Science of the Total Environment 688 (2019) 780–786

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The spatial distribution of microplastic in the sands of a coral reef islandin the South China Sea: Comparisons of the fringing reef and atoll

Linlin Zhang a,b,c, Shuaipeng Zhang a,b,c,1, Yinghui Wang a,b,c,⁎, Kefu Yu a,b,c,⁎, Ruilong Li a,b,c,⁎a School of Marine Sciences, Guangxi University, Nanning 530004, PR Chinab Guangxi Laboratory on the Study of Coral Reefs in the South China Sea, Guangxi University, Nanning 530004, PR Chinac Coral Reef Research Center of China, Guangxi University, Nanning 530004, PR China

H I G H L I G H T S G R A P H I C A L A B S T R A C T

• Firstly determination of microplastic inthe sand of coral island at South ChinaSea

• Higher content of microplastic wasdetected in the Xisha Islands thancoastal sites.

• Human activities were not the onlysource for microplastic in the sand ofcoral island.

• Mineral type was one of the dominantfactor affect the distribution ofmicroplastics.

• No obviously differences were foundbetween the sand in reef flat and ragoonzones.

⁎ Corresponding authors.E-mail addresses: wyh@gxu.edu.cn (Y. Wang), kefuyu

1 Co-first author.

https://doi.org/10.1016/j.scitotenv.2019.06.1780048-9697/© 2019 Elsevier B.V. All rights reserved.

a b s t r a c t

a r t i c l e i n f o

Article history:Received 15 March 2019Received in revised form 11 June 2019Accepted 11 June 2019Available online 21 June 2019

Editor: Thomas Kevin V

Microplastic pollution of coral reef ecosystems has received increasing attention since the discovery that severaltypical coral types have the ability to ingest (micro-) plastics. However, data on the distribution of microplasticsin coral reef ecosystems are still very limited. The study reported here selected sands/sediments from coral reefislands located in the South China Sea as a representative study site. The abundance ofmicroplasticswas found toreach 90 ± 5 items/kg and 530 ± 7 items/kg at the Weizhou Island and Sanya Lu Hui Tou (LHT) sites (fringingreef), respectively. Each of these qualities are lower than the quantity of microplastics collected from the XishaIslands (atoll) (60 ± 3 to 610 ± 11 items/kg), which experiences less human activity and pollution. Moreover,further investigation demonstrated that the differences in themicroplastics in the sands of these atolls and fring-ing reefs were determined not only by their sources, but were also dependent on their water exchange rates. Theprimary type and color of themicroplastics found in these four sampling zones was red polypropylene and therewas a greater proportion of smaller size particles (b1 mm) in the remote atolls of the Nansha and Xisha islandsthan in the other fringing reef sites. Additionally, there were no obvious differences found in the abundance ofmicroplastics and the compositions/structures of coral sand in the Weizhou Island and Sanya LHT sites.

© 2019 Elsevier B.V. All rights reserved.

Keywords:MicroplasticsCoral reefSandFringing reefAtoll

@scsio.ac.cn (K. Yu), liruilong1989@163.com (R. Li).

Fig. 1. Geographic location and sampling sites.

781L. Zhang et al. / Science of the Total Environment 688 (2019) 780–786

1. Introduction

Plastics are widely used in nearly all aspects of our daily life. It is es-timated that plastic production worldwide has increased from 1.7 t inthe 1950s to 322 million tonnes in 2015 (Galloway et al., 2017; Chaeand An, 2018; Lambert and Wagner, 2016). Some environmental andecological problems have been shown to occur once plastics enterwater, air, or soil/sediment, because they persist for hundreds or eventhousands of years (Burns and Boxall, 2018; Auta et al., 2017).More im-portantly, smaller plastics (b5 mm) have been found to be generatedduring a variety of biotic and abiotic decomposition processes andthese materials can have a negative impact on marine biota (e.g. algae,fish, and coral reefs). In particular thesemicroplastics can: 1) act as car-riers of contaminants or harmfulmicroorganisms that can increase theiravailability to biota inducing uncontrolled hazards (Hankins et al., 2018;Hall et al., 2015), 2) are small enough to be ingested by organisms,which can result in bioaccumulation in the food chain (Lonnstedt andEklov, 2016; Lamb et al., 2018), and 3) disturb the soil biophysical envi-ronment, including the bulk density, water capacity, and the functionalrelationship between microbial activity and water-stable aggregates(Machado et al., 2018).

To improve our understanding of the potential hazards ofmicroplastics, their sources, distributions, and pathways have been in-vestigated from the earth/river to the coast and the open sea (Yuet al., 2018; Tang et al., 2018; Wang et al., 2019; Slootmaekers et al.,2019; Hitchcock and Mitrovic, 2019). Coastal zones always serve asbuffers and barriers to the delivery of land-based contaminants to thesea, which has received increasing attention in recent years (Cesaet al., 2017; Curren and Leong, 2019). For example, due to their variousterrestrial and ocean sources, Karthik et al. (2018) reported that thecontent and characteristics of microplastics in the coastal sediment ofIndia were closely related to their tidelines, with values ranging from48.9 to 4747.6 mg/m2 in high tidelines, and four times higher than inlow tidelines (14.3 to 1020.4 mg/m2).

Some recent studies have demonstrated that there is a significantdifference between typical coastal ecosystems (mangroves, seagrass,and coral reefs) and other coastal zones in the transport and transfor-mation of contaminants due to the high productivity and biomass ofthe former (Li et al., 2016; Booth and Sear, 2018; Fourqurean et al.,2012). Bayen et al. (2019) reported that the total concentration ofeight polycyclic aromatic hydrocarbons (Σ8PAHs), twenty-eightpolychlorinated biphenyls (Σ28PCBs), and the total p,p′-Dichlorodiphe-nyltrichloroethane (ΣDDT) in mangrove sediments can reach 122 ±115 ng/g, 771 ± 61 ng/g, and 19.1 ± 17.5 ng/g, respectively. Addition-ally, much lower quantities of microplastics were also found inmangrove-adjacent zones in the Maowei Sea in the Beibu Gulf (170± 6 to 990 ± 3 items/kg), compared to those in mangrove sediments,with values ranging from 1780 ± 18 to 2310 ± 29 items/kg (Li et al.,2019).

Unfortunately, limited information is available on the distribution ofthese three typical coastal ecosystems, especially with respect to thecoral reef ecosystem. To date, to the best of our knowledge, only threerelevant studies reported by Vidyasakar et al. (2018), Saliu et al.(2018), and Imhof et al. (2017), have investigated the spatial distribu-tion of microplastics in the Faafu Atoll, Maldives Island, andRameswaram Island located in the Indian Ocean, with the quantitiesranging from 4.2 ± 2.0 items/m2 to 38.5 ± 15.6 items/m2 (meanvalue: 22.7 ± 10.5 items/m2), from 20.6 ± 19.8 items/m2 to 69.7 ±57.5 items/m2 (mean value: 35.8 ± 42.5 items/m2), and 403 items/m2, respectively. Polypropylene (PP), polyethylene (PE), and polysty-rene (PS) have been identified as the dominant types of microplastics.However, all three studies focused on exploring the distribution ofmicroplastics in the sands of coral reef islands located in the IndianOcean, while microplastics in other open oceans, especially the PacificOcean, may present different features (Connors, 2016; Law et al.,2014). Moreover, many previous reports have demonstrated that the

sand composition, topography, and landform characteristics of thefringing reefs and atolls are significantly different, which may producevariations in the sorption or themolecular interactions of inorganic con-taminants, hydrophobic organic contaminants, and microplastic parti-cles in these important types of coral reef islands (Wear and Thurber,2015; Calhoun and Field, 2008; Carvalho-Souza et al., 2018). Thesetwo limitations have inspired us to investigate the distribution charac-teristics of microplastics and their related decomposition mechanismsin the local environment.

The South China Sea is the largest semi-enclosedmarginal sea in thewestern Pacific Ocean, and it has some special characteristics thatlargely affect the distribution of microplastics in coral islands, necessi-tating special attention. For example, the unique tidal/ocean currentconditions facilitate the transfer of contaminants that surround severaldeveloping countries with large populations and an abundance of in-dustry, agriculture, and shipping that provide other important sourcesof plastics and microplastic particles. Therefore, the objectives of thisstudy were to: (1) investigate the spatial distribution of microplasticsin the sand of coral reef islands located in the South China Sea, (2) eval-uate the difference in microplastic abundance and characteristics in thesands of a fringing reef and atoll, and (3) further explore the relation-ships between the physicochemical properties of the island sands andthe microplastic content.

2. Materials and methods

2.1. Sample collection

Sand samples were collected from several coral reef islands locatedin the South China Sea, a typical (and the largest)marginal sea in South-east Asia. This zone is bounded by the Asian continent, Philippine Archi-pelago, and Great Sunda Islands which includes many river systeminputs. The sampling sites included remote atolls (Xisha Islands andNansha Islands) and nearshore fringing reefs (Weizhou Island and theSanya LuHui Tou (LHT) site). Other detailed information about the loca-tions of the sampling sites is presented in Fig. 1. At each site, the sandsamples were collected from the edge of the island, including the reefflat and lagoon zones, at the same depth (0.5m in high-tide conditions)in January to July of 2016. The samples were passed through a 0.3 mm

782 L. Zhang et al. / Science of the Total Environment 688 (2019) 780–786

mesh sieve, and relatively large plastic debris was rinsed into a glassbottle, in a procedure detailed by Hu et al. (2018).

2.2. Extraction, identification, and quantification of microplastics

In contrast to themeasurements reported by Zhang et al. (2017), theextraction procedures hereinmainly included three procedures: 1) aciddigestion, 2) density separation, and 3) filtration. Firstly, 100 g of ho-mogenized and dried coral sand (sieved through 4 mesh) was digestedsequentially by 200 mL of 1 mol/L boiling nitric acid and 100 mL of0.5 mol/L hydrochloric acid via microwave-assisted digestion (Zhaiet al., 2018). After this, 500mL of a potassium formate aqueous solutionwith a density of 1.5 g/cm3 was added to Erlenmeyer flasks and themass was allowed to settle overnight. Three replicates were performedin each sampling sites and the mean value/standard deviations werecalculated (Table 1). Then, the supernatant was filtered onto the 1.2μm GF/C filter membranes purchased from Whatman Co. Ltd. (UK)and oven-dried for about 1 h at 40. Immediately after this, the numberof suspected microplastic particles on the filter were counted usingstereomicroscopy (Olympus SZ 53, Japan) at 3–4 times magnification.The typical microplastic images collected from the sands of a coral reefisland in our study are presented in Fig. S1. Finally, all of the suspectedparticles were placed on a slide and identified by a Renishaw micro-Raman spectrometer (inVia, UK). The parameters of this instrumentwere as follows: laser wavelength/energy, 785 nm/15 mW (5%); num-ber of micro-zones, 6; exposure time, 2.0 s; emission wavenumberrange, 130–4000 cm−1. The types of suspected microplastics were con-firmed by comparing the Raman spectra of the experimental sampleswith typical microplastic spectra (Fig. S2).

2.3. Quality assurance (QA) and control (QC)

The following three QA and QC measurements were employed inour study, which are similar to those used in a previous study (Liet al., 2019). Firstly, to avoid potential contamination, all sampleswere collected and stored in metal containers, and all the beakers, sep-arating funnels, and flasks were rinsed three times with Milli-Q water.Secondly, the sample holders and microscope were carefully cleanedbefore identification and quantification of the microplastics. Thirdly,blank tests were performed before analysis of the field sand/sedimentsamples, andnomicroplasticswere found in the blank samples. Calciumcarbonate particles are one of the dominant constituents of coral sand.We employed a commercially pure calcium carbonate, purchasedfrom the J&K Scientific Co. Ltd. containing no polymeric substances (pu-rity 99.95%) as the blank samples.

2.4. Characteristics of the sand samples

About 20 g of the coral sand samples were first digested in 200mL of1.0 mol/L hydrochloric acid in the beaker and then immediatelytransported to the shaker with a rotational speed of 120 rpm for 24 hto obtain the organic matter fractions. The C, H, and N content of these

Table 1The total abundance of microplastic in sand samples collected at coral island from the South C

Sites Microplastic (items/kg) Sites

Xisha Island

Bei Jiao (BJ) 60 ± 3a

Nansha IslandXin

Qi Lian (QL) 180 ± 5 XinPan Shi (PS) 610 ± 11 SanLang Hua (LH) 220 ± 8

Weizhou islandb

W1Yu Zhuo (YZ) 110 ± 5 W2Huang Yan (HY) 280 ± 16 W3Hua Guang (HG) 360 ± 2 W4

Some detailed information of these sampling sites have been listed in the Fig. S3.a The mean and standard deviation of three replicates.b The W1-W4 and D1-D6 represented the four and six sampling sites in the Weizhou island

fractions was determined using the Vario EL Elemental Analyzer (Ger-man). Then, NMR data for the organic matter fraction were obtainedusing solid-state, cross-polarization, magic-angle spinning (CPMAS)13C NMR analysis using the Bruker Avance III 400 MHz NMR spectrom-eter (German) operated at a 13C frequency of 100 MHz. The other in-strumental test conditions were as follows: recycle delay time of 4 s,line broadening of 50 Hz, spinning rate of 5 kHz, and calibration usingglycine as the external standard (Yao et al., 2019). The pore volumes(PVs) of the coral sand were determined using our previously reportedmethod (Li et al., 2019).

2.5. Statistical analysis

One-way analysis of variance tests (ANOVA) were used to comparethe mean values and relative standard deviation of the replicates. Allstatistical analyses were run using SPSS version 19.0.

3. Results and discussion

3.1. Abundance and characteristics of microplastics in the sands of a coralreef island

The microplastics found in the coral sand were detected in all theXisha Islands (BJ, QL, PS, LH, YZ, HY, and HG), Nansha Islands (XE, XY,and SJ), Weizhou Island, and Sanya LHT sites, where their abundancevaried from 60 ± 3 items/kg to 610 ± 11 items/kg, from 40 ± 4items/kg to 100 ± 2 items/kg, from 60 ± 2 items/kg to 90 ± 5 items/kg, and from 50 ± 3 items/kg to 530 ± 7 items/kg, respectively(Tables 1). In contrast to our earlier assumptions, although these areaswere far from zones of human activity, the quantities were smallerthan our previous observations in the Maowei Sea located in the BeibuGulf (river estuary: 520 ± 8 to 940 ± 17 items/kg) (Li et al., 2019)and much higher than those detailed in three other reports concerningcoral reef islands in the IndianOcean (Vidyasakar et al., 2018; Saliu et al.,2018; Imhof et al., 2017). The surrounding countries were experiencinga period of rapid economic development, which increased the dischargeof plastic particles into the South China Sea.Moreover, because the plas-tics or microplastics affect the normal physiological activities of thecoral, some effort should be made to eliminate the plastic andmicroplastic pollution in the coral reefs located in the South China Sea.

It is interesting to note that the abundance of microplastics detectedin the marine open sediment (with the absence of coral reef) rangedfrom 5.30 items/kg to 68.88 items/kg in the northern Bering and Chuk-chi seas (Mu et al., 2019), a range that was relatively lower than thatfound in the sands of the coral reef islands. The depth of the sand inthe collection sites (about 3 m) was less than that in the sediment col-lection sites, and thus the deposition rate of the microplastics, one ofthe dominant factors that affects their abundance, at coral reef areawashigher than in the open sea (Hoellein et al., 2019).Moreover, the re-sults of some lab studies have indicated that the microplastics may bestrongly “immobilized” at the gut of a coral reef and then concentratedin the sediment/sand of this area after the decay of indigenous

hina Sea.

Microplastic (items/kg) Sites Microplastic (items/kg)

E (XE) 80 ± 6

Sanya LHT

D1 120 ± 9Yi (XY) 40 ± 1 D2 60 ± 3Jiao (SJ) 100 ± 2 D3 170 ± 15

90 ± 5 D4 530 ± 780 ± 11 D5 50 ± 360 ± 2 D6 80 ± 870 ± 4

and Sanya LHT with nearly the same hydrodynamic characteristics.

783L. Zhang et al. / Science of the Total Environment 688 (2019) 780–786

organisms following their life cycle (Hankins et al., 2018; Hall et al.,2015). This special pathway for microplastics accumulation may be an-other reason for the higher quantities of microplastics in the coral reefarea, which needs special attention and further investigation.

Moreover, themicroplastics in coral sandwere exclusively identifiedto be PP, PE, and PET, which differs significantly from the results fromother reports concerning the South China Sea (consisting of ~22.5%alkyd resin, ~20.9% polycaprolactone, ~15.5% poly ethyl acrylate,~14.7% PS, and some other polymer types, each b5%) (Cai et al., 2018).The sands of the Rameswaram coral reef island located on the southeastcoast of India (Vidyasakar et al., 2018) were also different (consisting of~39.7% PP, ~17.9% PE, ~15.6% PS, ~14.6% nylon, and ~12.2% PVC) (Fig. 2).In contrast to the microplastics in nearly all other marine and coastalsediments (Li et al., 2019; Zhang et al., 2019), red was the dominantcolor of the microplastics found in the coral sand rather than white ortransparent, with values of 36.36%, 46.15%, 39.60%, and 52.63% for theNansha Islands, Xisha Islands, Sanya LHT site, and Weizhou Island, re-spectively (Fig. 3 and Table S1).

3.2. Comparing the microplastic pollution status in a fringing reef and atoll

3.2.1. AbundanceSpatially, it is interesting to note that the microplastic content in

Xisha Islands and Nansha Islands (mainly the atoll) that has a verysmall number of inhabitants, presented a relatively higher abundanceof microplastics. The microplastic content the in Xisha Islands washigher than theWeizhou Island and the Sanya LHT site. The abundanceof microplastics followed the sequence of Xisha Islands N Sanya LHT siteN Nansha Islands ≈ Weizhou Island. The highest abundance for thesampling sites was detected at the PS island (Xisha Islands, 610 ± 11items/kg), while the lowest values were at the XY island (NanshaIslands, 40 ± 4 items/kg) (Table 1). From the viewpoint of plasticsources, these results were confusing for both the Sanya LHT site andWeizhou Island, which are tourist destinations that encompass manyavenues for plastic input.

As many reports have shown, once the plastics enter the ocean(Lebreton et al., 2017), the plastic or microplastic particles are ubiqui-tously transported by the effects of tides, ocean currents, andmonsoonsbefore being deposited in the coral sands. In addition to the aforemen-tioned sources and their deposition rates, the exchange of water

Fig. 2. The type characteristics of microplastic in the sa

between the coral reef and the adjoining ocean may be another impor-tant factor in the abundance of microplastics in these two zones (Songet al., 2018). Suzuki et al. and Monismith et al. indicated that thecross-shore water exchange rates were controlled by multiple factorsincluding the force of the surface and internal waves, boundary mixing,longshore flows caused by variations in roughness and convectiveflows(Suzuki and Kawahata, 2003; Monismith et al., 2007). In general, therate of water exchange at the fringing reef was found to usually behigher than at the atoll, so that the microplastics could be more easilytransported to other areas of the adjacent ocean, whichmay be the rea-son why the Xisha atoll experienced the highest plastic contamination.However, in the Nansha atoll islands, although the exchange rates werestill relatively low compared to the fringing reef, their distance from themainland and associated rivers (which are major sources of plastic con-taminants; about 1.15–2.41 million tonnes of plastic waste currentlyenter the ocean every year from rivers) hindered transport of the plas-tics and microplastics to these zones by ocean currents and other path-ways, which lowered the content of microplastics on these atolls.

3.2.2. CharacteristicsIn the remote atoll islands, the mean percentage of PP was 87.91%

while it was 90.91% for the Xisha and Nansha islands. The PP polymerwas the only type of microplastic detected in the BJ island, XE island,and SJ island, while at the HY island, which is adjacent to the Philippineislands, the medium level of PP was 78.57% (Fig. 2 and Table S2). Theproportions of PP microplastics in the fringing reefs were about70.00% and 81.19% for Weizhou Island and the Sanya LHT site. Theseslightly lower PP percentages and the slightly higher PE percentages(26.67%) at Weizhou Island were believed to be mainly due to thewidely used PE nets in the fishing industry (Table S2). Moreover, no ob-vious differences were found between themicroplastics detected in theSanya LHT fringing reef and the remote Nansha and Xisha atolls (p N

0.05). These divergent findings may have been induced bymultiple fac-tors (sources/transport pathways of microplastics, hydrodynamic char-acteristics of these three zones and so on), which require furtherinvestigations to elucidate.

Fig. S3 and Table S3 show the percentages of microplastics of differ-ent sizes (1–5 mm and b1mm) in the sands of a coral reef island. Muchlike many other previous observations (Li et al., 2019; Cai et al., 2018),the smaller sized microplastics (b1 mm) were dominant, these particle

nds of coral island located on the South China Sea.

Fig. 3. The color characteristics of microplastic in the sands of coral island located on the South China Sea.

784 L. Zhang et al. / Science of the Total Environment 688 (2019) 780–786

fractions accounted for 83.18%, 80.77%, 70.00%, and 70.30% at theNansha Islands, Xisha Islands, Weizhou Island, and Sanya LHT sites, re-spectively. The much higher percentages of smaller size microplasticsat the Nansha Islands and Xisha Islands suggested that the extent oftheweathering of the plastic productswas relatively strong after the ex-tended time drifting to and depositing on the remote atoll island.

Fig. 4. The abundances (a), type (b), color (c) and size (d) of microplastic in the r

3.2.3. Microplastics in the reef flat and lagoon of two typical atolls in theXisha Islands

At the atoll, the coral reef environmentswere divided into two parts:the reef flat and the lagoon. The formerwas the shallow part of the coralreef that offered the plastics a short residence time in thewater (about afew hours) and high photosynthesis/calcification, while the lagoon had

eef flat and lagoon of BJ island (left two bars) and PS (right two bars) island.

Table 2The relationships between the abundances of microplastics and the compositions of thesand of coral island.

Site Organic matter content(g/kg)

R2/p PV(cm3/g)

R2/p

Weizhou

W1a 0.84

0.7058/N0.05

0.83

0.0247/N0.05W2 1.12 1.39W3 2.40 0.92W4 1.05 0.78

Sanya LHT

D1 0.63

0.0919/N0.05

1.45

0.0413/N0.05

D2 0.55 1.32D3 1.09 2.03D4 1.40 0.88D5 1.85 0.74D6 0.61 1.20

785L. Zhang et al. / Science of the Total Environment 688 (2019) 780–786

opposite characteristics (Hamner et al., 2007). Therefore, it was initiallyassumed that there would be more microplastics in the sands of the la-goon may be much higher than in the reef flat.

Unexpectedly, this was only the case at BJ island (390 ± 9 items/kgand 60 ± 5 items/kg for the lagoon and reef flat, respectively), while atPS island the abundance of microplastics in the reef flat (610 ± 17items/kg) was much higher than in the lagoon (300 ± 11 items/kg) (pb 0.05) (Fig. 4a). Furthermore, the type, size, and color of themicroplastics detected in these two featured regions (reef flats and la-goons) of the BJ and PS islands were quite different from one another(Fig. 4b, c, and d). As Halle et al. (2017) reported, the decompositionof microplastics into much smaller size particles (that cannot be de-tected by existing methods) in water happens during their residencein the lagoon as a result of the strong UV irradiation at these low-latitude regions. Therefore, the amount of microplastics in the lagoondepends on the input of microplastics through the water exchange be-tween the lagoon and open sea, but is also a result of rate ofmicroplasticdecomposition. In other words, the decomposition of microplastics inthe lagoon sand of PS island becomes an important output pathwaythat produces creates opposing results.

3.3. Identification of the dominant sand composition controlling the abun-dance of microplastics

To avoid the influence of the source and other potential factors, themicroplastics in identical sampling zones (i.e. four sites of Weizhou Is-land and six sites in Sanya LHT) were detected using establishedmethods, and the results are shown in Table 1. The differences in thehighest and lowest values of microplastics in the same zones reached1.5 times and 10.6 times those for Weizhou Island and Sanya LHT, re-spectively, far from their standard deviations (Table 1). Meanwhile,the types, colors, and sizes of the detected microplastics in the samesampling zones were nearly identical (p N 0.05), which indicated thatthe microplastics in the coral sands were originally from the samesources and input pathways. Therefore, the reasons for the differencesin themicroplastics at the same sampling sites need further exploration.

Previous studies have demonstrated that microplastics are likely toincorporate and integrate into the aggregateswithmangrove sedimentsand therefore, closely related to hydrodynamics as well as the composi-tion and structure of the free particulate organic matter fraction in thewater. However, in this reported study, no correlation was found be-tween the abundance ofmicroplastics and the amount of organicmatterin the soil atWeizhou Island and the Sanya LHT sites (n= 25, p N 0.05).

As we previously reported (Li et al., 2019), pore volume (PV) limitedthe transport of fine particles and organic carbon in sand or sediment.However, this conclusion did not apply to the microplastics distributedin coral sands. That is to say that there was no linear relationships be-tween the microplastic content (items/kg) and PV of coral sand (p N

0.05). Results like these confirmed that the composition and conforma-tion of organic matter andminerals in coral sand in the South China Seawere not independently responsible for the microplastic content of thesoil. However, further studies should be conducted to determine thejoint effects of the composition and structure of the soil system(Table 2).

4. Conclusions

In this study, microplastics in the sands of coral reef islands locatedin the South China Seawere found to be present in relatively large quan-tities (ranging from 40 ± 4 items/kg to 610 ± 11 items/kg), with dis-tinctive compositions (mainly PP, PE, and PET), and small sizes(b1 mm accounting for N75%), even in the remote Nansha Islands andXisha Islands. Moreover, variations in the microplastic content in thesands of the atolls and fringing reefs were identified based on theirsources and water exchange rates. Degradation of the microplasticsmay be one of the important factors that induced the variations of

microplastics in reef flats and lagoons. Additionally, it was found thatthe quantity of microplastics in the sands was not independent oftheir composition or the structure of the coral sand.

Acknowledgments

The authors are grateful for financial support from the Natural Sci-ence Foundation of China (No. 91428203, No. 21806026, No.41673105, No. 41273139), Science and Technology Major Project ofGuangxi (AA17202020).

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.scitotenv.2019.06.178.

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