Microplastic in beach sediments of the Isle of Rügen (Baltic Sea

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A median abundance of 88.10 (Q1 = 55.01/Q3 = 114.72) microplastic particles per kg dry ... were determined between the beaches with different exposition and ... beach environments in marine habitats. .... from a beach at the River Elbe close to Hamburg. ...... contamination in an urban area: a case study in Greater Paris.

Marine Pollution Bulletin 126 (2018) 263–274

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Microplastic in beach sediments of the Isle of Rügen (Baltic Sea) Implementing a novel glass elutriation column Elena Hengstmann, Matthias Tamminga, Constantin vom Bruch, Elke Kerstin Fischer

T ⁎

Center for Earth System Research and Sustainability (CEN), University of Hamburg, Bundesstraße 55, 20146 Hamburg, Germany

A R T I C L E I N F O

A B S T R A C T

Keywords: Microplastics Density separation Elutriation Beach sediment Baltic Sea

To extent the understanding on microplastics in the marine environment we performed a case study at four beaches on the Isle of Rügen considering abundance and spatial distribution of microplastics in beach sediments. For the analysis, density separation via a glass elutriation column was implemented. In advance, efficiencies were tested for two polymers, being not buoyant in water. Recovery rates of 80% for PET and 72% for PVC particles in sandy samples were achieved. A median abundance of 88.10 (Q1 = 55.01/Q3 = 114.72) microplastic particles per kg dry sediment or 2862.56 (Q1 = 1787.34/Q3 = 3727.28) particles per m2 was found at the beaches on Rügen. Fibers were more abundant than fragments at all beaches. In this study, no statistically significant differences but only tendencies were determined between the beaches with different exposition and anthropogenic activity as well as for distribution patterns which showed that microplastic fragments accumulate in topographic depressions, similar to macrolitter items.

1. Introduction The contamination of ecosystems by plastic has received increased attention in the last decades (Galgani, 2015; Galgani et al., 2013; Wright et al., 2013; Thompson et al., 2004). Low degradation rates, resulting persistence in the environment as well as non-sustainable use and inadequate waste management of plastic products lead to a rising importance of plastic as environmental pollutant (Geyer et al., 2017; Andrady, 2015; Barnes et al., 2009). Simultaneously, global plastic production increased from 225 to 322 million tons per year between 2004 and 2015 (PlasticsEurope, 2016). The consequences of plastic debris in ecosystems are diverse. It can pose a risk to biota, for example in cases where aquatic species are physically entangled or when particles are ingested by organisms (Werner et al., 2016; Gregory, 2009; UNEP, 2005; Thompson et al., 2004; Laist, 1987, 1997). Ingestion of microplastics in combination with adsorbed chemicals can have impacts on the metabolism of aquatic organisms (e.g. Lee et al., 2016; Galloway, 2015; Lusher et al., 2015; Rochman, 2015; Cole et al., 2011). Furthermore, social (e.g. decrease of aesthetics at beaches and subsequent decrease of the recreational value) and economic impacts (e.g. additional costs due to impacts on fishing industry) can be observed for plastic pollution in the environment (Werner et al., 2016; Newman et al., 2015). The coastal environment, being the interface between the terrestrial and marine



ecosystems, is characterized by a high degree of biodiversity. Therefore, plastic pollution is even more prone to have impacts on biota (Hardesty et al., 2017). Several local studies focused on sandy beaches and aimed for the quantification of plastic particles (Hanvey et al., 2017; Van Cauwenberghe et al., 2015; Browne et al., 2015). In Europe, beaches on the Baltic Sea, North Sea and Atlantic coast were analyzed for microplastics (i.a. Graca et al., 2017, Stolte et al., 2015, Dekiff et al., 2014, Antunes et al., 2013, Van Cauwenberghe et al., 2013a). Microplastics are defined as plastic particles < 5 mm (Arthur et al., 2009). For the analysis of microplastics in sediments no standard operation procedures have been determined, so far. On the contrary, a great variety of methods concerning both the sampling and laboratory analysis were applied in studies investigating plastic abundances on beaches (Van Cauwenberghe et al., 2015; Hidalgo-Ruz et al., 2012). Concerning the separation of microplastics from sediment in beach samples the principle according to Thompson et al. (2004) is widely implemented taking advantage of density differences between plastic and sediment particles. On the one hand, different high density salt solutions have been applied for this purpose (i.a. Corcoran et al., 2015, Dris et al., 2015, Stolte et al., 2015, Dekiff et al., 2014, Nuelle et al., 2014, Van Cauwenberghe et al., 2013b, Ballent et al., 2012, Imhof et al., 2012). On the other hand, the concept of elutriation was adapted for microplastic analysis. Here, a continuous upward flow of water or air within a column leads to the rising of lower-density materials. The

Corresponding author. E-mail address: elke.fi[email protected] (E.K. Fischer).

https://doi.org/10.1016/j.marpolbul.2017.11.010 Received 14 August 2017; Received in revised form 6 November 2017; Accepted 7 November 2017 0025-326X/ © 2017 Elsevier Ltd. All rights reserved.

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underlying idea was developed in the field of biology (Southwood and Henderson, 2000), was transferred to microplastic analysis by Claessens et al. (2013) and was subsequently enhanced to facilitate higher recovery rates (Kedzierski et al., 2016; Zhu, 2015). In continuation, this study presents a new elutriation column of smaller dimension and manufactured of glass, completely. Recovery rates focusing on highdensity polymers (PET, PVC) are presented. Furthermore, this study quantifies microplastics in sediments from beach environments in marine habitats. A case study was conducted at four sandy beaches on the Isle of Rügen at the Baltic Sea in Mecklenburg-Vorpommern, Germany. The goal of this study was also to evaluate accumulation patterns for microplastic particles. The four beaches are mainly characterized by different expositions, grain size compositions and levels of touristic frequentation and were analyzed as well as compared with regard major differences concerning microplastic abundance and distribution.

necessary to reduce the particle-size variability of the sample by separating it into different size classes.” (Kedzierski et al., 2016). However, the size fractions that are currently in use for the classification of plastics (Galgani et al., 2013; Van Cauwenberghe et al., 2015) are not suitable for the creation of subsamples (Kedzierski et al., 2016). The classification used for the elutriation of microplastic samples here is based not only on microplastic specific size classes, but also on granulometric size categories following the approach of Kedzierski et al. (2016) applying size separation prior to elutriation. Microplastics are often defined as particles < 5 mm or < 1 mm, resulting in the first size delimitation. A second survey mark originating in microplastic research is 300 μm representing the limit of a common water sampling method using manta trawls. All other size limits implemented in this study derived from the classification of soil grain sizes by DIN 4022 and DIN EN ISO 14688-1 (German Institute for Standardization, European Norm, International Organization for Standardization). Granulometry refers to the differentiation of mass fractions of grains or lithified particles in sediments or clastic rock based on their equivalent diameter. Particles smaller 5 mm are grouped homogenously into fine gravel (> 2–6.3 mm), sand (> 0.063–2 mm), silt (> 2–63 μm) and clay (> 0.063–2 μm) (Blum, 2007). These are again subdivided into subgroups of coarse, medium and fine fractions. Taking into account these categorizations from sediment grain size analysis and commonly set size delimitations in microplastic analysis, the resulting classification implemented in this study includes five size fractions: > 0.063–0.2 mm, > 0.2–0.3 mm, > 0.3–0.63 mm, > 0.63–1 mm and > 1–5 mm. Based on this classification all polymer materials were grinded and sieved to provide the different size classes for the recovery test. According to Kedzierski et al. (2016) recovery rates are higher for samples including sand. On the one hand, the terminal velocity due to pseudo-homogenous suspension fluid of water and sand is supposed to be reduced. On the other hand, the reduction of edge frictions within the column might be favored due to particle collision. To address this specific topic, two samples for each material in each size fraction were prepared. One sample contained only 30 microplastic particles while the second one additionally contained 25 ml sediment of respective grain size. The sediment required for the artificial samples was obtained from a beach at the River Elbe close to Hamburg. It was sieved into the same size classes as polymer particles by an automatic sieving machine (Retsch GmbH, AS200 control). Subsequently, sand subsamples were annealed at 900 °C for 4 h in a muffle furnace (Nabertherm, L 24/11/ P330), to ensure that no organic or polymer material remained.

2. Material and methods 2.1. Pre-tests elutriation An elutriation column was manufactured for the purpose of density separation of microplastic and sediment particles. Different elutriation systems have already been tested and used in former studies (Kedzierski et al., 2017, 2016; Zhu, 2015; Claessens et al., 2013). These columns, however, were made out of PVC while the newly developed one is made of glass. On the one hand, it is important to avoid plastic components in the microplastic quantification process at any point; on the other hand, a glass column also provides a view on the separation process. Additionally, a glass column is more resistant concerning chemicals; however the risk of breakage is higher. The elutriation column was also optimized concerning its dimensions to reduce edge effects. The manufactured glass column has a length of 100 cm, an inner diameter of 5 cm and is made of 2 mm thick glass. The outlet is located at the top of the column (3 cm from the top). A stainless-steel frit (pore size: 37 μm; Sartorius AG) is situated at the bottom of the column to avoid any contamination by the tap water being introduced via a separated flange, which is fixed to the column for the elutriation process. Water from the faucet is channeled through a tube, which is equipped with a flow meter (digiflow6710m, Savant) to measure the exact flow velocity for the elutriation process. The detailed setup is illustrated in Fig. 1. Samples are inserted at the top of the column. With the inflow of water at the bottom the water level and the buoyant sample aliquots rise within the column. The outflowing suspension is percolated through a fixed sieve with a mesh size of 63 μm before being drained. Subsequently, the water in the column is drained by an outlet at the bottom and the sample residues mostly consisting of sandy sediment are disposed by releasing the flange and thoroughly rinsing the whole column from the top inlet with solvents and deionized water.

2.1.2. Elutriation process The prepared samples were introduced into the elutriation column and the column was filled with water to two thirds with a higher flow rate than required to allow the complete mixing of samples. Subsequently, the particles were given time (5 min) to settle. In between, the water surface was agitated three times by sprinkling with deionized water in order to break surface tension, which had caused dense particles to float as well. Then, different flow rates according to the size fraction of the sample were applied. These were obtained in pre-tests which accounted for the recovery of different non-buoyant polymers (PS, PET and PVC) in specific size classes while the upwelling of sandy sediment was suppressed. Based on these pre-requisites the fluidization of plastic (ten particles per polymer in three replicates) and sand particles (50 ml in three replicates) was observed in the elutriation column and flow rates were noted. The final specific flow velocities for the elutriation column used in the experiments are presented in Table 1. The elutriation was processed for 10 min during which a stirring bar was used regularly to avoid the clustering of sediment and plastic particles at the bottom of the column. The period was determined based on elutriation times of former studies ranging between 5 min (Kedzierski et al., 2017, 2016) and 15 min (Claessens et al., 2013) and was further adjusted empirically to the here implemented column by visual examination of the total recovery of a specific number of plastic

2.1.1. Reference material To test the performance of the described elutriation column polymer reference particles were used as well as spiked sand samples. Polymers with densities below 1 g/cm3 are buoyant in water anyway; tests on recovery by elutriation with particles in the size fractions of 0.3 to 1 mm and 1 to 5 mm led to recovery rates of 100% of polyethylene and polypropylene particles. Therefore, the focus within this study was on high-density microplastics, only. Reference materials purchased from Goodfellow USA were utilized for the efficiency tests: Polyethylene terephthalate granules (PET; ES306311/1; 1.38 g/cm3) with a diameter of 3 mm and a polyvinylchloride film (PVC; CV311450; 1.37 g/cm3) with a thickness of 0.38 mm that was sliced into different size categories. No post-consumer products were used as reference polymers due to high variations and uncertainties in their density. “To achieve the separation of particles according to their density, it is 264

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Fig. 1. Schematic representation of the elutriation column (left) and picture of the elutriation column (right).

the village Varnkevitz, called “North beach 1” (N1) and “North beach 2” (N2) in the following. N1 is quarterly cleaned as part of the beach monitoring program of the state Mecklenburg-Vorpommern, while N2 is not included in this program and can serve as an untouched reference beach unit concerning macrolitter. A third beach, the “East beach” (E), was situated close to the Village Vitt and had an eastern exposition. The “West beach” (W), facing to the west, is located close to newly built vacation homes in the area of Dranske. In general, the eastern beach can be described as the beach with the highest anthropogenic and touristic influence due to its proximity to the Kap Arcona (a headland with a cliff consisting of chalk and till). For a more detailed description of the beaches see Hengstmann et al. (2017).

particles. This procedure was applied for all samples with and without sand. Three replicates were conducted for all polymer fractions. Captured particles in the 63 μm sieve were transferred onto glass fiber filters (613, VWR International, 5–13 μm retention) by thoroughly rinsing into a filtration device (Sartorious Stedim 16828-CS). These filters were placed in glass petri dishes and dried at room temperature. For the identification of microplastic particles the filters were stained by adding 1 ml of Nile red dissolved in Chloroform (1 mg/ml) (Tamminga et al., 2017). The stained filter membranes were covered with a watch glass and were, again, dried at room temperature under the fume hood for 48 h. Subsequently, the filters were photographed (Pentax K-30, exposure time 2″, ISO 100, resolution 2420 × 2343) under UV-light (Omnilux UV 18W G13, 365 nm). Microplastic particles fluoresce with a maximum in the red visible spectrum under UV-light when stained with Nile Red solved in Chloroform and can therefore be identified and counted in digital image analysis (Tamminga et al., 2017).

2.2.2. Sampling At the investigated beaches 50 or 100 m sequences were chosen for the sampling process. The basic criteria for the extraction were: i) lack of vegetation, ii) width > 5 m and iii) sand content > 40%. In total, 57 sediment samples were taken for laboratory analysis on microplastics. Sampling transects were placed every 10 m, except for the first northern beach segment, where transects were 25 m apart from each other (see Fig. 2c). Due to a high number of pebbles at the beach close to the Kap Arkona, three transects were situated at the beginning of the segment whereas two transects were located 100 m towards the north. The decision on where to sample beach sediment has a strong impact on the results (Fisner et al., 2017). Studies sampling the high tide line only aim to find microplastic debris rather than analyzing the microplastic concentration in the beach environment systematically

2.2. Case study 2.2.1. Study area A case study was conducted at the German Baltic Sea coast in Mecklenburg-Vorpommern (MV) on the Isle of Rügen (Fig. 2a/b) in July 2015. Four beaches were selected due to their different exposition, accessibility and according to certain criteria of the OSPAR beach monitoring program such as dimension, composition and frequency of use (OSPAR, 2010). The two beaches facing to a northern direction were located close to Table 1 Flow rates for the elutriation process according to the size fraction. Size fraction

> 1–5 mm

> 0.63–1 mm

> 0.3–0.63 mm

> 0.2–0.3 mm

> 0.063–0.2 mm

Flow velocity

9.0 l/min

4.0 l/min

3.3 l/min

2.2 l/min

0.8 l/min

265

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Fig. 2. (a) Study area and (b) study sites at the northwestern coast of the Isle of Rügen (arrows indicating mean currents seven days prior sampling) as well as (c) microplastic sampling positions at one of the beaches and (d) prevailing winds (frequencies of observed wind speeds) seven days prior to sampling (Arcona, 54.68°N/13.43°E). Coordinate system: ETRS_1989_UTM_Zone_33N, Projection: Transverse Mercator, wind data: DWD (2016), visualization of wind data: R Core Team (2016), RStudio Team (2015), Carslaw and Ropkins (2012).

results in good efficiencies whereas not destroying or altering plastic particles. Samples were rinsed with MilliQ water in a sieve (63 μm) via “gold panning” to stop the reaction. As a second step for the elimination of organic matter sodium hypochlorite (NaClO) was added in a volume ratio of 3:1 to the water/sample mixture according to Collard et al. (2015). After a reaction time of 24 h wet sieving was implemented. For this process, the dry sieving machine was converted using a lid with a let-in for water. MilliQ water (15 l) was added slowly to the sample while sieving it for 5 min at an amplitude of 0.75 mm/“g”. The sieving cascade was composed of five sieves (5 mm, 1 mm, 0.63 mm, 0.3 mm, 0.2 mm, 0.063 mm). The > 5 mm size fraction was rejected since microplastics were defined as particles smaller 5 mm according to Arthur et al. (2009). The principle of density separation was applied to extract microplastic particles from the sediment samples. The elutriation column described in Section 2.1 was employed for this purpose, and the elutriation process was the same as for the recovery experiments. The only difference was a change of the frit at the bottom of the column. In this case the stainless-steel frit was replaced by a glass frit (pore size: 16–40 μm). As described for the efficiency tests, the residues of the elutriation were transferred onto filter membranes. In cases of high amounts of interfering material (sand and residual organic matter) the sample was evenly distributed onto more than one filter. The photographs of the stained filters (see Section 2.1) were analyzed based on digital images in order to identify and count stained microplastic particles.

(Hanvey et al., 2017). In this case study, we conducted a survey on microplastic abundance considering three positions within the littoral zone and four to five transects along a segment to provide indications for microplastic distribution. Within each perpendicular, the three positions were differentiated as follows (Fischer et al., 2016): The first one (A) was placed in the intertidal zone; therefore, this area was partly influenced by waves and oscillations. The second location (B) was situated at the high tide line and the third (C) upon the plateau of the beach. Quadrates of 25 × 25 cm were sampled (area: 625 cm2). The area was stabbed with stainless steel plates before the first 2–3 cm were removed (1250–1875 cm3) with a stainless-steel spoon. The sediment was transferred into glass jars for transportation. Beside loose sediment samples, samples with core cutters were taken next to each quadrate. These were intended to later receive the bulk density of the sediment. 2.2.3. Laboratory analysis For microplastic quantification 50 ml subsamples were extracted and weighed. A purification protocol containing two steps was applied: First, 60 ml of hydrogen peroxide (H2O2 50%) were added to the sediment subsample. H2O2 is used for soil analysis according to the DIN standard (DIN ISO 11277) and has been used for the destruction of organic material in microplastics analysis before (i.a. Esiukova, 2017, Fischer et al., 2016, Retama et al., 2016, Faure et al., 2015, Stolte et al., 2015, Nuelle et al., 2014, Imhof et al., 2012, Liebezeit and Dubaish, 2012). To allow an appropriate reaction, samples were covered and placed under a laboratory hood for seven days at room temperature. Pretests on the destruction of organic material showed that H2O2 (50%) 266

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2.2.4. Contamination Contamination was avoided as much as possible by covering samples between all processing steps with watch glasses, by increasing the humidity in the laboratory and by wearing coats made of 100% cotton. Additionally, blank tests were processed parallel to the samples to better estimate the contamination as suggested by Torre et al. (2016) and Nuelle et al. (2014). All methods for the field samples described above have also been adapted to these blanks. In total, 19 blank samples were processed.

Table 3 The mean number of fibers and fragments in different size classes found in blank samples (n = 17). Size fraction

> 1 mm

> 0.63–1 mm

> 0.2–0.63 mm

> 0.063–0.2 mm

Fragments Fibers

0 0

0 0.421

1.070 2.182

1.167 1.895

Taken as a whole, average recovery rates are higher for samples without sediment for the bigger size fractions > 1 to 5 mm and > 0.63 to 1 mm. In contrast, mean extraction efficiencies are higher for the smaller size classes for samples including sediment (see Table 2).

2.2.5. Statistics and geospatial analyses Mean concentrations of microplastics were calculated by weight (particles per kg dry sediment) and area (particles per m2). The data was moreover analyzed by nonparametric statistics due to a non-normal distribution (Shapiro-Wilk-Test). The Kruskal-Wallis-Test (followed by Dunn-Bonferroni post-hoc tests) was applied for the comparison of microplastic abundance between i) the four beaches and ii) the position within the littoral zone. The significance level for all analyses was set to 95% (p = 0.05). The Spearman-Rho correlation coefficient was calculated for the relation of microplastics and organic material. Calculations were performed with the software SPSS Statistics (IBM Cooperation, Version 23) and R scripting language (R Core Team, 2016, Version 3.3.1) in an RStudio environment (RStudio Team, 2015, Inc., Version 1.0.36). Visualizations were also performed using R scripting and RStudio. Furthermore, the geographic coordinates of microplastic sampling points were corrected and converted to a shapefile to visualize the findings in a Geographic Information System (GIS; ArcGIS ©ESRI, Version 10.1). The blank filters were analyzed separately to confirm the contamination by fibers and fragments in the laboratory process. The mean of all filters was calculated and subtracted from the results of the sample filters for each size fraction, respectively.

3.2. Background contamination No blank sample contained any fiber or fragment bigger than 1 mm. Only two filters were contaminated by fragments between 0.63 and 1 mm while fibers were more abundant in this size fraction. The highest number of fragments on blank filters was found in the smallest size class. For fibers, the contamination was highest for the size class > 0.2 to 0.63 mm. Table 3 shows the mean numbers of fibers and fragments in blank samples for the different size fractions, respectively. These values were subtracted from the counts of fibers and fragments in the sediment samples to exclude the bias of contamination. 3.3. Microplastics in beach sediments The median abundance of microplastics for this study was 88.10 (lower quartile Q1 = 55.01/upper quartile Q3 = 114.72) particles per kg dry sediment (DW). Fragments were less abundant (22.96 particles per kg DW; Q1 = 10.86/Q3 = 40.93) than fibers (54.37 particles per kg DW; Q1 = 30.84/Q3 = 81.77). In terms of the concentration per area the mean value was 2862.56 (Q1 = 1787.34/Q3 = 3727.28) particles per m2, showing again the difference between fibers and fragments with means of 1766.46 (Q1 = 1002.19/Q3 = 2656.77) and 746.00 (Q1 = 352.76/Q3 = 1329.88) particles per m2, respectively. Abundances for all individual sampling points are listed in the Supplementary information. Fibers were more abundant than fragments at all beaches (see Fig. 3). No significant differences were apparent between the abundances, neither of microplastics in total (p = 0.079), nor for fragments (p = 0.592) between the four beaches. Only the fiber abundance between North beach 1 and North beach 2 showed a significant difference (significance: 0.09, p = 0.05). However, tendencies were visible concerning dissimilarities in microplastic concentrations at the investigated beaches. North beach 2 showed the highest contamination by microplastics with 106.39 particles per kg DW (Q1 = 88.33/Q3 = 139.83) followed by the eastern beach (94.41 particles per kg DW; Q1 = 66.24/Q3 = 113.31). At the first northern beach a mean concentration of 76.27 particles per kg DW (Q1 = 48.42/Q3 = 109.73) was found while the western beach showed the least contamination (63.11 particles per kg DW; Q1 = 39.91/

3. Results 3.1. Recovery rates of the elutriation process Overall recovery rates (for both polymers and across all size fractions) were experimentally determined as 75.89% ( ± 14.13) for samples with sediment and 68.22% ( ± 19.71) without sediment. Table 2 gives a detailed overview concerning mean recovery rates in different size fractions and for both polymers. Concerning the different size fractions mean extraction efficiencies differed, being the highest for particles between 0.2 and 0.3 mm in samples with sand (85.00% ± 10.90) and for the fraction > 1 to 5 mm in samples without sediment (86.11% ± 7.43). The lowest recovery rates were in both cases achieved for the smallest size group (> 0.063 to 0.2 mm) with 65.56% ( ± 16.69) and 42.22% ( ± 16.42), respectively. The average recovery rate of PET samples with and without sediment across all fractions was 80.00% ( ± 10.62) and 68.89% ( ± 20.99), respectively. In comparison, recovery rates for PVC samples across all fractions were slightly lower with 71.78% ( ± 16.27) with sand and 67.56% ( ± 19.04) without sand.

Table 2 Mean recovery rates and standard deviation by polymer type and fraction, with and without sediment. Size fraction [mm]

Recovery rates with sediment [%] Overall

> 1–5 > 0.63–1 > 0.3–0.63 > 0.2–0.3 > 0.063–0.2

82.78 69.44 76.67 85.00 65.56

± ± ± ± ±

Recovery rates without sediment [%]

PET 14.21 13.24 6.99 10.90 16.69

87.78 74.44 80.00 81.11 76.67

PVC ± ± ± ± ±

6.94 1.92 6.67 15.03 17.64

Overall

77.78 64.44 73.33 88.89 54.44

± ± ± ± ±

267

19.53 18.95 6.67 5.09 3.85

86.11 79.44 67.22 66.11 42.22

± ± ± ± ±

PET 7.43 12.19 11.63 17.05 16.42

88.89 83.33 67.78 57.78 46.67

PVC ± ± ± ± ±

8.39 8.82 18.36 20.37 18.56

83.33 75.56 66.67 74.44 37.78

± ± ± ± ±

6.67 15.75 0.00 10.18 16.44

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Fig. 3. Concentration (median) of microplastic particles per kg dry sediment by shape at the different beach segments on Rügen. Table shows median as well as lower and upper quartile values. Coordinate system: ETRS_1989_UTM_Zone_33N, projection: Transverse Mercator, base map: OSM World Topographic Map.

Q3 = 81.69). The same descending order is true for fiber abundances. In comparison the variation between the beaches was lower for fragments. Highest abundances were revealed for the two northern beaches followed by the eastern beach. Again, the western beach showed the least contamination. Fig. 4 shows the sampling positions with their corresponding results for microplastic fiber and fragment abundances at the four beaches. Overall, it can be stated that universal patterns of microplastic distribution at the four beaches on the Isle of Rügen are hardly recognizable. Faint distribution patterns for fragments are revealed while fibers are distributed homogenously. No significant differences were identified for the total microplastic abundance (p = 0.393), for fibers (p = 0.448) or fragments (p = 0.927) at the different positions within the littoral zone. A slight tendency is visible, though. Microplastics were less abundant in the intertidal zone compared to the high tide line, with means of 76.27 (Q1 = 50.34/Q3 = 100.75) and 93.45 (Q1 = 62.39/Q3 = 147.63) particles per kg DW, respectively. More particles were identified on the plateau (92.43 particles per kg DW; Q1 = 56.96/Q3 = 119.10) than at the water's edge, but less compared to the high tide line. This distribution can be transferred onto fibers as well, while fragments are nearly evenly distributed between these three sections (Fig. 5). The abundance of microplastic particles highly varied regarding the size fraction. Microplastics increased with decreasing size except for the smallest size fraction considered in this study (> 0.063 to 0.2 mm). The smallest amount of fibers and fragments were found in the biggest size class (> 1 mm to 5 mm) with 8.8% and 3.6%, respectively. For fragments, 12.0% of particles belonged to the size class > 0.63 to 1 mm, 48% had a size between 0.2 and 0.63 mm and 36.4% were found within the smallest size class. By far the highest amount of fibers was found in the size class > 0.2 to 0.3 mm with nearly 50%, followed by the second biggest size fraction (> 0.63 to 1 mm) with 22.7% of all fibers identified. The smallest size class still contained 18.8% of fibers (see Fig. 6).

4. Discussion 4.1. Elutriation efficiency Compared to other studies implementing elutriation, the detected efficiency rates in this study show differing results. Zhu (2015) achieved lower recovery rates of 44% while recovery rates for PVC particles achieved by Claessens et al. (2013; 100%) and Kedzierski et al. (2016; 92.0% ± 7.1) were higher than the here presented overall recovery rates. However, differences in the methodical protocols such as the additional application of NaI-solution and considered size fractions may explain lower recovery rates in this study. As investigated by Kedzierski et al. (2016) the size fraction from > 0.2 to 0.3 mm in this study showed a high recovery rate, as well. Thus, for the two polymers investigated in this study being among the densest polymers fairly high recovery rates were achieved. For lower-density polymers the efficiency is strongly increased due to their per se buoyancy. In contrast to a former study stating that recovery rates are increased when sand is involved in the elutriation process (Kedzierski et al., 2016), this study could only partly confirm this result. The two largest size fractions (> 1–5 and 0.63–1 mm) showed an opposite trend. The weight of sediment might prevent particles to rise in the column and bigger plastic particles were observed to stick to sediment particles so that they stayed in the lower part of the column. For smaller particles (> 0.063–1 mm) however, increased recovery rates were confirmed when sand was included in the prepared samples. Future recovery tests should include different shapes of polymer particles since the shape of particles could possibly influence the extraction rates (Kedzierski et al., 2017).

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Fig. 4. Microplastic concentrations for fibers and fragments at the sampling positions within the different beach segments on Rügen (aerial images via drone for the northern beaches; Google Earth images for eastern and western beach). Coordinate system: ETRS_1989_UTM_Zone_33N, projection: Transverse Mercator.

Ruz et al., 2012). Table 4 presents an excerpt of comparative values for microplastic concentration in beach sediments, though. For comparability, the results of this study are presented as mean ± standard deviation in this table and reference studies were selected based on geographical location, matching sampling or laboratory analysis protocols as well as particle sizes. Especially the depth of sampling may influence results. In this study the first 2–3 cm were sampled. Most plastic particles are found in the top 5 cm of beach sediments and an overall decrease with depth is observable (Turra et al., 2014; Carson et al., 2011). Overall, this study predominantly revealed higher microplastic abundances per kg DW or per m2 compared to other studies on the Baltic Sea coast. Contamination of sediments in the Rostock and Oder/ Peene region examined by Stolte et al. (2015) is higher. Rügen beaches are less influenced by touristic activities than the ones in the Rostock area leading to lower microplastic abundances (Stolte et al., 2015). However, the concentrations measured in this study are higher than the

4.2. Background contamination Contamination of samples plays an important role for microplastic analysis. The introduction of fragments and especially fibers, e.g. via air, was present in the laboratory processes of microplastic analysis. Therefore, this study recommends the parallel processing of blanks in the analysis to restrict the bias of contamination on results of microplastic abundance according to former studies (Torre et al., 2016; Woodall et al., 2015; Nuelle et al., 2014). 4.3. Microplastics in beach sediments 4.3.1. Comparison to other studies The comparison of microplastic abundances to other studies is hampered by the variety of sampling and laboratory methods, different size definitions for microplastic particles as well as by varying units reported (Hanvey et al., 2017; Van Cauwenberghe et al., 2015; Hidalgo269

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Fig. 5. Microplastic abundance at different positions within the littoral zone. The black bar indicates the median, the colored box the lower (Q1) and upper quartile (Q3). The upper whisker is defined as the largest value equal to or lower than min (max(x), Q3 + 1.5 * (Q3 − Q1)) and the lower whisker as the lowest value equal to or larger than max (min(x), Q1 − 1.5 * (Q3 − Q1)).

sediment. Despite using a high-density solution (ZnCl2; 1.6 g/cm3) the concentration is considerably lower compared to the one in this study. However, the particle size analyzed differs significantly. Only microplastics between 0.5 and 5 mm were considered in the study by Esiukova (2017). When comparing the results from Rügen to the North Sea coast, no distinct classification is possible but concentrations may be higher or lower compared to this study (see Table 4). The vast differences between the results of studies at the North Sea themselves stress the difficulty of comparing these to the here presented study. Microplastic concentrations seem to be highly variable depending on geographic location (Stolte et al., 2015; Van Cauwenberghe et al., 2013a; Claessens et al., 2011; Cole et al., 2011; Ryan et al., 2009). Also, as mentioned before, differences in sampling processing distort findings even more. In accordance with other studies, fibers were the predominant type of microplastics found in beach sediment samples (Graca et al., 2017; Esiukova, 2017; Stolte et al., 2015; Qiu et al., 2015; Van Cauwenberghe

concentrations measured by the same authors on the Isle of Rügen. The dissimilarity in particle size analyzed and in sampling and processing methods, may be a reason for the differing results. Graca et al. (2017) found microplastic concentrations in the range of 25 to 53 particles per kg while using similar sampling methods. This is slightly below the results of the study presented here. Sampling was partly conducted in the Gdansk Bay by Graca et al. (2017) so the anthropogenic influences are probably higher. However, beaches might be more protected from direct introduction of microplastics by wind and water currents compared to the beaches on Rügen, exposed to the open sea. Additionally, the method used for density separation by Graca et al. (2017), relies on a concentrated NaCl solution (1.2 g/cm3) being less effective in recovering high-density polymers (Crichton et al., 2017; Ivleva et al., 2017; Kedzierski et al., 2016; Qiu et al., 2016; Shim et al., 2016; Nuelle et al., 2014). Esiukova (2017) investigated beach sediments along the Russian Baltic coast resulting in 1.3 to 36.6 microplastic particles per kg

Fig. 6. Share of microplastics in different size fractions.

270

271

High High High High

Random Several positions

Rügen Rostock Oder/Peene Norderney

Norderney Spiekeroog/ Kachelotplate Kaliningrad Region

Gulf of Gdansk

North Sea coast North Sea coast North Sea coast

Strait of Singapore/Strait of Johor Greater Canterbury region

Russia

Poland

Belgium

Singapore

New Zealand

Plateau

Rügen

Middle part of beach High tide line Intertidal Low and high tide line 0.5 m above high tide line High tide line

High tide line

line line line line

High tide line

Rügen

tide tide tide tide

Intertidal

Rügen

Germany

Sampling site

Location

Country

77.9 ± 36.6 (24.2–170.1) 107.3 ± 73.8 (8.5–318.5) 93.8 ± 46.7 (34.5–222.4) 18.5–77.4 134.4–537.7 15.7–431.7 – – – 1.3–36.3 25–53 125.7 ± 28.9 92.0 ± 25.6 13 ± 9 (2–48) 0–16 21.2 ± 16.5

63 μm–5 mm 63 μm–5 mm 55 μm–1 mm 55 μm–1 mm 55 μm–1 mm < 1 mm 1 μm–1 mm 1.2 μm–5 mm 500 μm–5 mm 45 μm − 5 mm 38 μm–1 mm 38 μm–1 mm 35 μm–1 mm 1.6 μm–5 mm 32 μm–5.6 mm

Microplastics





109.5 ± 22.9 87.7 ± 25.5 –





– 1–14

17.2–73.3 134.4–542.1 14.4–424.7 4–213

61.1 ± 31.6 (18.9–128.0)

79.1 ± 72.2 (0.6–310.4)

50.2 ± 34.5 (0–120.9)

Fibers

Abundance [particles/kg DW]

63 μm–5 mm

Particle size





8.1 ± 2.9 4.7 ± 1.8 –





0.5–1 0–62,100

1.3–4.1 0–5.5 1.3–7.0 1.3–2.3

32.7 ± 34.4 (8.5–318.5)

28.1 ± 22.3 (0–85.7)

27.7 ± 25.8 (0–105.4)

Fragments/granules

Table 4 Comparison of microplastic abundance between the beaches on Rügen and other studies including differences in sampling and laboratory methods.

2500 cm2

625 cm2

Quadrates 2500 cm (2 cm)

−(1 cm) 2

NaCl

NaCl

NaCl NaCl NaI + elutriation

NaCl

ZnCl2

NaI ZnCl2

CaCl2 CaCl2 CaCl2 NaCl + NaI

Elutriation

Elutriation 625 cm

Elutriation 2

Density separation

625 cm2

Quadrates 1500 cm2 (2 cm) Circle 700 cm2 (2.5 cm) Cores (2–7 cm) Cores (2–7 cm) −(5 cm)

Quadrates (2–3 cm) Quadrates (2–3 cm) Quadrates (2–3 cm) −(1 cm) −(1 cm) −(1 cm) Quadrates (3 cm) −(3 cm) −(1 cm)

Sampling method (depth)

Clunies-Ross et al., 2016

Claessens et al., 2011 Claessens et al., 2011 Van Cauwenberghe et al., 2013a Ng and Obbard, 2006

Graca et al., 2017

Nuelle et al., 2014 Liebezeit and Dubaish, 2012 Esiukova, 2017

Stolte et al., 2015 Stolte et al., 2015 Stolte et al., 2015 Dekiff et al., 2014

This study

This study

This study

Reference

E. Hengstmann et al.

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and distribution and/or accumulation tendencies were apparent. The second northern beach is characterized by a depression, which is partly flooded and where macrolitter accumulation is increased (Hengstmann et al., 2017). Microplastic fragments are increasingly gathered in this depression (transects A to C) as well. When flooded, the depression contains a small pool of salt water with no strong currents or wave activity. In combination with biofouling also low-density microplastics can sink down to the bottom within this calm habitat (Cozar et al., 2014; Lobelle and Cunliffe, 2011; Morét-Ferguson et al., 2010; Ye and Andrady, 1991). Furthermore, waves reaching the area in front of the depression (the crest of the beach ridge) flow slowly in a thin water layer. Calmer conditions and only infrequent submerging of this zone supports the settling of microplastic particles (Van Cauwenberghe et al., 2013a). Sampling in a raster with higher resolution, especially for the depression and the back of the beach, is currently undertaken to confirm first hypotheses. The beach N1 and W both show an accumulation of microplastic fragments on one side of the segment. These accumulation tendencies coincide with an increased recreational activity at the northern beach which is interrelated with microplastic contamination in beach sediments (Graca et al., 2017; Retama et al., 2016; Stolte et al., 2015). However, this influence is not applicable for the western beach. The western beach is directly located at a cliff. According to Graca et al. (2017) cliff coasts are more protected from microplastics being directly introduced via the land compared to e.g. dune beaches. Thus, microplastics must be predominantly washed ashore by waves. Though, Dekiff et al. (2014) found out that within 100 m longitude of a beach water currents and wind influences are similar so that high microplastic concentrations within one transect are hardly explained by the increased introduction due to waves or wind at the western beach segment. A more comprehensive sampling in front of the cliff is necessary to further determine the crucial impacts on microplastic distribution at this beach. The beach facing to the east does not show any accumulation zones for microplastic fragments. Samples were exclusively taken where fine substrate occurred, to allow consistent sampling processing. Coarser material might act as a trap for microplastic fragments, as already confirmed for macroplastic items at this beach (Hengstmann et al., 2017), revealing more distinct microplastic distribution patterns in relation to grain sizes.

et al., 2013a; Hidalgo-Ruz et al., 2012; Claessens et al., 2011; Browne et al., 2011). 4.3.2. Spatial variability in microplastic concentrations In general, it has to be emphasized that no significant differences were present between the four beaches analyzed on Rügen concerning microplastic concentrations in sediments but tendencies for spatial variability were observable. Whereas Tsang et al. (2017) also reported no spatial variations between different coastal regions of Hong Kong, studies in the Baltic Sea region detected high spatial variations between sampling sites (Graca et al., 2017; Stolte et al., 2015). However, the four sampling sites in this study were closer to each other than in former studies. Several studies detected an impact of anthropogenic activities on the abundance of microplastics in beach sediments (e.g. Graca et al., 2017; Lozoya et al., 2016; Stolte et al., 2015; Davis and Murphy, 2015). These results give reason to expect the highest microplastic concentration at the eastern beach on Rügen, since it is easily accessible, most frequently visited by tourists and closest to a village. Nevertheless, the eastern beach does not show significantly higher concentrations of microplastics. Therefore, other sources, e.g. the introduction of microplastics from the sea side, might play a more important role. Microplastic particles present in the water are likely to be washed onto beaches (Davis and Murphy, 2015; Ivar do Sul and Costa, 2014). Winds as well as surface currents were predominantly coming from the northwest prior to sampling (DWD, 2016; BSH, 2016). Therefore, the eastern beach, being more sheltered due to its exposition, would be expected to be less contaminated. Tendentially, the microplastic contamination at the eastern beach is lower than at the second northern beach, however, the difference is not statistically significant. Considering wind and water currents as important factors, according to Esiukova (2017) and Debrot et al. (1999), the western beach is expected to have high microplastic concentrations as well. However, no significantly increased microplastic abundance could be found here, either. The broad strand line at the western beach, resulting in a wider accumulation area (Clunies-Ross et al., 2016), as well as the cliff, indicating regular flooding and remobilization of microplastics, may reduce microplastic concentration here. Focusing on fragments only, again, no statistically significant differences could be determined between the four beaches, though, similar tendencies were observable as for the total microplastic concentration. When correlating only microplastic fragments to macroplastic items a moderate positive relation is apparent. This finding is in accordance with other studies, where a relationship between smaller and larger plastic particles has been confirmed (Naji et al., 2017; Lee et al., 2015; Lee et al., 2013).

4.3.4. Particle size distribution Due to the minimum size of 63 μm for particles analyzed in this study microplastic contamination might be underestimated. Most particles identified in this study were smaller than 1 mm, though, making them available for ingestion by coastal fauna (Qiu et al., 2015) and therefore posing a high risk for several species. Microplastics resulting from the weathering of macroplastic items may become smaller, the longer they stay in the environment. Larger plastic particles disintegrate into smaller ones, increasing the number of small microplastics (Magnusson et al., 2016; Andrady, 2011). Therefore, an increasing number of microplastics with decreasing size as reported by Lee et al. (2013) seems reasonable. Other authors, however, have stated that there is no linear or exponential dependence of microplastic abundance on particle size, but that a maximum exists at a certain size range when considering smaller particles (Crichton et al., 2017; Imhof et al., 2016; Young and Elliott, 2016). This study also shows that no linear or exponential growth in the number of microplastics with decreasing size is observable. Instead, microplastics are increasingly found within the size class between 0.2 and 0.63 mm. This maximum is higher than the one identified by Imhof et al. (2016; 0.05 to 0.5 mm in limnic environments) but lower than the one detected by Crichton et al. (2017; 0.5 to 0.99 mm). Lee et al. (2015) stated that plastic fibers might behave differently concerning their fragmentation compared to plastic fragments, giving a reason for differing size distributions for fibers compared to fragments in this study.

4.3.3. Distribution within beach segments No significant differences were found for microplastic concentrations at different positions within the littoral zone, hence indicating that it is nearly evenly distributed over the three positions sampled. Similarly, former studies on the small-scale distribution of microplastics found no significant differences between tidal heights (e.g. Crichton et al., 2017; Dekiff et al., 2014). Lee et al. (2015) stated that no significant differences are apparent between high tide line and backshore whereas Heo et al. (2013) reported an accumulation of small plastic debris in the upper littoral zone compared to the high tide line. Since microplastic was not exclusively or increasingly found at the high tide line studies only considering microplastic abundance in this area may falsify the microplastic pollution at beaches as already stated by other authors as well (Hanvey et al., 2017). Fibers are easily transported via air (Dris et al., 2016; Torre et al., 2016). Not only wind, but also waves can easily relocate fibers disabling the establishment of specific accumulation areas which is in accordance with Liebezeit and Dubaish (2012). In contrast, microplastic fragments are not as easily moved as fibers 272

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Strand et al. (2013) found a correlation between microplastic abundance and organic contents (% Total Organic Carbon). The proportion of organic matter (%) was analyzed in this study as well. However, no correlation to microplastic contamination could be proven. A reason might be the very low organic content on the beaches sampled in general (ranging between 0.03 and 0.96%), especially compared to the samples analyzed by Strand et al. (2013) originating predominantly from sea bed sediments.

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5. Conclusion Tests on the efficiency of the newly developed glass elutriation column showed that it is applicable, allowing robust recovery rates for high-density polymers. Its applicability was moreover confirmed as the column was successfully used for the separation of microplastic and sediment particles in field samples. Considering the complete laboratory analysis of microplastics, the integration of blank samples is highly recommended especially when investigating fibers. The investigation of four beaches on the Isle of Rügen with different exposition and anthropogenic frequentation did not reveal significant distribution patterns for microplastics in total nor for fibers or fragments. Based on this study, anthropogenic influences as well as surface currents and wind could not be statistically verified as influencing factors for the occurrence of microplastics. More comprehensive studies are needed to further analyze the spatial distribution of microplastics within beach segments. Furthermore, long-term data is necessary to reveal significant trends over time. In order to increase the reliability of results and to receive further information on the kind of individual particles (i.e. chemical composition), a spectroscopic analysis should be added to the proposed process in the future. Supplementary data to this article can be found online at https:// doi.org/10.1016/j.marpolbul.2017.11.010. References Andrady, A.L., 2011. Microplastics in the marine environment. Mar. Pollut. Bull. 62, 1596–1605. http://dx.doi.org/10.1016/j.marpolbul.2011.05.030. Andrady, A.L., 2015. Persistence of plastic litter in the oceans. In: Bergmann, M., Gutow, L., Klages, M. (Eds.), Marine Anthropogenic Litter. Springer International Publishing, Cham, pp. 57–72. http://dx.doi.org/10.1007/978-3-319-16510-3_3. Antunes, J.C., Frias, J.G.L., Micaelo, A.C., Sobral, P., 2013. Resin pellets from beaches of the Portuguese coast and adsorbed persistent organic pollutants. Estuar. Coast. Shelf Sci. 130, 62–69. http://dx.doi.org/10.1016/j.ecss.2013.06.016. Arthur, C., Baker, J., Bamford, H., 2009. Proceedings of the International Research Workshop on the Occurrence, Effects, and Fate of Microplastic Marine Debris, September 9–11, 2008. (NOAA Technical Memorandum NOS-OR&R-30). Ballent, A., Purser, A., de Jesus Mendes, P., Pando, S., Thomsen, L., 2012. Physical transport properties of marine microplastic pollution. Biogeosci. Discuss. 9, 18755–18798. http://dx.doi.org/10.5194/bgd-9-18755-2012. Barnes, D.K.A., Galgani, F., Thompson, R.C., Barlaz, M., 2009. Accumulation and fragmentation of plastic debris in global environments. Philos. Trans. R. Soc. B 364, 1985–1998. http://dx.doi.org/10.1098/rstb.2008.0205. Blum, W.E.H., 2007. Bodenkunde in Stichworten, 6th edition. Borntraeger, Berlin. Browne, M.A., Crump, P., Niven, S.J., Teuten, E., Tonkin, A., Galloway, T., Thompson, R., 2011. Accumulation of microplastic on shorelines woldwide: sources and sinks. Environ. Sci. Technol. 45, 9175–9179. http://dx.doi.org/10.1021/es201811s. Browne, M.A., Chapman, M.G., Thompson, R.C., Amaral Zettler, L.A., Jambeck, J., Mallos, N.J., 2015. Spatial and temporal patterns of stranded intertidal marine debris: is there a picture of global change? Environ. Sci. Technol. 49, 7082–7094. http://dx. doi.org/10.1021/es5060572. BSH (Bundesamt für Seeschifffahrt und Hydrographie), 2016. Berechnete Strömungen des operationellen Modellsystems des BSH. Archive (01.07.2015–15.07.2015) (Assessed: June 2016). http://www.bsh.de/aktdat/modell/stroemungen/Modell1.htm. Carslaw, D.C., Ropkins, K., 2012. openair — an R package for air quality data analysis. Environ. Model. Softw. 27–28, 52–61. Carson, H.S., Colbert, S.L., Kaylor, M.J., McDermid, K.J., 2011. Small plastic debris changes water movement and heat transfer through beach sediments. Mar. Pollut. Bull. 62, 1708–1713. http://dx.doi.org/10.1016/j.marpolbul.2011.05.032. Claessens, M., Meester, S.D., Landuyt, L.V., Clerck, K.D., Janssen, C.R., 2011. Occurrence and distribution of microplastics in marine sediments along the Belgian coast. Mar. Pollut. Bull. 62, 2199–2204. http://dx.doi.org/10.1016/j.marpolbul.2011.06.030. Claessens, M., Van Cauwenberghe, L., Vandegehuchte, M.B., Janssen, C.R., 2013. New techniques for the detection of microplastics in sediments and field collected organisms. Mar. Pollut. Bull. 70, 227–233. http://dx.doi.org/10.1016/j.marpolbul.

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