Plastic waste pollution of our planet has
reached crisis point, especially in the oceans (see  Plastic Plague
in Our Oceans, SiS 65), where it poses
unprecedented threat to marine life. Distressing photographs of marine mammals,
birds, and amphibians mangled by plastic bags are all too familiar. Those are but
the most visible signs of a much more extensive and insidious assault on life
in and around the oceans. There is abundant literature on the danger of plastic
waste to wild life at the top of the food chain, which has been further highlighted
in numerous reviews (see [2-6] for example). Birds, sea turtles, and marine mammals,
have all been found entangled in plastics, or with ingested pieces of plastics;
as a result, they suffer impaired movement, ability to feed and reproduce; as
well as lacerations, ulcerations and death.
In comparison, there have been few studies on microscopic
pieces of waste plastics - mm to nm dimensions - that could affect increasingly
greater numbers of species down the food chain.
more harmful to greater numbers of organisms
Plastic wastes are not only physically
harmful. They may be chemically harmful either because they are inherently
toxic, or because they absorb other pollutants that are toxic. As pointed out
in a recent review , microplastics can be ingested by suspension- filter-
and deposit- feeders, detritivores and planktivores, all at the bottom of the
food web. They may accumulate within the organisms, resulting in both physical
and chemical damage. They can cause abrasions and blockages. And toxicity could
arise from contaminants leaching from the microplastics such as monomers and
plastic additives that are carcinogenic and/or endocrine disrupting. Moreover,
microplastics can concentrate hydrophobic persistent organic pollutants (POPs)
that have a greater affinity for the hydrophobic surface of plastics compared
to seawater. On account of their large surface area to volume ratio,
microplastics can become heavily contaminated, at up to 6 orders of magnitude
greater than ambient seawater in the case of waterborne POPs [7, 8].
Several recent studies are
beginning to address the effects of microplastics in the marine food chain.
Medaka fish bioaccumulate chemical
pollutants adsorbed on microplastics
A team of researchers at University of
California Davis, and University of California, San Diego showed that fish
exposed to a mixture of polyethylene with chemical pollutants adsorbed from the
marine environment bioaccumulate these chemical pollutants and suffer liver
toxicity and pathology . Fish fed virgin polyethylene fragments also showed
signs of stress, although less severe than fish fed marine polyethylene
Japanese medaka (Oryzias
latipes), a widely accepted model fish species, were exposed chronically to
low density polyethylene (LDPE) plastic (used for carrier bags). Polyethylene
has a greater affinity for organic contaminants than other mass produced
polymers, comprises the largest component of plastic production globally (29 %),
and is one of the most common polymers recovered as aquatic debris.
The fish were exposed to three
treatments: a negative control with no LDPE, a virgin-plastic treatment, and a
marine plastic treatment (where LDPE was pre-exposed to water in an urban San
Diego Bay). The medaka were given 10 % plastic (by weight) mixed into treatment
diets and sprinkled at the top of each tank. This translates to 8 ng plastic/ml.
of water, which is within the range of concentrations found in seawater (maximum
reported in the North Pacific subtropical Gyre was 300 ng/ml). Chemical
analyses targeted polycyclic aromatic hydrocarbons (PAHs), PCBs
(polychlorinated biphenyls) and PBDEs (polybrominated biphenyls), all of which are
known to accumulate on plastic debris in marine habitats. In addition, PBDEs
are additives on several plastics and PAHs are a likely byproduct of plastic
The team probed
for 12 PAHs, 27 PCBs and 13 PBDEs in virgin- and
marine- LDPE pellets and detected and quantified 6 PAHs, 10 PCBs and 7PBDEs. The
concentrations of total PAHs, PCBs and PBDEs on marine-LDPE were 4-, 15- and 1.4- fold respectively of those
on virgin-LDPE pellets. Small amounts of all the contaminants were also in the
control diet (contained in the cod liver oil).
two months, there were greater concentrations of total PAHs, PCBs and PBDEs in
fish from the marine-plastic treatment at 2.4-, 1.2-, and 1.8-fold respectively
of those from negative control treatment; but the differences were not
significant among treatments except for the concentrations of chrysene and
PCB28. There were small differences in mortality: 4 % from negative controls
and virgin plastic and 6 % from marine plastic.
fish exposed to virgin and marine plastic showed signs of stress in their liver,
including glycogen depletion, fatty vacuoles and single cell death (necrosis).
Severe glycogen depletion was seen in 74% of fish from marine plastic
treatment, 46 % from virgin plastic and 0% from controls. Fatty vacuolation was
seen in 47% of fish from marine plastic treatment, 29 % of fish from virgin
plastic and 21 % from controls. Single cell necrosis was 11 % of fish from
marine plastic treatment compared to 0 % from virgin plastic treatment and
controls. An eosinophilic focus of cellular alteration, a precursor to a tumour
was see in one fish from the virgin-plastic treatment, while a tumour - a
hepatocellular adenoma comprising 25 % of the liver - was seen in one fish from
marine plastic treatment.
Summing up, the researchers wrote :“Overall, we conclude that
polyethylene ingestion is a vector for the bioaccumulation of PBTs [polybutylene
terephthalates, a collective term for the PAHs, PCBs and PBDEs] in fish and
that toxicity resulting from plastic ingestion is a consequence of both the
sorbed contaminants and plastic material.”
Crucian carp bioaccumulate nanoplastics
via the food chain and became profoundly disturbed in their feeding behaviour
Research led by
Sara Linse at Lund University in Sweden showed that commercially manufactured
polystyrene nanoparticles were transported through an aquatic food chain from
algae to zooplankton to fish (see Figure 1). The polystyrene nanoparticles
affected lipid metabolism and behaviour of the top consumer . At least
three independent metabolic parameters were found to differ between control and
test fish: weight loss, triglycerides:cholesterol ratio in blood serum, and distribution
of cholesterol between muscle and liver. Moreover, they demonstrated that the
nanoparticles bind to apolipoprotein A-I (apoA-1) in fish serum in vitro,
thereby preventing the fish from properly utilising their fat reserves. In
addition to the metabolic effects, the feeding behaviour of the fish was
profoundly affected. The time it took the fish to consume 95% of the food
presented to them was more than double in the nanoparticle-exposed fish
compared to controls.
Figure 1 Experiment simulating the accumulation of polystyrene
nanoparticles in the ocean in fish via the food chain
Polystyrene nanoparticles 24 nm in diameter were added at a
concentration of 0.01% (w/v) to a culture of the green (Scenedesmus sp)
for 24 h, filtered, and fed to herbivorous zooplankton (algae from 250 ml
culture given to 30 adult Daphnia). After another 24 h, the Daphnia
were washed on a net to remove free nanoparticles before being fed to the top consumers of the food
chain, the Crucian carp, 4 individuals per replicate tank. The food
chain was restarted every third day and the fish remained the same throughout the study. The control
food chain worked in the same way except that no nanoparticles were added. Each food chain started with 16 fish
divided into four tanks. The number of fish in each tank decreased over time as
they were sacrificed for sampling.
The feeding time – the time it took for the fish to eat 95 % of the Daphnia
added to the tank – was measured at day 18, 21, 24, 27 and 30. The average
feeding time over the five time points were more than twice as long for fish
exposed compared to controls (16.6 + 2.7 versus 6.0 + 0.7
minutes, p < 0.035). The exposed fish were moving more slowly and to a much
lesser extent than control fish and they did not actively hunt for the
zooplankton during the feeding. Remarkably, the test fish let Daphnia
swim in and out of their mouth without trying to eat them. This indicates a
strong behavioural disturbance in fish that have eaten food containing the
identify proteins that bind to polystyrene particles in fish serum, the
researchers incubated polystyrene nanoparticles with serum collected from the
Crucian carp and several fish species: pike, tench, rudd, bleak, and Atlantic
salmon. For all fish species investigated, one of the main proteins bound to
the nanoparticles migrates as expected for a protein with molecular weight
around 25 kDA. The protein band from Atlantic salmon (Salmo solar),
whose genome is the only one that has been sequenced, was cut out and subjected
to trypsin proteolysis, followed by mass spectrometry, and identified as apoA-I,
the carrier protein for high density lipoprotein (HLP), an important component
for fat metabolism. Unlike mammals which use glycogen as the main energy
reserve, fat is the major energy reserve for fish.
is possible that the polystyrene nanoparticles bind to both apoA-I and the HDL
particles in serum after being ingested and passed through the intestinal wall
into the blood stream, and from there to other tissues, where it may have
further influences on lipid metabolism. The researchers therefore investigated
changes in the concentrations of triglycerides and phospholipids in blood
serum, liver and muscles throughout the experiment. They found two significant
differences between the test and control fish. The triglyceride:cholesterol
ratios in blood serum were similar after 14 days. After 22 days, the ratio for
the control fish was very low whereas only a small decrease was seen in the
test fish. After 29 days, the ratios had increased for both the control and
test group. In addition, the distribution of cholesterol among muscle and liver
changed during the experiment. After 14 days, the distribution of cholesterol
was the same in control and test fish. However, after 22 days, the cholesterol
concentrations in the control group were elevated in muscle and liver by
comparison. After 29 days, the distribution of cholesterol was again similar.
These results indicated that control fish were able to alter their fat
metabolism to cope with the spare dietary regime, whereas the test fish were
Throughout the experiment, the weight of the fish was measured. As
the fish is fed with a limited amount of zooplankton, a weight loss is expected
because the fish is forced to use its energy reserves. A significant weight
loss was observed in both test and control fish from the first feeding to the
15th day. Between day 15 and 21, the weight loss slowed down for
both groups. After this, the control group continued to lose weight whereas the
test fish actually gained weight at the end of the experiment. A possible
explanation is that the test fish were unable to draw upon their energy fat reserve
due to the accumulation of nanoparticles.
Taken altogether, the results suggest that there is a disturbance of
lipid metabolism as a consequence of nanoparticle intake, which make the fish
less adaptable to the starvation diet (and may also account for their
inactivity during feeding due to lack of energy).
The behaviour of the fish
were further investigated by video recording as described in a subsequent
publication of a follow up study carried out in collaboration with scientists
at University of Copenhagen, Denmark  with the same experimental design.
suphonated polystyrene nanoparticles 24 and 27 nm in diameter were used at a
concentration of 0.01 % (w/v), or 9.3 x 1012 particles/ml. The
number of nanoparticles reaching each fish was calculated to be approximately 1
The behaviour of the fish was
monitored by filming during feeding on day 0, 24, and 61. Each aquarium (with
four fish) was filmed for 30 min. Blood and organs were also taken for analysis
at the end of the experiment.
The study confirmed that
feeding time was almost twice as long in test fish as in controls. During
feeding, the control fish showed significantly higher activity than the test
fish as they actively searched for food. The test fish moved much more slowly
and did not hunt as actively for food. The distance between fish in each
aquarium was smaller for test fish than controls, suggesting that the
nano-particle fed fish behaved more as a group and exhibited stronger shoaling
behaviour. The nano-particles fed fish occupied less of the available space in
the aquarium than control fish during feeding, as consistent with their
Fish organs blood, brain,
gills, liver and muscle samples were analysed by NMR spectroscopy to identify
effects of the nanoparticles diet on metabolite concentrations. The
nanoparticles-fed fish showed increase in ethanol in the liver and decrease in
muscle, and increases in inosine/adenosine and lysine in muscle, and also
increases in leucine, phenylalanine and tyrosine in the liver. These results
suggest a collective effect of many metabolite changes as the result of a
general disturbance of cellular function.
The brain and the muscle
differed between the groups, both in texture and colour. The brains in the
nanoparticle-fed fish were much more fluffy, whiter, and appeared swollen, and
significantly heavier than the brains of control fish, as more water was
The fish were given a
restricted diet to test the effects of nanoparticles when they needed to use
their fat reserves. The more pronounced decrease in activity of the
nanoparticle-fed fish suggests that their energy reserves were smaller or that
the access to the reserves was impaired.
the results show that polystyrene nanoparticles induce considerable changes in
metabolism and hunting behaviour. A reduced feeding activity may result in
reduced growth and ability to avoid predators and thereby reduce their fitness
in the natural ecosystem.
There is no longer any doubt that waste plastics in the
ocean are a menace to all marine life. Especially insidious are the invisible
micro- and nano-plastics that can be taken up by microorganisms at the bottom
of the food web and bio-accumulate in top predators with profound effects on
their feeding behaviour, metabolism and morphology, as evident from the first
studies that have been carried out. The effects on other species lower down the
food web have yet to be determined, but the effects on human health can already
be predicted from existing data on the carcinogenic and endocrine disrupting
effects of POPs and numerous chemical associated with waste plastics. There is
an urgent need to drastically reduce plastic pollution by classifying plastic
wastes hazardous (see ).
Désirée Röver Comment left 2nd February 2015 15:03:20 Greetings, Mae-Wan! Thank you for this sad article.
This plastic toxicity is bad enough, but what about the radioactive contamination that daily is being spewed into the waters of the Pacific Ocean?
The multitude of photographs by Dana Durnford shows that in some regions of the West coast of Canada marine life already is almost totally extinct (www.thenuclearproctologist.org).
And next to chemical toxicity, doesn't radioactivity also accumulate in the plastic materials mentioned in this article?
Adrian S Hepworth Comment left 2nd February 2015 16:04:07 You may be interested in this short film which my daughter helped make for TED Ed as the animator.
http://ed.ted.com/lessons/the-nurdles-quest-for-ocean-domination-kim-preshoff It tries to make this polution problem understandable by all.
Rory Short Comment left 2nd February 2015 18:06:50 Nature through 3.8 billion years of evolution produced a biosphere where everything worked together effectively for the survival of the whole. One of Nature's products, humankind, has however, in its arrogance, seen itself as being beyond Nature. Consequently humankind does not even try to consult the wisdom of Nature before embarking on activities which will effect the biosphere in new ways. Man made chemicals are one such product and Nature was and is not consulted when they are released. Such consultation should be mandatory before a product can be released into the biosphere
victoria lewis Comment left 30th March 2016 03:03:50 where does polyester fit into this research? I have read stuff that suggests it is a very significant contributor to ocean pollution.