Post PN 0528
Post PN 0528
Post PN 0528
POSTNOTE
Number 528 June 2016
Background Sources
Plastic is an extremely versatile resource whose production It is frequently possible to identify what type of plastic
levels have increased dramatically since the 1950s.1 It can polymer (Box 1) a particular piece of ocean debris is made
be made into a wide range of products that are strong, of, regardless of its size. However, when pieces become
durable, inexpensive and lightweight. However, some of the small, fragmented and degraded they are almost impossible
properties of plastic that make it such an attractive material to trace to their original source. As a result, the relative
during use also make it problematic when it becomes waste. importance of different microplastic sources is unknown.
The primary issue is that it is highly resistant to degradation. The three largest sources are thought to be fibres from
Indiscriminate discarding and the accidental release of textiles, microbeads and large pieces of plastic debris,10
plastic into the marine environment has resulted in the rapid which will become microplastics as they fragment and
accumulation of persistent marine plastic debris in the degrade. However, a 2014 report by the Norwegian
world’s oceans. By weight, most of this consists of large Environment Agency also highlighted the potential
pieces of debris such as fishing gear, bottles and plastic importance of microplastic emissions from normal wear and
bags; but by number, the dominant type of debris in the tear of plastic products such as tyres, fishing nets, rope and
world’s oceans are small pieces that are under 5 mm in size carpets, as well as plastics in paints and varnishes.11
– these are known are microplastics.2 It has been estimated
Fibres
that there were between 15 to 51 trillion microplastic
Small fibres from synthetic clothing, such as polyester and
particles floating on the surface of the world’s oceans in
nylon, are released into waste water through the process of
2014, weighing between 93 and 236 metric tons.3
washing clothes.12 Waste water treatment plants are not
Sources and Spread designed to retain microplastics, and the resulting sewage
Microplastics can either be manufactured (for example, as effluent can carry fibres out to rivers, lakes, estuaries and
microbeads for use in cosmetic scrubs, toothpastes, and the sea. Fibres are commonly the most abundant type of
cleaning products), or can result from the fragmentation of microplastic found in marine wildlife and sediments.7,13-16
larger items of plastic debris. They are ubiquitous
Microbeads
throughout the marine environment and have been found in
Microbeads are small spheres or fragments of plastic that
estuaries, lakes, coasts, sediments, the open ocean, deep
are used in cosmetics, household cleaning products and
seas, and arctic sea ice.4-9
industrial blasting. They include beads used in exfoliants
The Parliamentary Office of Science and Technology, 7 Millbank, London SW1P 3JA T 020 7219 2840 E post@parliament.uk www.parliament.uk/post
POSTnote 528 June 2016 Marine Microplastic Pollution Page 2
were contaminated with plastic, mainly in the form of affected only at certain stages of their lifecycle (Box 4). Field
fibres.38 Similarly, trawls in the English Channel found studies in this area face several difficulties. Wildlife in the
microplastic contamination in 36.5% of fish caught,32 a marine environment is exposed to a wide range of other
proportion similar to that found in fish from the North Pacific pressures, including rising temperatures, ocean acidification
Central Gyre, known as the ‘Great Pacific Garbage Patch’. and other types of pollutants such as heavy metals.
Disentangling the effects of microplastics from the effects of
Toxicity to humans and wildlife could potentially be caused these other factors will be challenging.
by the plastic polymer itself, by the additives it contains (Box
2), or by other chemicals that are known to associate with Environmental Effects
microplastics once they are in the ocean (Box 3). However, There are several concerns over the potential ecological
there are a variety of polymers that behave differently effects of microplastics that are not related to the ingestion
according to their size and shape39 and thousands of of these particles by animals or algae. Examples include:
different additives used in products. This makes it difficult to ◼ Pieces of microplastic can provide a surface on which
make general predictions about the effects of ingesting marine insects can lay their eggs. The number of marine
them. Little is known about the rate at which plastic pond skaters has been shown to increase with growing
additives leak into their surrounding environment (whether amounts of microplastics in the North Pacific.49 Such
this be the ocean or biological tissues), as well as the proliferation of species that were previously limited by the
potential levels of exposure for humans and wildlife. scarcity of places on which to lay their eggs has unknown
ecological consequences, but may allow several species
Human Health to become more abundant and expand their range.
No studies have investigated whether microplastics that are ◼ The community of microbes associated with plastic
unintentionally ingested by humans can be subsequently fragments is different to that normally found in seawater.50
transported into tissues.40 Several studies show that A study looking at the microbial communities on pieces of
microplastics are present in sea food sold for human polyethylene (the most commonly produced plastic
consumption,15,16,28,29,41 including mussels in North Sea worldwide) and polypropylene (frequently used in
mussel farms and oysters from the Atlantic. Although the gut packaging) found that of a total of 3,484 species of
wall may be an important barrier,40 there is a possibility that microbe, only 53 were shared by polypropylene,
very small particles such as nanoplastics could penetrate polyethylene and seawater, whereas 799 were unique to
gut tissues. Experiments in rats have showed that polypropylene and 413 were unique to polyethylene. The
polystyrene microspheres of 50-100 nm can be absorbed ecological consequences of this are also unknown.
into the body through the gut and transported to the liver ◼ The presence of high concentrations of microplastics in
and spleen.42 The ability of different plastics to enter tissues beach sediments can change their permeability and heat
is likely to depend on their size and chemical properties. absorbance,51 raising concerns about the effects on
Once inside, there are number of ways in which species where sex is determined by temperature (e.g.
nanoplastics could theoretically interact with biological sea turtles) and sediment-dwelling species that would be
tissues in a way that could be toxic; but these have not been at a higher risk of desiccation (including worms,
tested, and the risk to human health remains unknown.40 crustaceans, and molluscs).
Wildlife Addressing the Risks of Microplastics
Laboratory experiments have shown that plastic ingestion Three policies covering marine plastic litter are outlined in
can have detrimental effects in a range of species that have Box 5. In addition, in January 2014 the European Parliament
key roles in marine ecology, though some of these passed a resolution on plastic waste in the environment
experiments expose animals to higher concentrations of calling for single use plastics that cannot be recycled
microplastics than those that have been reported in (including microbeads) to be phased out.
sediments and the water column. The magnitude of effects
varies between species, and some animals appear to be Box 3. Plastics as Transport for Other Pollutants
The chemical and physical properties of microplastics enable them to
Box 2. Effects of Additives attract and accumulate a number of other chemicals in the oceans.
Some additives that are incorporated into plastics during the These include most persistent organic pollutants (POPs), and
manufacturing process, including bisphenol A (BPA), phthalates and persistent bioaccumulative and toxic substances.52-54 Chemicals on
brominated flame retardants, are known hormone disruptors.43-45 microplastics ingested by an organism can dissociate from plastic
Studies have found that exposure to BPA at levels found in the particles and enter body tissues. This has been demonstrated in
general population can be associated with the onset of obesity, lugworms and seabirds.52 In the latter case, contaminants were
cardiovascular disease, increases in hormonally-mediated cancers passed to the birds as a result of eating polyethylene resin pellets as
and changes in behavioural development.46 All plastics, especially well as eating fish that were exposed to contaminants in the water,
those in packaging, undergo rigorous testing to ensure that levels of suggesting that they have the potential to travel through the food
toxic chemicals are kept below defined levels; but the behaviour of chain. However, natural sediments can also attract substances such
plastics and additives in the sea and potential levels of exposure are as POPs, and there is debate over the importance of microplastics as
still being investigated. Items made from PVC and printed a transmitter of POPs and other substances into tissues compared to
polyethylene bags appear to have the highest potential to leach other subtrates. There is evidence that certain chemicals preferentially
additives into seawater.47 The risk of exposure to additives such as attach to plastic,53,54 but there are only limited data on the extent to
BPA through marine microplastics is considered low compared to which chemicals dissociate from plastic and migrate into tissues in
other sources.48 different environmental conditions and on how quickly they
accumulate in the food chain.
POSTnote 528 June 2016 Marine Microplastic Pollution Page 4
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