7 December 2019 | New Scientist | 39it difficult to predict and explore the health
effects,” says Stephanie Wright, who leads
microplastics research at the UK Medical
Research Council Centre for Environment and
Health at King’s College London.
That isn’t to say that we are completely in the
dark. There is a body of existing work to draw
on and scientists are filling in the gaps as fast as
they can. Toxicologists agree that, in theory,
there are two main routes by which
microplastics might get into the human body:
ingestion and inhalation.
They also agree that, in theory, there are>SA
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billion
Tonnes of plastic now in landfill or
discarded into the environmentthree potential hazards: physical, chemical
and microbiological. The first comes from the
particles getting lodged in organs and tissues
and causing damage and inflammation. The
second is from toxic chemicals leaching out
into the body. These could be the remnants
of chemicals that are used to make plastics,
additives in the plastics such as flame
retardants, and pollutants soaked up by
plastics from the environment. The third
comes from the pathogenic microbes that
appear to grow enthusiastically on the surface
of plastic particles.
All of which sounds troubling. But the key
words are “in theory”. As yet there is almost
no evidence of actual health effects, let alone
long-term risks.
Consider the microplastics we swallow,
which is probably the way most get into our
bodies. Microplastics have been detected in
drinking water and food; bottled water
contains up to 106 particles per litre, and beer,
sea salt, seafood, honey, sugar and teabags have
also been found to be contaminated. Shellfish,
which feed by filtering seawater and which we
eat whole, including their digestive systems,
are a rich source. A portion of mussels typically
contains 800 microplastic particles.
Microplastics also rain out of the air and
onto our food. One estimate suggests thatcomprehensive report by the European
Commission’s Group of Chief Scientific
Advisors. It came to a similar, inconclusive,
conclusion: “Research on microplastics and
their potential threats to humans is in its
infancy and is complex – a lot remains
uncertain.” The third, by the World Health
Organization, which is specifically about the
hazards of microplastics in drinking water,
described the evidence base as “limited”
and “insufficient”.
One major challenge is the almost limitless
diversity of microplastics. In terms of size,
they are thought to span at least seven orders
of magnitude, from 5 millimetres down to a
nanometre or maybe less – known as
nanoplastics. Shape varies enormously too,
from perfect spheres to bobbly lumps, jagged
shards and pointy fibres.
Then there is their chemical composition.
“They consist of hundreds or even thousands
of different polymers,” says Vethaak.
Microplastics also contain additives such as
plasticisers and flame retardants, and have
the capacity to absorb contaminants from the
environment, like hydrocarbons, pesticides
or even metals. To complicate matters further,
each particle is surrounded by an “eco-corona”
of organic matter and microorganisms.
“Almost every particle has its own identity,”
says Vethaak.
All that diversity makes them fiendishly
hard to study. “They are a class of pollutants
rather than a type, and this complexity makes