean and educate others through technology transfer to perform quality science that can inform policy and improve environmental measurement.