Mark
Browne had a suspicion. He hoped the samples of dried blood taken from a
blue mussel and placed under a special microscope would tell him if he
was correct. As a fuzzy, three-dimensional image of the mussel’s blood
cells appeared, there they were, right in the middle—tiny specks of
plastic.
Whereas
photos of sea turtles eating plastic bags have become the poster child
of the environmental harm wrought by humanity’s plastic waste, research
like Browne’s illustrates the scope of the problem is far larger than
the trash we can see. Tiny pieces of degraded plastic, synthetic fibers
and plastic beads, collectively called microplastics, have turned up in
every corner of the planet—from Florida beach sands to Arctic sea ice,
from farm fields to urban air.
Their
size—from about five millimeters, or the size of a grain of rice, down
to microscopic—means they can be ingested by a wide range of creatures,
from the plankton that form the basis of the marine food chain to
humans. As Browne’s 2008 study
was one of the first to demonstrate, those plastic particles don’t
always pass harmlessly through the body. The finding “was one of those
sort of bittersweet moments,” the ecotoxicologist at the University of
New South Wales in Sydney says. “You’re pleased that some prediction
you’ve made has come true—but then you’re devastated” because of the
potentially profound ecological implications.
Ingested
microplastic particles can physically damage organs and leach hazardous
chemicals—from the hormone-disrupting bisphenol A (BPA) to
pesticides—that can compromise immune function and stymie growth and
reproduction. Both microplastics and these chemicals may accumulate up
the food chain, potentially impacting whole ecosystems, including the
health of soils in which we grow our food. Microplastics in the water we
drink and the air we breathe can also hit humans directly.
Browne
is one of dozens of scientists trying to sort out exactly what this
widespread, motley assortment of microplastics pollution might be doing
to animals and ecosystems. Tantalizing evidence is emerging, from the
impaired reproduction of fish to altered soil microbe communities. As
researchers accumulate more data, “we start realizing we’re just at the
tip of the iceberg with the problem,” Browne says.
A Threat to Organs and Bloodstream
When
Browne experimented with blue mussels back in 2008, many researchers
thought animals would just excrete any microplastics they ate, like
“unnatural fiber,” as Browne called it—but he wasn’t so sure. He tested
the idea by placing mussels in water tanks spiked with
fluorescent-tagged microplastic particles smaller than a human red blood
cell, then moved them into clean water. For six weeks he harvested the
shellfish to see if they had cleared the microplastics. “We actually ran
out of mussels,” Browne says. The particles “were still in them at the
end of those trials.”
The
mere presence of microplastics in fish, earthworms and other species is
unsettling, but the real harm is done if microplastics
linger—especially if they move out of the gut and into the bloodstream
and other organs. Scientists including Browne have observed signs of
physical damage, such as inflammation, caused by particles jabbing and
rubbing against organ walls. Researchers have also found signs ingested
microplastics can leach hazardous chemicals, both those added to
polymers during production and environmental pollutants like pesticides
that are attracted to the surface of plastic, leading to health effects
such as liver damage. Marco Vighi, an ecotoxicologist at the IMDEA Water
Institute in Spain, is one of several researchers running tests to see
what types of pollutants different polymers pick up and whether they are
released into the freshwater and terrestrial animals that eat them. The
amount of microplastics in lakes and soils could rival the more than 15
trillion tons of particles thought to be floating in the ocean’s
surface alone.
What matters most is whether these physical and chemical impacts
ultimately affect an organism’s growth, reproduction or susceptibility
to illness. In a surprising study published in March 2018,
not only did fish exposed to microplastics reproduce less but their
offspring, who weren’t directly exposed to plastic particles, also had
fewer young, suggesting the effects can linger into subsequent
generations. Some organisms such as freshwater crustaceans called
amphipods haven’t yet exhibited any ill effects, perhaps because they
can handle natural indigestible material like bits of rock, says Martin
Wagner, an ecotoxicologist at Norwegian University of Science
and Technology, who studied them. And some species have shown toxic
effects from microplastics exposure from certain types of plastic, but
not others, says Chelsea Rochman, a microplastics researcher at the
University of Toronto.
Most
work on microplastic impacts has been done in the lab for short stints,
with only a single type of plastic, often with larger particles than
some species tend to eat, and at higher concentrations than are found in
the environment. The studies “won’t tell us about long-term ecological
consequences happening at low concentrations,” Wagner says. He is one of
several researchers starting to bridge that gap by matching animals to
the polymers and pollutants they are most likely to encounter and
incorporating the intricacies of the real world where microplastics
“won’t be the only stressor,” Wagner says. Microplastics could be a last
straw for species subject to pressures as chemical pollutants,
overfishing and climate change. “It’s just damn complicated,” Wagner
says.
Inviting Chaos
Messy,
real-world conditions are the goal on the green lawn of a botanical
garden in Frankfurt, Germany. A row of small, identical ponds stretch
across the grass, exposed to the elements. Wagner spiked each one with
different microplastic particles—some virgin polymers, some contaminated
with pollutants—to see how freshwater insects and zooplankton fare.
Although Wagner hasn’t yet observed any overt impacts, he is
investigating whether certain organisms exhibit more subtle signs of
harm, which could have a ripple effect throughout an ecosystem’s food
web.
Such
cascading impacts could happen even when individual species don’t seem
to suffer. Browne’s mussels showed no short-term ill effects but he
worries their accumulated microplastics could be transferred to animals
that eat them. “They might not be so kind to the other organisms,” he
says.
Like
Wagner, Browne is venturing farther out into the real world. He has
several freezers’ worth of fish and other organisms plucked from Sydney
Harbor that he will examine for ingested microplastics. His team will be
linking those to the routes by which microplastics might be entering
the harbor and looking for signs of ecological damage such as changes in
population size. The approach means animals can behave normally and are
exposed to typical environmental conditions such tides and storms, as
well as a host of other stressors such as changing ocean temperatures
and industrial pollutants. “We want a chaotic system because if
something can cause an impact in that chaotic system, above those other
stresses, we know that we really, really need to be worried about it,”
Browne says.
Matthias
Rillig, a plant ecologist at Free University of Berlin, has shown how
microplastics can affect organisms by altering their environments. In a study
he co-authored, soil laden with polyester microfibers was much
fluffier, retained more moisture and seemed to affect the activity of
microbes that are crucial to the soil nutrient cycle. The finding is an
early but concerning one, given that farmers around the world apply
microfiber-rich treated sewage sludge as fertilizer to agricultural
land. Rillig is also one of several scientists looking to see how
microfibers in soils might be affecting crop growth.
Full Circle
Microplastics may threaten people more directly. A study published in April 2018
found particles and microfibers in packaged sea salt, beer, bottled
water and tap water, making it virtually certain we are ingesting
microplastics. In bottled beverages microplastics could be infiltrating
during the bottling process; microfibers could be falling from the
atmosphere into the reservoirs that supply tap water. Even for
researchers steeped in the field, “it still comes as a shock,” Rochman
says. “It just shows that the mismanagement of our waste is coming back
to us.”
Because
it is unethical to intentionally feed doses of microplastic particles
to humans, some researchers, like Browne, have turned to medical studies
that use particles to deliver precise amounts of drugs to specific
areas of the body to get a better sense of how easily microplastics
might move through humans. If particles are small enough, they might
migrate through the body and potentially accumulate in places like the
bloodstream. A study of hamsters injected with microplastics suggests
such particles can lead to blood clots.
Humans
could also be inhaling microfibers as they fall from the sky—everywhere
from the heart of Paris to the remote Arctic. Small airborne particles
are known to lodge deep in the lungs where they can cause various
diseases, including cancer. Factory workers who handle nylon and
polyester have shown evidence of lung irritation and reduced capacity
(although not cancer), but they are exposed to much higher levels than
the average person. Stephanie Wright, a research associate at King’s
College London, is trying to better understand how much microfiber
humans are actually exposed to and whether airborne microplastics might
penetrate the lungs. She is also teaming up with the university’s
toxicology unit to examine their lung tissue collection for signs of
microfibers and related damage.
Some
scientists say the focus on microplastics in humans might be missing a
larger point: People are continually exposed to plastic food and
beverage containers, which could be a much bigger source of at least the
chemicals added to plastics such as the endocrine disruptor BPA. The
potential exposure to microplastics hasn’t stopped Rochman from eating
seafood, however. “To the best of my knowledge the benefits outweigh the
costs,” she says. It could be that, as with many pollutants, there is a
threshold beyond which microplastics become toxic to humans or other
species. “We just need to try to understand what that threshold is,” she
notes.
Experts
say the sheer ubiquity of the contaminant combined with the harm that
has already been observed is enough for humanity to start to clean up
its act. “There are always questions to be answered,” Rochman says, but
we have reached the point where “it’s enough information to act toward
solutions.”
Andrea Thompson, an associate editor at Scientific American, covers sustainability.
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