Occurrence and spatial distribution of microplastics in river shore sediments of the Rhine-Main area in Germany

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1 SUPPORTING INFORMATION Occurrence and spatial distribution of microplastics in river shore sediments of the Rhine-Main area in Germany Authors Sascha Klein,, Eckhard Worch, Thomas P. Knepper*, Department of Chemistry and Biology, University of Applied Sciences Fresenius, D Idstein, Germany Institute of Water Chemistry, Technische Universität Dresden, D Dresden, Germany Corresponding Author *Phone: + 49 (0) Fax +49 (0) knepper@hs-fresenius.de. Summary: 11 pages, supporting, 5 tables, 8 supporting figures

2 MATERIAL AND METHODS Chemicals Hydrogen peroxide, sulfuric acid, sodium chloride and sea sand were obtained from Roth (Carl Roth, Karlsruhe, Germany) in ultra-pure grade. Polymer standards were purchased from Polymer Standards Services (PSS, Germany). Deionized water was used for the saturated sodium chloride solution. All solutions were filtered (glass fiber filter; Whatman GF/A 47 mm, GE Healthcare Europe GmbH, Germany) prior usage. Sampling sites All samples were taken on 4 th December The water level of the river Rhine was at 2480 mm in Mainz, Germany ( ' N, ' E) and the water level of the River Main at 1340 mm in Raunheim, Germany ( ' N, ' E). The ten sampling sites are shown in Table S1. Table S1. Sampling sites at the river Rhine and the river Main with abbreviation used and coordinates of the sites. Abbreviation Location Coordinates R1 Ginsheim-Gustavsburg 49 58'18.6N 8 19'39.7"E R2 Mainz-Kastel 50 00'22.5"N 8 16'49.7"E R3 Mainz-Kastel 50 01'24.4"N 8 15'51.1"E R4 Wiesbaden-Biebrich 50 02'14.7"N 8 13'48.6"E R5 Wiesbaden-Schierstein 50 02'14.3"N 8 10'45.7"E R6 Walluf 50 01'55.2"N 8 09'26.5"E R7 Erbach 50 01'03.5"N 8 05'16.0"E R8 Geisenheim 49 58'52.5"N 7 58'19.0"E M1 Mainz-Kostheim 49 59'57.3"N 8 18'25.9"E M2 Mainz-Kostheim 50 00'08.0"N 8 19'33.7"E Sampling procedure for river shore sediments Figure S1 shows the design of the sampling procedure (random sampling) for river shore sediments. For comparison, sampling of distinct areas (zone sampling) is included in the Figure but was not used in this study. Sediment sampling was done at small spots between the water line and the lowest flotsam line at each sampling site. In a distance of m a number of spots were sampled. At each sampling site, half of the spots were located in S1

3 or close to the flotsam line to prevent underestimation of buoyant plastic particles. To assess if the within-site variability can be kept at a minimum with this sampling technique, three independent replicates were taken at the sampling sites R4 and R8. The results of the analysis of these samples are shown in Table S3. Figure S1: Design of the random spot sampling procedure of river shore sediment. The sample spots are represented by green circles, which are located between the water line and the lowest flotsam line. For comparison, theoretical coverage of zone sampling of distinct areas (0.5 m x 0.25 m) is represented by red rectangles. Density of Polymers Table S2. Density of different polymer types in g cm -3. Data is taken from Hidalgo-Ruz et al. (2012). 1 Polymer type Polymer density (g cm -3 ) Polyethylene Polypropylene Polystyrene Polyamide (nylon) Polyester Acrylic Polyoxymethylene Polyvinyl alcohol Polyvinyl chloride Poly (methyl methacrylate) Polyethylene terephthalate Alkyd Polyurethane 1.20 S2

4 Microscopic image of the polymer powders used for recovery experiments B A C Figure S2. Microscopic images of polycarbonate (A), polyvinyl chloride (B) and polystyrene (C) at a 40-fold magnification. Density separation Aside from the sampling process, a crucial step for reliable investigation of the plastic content of different river sediments is the separation of plastic particles. This method needs to be capable of separating most of the different synthetic polymers present in sediments, combined with good reproducibility. A straightforward method is density separation with a high density solution. To be capable of comparing microplastic concentrations in river sediments to former studies of marine habitats, the use of density separation with saturated sodium chloride solution described by Thompson et al. (2004) is the method of choice, despite the poor separation of high density polymers e.g. polyethylene terephthalate (PET). Solutions with higher densities can be generated e.g. by using zinc chloride.2 Besides comparability issues to former studies, zinc chloride solution was not favored although it offers separation of most high density polymers because of its ecological hazards. All glass ware was rinsed with deionized water and acetone before usage and heated out at 70 C. Aluminum foil was used to cover clean devices and open parts of the filter flasks to avoid blank values. S3

5 To assess the separation power of the method described by Thompson et al. (2004), recovery experiments with clean sand and polymer standards were performed (Figure S3, left-hand side). Powders of poly(methyl methacrylate) (PMMA), polycarbonate (PC), polystyrene (PS), polyvinyl chloride (PVC) and polyethylene (PE) pellets were used to simulate the microplastic portion of a sediment sample. The particle size of the powders polymer did not exceed 200 µm in diameter (Figure S2), thus the polymer powders represented the smaller microplastic particles. The experiments showed excellent recoveries (100%) for PE pellets, which simulated larger microplastics with sizes between 500 to 5000 µm. However, insufficient separation of the synthetic polymer powders was revealed by the experiments, yielding recoveries between 28 and 68% for all polymer powders. Poor separation of powders was caused by adherence of the polymer particles to glass ware during decantation steps. Additionally, low recovery of PVC can be explained by its high density, which is equal to or higher than the density of saturated sodium chloride solution. Figure S3. Recovery of the vacuum-enhanced separation of poly ethylene (PE) pellets and powders of poly(methyl methacrylate) (PMMA), polycarbonate (PC), polystyrene (PS), polyvinyl chloride (PVC) from sand in comparison to a separation method proposed in literature. Separation was done in duplicates. Values are expressed as means with standard deviation. A new instrumental setup was developed and validated to improve recoveries and repeatability of the density separation, especially for smaller particle sizes. A schematic of the apparatus used for density separation is shown in figure S2. The application of filter flasks as separation vessels and a vacuum-enhanced transfer through the nozzle of the filter flask to a glass fiber filter resulted in recovery rates of all synthetic polymer powders tested from 87- S4

6 100%, except for PVC (69%) (Figure S3, right-hand side). Besides better recovery of small microplastics, the new separation technique allows better repeatability by improving the relative standard deviations from 3-14% to 1-5% for each polymer. The accuracy of a method for the determination of microplastic particles is strongly influenced by blank values. Despite proper sample handling it was impossible to avoid high blank values in the size fraction <63 µm. For this reason the fraction of particles <63 µm was not included in the study. Other size fractions were not affected and tests without polymers did not show any blank values in the fractions between µm. Figure S4. Schematic of vacuum-enhanced density separation; floating plastic debris are transferred by addition of saturated sodium chloride solution by means of a vacuum directly to the glass fiber filter. The destruction of natural debris with a mixture of concentrated sulfuric acid and hydrogen peroxide did not affect polymer particles. Neither differences of the shape nor losses of weight of polymer particles could be observed when testing the procedure with powders of polyethylene, polystyrene, poly(methyl methacrylate) and polycarbonate. The exact procedure of treatment with sulfuric acid and hydrogen peroxide for particles from size fraction µm did vary slightly compared to the smaller size fractions. Visible plastic particles in the fraction µm were collected with tweezers first, placed on a S5

7 pre-weight glass fiber filter and rinsed with deionized water. Afterwards, the destruction of natural debris was performed as described for the smaller size fractions. The weights and numbers of polymer particles of size fraction µm before and after the destruction of natural debris were combined to determine the abundances given in the result section. This two-step selection of the plastic particles was done to maintain the opportunity for an extraction of the plastic particles from size fraction µm to analyze sorption of contaminants. Treatment with hydrogen peroxide/sulfuric acid would possibly destroy adsorbed contaminants. ATR-FTIR identification FTIR analysis was performed only on particles from size fraction µm. If possible, a small slice was cut off the polymer particles with a scalpel to measure the IR spectra of a fresh polymer surface. The polymer particles were placed on the ZnSe crystal of the ATR unit with tweezers or a dissecting probe and covered by a stainless steel plate. Pressure was applied on the particles to maximize the contact surface with the ATR crystal. Ten scans per sample were acquired from nm and a database search was carried out with Spectrum Search Plus (V ). Matching factors for the identification were above 0.70 depending on the quality of the spectrum. Exemplary spectra are shown in Figure S5. S6

8 (0.79) Figure S5. IR spectra of polyethylene, polypropylene, polystyrene, acrylic polymer, polyamaid and ethylene vinyl acetate, compared to reference spectra (REF). Match factors are shown in brackets. Data To estimate area-related results for this study, the sediment mass-related values were transformed. This was done by the known sampled volume of sediment, which was approximately 2.5 L, given by the sampling vessels. The volume was transformed to an area with the lowest sampling depth (2 cm) resulting in an area of m². Thus, the S7

9 transformation of the particles kg -1 to particles m -2 was done by multiplying our results with a factor of eight and are shown in Table S5. RESULTS Table S3. Mass fraction and item numbers of the analysis of three replicates from sediment samples which were taken at the sampling sites R4 and R10. Data is shown as means and standard deviation in parentheses. Size fraction Weight of plastic particles (mg kg -1 ) Number of plastic particles (items kg -1 ) R4 R10 R4 R µm (38.2) 99.6 (17.3) 65.0 (11.0) 15.0 (5.4) µm 5.4 (2.5) 5.5 (1.5) (14.3) 83.7 (23.4) µm 2.3 (0.4) 1.5 (0.3) (68.0) (33.5) Total (40.2) (18.7) (47.4) (55.9) Table S4. Mass fraction of plastic in the sediments analyzed. All values are given in mg kg -1. Size fraction µm µm µm Total R M M Sample location R R R R R R R S8

10 Table S5. Number of plastic items in the sediments analyzed. All values are given as plastic particles kg -1 except the estimation of total amount of microplastics for area-related results. Although exact numbers are provided, these should be considered as estimation. Size fraction µm µm µm Total Total (particle m -2 ) R M M Sample location R R R R R R R Despite the varying abundance of item numbers and item weights in the size fractions, a good correlation (R 2 =0.84) of the number of plastic items and weight of plastic items exists between all samples analyzed (Figure S6). The correlation of the weight of plastic particles and the item numbers of plastic particles was carried out with Microsoft Excel The plastic weight was plotted against the number of plastic items obtained for each of the sediments and a linear trend line was added Number of microplastics (particles kg -1 ) R² = Weight of plastic items (mg kg -1 ) Figure S6. Correlation between plastic weight and plastic number including particles >5000 µm (A) and excluding particles >5000µm (B) S9

11 Spatial distribution of polymer types in the investigated sediments. Figure S7. Abundance of the polymer types polyethylene (PE), polypropylene (PP), polystyrene (PS), polyamide (PA), acrylic polymers, ethylene propylene diene monomer (PB rubber), ethylene vinyl acetate (EVA), polyvinyl chloride (PVC), poly(methyl methacrylate) (PMMA) and polyethylene terephthalate (PET) of the size fraction µm at each sampling site differed by the numerical abundance and the abundance by weight. Transport of pellets from Main to Rhine Similar pellets were observed in sediments of two (silver pellets; M2 and R2) or three (blue pellets M2, R2 and R3) consecutive sampling sites, respectively (figure S8A). IR S10

12 measurements showed identical spectra in the range of nm -1 for these similar pellets (figure S8B and S8C). Figure S8. Detail of the map and photographs of blue-colored and silver-colored pellets, which were separated from the sediments M2, R2 and R3 (A). IR spectra of blue-colored (B) and silver colored pellets (C). REFERENCES 1. Hidalgo-Ruz, V.; Gutow, L.; Thompson, R. C.; Thiel, M., Microplastics in the marine environment: a review of the methods used for identification and quantification. Environ. Sci. Technol. 2012, 46, (6), Imhof, H. K.; Schmid, J.; Niessner, R.; Ivleva, N. P.; Laforsch, C., A novel, highly efficient method for the separation and quantification of plastic particles in sediments of aquatic environments. Limnol Oceanogr-Meth 2012, 10, S11