John Fox is in a hurry to find a faster way to count the little blobs and strings that appear randomly on his microscope slides. They tend to be smaller than the width of a human hair, and counting them one by one on a single slide takes a week of full-time work. He has 93 samples, collected last summer from Lake Superior, and there are many more out there, waiting to be collected. These blobs and strings are microplastics, and Fox is about to earn a master’s degree in chemistry, based on his work with a team of researchers at the University of Minnesota Duluth. They are not only exploring the concentrations of microplastics in Lake Superior; they are also noting the types of microplastics and figuring out the chemical processes involved in their degradation.
“I’m running out of time,” Fox says. “I need data for my thesis; then I’ll be off doing something else.” He is sharing the techniques he’s developed with another student who will take over his counting and other duties once his thesis is done.
There has been a lot of research about microplastics in the oceans. We’ve all seen distressing images of plastic debris in “gyres,” the swirling oceanic vortices that seem to round up trash and hold it fast. Gyres are not a permanent feature of the Great Lakes, but there’s still plenty of plastic floating around in these precious sources of fresh water. A study from 2017 estimates the yearly burden of plastics deposited in the Great Lakes is 9887 metric tons, or nearly 22-million pounds.
John Fox’s advisor, Dr. Elizabeth Minor, and other researchers reported in 2018 that microplastic particles are found in western Lake Superior surface waters in roughly in the same concentrations as in Lake Michigan, the North Atlantic, and the south Pacific oceans. .
Fox’s own work identified a range of between ten and 100,000 particles per square kilometer of water surface. It’s a lot of work to collect, identify, and count those pieces of plastic.
The team went out on Lake Superior in the research vessel Blue Heron last August, taking samples at four locations just outside the port of Duluth-Superior. They used a variety of collection techniques. They lowered a McLean pump to various depths, where it pulled water through a filter adjusted to collect any tiny particles, and then pumped the water back into the lake. To collect surface water, they used a Manta net, which looks a bit like a manta ray, with long wings designed to hold it on the surface. After traveling one mile, they raised the net and sprayed it down to push the microparticles to the bottom of the net.
Once in the lab, Fox processes the samples to remove any organic matter. Plastics are made of carbon and hydrogen, and so is natural organic material. Fox needs to eliminate the natural organic matter in order to concentrate on the plastic. He’s looking for material that’s between five and 300 microns (one micron is one-millionth of a meter). A human hair is about 70 microns in thickness.
“I can see pieces 300 microns or larger in an ordinary visual microscope,” he says. “For smaller pieces, we use FTIR.” For the uninitiated, that’s Fourier-transform infrared spectroscopy. It shines a beam of infrared light on the sample and measures which parts of the spectrum the particle reflects back, and which parts it absorbs. Then Fox uses an algorithm called the Fourier transform to convert the data to useable information.
“That way, we rely on a chemical signature rather than my eye to determine that it’s plastic,” Fox says. “We also use the hot needle test: we heat the end of a needle, put it close to a particle, and if it melts, we can be sure it’s plastic. If it were natural organic matter, it would burn up, and if it were sand, it wouldn’t react at all.”
A microfiber and several particles on a grid on a microscope slide in Dr. Elizabeth Minor’s lab. Image is magnified by 90 times. Photo courtesy John Fox
This work serves multiple purposes. Fox and his team want to learn the concentration of microplastics in Lake Superior, and this will be important for future studies. “If we know the concentrations of plastics in the Lake, biologists will be able to do studies in the lab using those concentrations, and they’ll know it’s true to the real world,” says Fox. “We also think these microplastics might be concentrating somewhere: in sediments, or at the surface, or elsewhere. Identifying any sinks will allow us to find out if remediation (cleanup) is feasible.”
They also want to learn if microplastic concentrations change with the seasons. “The Lake goes through cycles of stratification with changes in air temperature and water density,” Fox says. “We’ll cooperate with physical limnologists to learn more about that.”
So far, scientists don’t know how much of the microplastic pollution comes from the air and how much is deposited directly into the Lake from land-based sources. These could include stormwater—which picks up plastic detritus from the streets, and wastewater treatment plants—which typically don’t have filters fine enough to capture these materials.
Health costs of plastic in our waters
Microplastics are roughly the same size as the food sources for many creatures living in water. These tiny pieces can get tangled up in aquatic organisms, and when ingested, they can block the critters’ digestive systems. In addition, some of the materials used to produce plastics are endocrine disruptors, which can interfere with many life processes. In humans these chemicals can lead to learning disabilities, faulty brain or sexual development, and cancers.
Another danger lies in the toxic substances plastics can carry with them. There are plenty of tiny pieces of metals, bacteria, and organic compounds in the water, and plastics can absorb these, leaching them over time. Persistent, bio-accumulative, and toxic substances can be especially destructive because some of them can hitch a ride on microplastics, enter an organism, detach from the plastic, and then magnify as they move up the food web. These include DDT (a now-banned pesticide), dioxins (by-products of industrial processes and waste incineration), polycyclic aromatic hydrocarbons (PAHs, which come from coal-burning, wildfires, and grilled foods), Per- and polyfluoroalkyl substances (PFAS, found in grease-resistant paper, food packaging, and non-stick cookware), and polychlorinated biphenyls (PCBs, used in electrical equipment and paints until it was banned in 1979). Thus, the sport fish that humans love to catch and eat may have much higher levels of these toxic compounds than the algae or smaller fish which serve as food for larger fish.
Another member of the UMD team, and another advisor for John Fox, chemist Melissa Maurer-Jones, has discovered markers in the degrading plastic that show how the process occurs. “Polyethylene, which is a main polymer in lot of plastic products, is normally a carbon backbone with hydrogen atoms,” she says. “But when it’s exposed to sunlight and wave action, it starts incorporating oxygen.” Sunlight provides the energy to break the bond between carbon and hydrogen, “and once the bond is broken, oxygen likes to swoop in and do some of the reacting. We can identify and quantify that oxygen,” she says.
Maurer-Jones and her colleague Katherine Schreiner, a biogeochemist at UMD’s Large Lakes Observatory, want to use these markers to determine how long a piece of plastic has been exposed to sunlight and how long it has been floating in the water. “That will help us to understand the long-term impacts of plastics in the environment,” she says. Science tells us that most plastics will never completely degrade.
A useful product
As a chemist and a realist, Maurer-Jones doesn’t expect us to stop using plastics. “Plastics are useful, and it’s naïve to think we can get rid of them. We need them in hospitals; they’re in pacemakers; even parts of photovoltaic panels are made out of plastic.” But she’s all in favor of keeping plastic out of the environment. “We should use less of it and dispose of it properly,” she says. “And as a scientist, I think about how to redesign plastic to make it work betterIn long-lasting infrastructure, such as the insulation on electric transmission lines, they should be made to degrade in a predictable way, so they can be replaced before they fall apart.
Some plastics attract oils to their surface. Absorbent pads made of oil-attracting polypropylene are useful in oil spill response and industrial workplaces. Maurer-Jones says she’d like to find a way to make plastic that could help remove toxins from the environment—not in the form of microplastics, which would just float away, but as pads or in some other formulation.
Another UMD group plans to build on Maurer-Jones’ work by determining which types of plastics pose the greatest risk of carrying toxic contamination. Research in San Diego Bay found that concentrations of PAHs and PCBs attached to high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene (PP) in much higher concentrations than to two other common plastic types, polyethylene terephthalate (PET) and polyvinyl chloride (PVC).
Other investigators, other institutions
To learn how microplastics might be affecting humans directly, a 2018 study from the University of Minnesota examined microplastics in tap water from around the world, 12 brands of beer made in the Great Lakes, and commercial sea salt. Eighty-one percent of the tap water had particles, along with all the beer and salt samples. Fibers were by far the most common types of microplastic in these samples.
Authors of the study offer this helpful warning: “Based on consumer guidelines, our results indicate the average person ingests over 5,800 particles of synthetic debris from these three sources annually, with the largest contribution coming from tap water (88%).” It seems it’s difficult to avoid adding microplastics to our own bodies.
At the University of Wisconsin Superior, Dr. Lorena Rios Mendoza has been researching microplastic pollution for more than 15 years. Her groundbreaking study in 2013, which showed for the first time microplastics spreading in the Great Lakes, prompted immediate concern. Several states, and later (in 2015) the federal government, passed laws phasing out the use of plastic microbeads in cleansers and cosmetics.
Rios has been investigating the uptake of microplastics by plankton such as Daphnia, an important food for fish in rivers and lakes. “In 24 hours they can ingest a lot of microbeads but they can eject it too, so it flows in and out; we don’t think it’s enough time to damage the Daphnia, but how many Daphnia can one fish ingest?”
That’s the beginning of biomagnification, as the plastics and their destructive cargo move into the food system. Rios tested more than 2,000 fish stomachs from Lake Superior. “This is cleanest of the Great Lakes,” she points out, “but we found microplastics in about half of the fish.” They were primarily fibers, mixed with cotton fibers, most likely from clothing. “We think wastewater treatment plants are the main source of the fibers,” Rios says. Their main function is to kill pathogenic bacteria, not to capture tiny bits of plastic.
Researchers examining influent and effluent at wastewater treatment plants have found up to 90-percent of microplastics can be removed, but a study published in 2016 concluded that “when dealing with such a large volume of effluent even a modest amount of microplastics being released per liter of effluent could result in significant amounts of microplastics entering the environment.”
Indeed, pioneering British researcher Mark Anthony Browne showed in 2011 that up to 1,900 fibers were released during each wash of synthetic clothing.
Rios and her students do a beach clean-up on Wisconsin Point every year, and every year they find the same amount and types of plastics. “In schools they teach the ‘three Rs,’ Rios says: “Reduce, reuse, and recycle. I like to add ‘refuse’ and ‘remove.’ If you don’t want to use plastic, refuse it. And when you’re walking along and you see plastic, pick it up.”