Nate Seltenrich covers science and the environment from Petaluma, CA. His work has appeared in
High Country News,
Sierra,
Yale Environment 360,
Earth Island Journal, and other regional and national publications.
PDF Version (4.4 MB)
In recent years plastic pollution in the
ocean has become a significant environmental concern for governments,
scientists, nongovernmental organizations, and members of the public
worldwide. A December 2014 study derived from six years of research by
the 5 Gyres Institute estimated that 5.25 trillion plastic particles
weighing some 269,000 tons are floating on the surface of the sea.
1
At the same time, plastics in consumer products have become subject
to increasing scrutiny regarding their potential effects on human
health. Bisphenol A (BPA),
2
a component of polycarbonate plastics and suspected endocrine
disruptor, is one of the most widely known chemicals of interest. But
BPA is only one of many monomers, plasticizers, flame retardants,
antimicrobials, and other chemicals used in plastics manufacturing
3 that are able to migrate into the environment.
At the junction of these two lines of inquiry is an emerging third
field that is in many ways even more complex and less well understood:
investigating human exposures to and potential health effects of
plastics that have entered the marine food chain. Studies have
demonstrated plastics’ tendency to sorb (take up) persistent,
bioaccumulative, and toxic substances, which are present in trace
quantities in almost all water bodies.
4
The constituents of plastics, as well as the chemicals and metals they
sorb, can travel into the bodies of marine organisms upon consumption,
5,6,7,8,9
where they may concentrate and climb the food chain, ultimately into
humans. This topic has attracted interest and funding from the U.S.
Environmental Protection Agency (EPA), the National Oceanic and
Atmospheric Administration (NOAA), and the National Academy of Sciences
(NAS), as well as researchers, nonprofit groups, and institutions around
the world.
At this point “there are more questions than answers,” says Richard
Thompson, a professor of marine science and engineering at England’s
Plymouth University. Thompson coined the term “microplastics” in 2004
10
and later undertook a three-year study of these particles in the marine
environment for the UK’s Department of Environment, Food, and Rural
Affairs.
11,12,13 “From a human perspective,” he says, “at the moment I think there’s cause for concern rather than cause for alarm.”
Viewpoints on the human health risks of marine debris are nearly as
complex as the underlying science, as was evident at an inaugural EPA
and NAS symposium on the topic held in Washington, DC, in April 2014.
In
addition to myriad small details, the researchers in attendance
considered an overarching question: Within the context of limited
oceanographic research funding, the variety of other problems affecting
ocean health (including overfishing and acidification), and the extent
of humans’ daily and direct exposures to potentially harmful chemicals
from consumer plastics and other sources—how concerned should we be
about marine plastics as far as human health goes?
Researchers don’t yet have an answer, even if they believe they’re
asking the right question. As EPA chemist Richard Engler concluded in a
2012 review, “While current research cannot quantify the amount, plastic
in the ocean does appear to contribute to [persistent, bioaccumulative,
and toxic substances] in the human diet.”
14
Plastic Vectors
The path from plastic pollution to chemical exposure through seafood
is a long one, figuratively and often literally, and tracing all the
individual steps in that theoretical journey is not the same as
identifying human health effects, researchers say. Actual exposures,
which are determined by innumerable variables along the way, including
seafood consumption, still need to be quantified. Then these levels must
be evaluated within broader contexts of consumer plastic use and
environmental pollutant levels.
Exposures to plastic debris have been clearly documented for marine
organisms at all trophic levels (i.e., positions within the food chain),
says Bradley Clarke, a lecturer at RMIT University in Melbourne,
Australia. “What remains to be determined is whether this exposure
increases the body burden of … marine organisms in the natural
environment and if it does, by what magnitude,” Clarke says.
There is a lack of controlled experimental work completed on the
topic, Clarke adds, and it’s very difficult to disentangle pollutant
exposures and bioaccumulation via plastic versus food and environmental
sources. Uncertainties also surround the transfer of plastic additives
to marine organisms and resultant human exposures through seafood.
We do know that plastic has become nearly ubiquitous on the planet.
It has washed up on the most remote beaches, amassed in distant gyres,
and been discovered in the bodies of dead organisms from fish to birds
to whales.
15,16
Numerous efforts have sought to quantify the amount of plastics
floating on or present throughout the ocean environment, and they’ve
arrived at vastly different numbers. The 5 Gyres paper
1
was preceded in July 2014 by a similar study suggesting that between
7,000 and 35,000 tons of plastic are floating on the ocean’s surface.
17
Anna-Marie Cook, one of two EPA lead scientists investigating the
potential health effects of marine plastics, believes that estimates
calculated through the use of surface trawl nets, including both of the
recent global studies, vastly underestimate the scope of the problem.
“Slightly more than half of all plastic is negatively buoyant, meaning
that it will sink upon reaching the ocean, either into the near-shore
sediment environment or to the ocean floor,” she explains. “Surface
trawls do not account for the fraction of plastic in sediments, on the
ocean floor, or suspended past the top few feet of the water column.”
World plastics production has experienced almost constant growth for
more than half a century, rising from approximately 1.9 tons in 1950
18 to approximately 330 million tons in 2013.
19 The World Bank estimates that 1.4 billion tons of trash are generated globally each year, 10% of it plastic.
20 The International Maritime Organization has banned the dumping of plastic waste (and most other garbage) at sea.
21
However, an unknown portion of the plastic produced each year escapes
into the environment—instead of being landfilled, incinerated, or
recycled
20—and at least some of it eventually makes its way to sea.
Plastics that reach the ocean will gradually break down into
ever-smaller pieces due to sunlight exposure, oxidation, and the
physical action of waves, currents, and grazing by fish and birds.
22
So-called microplastics—variably defined in the scientific literature
and popular press as smaller than 1 or 5 mm in diameter—are understood
to be the most abundant type of plastic in the ocean.
The 5 Gyres
authors found microplastics almost everywhere they sampled, from
near-shore environments to the open ocean, in varying concentrations,
and they estimated that particles 4.75 mm or smaller—about the size of a
lentil—made up roughly 90% of the total plastic pieces they collected.
1
But the degradation of larger pieces of plastic is not the only way
microplastics end up in the ocean. Nurdles—the plastic pellets used as a
feedstock for producing plastic goods—can spill from ships or
land-based sources,
23
and “microbeads” used as scrubbing agents in personal care products
such as skin cleansers, toothpastes, and shampoos, can escape
water-treatment facilities and pass into watersheds with treated water.
24 (In June 2014, Illinois became the first U.S. state to ban the manufacture and sale of products containing microbeads,
25 which have been documented in the Great Lakes
26 and Chicago’s North Shore Channel.
27)
Due to their hydrophobic nature, persistent organic chemicals—including polycyclic aromatic hydrocarbons (PAHs),
28 polychlorinated biphenyls (PCBs),
29 polybrominated diphenyl ethers (PBDEs),
30 dioxins,
31 and DDT
32—have been shown to preferentially sorb to plastics when they encounter them in the ocean.
33,34
Potentially thousands of such chemicals exist in the environment,
35 but researchers are limited to screening for compounds they can actually identify, Bradley says.
The extent and rate of sorption can vary widely depending on the
chemical, plastic type, and other variables, but plastic particles
recovered from the ocean have been found to contain pollutant
concentrations orders of magnitude higher than the water from which they
were collected.
14,36,37
Marine organisms throughout the food chain commonly consume plastics of various sizes.
38,39 The tiniest microplastics are small enough to be mistaken for food by zooplankton,
40
allowing them to enter the food chain at very low trophic levels. Some
larger predators are thought to confuse nurdles (which typically measure
less than 5 mm in diameter) with fish eggs or other food sources.
41
Once plastics have been consumed, laboratory tests show that chemical
additives and adsorbed pollutants and metals on their surface can
desorb (leach out) and transfer into the guts and tissues of marine
organisms.
14
Some researchers speculate that chemicals already present in the
organism may also be able to travel in the opposite direction by sorbing
to plastics in the gut, depending on the concentration gradients. Yet
neither process has been proven to occur in the natural environment.
We already know that many chemicals of concern are present in the
seafood we eat, particularly in higher-level predators such as tuna and
swordfish.
42
Research has shown that harmful and persistent substances can both
bioaccumulate (or increase in concentration as exposures persist) and
biomagnify (or increase in concentration at higher trophic levels)
within organisms as they assume some of the chemical burden of their
prey or environment. Yet again, no research has yet demonstrated the
bioaccumulation of sorbed pollutants in the environment.
Three key questions remain to be determined. To what extent do
plastics transfer pollutants and additives to organisms upon ingestion?
What contribution are plastics making to the contaminant burden in
organisms above and beyond their exposures through water, sediments, and
food? And, finally, what proportion of humans’ exposure to plastic
ingredients and environmental pollutants occurs through seafood?
Researchers are moving carefully in the direction of answers to these
questions.
Human Health Questions
Among U.S. agencies, the EPA is delving into the science to answer
key questions around marine plastics and human health. In addition to
convening the April meeting and producing a forthcoming white paper on
its findings, the agency collaborates with and directly funds
researchers in the field. Staff from the EPA and the U.S. Fish and
Wildlife Service are currently developing a risk assessment to quantify
the chemical loading effects of plastic litter on marine life.
43
And by 2016, the EPA plans to launch a similar long-term inquiry into
effects on human health, including an evaluation of outcomes such as
fetal formation, says Cook.
Any study of human health effects will likely depend on the
cooperation of a subject community where many types of seafood are
heavily consumed. “We have to have a potential threat and a potential
receptor present in a location and a community who is willing to work
with us on it,” Cook says. “There are a lot of repercussions to a
community to find out that their food supply is potentially
contaminated.” The agency also expects to award a new four-year marine
debris research contract designed to gain a better understanding of the
movement, distribution, and quantity of plastics off the remote
northwestern Hawaiian islands.
Researcher Chelsea Rochman of the University of California, Davis,
collaborated with Cook and the EPA on a 2014 study that showed an
association between concentrations of certain PBDEs in fish and levels
of plastic debris accumulation in the South Atlantic Ocean.
44 However, no such association was seen for concentrations of BPA, alkylphenols, alkylphenol ethoxylates, or PCBs in fish.
44
Rochman is also working on a separate study funded through NOAA’s
Marine Debris program. The aim of the NOAA study is to demonstrate for
the first time the biomagnification in marine organisms of chemicals
introduced via plastics. This highly controlled laboratory experiment
involves feeding contaminated plastic pellets to mussels, feeding the
mussels to sturgeon, and then testing levels of PCBs within the bodies
of the sturgeon. Results are still awaiting analysis and publication.
One of Rochman’s collaborators on the project, researcher Mark Browne
of the University of California, Santa Barbara, recently received a
grant from the Australian Research Council for a three-year program
addressing another question in the field: Beyond leaching chemicals,
what do plastic particles do when they enter an organism?
Browne showed
in 2008 that microplastics sized 3.0 and 9.6 µm in diameter can travel
beyond a mussel’s gut and into its circulatory system and hemocytes
(immune cells), where they may remain for a relatively long period of
time—in his study, more than 48 days.
45 A 2012 study by another group showed that microplastics taken up by mussels resulted in a strong inflammatory response.
46
The implications of these findings for humans that consume organisms
containing microplastics are not yet understood. Browne says his team is
currently working to develop a method to test human tissues for
microplastics. “We think that’s going to be a big turning point,” he
says.
Ecotoxicologist Heather Leslie of VU University Amsterdam is among
those concerned about the particle toxicity of microplastics themselves.
Even without chemical hitchhikers, she says, plastic particles can
induce immunotoxicological responses, alter gene expression, and cause
cell death, among other adverse effects. “Exposed organisms then deal
not only with chemical stress through multiple exposure routes, but also
particle stress,” she explains. Leslie is currently studying the
distribution and environmental fate of microplastics from cosmetics and
other sources and potential toxicological effects on marine organisms in
Europe’s multinational CleanSea Project.
A large body of literature about the mobility of nanoparticles offers
a glimpse at how nano-size plastic particles may behave in the human
body, Leslie says. “They can pass through the placenta and the
blood–brain barrier and can be taken up in the gastrointestinal tract
and lungs, potential sites where harm can occur,” she says. “There is a
lot to learn about microplastics from the fields of particle toxicity
and drug delivery technologies that apply to polymeric nanoparticles.”
In another example of ongoing research, Robert Hale, a professor at
the Virginia Institute of Marine Science, has funding from both the EPA
and NOAA to investigate how particle size, weathering, biofouling (the
accumulation of living organisms on wet surfaces), and water
characteristics including temperature, salinity, and organic carbon
content influence both the sorption of organic contaminants to and the
release of various additives from different types of microplastics.
47
“You look at these simple parameters together, and it can get very
complex,” Hale says. The EPA is particularly interested in evaluating
the release of flame retardant additives from plastics, he notes, and
may pursue development of a protocol to be used by manufacturers to
provide data on chemical migration.
A Matter of Perspective?
Government, academic, and independent sources interviewed for this
article almost unanimously expressed a mix of skepticism and concern
toward the thought of ocean plastics posing a human health risk. Without
exception, they also advocated for further research. A common viewpoint
is that although definitive evidence does not yet exist for real-world
human health impacts tied to marine plastic debris, this doesn’t prove
the hypothesis null, nor does it mean there aren’t other valid reasons
to address the long-lived plastic litter that washes into the world’s
oceans every year.
Many researchers pointed to the need to maintain perspective on the
issue. Human exposure to microplastics and plastic additives is more
likely to stem from intact goods prior to disposal than from seafood,
Thompson says. Clothing fibers make up a large proportion of the
microplastic found worldwide, says Browne,
48 and even drinking water and foods such as honey can be contaminated with microplastics, according to Leslie.
Kara Lavender Law, a research professor of oceanography with the Sea
Education Association in Woods Hole, Massachusetts, who collaborated
with Richard Thompson on a recent summary of current knowledge about
microplastics,
49
says that while overfishing and direct exposure to consumer plastics
concern her more than the marine-plastic pathway, the latter still
warrants investigation. “I think it’s something worth working on,” she
says. “Just because we don’t see it doesn’t mean it’s not there.”
In the case of plastic constituents thought to affect the human
endocrine system, any level of exposure, no matter the route, may be
potentially harmful, says Carol Kwiatkowski, executive director of The
Endocrine Disruption Exchange. Endocrine disruptors have shown evidence
of a nonlinear or nonmonotonic dose response,
50 meaning tiny doses may have larger effects than mid-level doses.
“Anything that interferes with hormone action potentially has an
effect at a very low dose, because the endocrine system is designed to
function at very small doses,” Kwiatkowski says. “So it’s possible this
pathway could bring some exposure. You’d have to find some evidence that
the chemicals were being carried through marine organisms and making it
into people.”
From there, she says, researchers would still need to learn how any
such exposures relate to or interact with other exposures to endocrine
disruptors, including rapidly metabolized chemicals such as BPA and
phthalates, and longer-lived additives such as flame retardants. In
other words, to what extent do all these exposures add up, and how does
that cumulative exposure translate to health outcomes? “It’s difficult
to study additive effects,” Kwiatkowski says. “But it’s very important
research to conduct.”
Nonetheless, the end goal, sources say, is not to abandon the use of
plastic. “The benefits of plastics can be realized without the need for
emission [to the ocean], ” Thompson says. “And for me that’s the tipping
point for taking policy action.” New laws, for example, could require
handling plastics more responsibly at the end of their useful life
through recycling, proper disposal, and extended producer
responsibility.
Rolf Halden, director of the Center for Environmental Security at the
Biodesign Institute at Arizona State University, advocates for another
solution: manufacturing more sustainable plastics from the start.
51
“We need to design the next generation of plastics to make them more
biodegradable so that they don’t have a long half-life, they don’t
accumulate in the oceans, and they don’t have the opportunity to collect
chemicals long-term,” he says. “There’s just no way we can shield
people from all exposures that could occur. Let’s design safer chemicals
and make the whole problem moot.”
References
1. Eriksen M, et al. Plastic pollution in
the world’s oceans: more than 5 trillion plastic pieces weighing over
250,000 tons afloat at sea. PLoS ONE 9(12):e111913 (2014); doi:
10.1371/journal.pone.0111913.
2. EPA. Bisphenol A (BPA) Action Plan
Summary [website]. Washington, DC:U.S. Environmental Protection Agency
(updated 29 January 2014). Available:
http://www.epa.gov/oppt/existingchemicals/pubs/actionplans/bpa.html [accessed 28 January 2015].
3. Deanin RD. Additives in plastics. Environ Health Perspect 11:35–39 (1975);
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1475198/.
4. Rochman CM, et al. Long-term field
measurement of sorption of organic contaminants to five types of plastic
pellets: implications for plastic marine debris. Environ Sci Technol
47(3):1646–1654 (2013); doi:
10.1021/es303700s.
5. Rochman CM, et al. Ingested plastic
transfers hazardous chemicals to fish and induces hepatic stress. Sci
Rep 3:3263 (2013); doi:
10.1038/srep03263.
6. Browne MA, et al. Microplastic moves
pollutants and additives to worms, reducing functions linked to health
and biodiversity. Curr Biol 23(23):2388–2392 (2013); doi:
10.1016/j.cub.2013.10.012.
7. Chua EM, et al. Assimilation of polybrominated diphenyl ethers from microplastics by the marine amphipod,
Allorchestes compressa. Environ Sci Technol 48(14):8127–8134 (2014); doi:
10.1021/es405717z.
8. Tanaka K, et al. Accumulation of
plastic-derived chemicals in tissues of seabirds ingesting marine
plastics. Mar Pollut Bull 69(1–2):219–222 (2013); doi:
10.1016/j.marpolbul.2012.12.010.
9. Besseling E, et al. Effects of microplastic on fitness and PCB bioaccumulation by the lugworm
Arenicola marina (L.). Environ Sci Technol 47(1):593–600 (2013);
10.1021/es302763x.
10. Thompson RC, et al. Lost at sea: where is all the plastic? Science 304(5672):838 (2004); doi:
10.1126/science.1094559.
11. Bakir A, et al. Competitive sorption
of persistent organic pollutants onto microplastics in the marine
environment. Mar Pollut Bull 64(12):2782–2789 (2012); doi:
10.1016/j.marpolbul.2012.09.010.
12. Bakir A, et al. Transport of
persistent organic pollutants by microplastics in estuarine conditions.
Estuar Coast Shelf Sci 140:14–21 (2014); doi:
10.1016/j.ecss.2014.01.004.
13. Bakir A, et al. Enhanced desorption of
persistent organic pollutants from microplastics under simulated
physiological conditions. Environ Pollut 185:16–23 (2014); doi:
10.1016/j.envpol.2013.10.007.
14. Engler RE. The complex interaction
between marine debris and toxic chemicals in the ocean. Environ Sci
Technol 46(22):12302–12315 (2012); doi:
10.1021/es3027105.
15. Safina C. No refuge: tons of trash
covers the remote shores of Alaska. Yale Environment 360, Opinion
section (1 July 2013). Available:
http://e360.yale.edu/feature/carl_safina_gyre_tons_of_trash_covers_shores_alaska/2668/ [accessed 28 January 2015].
16. de Stephanis R, et al. As main meal for sperm whales: plastics debris. Mar Pollut Bull 69(1–2):206–214 (2013); doi:
10.1016/j.marpolbul.2013.01.033.
17. Cózar A, et al. Plastic debris in the open ocean. Proc Natl Acad Sci USA 111(28):10239–10244 (2014); doi:
10.1073/pnas.1314705111.
18. PlasticsEurope. Plastics—The Facts
2013: An Analysis of European Latest Plastics Production, Demand and
Waste Data. Brussels, Belgium:PlasticsEurope AISBL (2013). Available:
http://www.plasticseurope.org/Document/plastics-the-facts-2013.aspx [accessed 28 January 2015].
19. PlasticsEurope. China Leads Global
Plastics Production while Europe Ranks Second [press release]. Brussels,
Belgium:PlasticsEurope AISBL (12 June 2014). Available:
http://goo.gl/Xgx5Is [accessed 28 January 2015].
20. Hoornweg D, Bhada-Tata P. What a
Waste: A Global Review of Solid Waste Management. Washington, DC:Urban
Development and Local Government Unit, World Bank (March 2012).
Available:
http://goo.gl/GZec84 [accessed 28 January 2015].
21. IMO. Prevention of Pollution by
Garbage from Ships [website]. London, United Kingdom:International
Maritime Organization (2015). Available:
http://www.imo.org/OurWork/Environment/PollutionPrevention/Garbage/Pages/Default.aspx [accessed 28 January 2015].
22. Zettler ER, et al. Life in the
“plastisphere”: microbial communities on plastic marine debris. Environ
Sci Technol 47(13):7137–7146 (2013); doi:
10.1021/es401288x.
23. Thompson RC, et al. Plastics, the
environment and human health: current consensus and future trends.
Philos Trans R Soc Lond B Biol Soc 364(1526):2153–2166 (2009); doi:
10.1098/rstb.2009.0053.
24. Fendall LS, Sewell MA. Contributing to
marine pollution by washing your face: microplastics in facial
cleaners. Mar Pollut Bull 58(8):1225–1228 (2009); doi:
10.1016/j.marpolbul.2009.04.025.
25. State of Illinois. Governor Quinn
Signs Bill to Ban Microbeads, Protect Illinois Waterways [press
release]. Chicago, IL:Office of the Governor, State of Illinois (8 June
2014). Available:
http://www3.illinois.gov/PressReleases/ShowPressRelease.cfm?SubjectID=3&RecNum=12313 [accessed 28 January 2015].
26. Eriksen M, et al. Microplastic
pollution in the surface waters of the Laurentian Great Lakes. Mar
Pollut Bull 77(1–2):177–182 (2013); doi:
10.1016/j.marpolbul.2013.10.007.
27. McCormick A, et al. Microplastic is an
abundant and distinct microbial habitat in an urban river. Environ Sci
Technol 48(20):11863–11871 (2014); doi:
10.1021/es503610r.
28. ATSDR. Polycyclic Aromatic
Hydrocarbons (PAHs) [website]. Atlanta, GA:Agency for Toxic Substances
and Disease Registry, U.S. Centers for Disease Control and Prevention
(updated 3 March 2011). Available:
http://www.atsdr.cdc.gov/substances/toxsubstance.asp?toxid=25 [accessed 28 January 2015].
29. EPA. Health Effects of PCBs [website].
Washington, DC:U.S. Environmental Protection Agency (updated 13 June
2013). Available:
http://www.epa.gov/wastes/hazard/tsd/pcbs/pubs/effects.htm [accessed 28 January 2015].
30. EPA. Polybrominated Diphenyl Ethers
(PBDEs) Action Plan Summary [website]. Washington, DC:U.S. Environmental
Protection Agency (updated 8 January 2015). Available:
http://www.epa.gov/oppt/existingchemicals/pubs/actionplans/pbde.html [accessed 28 January 2015].
31. EPA. Environmental Assessment: Dioxin
[website]. Washington, DC:U.S. Environmental Protection Agency (updated
12 August 2010). Available:
http://cfpub.epa.gov/ncea/CFM/nceaQFind.cfm?keyword=Dioxin [accessed 28 January 2015].
32. EPA. DDT [website]. Washington, DC:U.S. Environmental Protection Agency (updated 18 April 2011). Available:
http://www.epa.gov/pbt/pubs/ddt.htm [accessed 28 January 2015].
33. Müller JF, et al. Partitioning of
polycyclic aromatic hydrocarbons in the polyethylene/ water system.
Fresenius J Anal Chem 371(6):816–822 (2001); doi:
10.1007/s002160101025.
34. Pascall MA, et al. Uptake of
polychlorinated biphenyls (PCBs) from an aqueous medium by polyethylene,
polyvinyl chloride, and polystyrene films. J Agric Food Chem
53(1):164–169 (2005); doi:
10.1021/jf048978t.
35. EPA. Persistent Organic Pollutants: A
Global Issue, A Global Response [website]. Washington, DC:U.S.
Environmental Protection Agency (updated 12 June 2014). Available:
http://goo.gl/Pn5p7u [accessed 28 January 2015].
36. Rochman CM, et al. Long-term sorption
of metals is similar among plastic types: implications for plastic
debris in aquatic environments. PLoS ONE 9(1):e85433 (2014); doi:
10.1371/journal.pone.0085433.
37. Mato Y, et al. Plastic resin pellets
as a transport medium for toxic chemicals in the marine environment.
Environ Sci Technol 35(2):318–324 (2001); doi:
10.1021/es0010498.
38. Davison P, Asch RG. Plastic ingestion
by mesopelagic fishes in the North Pacific Subtropical Gyre. Mar Ecol
Prog Ser 432:173–180 (2011); doi:
10.3354/meps09142.
39. Murray F, Cowie P. Plastic contamination in the decapod crustacean
Nephrops norvegicus (Linnaeus, 1758). Mar Pollut Bull 62(6):1207–1217 (2011); doi:
10.1016/j.marpolbul.2011.03.032.
40. Cole M, et al. Microplastic ingestion by zooplankton. Environ Sci Technol 47(12):6646–6655 (2013); doi:
10.1021/es400663f.
41. Ellison K. The trouble with nurdles. Front Ecol Environ 5(7):396 (2007).
42. Gassel M, et al. Detection of
nonylphenol and persistent organic pollutants in fish from the North
Pacific Central Gyre. Mar Pollut Bull 73(1):231–242 (2013); doi:
10.1016/j.marpolbul.2013.05.014.
43. EPA. EPA and U.S. Fish and Widlife
Service Partner to Protect Wildlife at Hawaii’s Tern Island [press
release]. San Francisco, CA:U.S. Environmental Protection Agency, Region
9 (9 September 2014). Available:
http://www.epa.gov/region9/mediacenter/tern-island/ [accessed 28 January 2015].
44. Rochman CM, et al. Polybrominated
diphenyl ethers (PBDEs) in fish tissue may be an indicator of plastic
contamination in marine habitats. Sci Total Environ 476–477:622–633
(2014); doi:
10.1016/j.scitotenv.2014.01.058.
45. Browne MA, et al. Ingested microscopic plastic translocates to the circulatory system of the mussel,
Mytilus edulis (L.). Environ Sci Technol 42(13):5026–5031 (2008); doi:
10.1021/es800249a.
46. von Moos N, et al. Uptake and effect of microplastics on cells and tissue of the blue mussel
Mytilus edulis L. after an experimental exposure. Environ Sci Technol 46(20):11327–11335 (2012); doi:
10.1021/es302332w.
47. Hale RC, et al. Ghosts in the Machine:
Releases of Flame Retardants from Microplastics and Recycled Materials
[abstract]. Presented at: Society of Environmental Toxicology and
Chemistry North America 35th Annual Meeting, Vancouver, British
Columbia, Canada, 9–13 November 2014. Brussels, Belgium, and Pensacola,
FL:Society of Environmental Toxicology and Chemistry (2014). Available:
http://vancouver.setac.org/wp-content/uploads/2014/10/SETAC-Vancouver-Abstracts.pdf [accessed 28 January 2015].
48. Browne MA, et al. Accumulation of
microplastic on shorelines worldwide: sources and sinks. Environ Sci
Technol 45(21):9175–9179 (2011); doi:
10.1021/es201811s.
49. Law KL, Thompson RC. Microplastics in the seas. Science 345(6193):144–145 (2014); doi:
10.1126/science.1254065.
50. Welshons WV, et al. Large effects from
small exposures. I. Mechanisms for endocrine-disrupting chemicals with
estrogenic activity. Environ Health Perspect 111(8):994–1006 (2003);
http://www.ncbi.nlm.nih.gov/pubmed/12826473.
51. Halden RU. Plastics and health risks. Annu Rev Public Health 31:179–194 (2010); doi:
10.1146/annurev.publhealth.012809.103714.
52. Obbard RW, et al. Global warming
releases microplastic legacy frozen in Arctic Sea ice. Earth’s Future
2(6):315–320 (2014); doi:
10.1002/2014EF000240.
53. Chan K. Hong Kong plastic pellets
spill: Sinopec vows to clean up beaches. Huffington Post, Green section
(9 August 2012). Available:
http://www.huffingtonpost.com/2012/08/10/hong-kong-plastic-pellets-spill_n_1759119.html [accessed 28 January 2015].
