Plastics surround us. A vital manufacturing ingredient for
nearly every existing industry, these materials appear in a high
percentage of the products we use every day. Although modern life
would be hard to imagine without this versatile chemistry, products
composed of plastics also have a dark side, due in part to the very
characteristics that make them so desirable - their durability and
longevity.
Now Rolf Halden, associate professor in the School of
Sustainable Engineering at Arizona State University and assistant
director of Environmental Biotechnology at the Biodesign Institute
has undertaken a survey of existing scientific literature
concerning the hazards of plastics to human health and to the
ecosystems we depend on. His findings, which appear in the latest
issue of the Annual Review of Public Health, are
sobering.
Today, plastics accumulate in garbage dumps and landfills and
are sullying the world's oceans in ever-greater quantity. And
plastics and their additives aren't just around us, they are inside
virtually every one of us - present in our blood and urine in
measureable amounts, ingested with the food we eat, the water we
drink and from other sources.
Halden's study reiterates the fact that the effects to the
environment from plastic waste are acute. Measurements from the
most contaminated regions of the world's oceans show that the mass
of plastics exceeds that of plankton sixfold. Patches of oceanic
garbage - some as large as the state of Texas - hold a high volume
of non-biodegradable plastics. Aquatic birds and fish are
increasingly victims because biodegradation processes are
inadequate to eliminate this durable refuse.
The magnitude of society's burden of plastic waste is only
beginning to be fully appreciated. In the U.S., the average person
produces a half-pound of plastic waste every day. Around the world,
some 300 million tons of the material are produced each year - a
figure poised to expand, as new forms of plastics are devised to
serve a voracious global appetite. As Halden points out, this
annual production alone would fill a series of train cars
encircling the globe. "We're doomed to live with yesterday's
plastic pollution and we are exacerbating the situation with each
day of unchanged behavior," he said.
Adverse effects to human health remain a topic of fierce
controversy, though a growing consensus is emerging that plastics
and their additives are not always the benign companions we once
assumed them to be. Halden says he accepted the invitation to write
about plastics and human health "because the topic showcases the
bigger problem of how to create a sustainable future for modern
civilization."
Two broad classes of plastic-related chemicals are of critical
concern for human health - bisphenol-A or BPA, and additives used
in the synthesis of plastics, which are known as phthalates. Halden
explains that plastics are polymers - long chains of molecules
usually made of carbon, hydrogen, oxygen and/or silicon, which are
chemically linked together or polymerized. Different polymer chains
can be used to create forms of plastics with unique and useful
properties.
BPA is a basic building block of polycarbonate plastics, such as
those used for bottled water, food packaging and other items. While
it has been considered benign in the form of a heavily cross-linked
polymer, its bonds can break down over time, when plastics are
repeatedly washed, exposed to heat or other stresses, liberating
the building blocks of the chemical, which are toxic. BPA has been
recognized since the 1940s as an endocrine disrupting chemical that
interferes with normal hormonal function.
Adding to the health risks associated with BPA is the fact that
other ingredients - such as plasticizers - are commonly added to
plastics. Many of these potentially toxic components also can leach
out over time. Among the most common is a chemical known as
di-ethylhexyl phthalate or DEHP. In some products, notably medical
devices including IV bags or tubing, additives like DEHP can make
up 40 or 50 percent of the product. "If you're in a hospital,
hooked up to an IV drip," Halden explains, "the chemical that oozes
out goes directly into your bloodstream, with no opportunity for
detoxification in the gut. This can lead to unhealthy exposure
levels, particularly in susceptible populations such as
newborns."
What are the overall effects of the plastics we unwittingly
ingest? The literature Halden surveyed is ambiguous on this point,
despite more than half a century of study. Part of the difficulty
lies in the absence of good controls for studying health outcomes,
as plastic exposure is a global phenomenon, and finding unexposed
subjects for comparison is nearly impossible. It is known however
that health effects vary depending on who is exposed - and when.
Infants and pregnant or nursing mothers are at heightened risk for
toxic exposure or passage of BPA and additives like DEHP.
This January, the FDA announced an important reversal of its
2008 claims regarding the safety of bisphenol-A, expressing new
concern about "potential effects of BPA on the brain, behavior and
prostate gland of fetuses, infants and children," and pledging to
collaborate with other federal health agencies to reevaluate the
chemical's safety.
Studying the effects of low-dose exposure is tricky, usually
requiring a very large number of study subjects. Instead,
epidemiologists tracking the problem frequently base their
conclusions on data gathered from individuals known to have
unusually high levels of a chemical - often the result of
high-level occupational exposure. Halden insists that further study
on low-dose exposure is essential to settle the matter of health
risks, noting some evidence in the literature suggests that
high-dose studies may be inadequate to properly understand toxic
effects from continuous low-level exposures.
Halden explains that while plastics have legitimate uses of
benefit to society, their brazen misuse has led to a radically
unsustainable condition. "Today, there's a complete mismatch
between the useful lifespan of the products we consume and their
persistence in the environment." Prominent examples of offending
products are the ubiquitous throwaway water bottles, Teflon-coated
dental floss and cotton swabs made with plastic PVC sticks. All are
typically used for a matter of seconds or minutes, yet are
essentially non-biodegradable and will persist in the environment,
sometimes for millennia.
Despite the scourge of discarded plastics and the health risks
these substances pose, Halden is optimistic that society can begin
to make wiser choices and develop more sustainable products, formed
from biodegradable, non-toxic chemical building blocks.
New forms of polymer, some made from renewable materials that
are digestible by microorganisms, are being explored.
Ultimately, converting to petroleum-free construction materials
for use in smart and sustainable plastics will become a necessity,
driven not only by health and environmental concerns but by the
world's steadily declining oil supply. As Halden emphasizes, the
manufacture of plastics currently accounts for about 8 percent of
the world's petroleum use, a sizeable chunk, which ultimately
contributes to another global concern - the accumulation of carbon
dioxide in the atmosphere.
"We are at a critical juncture," Halden warns, "and cannot
continue under the modus that has been established. If we're smart,
we'll look for replacement materials, so that we don't have this
mismatch - good for a minute and contaminating for 10,000
years."
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