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Foamed Polystyrene in the Marine Environment: Sources, Additives,
Transport, Behavior, and Impacts
Andrew Turner*
Cite This: Environ. Sci. Technol. 2020, 54, 10411−10420
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ABSTRACT: Foamed polystyrene (PS) that may be either expanded (EPS) or
extruded (XPS) is a rigid, lightweight insulating thermoplastic that has a variety
of uses in the consumer, packaging, construction, and marine sectors. The
properties of the material also result in waste that is readily generated, dispersed,
and fragmented in the environment. This review focuses on foamed PS in the
marine setting, including its sources, transport, degradation, acquisition of
contaminants, ingestion by animals, and biological impacts arising from the
mobilization of chemical additives. In the ocean, foamed PS is subject to wind-
assisted transport and fracturing via photolytic degradation. The material may
also act as a substrate for rafting organisms while being exposed to elevated
concentrations of natural and anthropogenic surface-active chemicals in the sea
surface microlayer. In the littoral setting, fragmentation is accentuated by milling
in the swash zone and abrasion when beached, with wind transport leading to
the temporary burial of significant quantities of material. Ingestion of EPS and XPS has been documented for a variety of marine
animals, but principally those that feed at the sea surface or use the material as a habitat. As well as risking injuries due to gastro-
intestinal blockage, ingestion of foamed PS exposes animals to harmful chemicals, and of greatest concern in this respect is the
presence of the historical, but still recycled, flame-retardant, hexabromocyclododecane. Because foamed PS is particularly difficult to
retrieve as a constituent of marine litter, means of reducing its presence and impacts will rely on the elimination of processes that
generate foamed waste, modification of current storage and disposal practices, and the development of more durable and sustainable
alternatives.
1. INTRODUCTION
Marine pollution from plastics has received an enormous
amount of scientific, media, and public attention over the past
two decades. Studies on plastics have focused on methods of
sampling, sources, distributions, impacts on the environment
and on wildlife, and the uptake of pollutants, with a number of
reviews that attempt to synthesize research in each area or a
combination of areas.
1−4
For materials of comparable bulk
characteristics (e.g., density and crystallinity), distributions,
sinks, and physical impacts are expected to be broadly similar
and in most review articles plastics or microplastics are explicitly
or implicitly defined under a single umbrella. For foamed
plastics, however, densities are so much lower than unfoamed
equivalents that their behavior is distinctly different and they
should, strictly, be classified independently.
In the present paper, the focus is on one of the most important
and widely used types of foamed plastic, polystyrene (PS). This
material is a common component of marine litter and is
particularly problematic from both a local and transboundary
perspective.
5−9
Information and data are critically reviewed in
the scientific literature on the sources, chemical composition,
transport, fate, and impacts of foamed PS in the marine
environment. Where informative, comparisons are also made
with (unfoamed) polyethylene, another common component of
marine litter whose greater density ensures its pathways and
behavior are markedly different from foamed PS. The more
general challenges associated with the generation and disposal of
large quantities of foamed PS in society are addressed, and
current and proposed solutions to these problems are reviewed.
2. FOAMED PS: PRODUCTION, USES, WASTE, AND
MARINE LITTERING
PS is a rigid, amorphous thermoplastic produced by free radical
vinyl polymerization of styrene. The structure of the polymer
can be written thus: [CH2CH(C6H5)]n; where C6H5is a
pendant phenyl group which restricts rotation and is responsible
for many of the physical and mechanical properties of the
polymer. Both expanded PS (EPS) and extruded PS (XPS) are
forms of the polymer that contain a high proportion of air
(>95%).
10,11
EPS is produced when the raw, pelletized material
Received: May 19, 2020
Revised: August 5, 2020
Accepted: August 5, 2020
Published: August 5, 2020
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is expanded by heating with steam to form cellular beads. Dried
particles are then fused under steam and molded into blocks or
other shapes, with beads of 2−5 mm in diameter clearly visible in
the final product. The air within and between the beads gives
EPS its insulating properties but interparticle air, as irregular
gaps or voids, renders the material susceptible to (limited) water
absorption. XPS is formed when PS crystals, additives, and
blowing agents are extruded at high temperature to produce a
frothy liquid that is subsequently shaped in a die as it cools and
expands. XPS consists of tightly packed cells that have no gaps or
voids between them. This closed structure inhibits water
absorption and results in a smoother surface and a higher
density than EPS. Note that Styrofoam is often used
synonymously with foamed PS but is, strictly, a trademarked
brand of XPS produced for building insulation by Dow
Chemical.
Foamed PS is commonly employed in home and appliance
insulation, protective packaging, automobile parts, embankment
filling, lightweight concrete (as an aggregate), and food
packaging;
11,12
with regard to the construction sector, XPS is
favored over EPS where pressure, stability, and humidity are
especially high.
13
The durability, low density, and insulating
properties of foamed PS have also resulted in many applications
in the marine sector. Here, EPS (and less frequently, XPS) are
used in fish boxes, buoys, pontoons, floating docks, net floats, life
jackets, surfboards, and boat stands.
14−17
As a tethered floating
base, EPS is used directly, or for greater durability, may be
coated or covered by hard plastic or cement.
13
Because of growing demand and extensive use on land and at
sea, coupled with recycling that is constrained by bulk and
contamination (by food, for example), foamed PS represents an
important form of waste. European data for 2016/2017 suggest
that waste generation of foamed PS from construction and
packaging was about 530 000 tonnes, with a recycling rate of
27% in total for EPS (and 34% for single use packaging waste and
8% for construction waste) and energy recovery by incineration
as the most common method for its disposal.
13
Loss of foamed PS to the environment may occur via the
transport, storage, or cutting of construction material, escape-
ment of waste from controlled and historical landfill, storage or
compaction of waste before or during disposal or recycling,
deterioration or loss of structures in situ, and littering and fly
tipping. Waste enters the marine environment through rivers,
stormwater, and wastewater treatment plants, and from direct
littering and loss or structural damage at sea or in the littoral
zone. Not only is foamed PS a significant contributor to marine
litter worldwide,
9,18−24
its lightness and low density, ready
transportation by the wind, and propensity to readily fragment
ensure that it disperses more widely and rapidly than other forms
of (unfoamed) plastic, both at sea and when beached.
8,25,26
With
small fragments readily blown around by the wind when dry and
adhering to surfaces when wet, foamed PS is also particularly
difficult to retrieve during beach cleans.
The images in Figure 1 exemplify some of the uses of foamed
PS that may directly impact on the marine environment, along
with the volume, nature, and consequences of secondary
(fragmented) particles that can be readily washed up and
blown around. Material illustrated here ranges in size from EPS
beads of a few mm in diameter to slabs greater than 1 m across.
However, empirical studies suggest that, ultimately, weathering
may produce spherical and elongated particles of dimensions
down to hundreds of nm.
27
3. TRANSPORT AND PHYSICAL BEHAVIOR IN THE
MARINE ENVIRONMENT
The properties of foamed PS that are of relevance to its behavior
and fate in the marine environment are shown in Table 1. Here,
data are indicative and are based on the properties of a specific
brand or a range of brands of EPS, which is far better
characterized than XPS in the literature. Note, however, that in
general, XPS has a slightly higher density, greater tensile, impact,
and compressive strengths, and lower water absorption than
EPS.
28
Figure 1. Foamed PS captured around or retrieved from the coast of
southwest England. (a) An abundance of EPS and XPS among litter
along the strandline; (b) EPS remains of a weather balloon; (c) a
discarded EPS surfboard; (d) stacked EPS slabs used as boat stands; (e)
fouled and rounded fragments of beached EPS and XPS litter; (f) EPS
beads scattered at the base of a cliff. Photographs courtesy of Claire
Wallerstein and Tracey Williams.
Table 1. Properties of Foamed PS of Relevance to the
Discussion
a
property mean ±1 sd or range source
Physical
density 0.01 to 0.19 g cm−310
permeability 0.5 to 3.5 29
water absorption 0.03 to 9.0% 29
pore volume 0.02 ±0.005 cm3g−130
average pore diameter 39.3 ±0.5 nm 30
Mechanical
tensile strength, ultimate 0.08 to 0.91 MPa 29
compressive yield strength 0.069 to 10.9 MPa 29
tear strength 1.05 to 5.29 kN m−129
Surface
BET specific surface area 2.03 ±0.04 m2g−130
point of zero charge 4.7 ±0.2 30
a
Data are shown for a single, unspecified EPS product or a range of
EPS products.
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3.1. In the Ocean. The following discussion focuses on
floating and fragmented foamed PS in the ocean, with the effects
and forcing mechanisms acting upon this type of litter
conceptualized in Figure 2 as an aid to the narrative.
One of the key differences in the transport of plastics having a
density slightly lower than seawater (like polyethylene without
any inclusions of air) to those having a density significantly lower
than seawater and floating at the surface (foamed plastics) is the
influence of windage, or drift due to wind forces.
31
Specifically,
and neglecting any phenomena incurred by viscous forces, wind
pressure acting on the upper (“sail”) surface of a particle is
opposed by the drag force applied to its lower, submerged
(“drag”) surface, with the ratio of sail and drag surface areas
dependent on particle and fluid densities and determining the
magnitude of windage. The high buoyancy of foamed PS also
confers a relatively low floating stability, especially if objects are
rounded. Thus, because the center of gravity is well above the sea
surface, objects tend to repeatedly change position and
orientation during transportation.
33
The effect of windage on the ocean transport of foamed PS of
density = 0.05 g cm−3and polyethylene of density = 0.95 g cm−3
was considered theoretically by Chubarenko et al.
32
Specifically,
calculations were performed for spherical particles (of any
diameter) carried in inviscid (Baltic) seawater of density ∼1.01 g
cm−3and with a current speed, vc, of 0.3 m s−1that were subject
to a wind blowing in the same direction at a speed, vw,of10m
s−1. The drift speeds for PS and polyethylene, vPS, and vPE, were
estimated to be about 1.2 m s−1and 0.4 m s−1, respectively, or
four times and 25% higher than vc. In other words, and under
these environmental conditions, foamed PS whose density is not
significantly modified by fouling (see below) is predicted to
travel three times faster in seawater than polyethylene.
An additional consequence of foamed PS residing at the sea
surface is that it is exposed to a greater amount of sunlight than
plastics that are less buoyant and, through turbulence, are
transported in the bulk medium.
34
Moreover, the aromatic
backbone of PS acts as an effective absorber of solar radiation in
the ultraviolet (UV) region.
35
Absorption of sunlight causes
cleavage of polymer chains by chain scission, with styrene
monomers the principal product of degradation.
36
Resulting
embrittlement of the foamed PS surface causes fracturing and,
eventually, fragmentation.
8
Experiments performed by Song et
al.
37
showed that two months of exposure to UV light generated
by a metal-halide lamp was sufficient to break EPS beads (∼20
mm3) into microfragments, thereby exposing new surfaces to
UV radiation and promoting further degradation. A recent study
conducted by Zhu et al.
38
compared the degradation of
postconsumer EPS under simulated solar radiation with that
of other plastics (including polyethylene). Based on mass loss
over the experimental period employed, the authors estimated
lifetimes of 2.7 years for EPS and 33 years for polyethylene. By
comparison, microbial biodegradation of foamed PS can be
considered almost negligible over such timeframes.
39
Figure 2. Conceptual representation of the effects and forcing mechanisms acting on a foamed PS sphere in the ocean.
Figure 3. Conceptual representation of the effects and forcing mechanisms acting on foamed PS fragments in the sandy littoral zone.
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3.2. in the Littoral Zone. Ultimately, a significant fraction
of both oceanic and land-derived foamed PS will end up in the
littoral zone, including mangroves, beaches, and rocky
shores.
19,20,24
The effects and forcing mechanisms acting upon
this type of litter on a sandy shoreline are conceptualized in
Figure 3 as an aid to the following discussion.
When beached, both photolytic and thermal degradation of
foamed PS are accentuated because significantly higher
temperatures are possible in sand compared with seawater.
8
Moreover, mechanical fragmentation is highly favorable here
because wind-driven transport engenders frictional forces and
collisional impacts on material of inherently low tensile strength
(Table 1). For example, experiments that exposed EPS beads to
UV radiation under a metal-halide lamp for 12 months and
subsequently subjected them to mechanical abrasion (through
agitation with sand) resulted in the majority of the original
particle volume becoming fragmented to sizes too small (<1
μm) to be detected.
37,40
Mechanical fragmentation of foamed PS also takes place in the
swash zone where litter already weakened by photolytic
processes is “milled”with sand and pebbles as it is transported
under dynamic, asymmetrical wave motion. Chubarenko and
co-workers
41,42
conducted experiments in which plastics,
including EPS, were subject to simulated swash conditions for
24 h in the presence of sand, gravel, and pebbles. Results
revealed that material was smoothed, polished, torn, and
fragmented and that, although impaction of EPS with pebbles
was low compared with other plastics because of the high
buoyancy of the material, these interactions resulted in the
greatest number of fragmented particles. Significantly, despite
the low density of EPS, some beads formed on fragmentation
became attached to or trapped-buried by the sediment. The
burial and subsequent compaction of EPS beads also appears to
take place on more landward reaches of a beach. Here, material
blown against a physical barrier along with other light plastics is
subsequently buried by accumulations of drifting sand.
4. COMPOSITION AND CHEMICAL MODIFICATION OF
FOAMED PS IN THE MARINE ENVIRONMENT
Although the general behavior of foamed PS in the oceans and
when beached has been addressed above, the precise impacts of
the material in the marine setting are likely to be influenced by
the presence, concentrations, and mobilities of the monomer
(styrene), oligomers, reaction residues, and additives in the
matrix, and any chemicals and contaminants that have been
acquired from the environment.
Residues in foamed PS include Fe2O3, used as a catalyst in the
production of styrene,
43
and Zn stearate, often used to ensure
uniform cell nucleation in the production of EPS.
44
Additives are
sometimes applied as a thin surface finish for protection but
most are usually blended or molded into the raw material to
ensure uniform concentration and are tailored to the specific
requirements and applications of the material. For instance,
addition of graphite can improve insulation properties of
construction boards, various pigments may be employed to
impart a range of different colors, and TiO2may be added to
assist bacterial decomposition or as a pigment to provide a high
refractive index.
13,45
Plasticizers and biocides are not generally
used in foamed PS but the stabilizer and antioxidant tris(4-
nonylphenyl) phosphite, a source of the endocrine-disrupting
nonylphenols, is sometimes added.
46
Traces of other organic
additives in EPS have also been mentioned or implied but have
not been identified.
47,48
However, because of the inherent
flammability of foamed PS the most commonly employed
additives are flame-retardants.
4.1. Hexabromocyclododecane. Flame-retardants are
added to foamed PS destined for the construction industry
but are also encountered in packaging material because one
grade of material may be adopted for all production.
13
The most
important flame-retardant used in EPS and XPS since the 1980s
has been 1,2,5,6,9,10-hexabromocyclododecane (HBCD),
49−51
whose physical, chemical, environmental, and toxicological
properties that are relevance to the discussion are given in Table
S1. HBCD is added at concentrations that are low relative to
those of other halogenated compounds used to flame-retard
plastics; specifically, typical HBCD concentrations range from
about 0.7 to 2.5% by weight of the raw product, with XPS usually
containing more of the retardant than EPS.
52
Moreover, and
unlike flame-retarded plastics more generally and including
polyethylene, foamed PS impregnated with HBCD does not
require the addition of antimony trioxide (Sb2O3) as a synergist
to meet various building code specifications.
53
On health and
environmental grounds, however, HBCD was recently added to
Annex A of persistent organic pollutants in the Stockholm
Convention that require elimination,
54
effectively banning the
production and use of the compound in PS foams for
buildings.
55
The EU has also since introduced a low
concentration limit of 0.1% (1000 mg kg−1) by weight for
certain brominated compounds, including HBCD, above which
items may not be recycled, and a limit of 0.01% (100 mg kg−1)
above which products are not permitted for sale.
56
Recent focus has been on alternative flame-retardants, resins,
or designs for foamed polystyrene, with halogen-free retardants
considered best for the environment and human health.
57
However, despite the restrictions on HBCD, the flame-retardant
continues to be reported in an array of foamed PS consumer
products where fire suppression is neither required nor desired,
including food-contact articles and general purpose packaging,
suggesting a continuing uncontrolled use or recycling of the
chemical.
58,59
Moreover, it has been forecast that the amount of
construction and demolition waste containing HBCD will
continue to increase until 2050.
13
The historical use and contemporary recycling of HBCD,
together with its persistence in the marine environment, are also
reflected by its presence in foamed PS encountered in beach
litter and functional maritime constructions throughout the
ocean.
60,61
For example, in the north Pacific, HBCD was
detected in nearly all samples analyzed (n> 200) that had been
collected after the chemical was listed in the Stockholm
Convention, with concentrations ranging from 0.05 to 14 500
mg kg−1.
61
Some of the highest concentrations, and well above
the EU low concentration limit, were reported for aquaculture
buoys where flame-retardancy is clearly unnecessary. Signifi-
cantly, because HBCD is not covalently bonded to the polymer,
mobilization into the environment gradually takes place,
62
with a
lipophilicity (log Kow = 5.6
63
) ensuring that it will readily bind
with organic matter and concentrate in organisms.
4.2. Styrene. In theory, the polymerization of styrene results
in repeating monomer units that are covalently bonded and
difficult to break. In practice, however, this process is incomplete
and the styrene monomer and oligomers may contaminate the
final foamed PS product.
Styrene monomer released from PS is highly reactive toward
cell systems and causes widespread metabolic damage, raising
concerns about its migration from foamed PS packaging into
food.
46
In the environment, however, the monomer is rapidly
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volatilized and readily degraded and is not considered to
bioaccumulate.
64
On the other hand, the oligomers of styrene
appear to present a very low risk to consumers through food
packaging but are less mobile and more persistent in the
environment,
65
with the latter characteristics affording a
potential means of assessing contemporary and historical
pollution by PS.
66
For example, Kwon et al.
67
measured various
styrene-based contaminants (including the trimer, 2,4, 6-
triphenyl-1-hexene, and the dimer, 2,4-diphenyl-1-butene) in
coastal seawater and beach sand collected from different parts of
the world and found that combined concentrations were variable
but highest (and up to about 30 μgL
−1in seawater and 30 mg
kg−1in sand) along the most populated coastlines. Distributions
were attributed to the leaching of the oligomers from weathered,
foamed PS on beaches and their subsequent adsorption onto
sand, with transfer to seawater taking place via desorption from
contaminated sand or more directly through the leaching of the
chemicals from floating PS litter. A more recent study suggested
that oligomer concentrations in coastal seawater may also be
augmented by inputs from contaminated catchment runoff.
68
4.3. Surface Modification of Foamed PS and Acquis-
ition of Environmental Contaminants. The weathering and
chemical and biological fouling of foamed PS, evident in Figure
1e, result in significant modifications to the polymer surface. For
example, measurements made by Zhang et al.
30
on virgin and
beached EPS revealed an increase in specific surface area (from
about 2 to 8 m2g−1), micropore area (from <0.1 to 0.5 m2g−1),
and point of zero charge (from 4.7 to 5.0) on weathering; by
comparison, the specific surface area of aged polyethylene is just
0.13 m2g−1.
69
Not only do these characteristics confer a greater
reactivity in the aqueous medium, the high positive buoyancy of
foamed PS ensures that it is persistently exposed to a wide array
of chemicals in the sea surface microlayer (Figure 2). This is a
skin of water of 1−1000 μm thick enriched in various inorganic
salts, hydrophobic or surface-active biogenic compounds, fuels
and oils, and various trace contaminants of low solubility or that
have been deposited from the atmosphere.
70,71
Specifically,
concentrations of some pollutants, like chlorinated hydro-
carbons and heavy metals, may be up to 500 times higher in the
microlayer compared with the underlying bulk water column.
72
Hydrophobic chemicals have a propensity to interact with the
embrittled and fractured PS surface
47
and, while metal ions are
known to readily adsorb onto hydrogenous precipitates on
polyethylene,
73−75
this has yet to be empirically demonstrated
for foamed PS.
The acquisition of chemicals from the environment and the
more general biological fouling also act to increase the net
density of foamed PS. However, and in contrast to unfoamed
plastics, this increase is not likely to be sufficient to cause a
significant shift in buoyancy or effect sinking unless particles are
considerably smaller than the diameter of component PS cells.
76
5. IMPACTS ON MARINE ORGANISMS
Foamed PS does not represent a significant risk of entanglement
to marine wildlife but can exert impacts through ingestion and
interaction.
IngestionoffoamedPSmayarisedirectlyfromthe
inadvertent consumption of material mistaken for food that is
floating in the water column, deposited on beaches, trapped in
macroalgae, or acting as a substrate-habitat, and indirectly via
the consumption of contaminated prey. Consequently, ingestion
has been documented in the stomach contents or fecal matter of
a range of marine animals, including crustaceans, fish, birds,
turtles, and mammals, and as exemplified in Table 2. Seabirds in
particular are commonly observed to consume foamed PS
because floating fragments are similar in size and color to normal
prey items like fish, fish eggs, and larvae.
90
Birds that feed by
dipping, fluttering above the surface, surface plunging, surface
seizing, and scavenging are most likely to inadvertently ingest a
material. In addition, distinctive marks on fragments of EPS and
XPS retrieved from the shore suggest that some birds, including
fulmars and gulls, peck at foamed PS, resulting in the ingestion of
small particles.
91,92
Pecking may be practiced out of curiosity or
through confusion with the brittle and bright white, internal
shells of cuttlefish that act as a supplemental source of calcium
carbonate.
Many of the broad physical impacts resulting from the
ingestion of foamed PS are likely to be common to those
resulting from the ingestion of other plastics. These include
intestinal blockage and injury to the digestive tract, with
potential longer-term effects involving reduced body weight and
fitness and slower growth. However, given foamed PS’s relatively
low density, smooth surface, high flexibility, and propensity to
fragment, these impacts may be less severe or long-lasting than
those effected by harder and sharper plastics like polyethylene.
Plastic manufactured or fragmented to dimensions on the order
of a few μm or less (nanoplastics) may also be captured by
organisms as small as zooplankton and, in many cases, undergo
internalization and translocation.
93
Regular industrial (un-
foamed) PS nanoparticles (density ∼1.1 g cm−3) have been
frequently studied through in vitro cultures with crustaceans,
invertebrates, and fish and have resulted in a range of adverse
effects, including delayed growth, repressed immunity, histo-
pathological changes, behavioral changes, and decreased
reproduction.
94−97
It remains unclear, however, as to whether
these effects can be extrapolated to positively buoyant foamed
PS should fragments be weathered down into nanoplastic
dimensions.
Table 2. Examples of Reports of the Ingestion of Foamed PS
by Marine Wildlife
animal location material
description reference
black footed albatross Central Pacific foam,
including PS 77
laysan albatross Central Pacific foam,
including PS 77
atlantic ghost crab Southwest Atlantic XPS 78
sand hopper Mediterranean EPS 79
blue mussel English Channel foamed PS 80
gooseneck barnacles North Pacific
Subtropical Gyre foamed PS 81
kelp gull Southwest Atlantic foamed PS 82
red-footed booby South China Sea foamed PS 83
various albatrosses and
petrels South Atlantic foamed PS 84
northern fulmar Northeast Pacific Styrofoam 85
northern fulmar Northeast Atlantic expanded PS 86
green turtle Southwest Atlantic XPS 87
loggerhead turtle Southwest Atlantic XPS 87
narrow-ridged finless
porpoise Yellow Sea-Bohai Sea foamed PS 88
elephant seal Northeast Pacific Styrofoam 89
steller sea lion Northeast Pacific Styrofoam 89
polychaete worms Yellow Sea EPS 101
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An additional impact resulting from ingestion of foamed PS is
the exposure to chemicals associated with the material through
manufacturing or acquisition from the environment. Exposure is
normally evaluated in vitro by subjecting test material to
conditions that mimic the digestive environment and measuring
chemical mobilization or bioaccessibility (as an upper bound
estimate of bioavailability). Coffin et al.
48
determined the
quantities of various organic additives released from 16 different
plastics subjected to solutions representative of the digestive
environments of fish and seabirds as well as the estrogen-
receptor activities of the resulting extracts using an in vitro cell
line. Biological estrogenicity was significantly enhanced by
extracts of three plastics (including EPS) in both digestive
solutions but the precise additives or residues responsible were
not among the chemicals characterized by the authors. Turner
and Lau
60
report that neither Br (a proxy for HBCD) nor Zn
(indicative of Zn stearate) were detected by ICP in extracts of
aged, beached EPS subjected to a simulated avian digest, but that
Fe oxide was measurably mobilized (presumably together with
any contaminants associated with this phase) from the fouled
surface. More sensitive HPLC analysis of HBCD in EPS buoys
maintained in dark seawater, however, reveal that the
brominated flame-retardant is slowly mobilized from the
plastic
62
and, therefore, has the potential to be released under
harsher digestive conditions of sea birds and other animals.
Interactions refer to a variety of impacts arising from contact
of marine organisms with the material as an abiotic substrate and
that can also, ultimately, result in plastic ingestion. For instance,
certain organisms are able to colonize foamed PS as a rafting
substrate, an effect that was originally documented for bacteria
growing on EPS beads in the coastal waters of New England.
98
More recently, Carson et al.
99
determined concentrations of
bacteria up to 12 000 mm−2on EPS fragments retrieved from the
North Pacific Gyre; by comparison, maximum bacteria
concentrations on polyethylene fragments from the same region
were <5000 mm−2. It has been proposed that the initial
colonization of foamed PS is more favorable than on unfoamed
plastics because the greater rugosity of the former facilitates
adhesion and affords protection.
33
Foamed PS, however,
displays relatively low species richness because of floating
instability; that is, multiple positional changes that incur
frequent exposure to air and direct sunlight negatively affect
broader colonization.
33
Consequently, free-floating, foamed PS
likely acts as rafting and dispersing substrate for a limited
number of organisms that grow during initial stages of
community succession.
Jang et al.
100
describe marine mussels, Mytilus galloprovincia-
lis, inhabiting the EPS of tethered aquaculture buoys offthe
coast of South Korea and demonstrated that HBCD is
transferred from the substrate to the bivalve with resultant
lipid weight concentrations of up to 5.2 mg kg−1. The authors
suggest that HBCD is bioaccumulated through the direct
ingestion of fragmented EPS particles and via leaching of the
chemical and its subsequent adsorption onto food particulates.
Aquaculture buoy EPS also hosts a variety of polychaete worms,
both at the surface and, via burrowing, within the internal
structure.
101
Worms generate and subsequently consume debris,
with an average of over 100 EPS particles reported in the
digestive tracts of burrowing individuals.
Filter-feeding sphaeromatid isopods excavate burrows for
their habitat and dense colonies are known to cause extensive
damage to floating docks constructed of EPS.
102
Burrowing may
release large fragments of EPS that disperse isopods and are
responsible for the generation of significant quantities of
microplastics. Laboratory experiments conducted by David-
son
103
suggest that individual bioeroders can create several
thousand particles when excavating a burrow, which is
equivalent to 100 000 organisms per m3creating over 400
million particles. Microplastics may then be ingested by a range
of organisms, including those that are cultured near to floats for
human consumption.
Biotic interactions with foamed PS also take place in reaches
of the littoral zone that are never inundated but where debris
from both marine sources and beach littering may accumulate.
Poeta et al.
25
found that certain dunal plants were able to
perforate EPS debris on a sandy beach situated along the
Tyrrhenian coast of Italy. Although these observations were
attributed to opportunistic events, the authors suggested that the
thermal, mechanical, and water absorbing properties of EPS may
be generally favorable for this kind of interaction and that the
phenomenon might be more widespread on a global scale.
6. EMERGING SOLUTIONS TO FOAMED PS WASTE
GENERATION AND DISPOSAL
The discussions above highlight the problems of foamed PS in
the marine environment arising from the quantity and diversity
of applications of the material, its low density, ready
fragmentation and dispersal in the ocean and littoral environ-
ments, the presence of harmful additives, and difficulty in
retrieval of waste through, for example, beach cleans. Ultimately,
countering these problems requires a reduction in the usage of
foamed PS, modification or replacement of the material, or
better management and recycling of PS-bearing waste.
Alternative materials to or designs of foamed PS require an
ability to perform same function (e.g., insulation, fire-retardancy,
strength, flotation) and yet be cost-effective, long-lasting, and/or
more environmentally sustainable throughout their life cycle.
Examples that are becoming popular or that have been tested but
are not widely employed are reported by Lassen et al.
13,104
In the
construction sector, alternative materials are mineral and glass
wools, phenolic foams, natural fibers,perlite,andwood
fiberboards, with a modification of foamed PS that requires
less material to obtain equivalent insulation achieved by the
addition of graphite. Elsewhere, alternatives include corrugated
cardboard for single use products, with polyethylene or
polyethylene terephthalate lining where water absorption may
be a problem, inflated air packets or molded pulp loose fill for
single-use packaging, expanded polypropylene (a more robust
foamed plastic) for multiuse packaging, and higher density EPS
to enhance abrasion-resistance. In cities, states, and municipal-
ities where restrictions or bans on single-use foamed PS products
are in place, many compostable or readily recyclable alternatives
have been introduced.
19,105,106
Such alternatives also need to be
considered for Europe where legislation is being drafted
(Directive 2019/904, planned to be effective from July 2021)
to ban single-use plastics that include EPS-XPS food and
beverage containers.
9
(In the UK, recent legislation bans specific
single use plastics but thus far no specific mention is made of
foamed PS products
107
).
In the marine sector, modificationsoralternativesto
conventional floats and buoys include air-filled plastics, plastic-
coated EPS, or EPS contained by netting.
108
However, there are
additional problems with these constructions, such as increased
cost, difficulties in tying to other structures, and enhanced
biofouling. Incentive schemes for aquaculture farmers and
fishermen to retrieve floating devices constructed of EPS have
Environmental Science & Technology pubs.acs.org/est Critical Review
https://dx.doi.org/10.1021/acs.est.0c03221
Environ. Sci. Technol. 2020, 54, 10411−10420
10416
been trialed in Taiwan but have proven only partly successful,
with suggestions that the imposition of a mandatory recovery
rate might be more effective.
26
Aside from the potential presence
of HBCD in marine EPS, however, contamination of recovered
material by, for example, salt, sand, oil, and chemical
precipitates, precludes it from being recycled.
The construction and demolition industries generate
significant quantities of foamed PS waste and fugitive particles
through a variety of routes, including board cutting, and the
storage and transport of material and offcuts. Measures to
minimize the escapement of foamed PS from this sector include
making employers more aware of environmental damage caused
by the material, use of hot wires for cutting, careful separation of
demolition waste, covering and securing waste containers, and
incentivizing the return of unused material to the manufac-
turer.
13
Demolition waste is of greater concern than
contemporary construction waste because of the higher
probability of material containing HBCD.
109
The presence of
this additive may also pose challenges and constraints on how
the material can be disposed of and recycled. Rapid screening
methods based on portable X-ray fluorescence spectrometry
have been developed that detect the presence and solubility of
Br in foamed PS (HBCD is solvent-extractable while newer,
“safer”brominated compounds are not).
110
These methods
could assist with decisions concerning the fate of demolition
waste on site or as a waste disposal input control but to date
these do not appear to have been applied on an industrial scale.
To summarize, foamed PS has a number of distinctive
properties that renders it highly favorable for a wide range of
applications across multiple sectors. However, it is this usage and
these characteristics that ensure large quantities of foamed PS
waste enter the marine environment and present a diversity of
pervasive impacts. The chemical and biological risks of foamed
PS are further compounded by the widespread occurrence of
HBCD in historical and recycled products. Recommendations
to reduce these risks and impacts relate to better management of
foamed PS throughout its life cycle and replacing the material
with more durable and sustainable alternatives. Refs 77 and 78.
■ASSOCIATED CONTENT
*
sıSupporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.est.0c03221.
Table S1 provides information on the physicochemical
and environmental properties of hexabromocyclodode-
cane (PDF)
■AUTHOR INFORMATION
Corresponding Author
Andrew Turner −School of Geography, Earth and
Environmental Sciences, University of Plymouth, Plymouth PL4
8AA, U.K.; orcid.org/0000-0003-0505-4561;
Email: aturner@plymouth.ac.uk
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.est.0c03221
Notes
The author declares no competing financial interest.
■ACKNOWLEDGMENTS
This review benefitted greatly from discussions with Claire
Wallerstein and Rob Arnold (Rame Peninsula Beach Care,
Torpoint) and Tracey Williams (Lost At Sea Project, Newquay),
and the comments from three anonymous reviewers.
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