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Journal of Hazardous Materials 300 (2015) 359–367

Contents lists available at ScienceDirect

Journal of Hazardous Materials

journa l homepage: www.e lsev ier .com/ locate / jhazmat

lobal styrene oligomers monitoring as new chemical contaminationrom polystyrene plastic marine pollution

um Gun Kwon a,∗, Koshiro Koizumi b, Seon-Yong Chung c, Yoichi Kodera d, Jong-Oh Kim e,atsuhiko Saido d,∗∗

Department of Bioenvironmental & Chemical Engineering, Chosun College of Science & Technology, 309-1 Pilmundae-ro, Dong-gu, Gwangju 501-744,epublic of KoreaDepartment of Chemistry, College of Science and Technology, Nihon University, 7-24-1, Narashinodai, Funabashi-shi, Chiba 274-8501, JapanDepartment of Environment and Energy Engineering, College of Engineering, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju 500-757,epublic of KoreaNational Institute of Advanced Industrial Science and Technology (AIST), 16-1 Onogawa Tsukuba, Ibaraki 305-8569, JapanDepartment of Civil and Environmental Engineering, College of Engineering, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 133-791,epublic of Korea

i g h l i g h t s

This study reports styrene oligomers(SOs) as a new global pollutant.SOs can be leached from the weath-ering of polystyrene (PS) plastic.The high levels of SOs in sandybeaches around the world present thePS plastic pollution.

g r a p h i c a l a b s t r a c t

r t i c l e i n f o

rticle history:eceived 13 February 2015eceived in revised form 16 June 2015ccepted 10 July 2015vailable online 18 July 2015

eywords:tyrene oligomers

a b s t r a c t

Polystyrene (PS) plastic marine pollution is an environmental concern. However, a reliable and objectiveassessment of the scope of this problem, which can lead to persistent organic contaminants, has yet to beperformed. Here, we show that anthropogenic styrene oligomers (SOs), a possible indicator of PS pollutionin the ocean, are found globally at concentrations that are higher than those expected based on thestability of PS. SOs appear to persist to varying degrees in the seawater and sand samples collected frombeaches around the world. The most persistent forms are styrene monomer, styrene dimer, and styrenetrimer. Sand samples from beaches, which are commonly recreation sites, are particularly polluted with

olystyrenelastic pollutioneachingersistent

these high SOs concentrations. This finding is of interest from both scientific and public perspectivesbecause SOs may pose potential long-term risks to the environment in combination with other endocrine

disrupting chemicals. From SOs monitoring results, this study proposes a flow diagramfor SOs leaching from PS cycle. Using this flow diagram, we conclude that SOs are globalcontaminants in sandy beaches around the world due to their broad spatial distribution.

© 2015 Elsevier B.V. All rights reserved.

ttp://dx.doi.org/10.1016/j.jhazmat.2015.07.039304-3894/© 2015 Elsevier B.V. All rights reserved.

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60 B.G. Kwon et al. / Journal of Haz

. Introduction

Synthetic polymers currently constitute some of the mostniversally-used materials, with applications ranging from foodontainers to space suits [1–4]. In addition to poor waste manage-ent, the generation of small plastic debris in combination with

he extensive use of plastics has created serious pollution prob-ems in oceans and coastal aquatic environments [5–9]. Because oureliance on plastics will continue to increase [1,3], their sustainablese is in question.

The accumulation of minute plastic debris in ocean environ-ents is of considerable concern because it adversely affectsarine organisms [9–16]. Recent research on the occurrence and

azards of plastic debris [17–19], including microplastics [20–22],nd the hazards they may cause to ecosystems has focused on theransport of harmful persistent organic pollutants (POPs), such asCBs and DDTs [1,22–29], from the surfaces of discarded plastics.

n particular, POPs adsorbed onto the surfaces of the increasingmounts of plastic debris in the environment may lead to greaterccumulation of such contaminants and thus a greater hazard toildlife [22,28,29], potentially including to humans when we eat

eafood. Thus, the ubiquitous presence of plastic debris in thenvironment has given rise to a heightened awareness of seriouslastic pollution and increased concern regarding plastic pollution3,5,16,29].

Polystyrene (PS) is of major concern, and is found abundantly atea, has hazardous chemicals, and also is one of the 6 major poly-ers most produced and consumed, contributing to environmental

ollution [1,5,30,31]. Since the early 1970s [17], PS plastic pelletsave been reported on the surface of the western North Atlanticcean [32]. However, other than counting the quantity of plasticebris [33–36], there is no reliable and objective method to mon-

tor the extent of such pollution [30,34]. Plastic debris countingechniques can be easily influenced by differences in the samplingnd detection methods, such as sea conditions (wave, wind, sun-ight, and so on) and observer experience [3,35,36], causing biases31,35,36]. For example, in contrast to the results of previous stud-es [3,6,8,19,21], the quantities of plastic debris in the North Atlanticcean and Caribbean Sea during a 22-year period [32] and in theastern Pacific Ocean during an 11-year period [37] were reportedo show no strong, spatial and temporal trends. Even though gen-ral counting techniques exist for assessing contamination by othertable plastics [34], any new such method would be a useful alter-ative for assessing PS pollution in large-scale monitoring studies29–31,33]. Thus, the monitoring using an alternative indicator ismportant to identify the pollution routes of PS in natural environ-

ent.This study attempted to measure the levels of a chemical con-

amination resulting from PS in the coastal environment. Thisoncept is original and may provide a new strategy for quanti-atively assessing marine pollution arising from the disposal ofynthetic polymers. As with POPs, styrene oligomers (SOs) derivedrom PS are potentially toxic to wildlife because they may consti-ute endocrine disrupting chemicals [38–41] or PS plastic pollutionndicators [30,31]. However, SOs are conspicuously lacking in large-cale distribution maps of plastic contamination. Thus, the globalontamination by SOs needs to be better understood.

Here, we present analytical results from seawater and sandamples collected from beaches around the world. In the period003–2013, we conducted an extensive long-term study to mea-

∗ Corresponding author. Fax: +82 62 230 8501.∗∗ Corresponding author. Fax: +81 33 691 5579.

E-mail addresses: kwonbg0@daum.net (B.G. Kwon), ka-saido@aist.go.jpK. Saido).

Materials 300 (2015) 359–367

sure the concentrations and spatial distributions of artificial SOsderived from PS, focusing particularly on styrene trimers (ST:mainly 2,4, 6-triphenyl-1-hexene), styrene dimers (SD: mainly 2,4-diphenyl-1-butene), and styrene monomer (SM). Hereafter, thesum of the concentrations of SM, SD and ST will be mainly referredto as SOs.

This study investigates the SOs concentrations in the oceanicbeaches around the world, and uses monitoring results to generatea flow diagram (as a simple model) for SOs leaching from PS cycle.Additionally, in order to support SOs leaching from PS, we test thehypothesis whether sand relates to SOs leaching.

2. Experimental procedures

2.1. Study areas

More than five hundred seawater and sand samples were col-lected from selected coastal regions, which included 21 nations, 34sampling sites, and 244 locations (Fig. 1 and Table 1). Each sam-ple consisted of about 100 g of beach sand (by wet weight) and 5 Lof seawater. The sites ranging from Ullapool (UK, study No. 1 inFig. 1) to the Aleutian Islands (Alaska, US, study No. 34). The sam-pling locations are detailed further in Supplementary informationFig. S1–S13.

2.2. Sampling methods and sample preparation

Prior to the global monitoring program, we conducted an exten-sive study to develop suitable sampling and analytical proceduresto identify and measure the small concentrations of SOs found inregional seawater and sand samples. Further details on the sam-pling methods in the field and sample preparation in the laboratoryhave been provided in previous studies [30,31]. Briefly, almostall sampling was accessible by walking and performed in a safelocation. In each coastal region, seawater and sand samples werecollected carefully at depths of approximately 40 cm and 30 cmfrom the surface water and surface sand, respectively. Sand samplewas stored in a glass container and delivered in the laboratory. Afterdehydration by freeze–drying overnight, the sand sample was accu-rately weighed to 5.0 g using a balance and spiked with biphenyl(1 �g mL−1) as a surrogate prior to extraction. Then, the sand sam-ple was extracted with 5 mL benzene and evaporated to dryness bya rotary evaporator at 30 ◦C. After adding 0.5 mg L−1 phenanthreneas an internal standard, the eluate was completely dissolved into1 mL of benzene.

The seawater sample (5 L) in the field was subjected to cottonplug filtration and immediately extracted four times, with a totalof 100 mL dichloromethane by using a portable shaker (Sanada Co.,Tokyo, Japan) for 10 min. Other procedures for sampling and prepa-ration used in this study are described in details in the previousstudies [30,31].

2.3. Analytical methods and QA/QC

This analytical method is applicable to the measurement of SOscompounds extracted by benzene and dichloromethane as men-tioned above. The actual measurement of SOs compounds is basedprimarily upon gas chromatography/mass spectrometry using HP6890 GC with a JEOL Auto MS-II equipped with a 30 m × 0.32 mmi.d. (0.25 �m film thickness) DB-1 capillary column (J&W Scientific,Folsom, CA), with which it was possible to identify and measure the

SOs concentrations. Further details of the analytical methods havebeen provided in previous studies [30,31].

Data quality assurance and quality control included blanks (fordeionized water and sand), matrix spikes, and standard solution

B.G. Kwon et al. / Journal of Hazardous Materials 300 (2015) 359–367 361

Table 1Concentrations of SOs in seawater and sand samples collected from beaches around the world. Detailed sampling locations are shown in the Supplementary materials.

Study number Sampling locations Number of sampling Concentration of SOsa

Sand (�g kg−1) Seawater (�g L−1)

1 United Kingdom 4 389.6 4.02 France 1 4496.6 1.23 Portugal 2 274.2 1.34 Spain 4 1143.3 1.25 Tunisia 5 92.0 3.36 Slovenia 1 30.8 0.247 Italy 8 37.5 0.548 Croatia 1 15.4 1.79 Greece 9 31,400.0 1.410 India 3 940.4 3.911 Sri Lanka 2 237.6 11.512 Malaysia 4 18,924.8 4.013 Vietnam 1 439.0 Traceb

14 Philippines 9 153.2 2.015 Taiwan, Republic of China 19 150.4 13.016 Mainland, the People’s Republic of China 6 1408.2 8.917 Korean Peninsula, Korea 8 57.9 5.918 Okinawa, Japan 14 69.3 1.219 Honshu, Japan 34 335.3 4.720 Hokkaido, Japan 11 100.0 4.821 Chichijima, Japan 18 561.86 1.522 Guam, USA 5 1402.7 4.323 Hawaii, USA 9 16.1 0.2024 Washington, USA 5 505.8 30.425 San Francisco, USA 9 816.1 22.026 Los Angeles, USA 5 29106.8 1.327 Texas, USA 4 494.6 5.728 Illinois, USA 3 10.4 0.4829 Massachusetts, USA 1 7368.3 6.930 New Jersey, USA 2 158.7 3.531 Florida, USA 4 23,507.0 8.832 Puerto Rico 20 352.0 0.8533 Costa Rica 5 26,277.4 8.434 Aleutian, Alaska 8 0.74 0.93

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njection every 20 sample in order to monitor changes in the sensi-ivity of the instrument. SOs recoveries were tested for artificialeawater and sand media based on triplicate analysis of matrixpiked and extracted with the same analytical procedure andeported in the previous studies [30,31]. No equipment or materialomposed of PS plastic materials were adopted in this analysis.

.4. Experiments for surface observation of weathered PS virginellets and SOs leaching under simulated sand conditions

This experiment is to examine leaching of SOs from the inner anduter of PS virgin pellet. In order to show leaching of SOs, exper-

ments incorporating detailed textural analyses of the surface ofS plastic could provide crucial clues concerning the behavior of PSlastic under simulated sand weathering conditions. To investigatehe weathering of PS plastic under arbitrarily simulated sand con-itions, PS virgin pellets were mixed with sand and/or water (at aatio of 10 g sand and/or 10 mL deionized water per 1 g PS pellet)oured into an Erlenmeyer flask (300 mL) and shaken at 120 rpmt 25 ◦C as a room temperature on a rotary shaker for one month=30 days). The controls were a pure PS pellet and a submerged PSellet in deionized water.

As mentioned above, the weathering of the PS virgin pellet sur-ace was observed after one month with field emission scanning

lectron microscope (FE-SEM; JSM-6701F, JEOL, Tokyo, Japan). FE-EM, at an accelerating voltage of 10 keV, was used to characterizehe morphology of the weathered PS pellet surface, which wasoated with a layer of platinum via sputtering.

4 3679 ± 8199.2 5.1 ± 6.4

To examine SOs leaching from PS pellets, UV/vis spectropho-tometer (PerkinElmer, Lambda35, Shelton, CT, USA) was employedto simply and qualitatively analyses the outer and inner SOs relatedcompounds under simulated leaching conditions. The reason forthis is that the weathering of PS pellets with sand be generated asfine PS particles, and thus leached SOs could not be distinguishedwhether from inner or outer of PS particles. All experiments wereshaken at 120 rpm at 25 ◦C on a rotary shaker. The outer SOs wasdetermined using a PS surface without artificial knife scratching,and the inner SOs (or depth SOs) was determined after artificiallyscratching the PS surface with a knife. In the latter case, this knifescratching step was repeated ten times on each surface of PS.

3. Results

The data in Table 1 show that the seawater samples exhibitedsignificantly lower SOs concentrations than the sand samples atthe same location. With the exception of Vietnam, all the seawa-ter samples contained detectable concentrations of SOs, even inthe Aleutian Islands, Alaska, where the concentration was 0.93 �gL−1. The highest SOs concentrations in seawater were observedin densely populated eastern seaboard areas of the United States(US), with concentrations between 6.9 �g L−1 (study No. 29) and30.4 �g L−1 (study No. 24; Table 1 and Fig. 1).

Comparatively low SOs concentrations were measured along

the North-east Atlantic Ocean coastlines of developed countries;these concentrations ranged from 0.24 �g L−1 (study No. 6) to4.0 �g L−1 (study No. 1; Table 1). Intermediate concentrationsof SOs were observed in the seawater samples collected along

362 B.G. Kwon et al. / Journal of Hazardous

Fig. 1. Locations of samples collected around the world in the period 2003–2013.Numbers indicate the study number of each sampling location.

Materials 300 (2015) 359–367

the coastlines of the North-west Pacific Ocean; in particular,the samples from Korea (5.9 �g L−1, study No. 17), Japan (Hon-shu, 4.7 �g L−1, study No. 19), Mainland, the People’s Republic ofChina (8.9 �g L−1, study No. 16), and Taiwan, Republic of China(13.0 �g L−1, study No. 15) showed relatively high concentra-tions of SOs. The global mean SOs concentration in seawater was5.1 ± 6.4 �g L−1.

Table 1 shows the concentrations of SOs in other regionsin the world, including the Indian Ocean (studies No. 10–11 inFig. 1) and the Caribbean Sea (studies No. 31–33). The mean con-centration measured in the Caribbean Sea was 0.85–8.4 �g L−1,whereas the mean concentration measured in the Indian Ocean was3.9–11.5 �g L−1. These results are similar to those of the North-westPacific Ocean.

Table 1 also shows that the global SOs concentrations weretypically much higher in sand than in seawater. The global SOs con-centrations in the sand samples ranged from 10.40 �g kg−1 (studyNo. 28) to 31,400.0 �g kg−1 (study No. 9). The global mean SOsconcentration in the sand samples was 3679.0 ± 8199.2 �g kg−1,and very large variations in SOs were observed. With the excep-tion of Aleutian Islands (0.74 �g kg−1, study No. 34), Alaska, allsand samples contained relatively high concentrations of SOs. Thehighest concentration of SOs was found in the beach sand sam-ple from Greece (31,400.0 �g kg−1, study No. 9), followed by CostaRica (26,277.4 �g kg−1, study No. 33), Florida (23,507.0 �g kg−1,study No. 31), and Malaysia (18,924.8 �g kg−1, study No. 12). France(study No. 2), Spain (study No. 4), the People’s Republic of China(study No. 16), Guam (study No. 22), and Los Angeles (study No.26) and Massachusetts of USA (study No. 29) showed levels rangingfrom 1,143.3 �g kg−1 to 7,368.3 �g kg−1; India and other countrieshad concentrations ranging from 10.4 to 940.4 �g kg−1.

Fig. 2 shows the relative contributions of the types of styreneto the SOs concentrations in sand samples collected from beachesaround the world. In almost all the sand samples, the contribu-tions to SOs decreased in the following order: ST > SD (or ST) > SM.By contrast, the order in Massachusetts (study No. 29) and Florida(study No. 31) was the following: SM > SD (or ST) > ST (or SD). STwas the most abundant in sand, and its global mean concentra-tion was 2247 ± 5492.0 �g kg−1. The global mean concentrations ofSD and SM were 500.0 ± 1579.8 �g kg−1 and 932.0 ± 258.4 �g kg−1,respectively.

4. Discussion

This study aimed to quantify the mounting problem of PSplastic pollution by measuring the SOs in the oceanic environ-ment. In general, plastic synthetic polymers have been recognizedto be chemically stable and biologically non-biodegradablein the ocean environment [16,17,20,42]. Furthermore, photo-degradation, oxidative and hydrolytic processes, and mechanicalmovements in the marine environment cause many commonplastics to become embrittled and suffer mechanical breakdown[3,20,21], producing smaller plastic debris. Hence, most scientificstudies have investigated persistent plastic debris [3,19], includingmicroplastics (<5 mm [5,13,20,21] or <1 mm [12,43]) and nanoplas-tics (<100 nm) [7,20,21], and recent studies have focused on the roleof plastic surfaces in the transportation of contaminants such asPOPs [22–29]. In the midst of these studies, we feel that an objectiveindicator is needed to globally assess the extent of plastic pollu-tion in the environment. In particular, a new indicator is neededto evaluate the levels of the contamination resulting from PS itself

in the coastal environment, which is the focus of this study. In thisstudy, what is novel is the monitoring results that it shows thatthis material not only causes contamination of PS particle, but ofthe hazardous chemical ingredients worldwide. In this regard, this

B.G. Kwon et al. / Journal of Hazardous Materials 300 (2015) 359–367 363

Study number (or Sampling l ocations)

1 2 3 4 6 7 8 9 11 12 13 14 16 17 18 19 21 22 23 24 26 27 28 29 31 32 33 340 5 10 15 20 25 30 35

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ig. 2. Concentrations of SOs in sand samples collected from beaches around thupplementary materials. Also, the average concentration of SOs is shown in Table

tudy can contribute to the assessment of the fate and behavior8,29] of PS plastic deposited into the ocean.

Based on our results (Table 1 and Fig. 2), the SOs concentra-

ions in sand are approximately one to four orders of magnitudeigher than those in seawater along coastlines around the world. Ofhe various samples collected around the world investigated in thistudy, sandy beaches near populated coastlines were found to be

Fig. 3. Flow diagram of styrene oligomers (SOs)

ld. Detailed sampling locations for study number are shown in Table 1 and the

heavily contaminated with SOs; this is of particular interest fromboth an aesthetic [6,16,21] and public health stand [44] becausepeople spend considerable time at the beach. This result suggests

that the accelerating generation of SOs can have important effectson the sand of the world’s beaches, which produces SM, SD, and STat high concentrations.

leaching from polystyrene (PS) pollution.

364 B.G. Kwon et al. / Journal of Hazardous Materials 300 (2015) 359–367

Wavelen gth, nm

200 250 300 35 0 400 450 50 0

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As shown in Fig. 2, the presence of SOs in sandy beach appears toe a global rather than a regional or local problem. The lowest SOsoncentration was found in sand samples from the Aleutian Islands,laska, an area that lacks any notable factories and human popula-

ion. The SOs contamination along the populated coastlines aroundhe world could be more severe than in the Alaskan regions [30].he relative contributions to SOs contamination indicate a directelationship between SOs concentration and human activities.

As shown in Fig. 2, ST is the most predominant component pro-uced by PS after mechanical breakdown through an unknownrocess. This result, along with our other findings [30,31], suggestshat ST adsorbs onto sand at higher concentrations than are present

n seawater, and may persist in sand for an unknown period ofime. Similar results are obtained for SD and SM. In our previoustudies [30,31], the distribution of SOs compounds predominantlyollowed the order: ST > SD (or SM). This order of contributions is

ngth, nm

a scratched pure PS pellet and (B) standard SOs compounds.

similar to that for SOs in the seawater samples. Thus, beach sandserves as a hot spot for the formation of SOs.

SOs can appear to be persistent pollutants, as indicated by theirconsistently low concentrations in ocean water. Similarly to thesandy beaches in specific countries, the seawater of the coastlinesmeasured in this study was polluted with SOs. In particular, theSOs concentrations in the seawater samples collected from beachesaround the world were higher than would be expected if the sourceof SOs was stable PS.

Based on our results, SOs in the ocean is likely to originate fromanthropogenic PS. The formation and fate of SOs in the natural envi-ronment, particularly the generation of SD and ST from PS, have not

been reported [30,31]. There is no information on the physicochem-ical properties (i.e., sorption kinetics and partition coefficients) ofSD and ST [45–47], so far to the best of our knowledge. Particu-larly, the specific use of SD and ST has not been reported up to

B.G. Kwon et al. / Journal of Hazardous Materials 300 (2015) 359–367 365

ered

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Fig. 5. FE-SEM images showing the surface topographies of PS pellets weath

ow, except for SM mainly used for the production of PS [30]. Theurrently available evidence indicates that the SOs in the oceanicnvironment is primarily introduced by human activities, not bio-enic sources. The acceleration of SOs production in beach sandresents a credible route by which the SOs compounds enter sea-ater.

As mentioned above, we have measured global SOs concen-rations in different samples of seawater and sand to determineow SOs compounds are generated at beaches. Before 2014, mostesearchers were unaware that SOs can leach from PS plastics inhe environment [30,31], within the scope of knowledge that wenow. Therefore, the global extent of SOs pollution from PS plasticay be unknown.

There is one possible pathway that may account for the pres-nce of SOs detected in sandy beaches around the world. This studyddresses this issue using SOs leaching pathway with a potentialow diagram based on SOs monitoring results discussed above andxperimental results discussed below.

The proposed SOs leaching pathway is presented in Fig. 3.Os elution is initiated by the environmental exposure of PS. Theikely source for the generation of the majority of SOs is then situ weathering of PS discarded in the beach environment. Thehysicochemical weathering of PS plastics on beaches can result

n continuous cracking and micro-cracking by wind, wave action,nd other movements [5,6,21,20,48,49], producing and accelerat-ng SOs elution. SOs is leached from discarded PS plastics whenncomplete polymerization occurred during PS manufacturing [50].he origin of SOs leached from PS in beaches can be attributed towo main pathways: (1) the instantaneous elution of surface SOs

outer SOs) and (2) the depth elution of SOs (inner SOs) followedy weathering and cracking. SOs leached from the outer and innerurfaces of PS is delivered into sand and seawater media. As a result,he leached SOs can accumulate in the coarse sand fractions.

under simulated sand conditions (magnification = 10,000; scale bar = 1 �m).

In this study, several laboratory experiments clarified the loca-tion of SOs generation under simulated PS surface conditions usingknife scratch tests. The spectra of unknown compounds from bothouter SOs leached from a pure PS pellet and inner SOs leachedfrom a scratched PS pellet were qualitatively identified with aspectrophotometer (Fig. 4A). These results show that the spectralintensity is higher for the inner SOs leached from the scratched PSpellet. The spectrum of the solution of the outer SOs leached fromthe pure PS pellet is very similar to those of standard solutions ofSM, SD, and ST (Fig. 4B).

As mentioned above, the PS pellet discarded in natural beachsand most likely travels along the beach or toward the ocean, stay-ing in contact with the sand surface (Fig. 3). In this case, the force(i.e., drag and lift friction) exerted by the sand movement on the PSsurface can be enough to scratch the surface of PS [48,49], whichenhances the process of SOs generation. Depending on the surface,the PS pellet could also be scratched and/or disintegrated due toturbulent fluctuations in the fluid [20,48,49], increasing the spe-cific surface areas of PS particles [51,52]. Greater scratching of thePS particles leads to an increased concentration of inner SOs, whichmakes the SOs more likely to remain in the sand. This process maybe significant for the fate of discarded PS because it is primarily thefriction forces and saltation of sand particles that dislodge smallerPS particles from the beach sand. These smaller particles are thencarried by the wind and water along the sandy beach, which canresult in shallow grooves or strips on the surfaces of PS particles[48,49], increasing their specific surface area.

In a laboratory experiment under simulated sand conditions,the surface of a PS pellet aged in sand and stored in darkness

exhibited evident cracking and micro-cracking during and afterconstant shaking (Fig. 5). By contrast, several PS samples aged inwater showed no SOs signal during and after shaking (Fig. 4), withthe exception of outer SOs attached to the surface of the PS. The

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racking of a PS pellet in contact with sand increases the surfacerea [51,52], and the SOs leaching rate may be higher for weath-red and aged plastics [52,53]. Sand can yield SOs concentrationsroportional to both shaking time at a constant shaking rate andhe amount of spiked sand, whereas the breakdown by mechanicalrosion and chemical weathering is minimal in seawater [16,20].

PS on beaches is also subject to very high temperatures. Forxample, sandy beach surfaces and the associated plastic debrisan reach temperatures exceeding 40 ◦C in summer [20]. Addition-lly, these particles affect the amount of sunlight received by thetmosphere. SOs generated by direct leaching can easily reach theceans via runoff, and SOs is therefore prevalent along coastlines.

The annual disposal of plastics in the ocean is reported to bepproximately 6.4 million tons [54]. Of this quantity, approximatelyeveral hundred thousand tons a year are released into the ocean.ased on the experimental results indicating that synthetic PS poly-er leach SOs at low temperatures [55], SOs might be continuously

luted at quantities of several tens of thousands of tons per yearuring the next 50 years or more.

Although the global distribution of SOs concentrations was wellefined in our study, it remains insufficiently clear whether SOsre endocrine disruptors. That is still under debate [38–41,44].owever, possible endocrine-disrupting actions of SOs related

ompounds cannot be completely ruled out, due to the chemicalresence of suspected into endocrine disruptors. Considerable con-roversy still exists regarding which compounds released from PSdversely affect animals and humans.

. Conclusions

Finally, this study reports the results of leached SOs monitor-ng of seawater and ocean beach sand. The results suggest a newhreat of global contamination by styrene-related compounds. Fur-hermore, this study can provide insight into the global extent ofhemical pollution by PS polymers in the natural environment, par-icularly in sandy areas. Therefore, this study provides an importantaseline for future efforts to monitor pollution by other plastic poly-ers and quantitatively assesses the scope of the environmental

roblem in order to accurately inform policymakers and the public.

cknowledgements

Dr. Katsuhiko Saido and Dr. Bum Gun Kwon, as the correspond-ng authors, thank Prof./Dr. Masahiko Nishmura, Prof./Dr. Hidetoato, Dr. Naoto Ogawa, Dr. Mi-young Yoon and Mr. Sangjun Lee forheir help in the sampling and laboratory experiments. Dr. Bumun Kwon thanks Dr. Jae-hoon Kim for his special helps in theroduction of illustrations.

ppendix A. Supplementary data

Supplementary data associated with this article can be found, inhe online version, at http://dx.doi.org/10.1016/j.jhazmat.2015.07.39

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