11 JULY 2014 • VOL 345 ISSUE 6193 145 SCIENCE sciencemag.org
that pass through wastewater
treatment into the environment. Although the sources
are well known, knowledge
of their relative contribution
and geographic distribution is
Once in the ocean, floating
microplastics are transported
passively by complex two-and three-dimensional physical flows, resulting in very
large variability in surface
concentrations that makes
detection of long-term trends
difficult even in the heavily
sampled western North Atlantic (2) and eastern North
Pacific Oceans (3). Oceanographic models [including
(4)] and environmental observations find very high concentrations (up to 106 pieces
km–2) of floating microplastic
in subtropical ocean gyres,
far from land-based sources.
In these gyres, converging
surface currents trap and retain floating debris. Similarly
high concentrations have
been observed in enclosed
basins such as the Mediterranean Sea (5).
In coastal sediments around the world,
microplastics also appear to be ubiquitous,
with quantities typically ranging from 2
to 30 particles per 250 ml of sediment (6).
Arctic sea ice is the most recently identified
reservoir of microplastics (7). With the exception of localized spills, the relationship
between microplastic concentration and
its sources is poorly understood because
of complex transport mechanisms and unknown fragmentation rates.
Because of their size, microplastics may
have different effects from larger items of
debris. For example, floating microplastics
in open ocean gyres provide habitats for
diverse communities of microorganisms,
with assemblages that differ from those in
surrounding seawater and that vary with
polymer type (8). Furthermore, microplastics may be ingested by many diverse
organisms, and some animals such as mussels can retain particles after ingestion (9);
ingestion of small quantities of microplastics can disrupt physiological processes in
marine worms, compromising their ability
to store energy (10).
Plastic debris readily accumulates harmful chemicals such as dichlorodiphenyltrichloroethane (DDT), polychlorinated
biphenyls (PCBs), and polybrominated
diphenyl ethers (PBDEs) from seawater
worldwide (11), increasing their concentration by orders of magnitude. This process
is reversible, with microplastics releasing
contaminants upon ingestion (12) and laboratory evidence of uptake in marine worms
(13) and fish (14). Transfer depends on the
polymer, contaminant, and conditions in
the organism, particularly pH and temperature. These interactions are specific but
not yet fully predictable (15). There is also
concern that plastic debris might release
monomers and potentially toxic additives
such as plasticizers, flame retardants, and
antimicrobial agents that are incorporated
into plastics during manufacture.
This emerging evidence of harm comes
primarily from laboratory studies. It is
unclear whether microplastics in the en-
vironment transport chemicals to biota in
concentrations high enough to cause sub-
stantial damage. The potential for harm
from microplastics could increase with
decreasing particle size, but size distribu-
tions and generation and degradation rates
are essentially unknown, and the resulting
effects on natural populations are difficult
to ascertain. Nevertheless, ingestion of
microplastics by mammals,
fish, birds, and invertebrates
is now well documented. Al-
though quantities can be low,
the widespread incidence in
some natural populations
together with evidence of
potentially harmful effects is
cause for concern.
Major questions remain
about the risks from micro-
plastics to marine organ-
isms and ecosystems, as well
as to food safety and public
health. Research is urgently
needed on the behavior of
different polymers in the en-
vironment, including frag-
mentation, chemical release,
degradation, transport, and
accumulation; the rate at
which organisms encounter
microplastics, based on parti-
cle size and degradation time;
and the physical, chemical,
and interactive risks to organ-
isms from these encounters,
including possible magnifica-
tion with increasing trophic
Given the concerns over
microplastics, the temptation
may be to “clean up the mess,” but substan-
tial removal of microplastic debris from the
environment is not feasible. Identification
and elimination of some of the major inputs
of plastic waste is a more promising route, as
is reduced consumption and the recognition
of plastic waste as a resource. With the rap-
idly increasing human population, the need
for greater resource efficiency could have a
secondary benefit in reducing the quantities
of debris entering the environment. ■
1. R. C. Thompson et al., Science 304, 838 (2004).
2. K. L. Law et al ., Science 329, 1185 (2010).
3. K. L. Law et al ., Environ. Sci. Technol. 48, 4732 (2014).
4. N. Maximenko, J. Hafner, P. Niiler, Mar. Pollut. Bull. 65, 51
5. A.Collignon etal.,Mar.Pollut.Bull.64,861(2012).
6. M. A. Browne etal., Environ.Sci. Technol. 45, 9175 (2011).
7. R. W. Obbard et al ., Earth’s Future , (2014); http://
8. E.R.Zettler, T.J.Mincer, L.A.Amaral-Zettler, Environ. Sci.
Technol. 47, 7137 (2013).
9. M. A. Browne, A. Dissanayake, T. S. Galloway, D. M. Lo we, R.
C. Thompson, Environ. Sci. Technol. 42, 5026 (2008).
10. S.L. Wright, D.Rowe,R.C. Thompson, T.S.Galloway,Curr.
Biol. 23, R1031 (2013).
11. Y. Ogata et al., Mar. Pollut. Bull. 58, 1437 (2009).
12. E.L. Teuten et al., Phil. Trans. R. Soc. B 364,2027(2009).
13. M.A.Browne, S.J.Niven, T.S.Galloway, S.J.Rowland,R.C.
Thompson, Curr. Biol. 23, 2388 (2013).
14. C. M. Rochman et al ., Nat. Sci. Rep. 3, 3263 (2013).
15. A.Bakir, S.J.Rowland,R.C. Thompson, Environ. Pollut.
185, 16 (2014).
1Department of Oceanography, Sea Education Association,
Woods Hole, MA 02543, USA. 2School of Marine Science and
Engineering, Plymouth University, Plymouth PL4 8AA, UK.
E-mail: email@example.com 10.1126/science.1254065
Microplastics everywhere. Microplastics collected from seawater, shorelines, or marine
sediments are typically defined as particles with a diameter of 5 mm or less. Sources include
larger deteriorating plastic items, as well as microbeads used in the cosmetics industry. The
microplastics in the photo were collected in the North Pacific subtropical gyre with a surface