Validation of a method for extracting microplastics from complex, organic-rich, environmental matrices

Transcription

1 Validation of a method for extracting microplastics from complex, organic-rich, environmental matrices Rachel R. Hurley* a, Amy L. Lusher a, Marianne Olsen a, Luca Nizzetto ab a Norwegian Institute for Water Research (NIVA), Gaustadelléen 21, 0349 Oslo, Norway b Research Centre for Toxic Compounds in the Environment (RECETOX), Faculty of Science, Masaryk University, Kamenice 753/5, Brno 62500, Czech Republic Supporting Information Number of pages: 10 Number of figures: 7 Number of tables: 6 S1

2 Figure S1. Schematic diagram of the experimental design S2

3 Table S1. Production and applications of the eight selected polymer types tested in Phase 1 experiments. Polymer % Global plastic production Applications Polypropylene PP 23 % Polyethylene (low and high density) Packaging, food containers, textiles (carpet, rope), reusable containers LDPE 17 % Plastic bags, plastic bottles, packaging, HDPE 15 % plastic film, microbeads in personal care products Polystyrene PS 7 % Food containers, packaging Polyethylene terephthalate PET 7 % Plastic bottles, plastic containers, synthetic fibres (polyester) Polyamide 6,6 PA-6,6 1 % Synthetic fibres (nylon), plastic film Polycarbonate PC 1 % Plastic bottles, synthetic glass Poly(methyl) methacrylate PMMA <1% Synthetic glass S3

4 Table S2. Details of the eight reference polymers used in the Phase 1 experiments. Images of the particles are provided in Figure S2. Polymer density was provided by the corresponding manufacturer. Size range was measured by the authors. The term granule refers to cylindrical granulate particles, as described by the manufacturers. Product Manufacturer Shape Size range (mean) Density µm g cm -3 PP Borflow HL508FB Borealis, Austria Pellet (4614) LDPE Lupolen 1800 P LyondellBasell, Netherlands Pellet (3716) HDPE Lupolen 4261 AG UV LyondellBasell, Netherlands Pellet (4372) PS Styrolution PS 158N/L INEOS Styrolution, Germany Granule (3653) PET Neopet 80 Neogroup, Lithuania Bead (3258) PA-6,6 Ultramid A3K BASF SE, Germany Granule (3342) PC Makrolon 2658 Bayer MaterialScience AG, Germany Granule (3377) PMMA Plexiglas 7N Evonik Performance Materials GmBH, Germany Granule (3367) Figure S2. Micrograph (10x) images of plastic particles used in the Phase 1 experiments. The different polymer types are: PP (a), LDPE (b), HDPE (c), PS (d), PET (e), PA-6,6 (f), PC (g), and PMMA (h). Details of the particles are given in Table S2. The white bars in the lower right corner each represent 1 mm. S4

5 TEST SLUDGE AND SOIL SAMPLE DESCRIPTION Samples of soil and sludge that were used for testing were obtained from Oslo, Norway. Real environmental samples were collected to ensure that testing was environmentally-relevant. The sludge sample was taken from the Bekkelaget wastewater treatment plant. Bekkelaget is a tertiary treatment plant using simultaneous precipitation and biological nitrogen and phosphorus removal. The sludge is stabilised by thermophilic anaerobic digestion over 14 days. The sample was taken after the dewatering step. The moisture content of the sample was 65.7% (Table S3). The organic content of dried sludge was 51.5%. The WWTP was opened in 2000 and has a population equivalent of 330,000. It has a dry weather flow of approximately 100 million l d -1. The sludge produced at Bekkelaget is applied to agricultural land, primarily for growing grain. The soil sample was taken from outside the Norwegian Institute for Water Research (NIVA) facility in Oslo. Soils were taken from a bank next to an artificial stream. The area is characterised by brown podzol soils. Soil texture analysis was performed: the sample represents a loamy sand with a low moisture and organic content (Table S3). Table S3. Moisture and organic matter content of test sludge and soil samples. Organic matter content is given as a percentage of the total dry mass, measured as % loss-on-ignition. Results are presented as the mean of 5 replicates ± SD. Moisture content Organic matter content Sludge 65.7% ± 0.65% 51.5% ± 0.94% Soil 17.4% ± 0.15% 5.79% ± 0.19% Microplastic content of test sludge and soil samples As the sludge and soil samples used for testing were real environmental samples, three replicates of each sample type were analysed for existing microplastic contamination. 10 g of sample was subjected to Fenton s reagent, followed by density separation representing the optimum method identified in Phase 1 and 2 testing. Two density solutions were used (1 and 1.8 g cm -3 ) and three extracts were performed for each one. On average, the soil contained 200 particles kg -1 (d.w.). A maximum of 4 particles were identified per 10 g sample. The microplastics were composed of 83% fibres and 17% fragments, where 50% were extracted at freshwater density and the remaining half were extracted using the high density (1.8 g cm -3 NaI) extract. All microplastics were isolated in the first extraction of each solution. The fibres were all longer than 1000 µm and were exclusively blue or black. The sludge samples contained 3328 ± 924 particles kg -1 (d.w.). Microplastic contamination was composed of 55% fragments, 36% fibres, and 9% beads. All of the beads were significantly smaller ( µm) than those used to spike sediments ( µm). All fibres were longer ( µm) than the spiked fibres ( µm) and no orange fibres were observed in any of the replicates (identified colours: blue, black, and grey). 94% of microplastic particles were extracted using the high-density solution. S5

6 Table S4. Details of the microplastic particles used in the Phase 3 testing. Two sizes of polyethylene (PE) microbeads were used, in addition to PET fibres that were produced at NIVA. The fibres were individually characterised as they were added to the solid matrices to establish an accurate particle size range for this testing. Images of the particles are provided in Figure S3. Manufacturer Size range Large PE beads Cospheric, CA, USA µm a Small PE beads Cospheric, CA, USA µm a PET fibres NIVA, Norway µm b a Provided by the manufacturer b Calculated by the authors, based on the particle long axis Figure S3. Micrograph (20-30x) images of plastic particles used in the Phase 3 experiments. The different particles types are: Large PE beads (a), small PE beads (b), and PET fibres (c). Details of the particles are given in Table S4. PRODUCTION OF FIBRES AS CERTIFIED REFERENCE MATERIAL The fibres used in this study are part of an ongoing initiative at the Norwegian Institute for Water Research (NIVA) to produce certified reference material (Certified reference material CRM-FOPET- 1-18, NIVA, Norway). The project aims to produce environmentally-relevant microplastic fibres. Polyester is commonly observed in aquatic environments and ingested by fauna. A large proportion of this fibre contamination is expected to be derived from the washing of synthetic garments. Large numbers of fibres are released in washing machine effluent. Hence, the microplastic fibres produced at NIVA are created by washing polyester (PET) fleece blankets. Orange blankets are used to improve the visibility of fibres in spiked matrices. The blanket ( Skogsklocka, IKEA, Norway) is washed in a clean washing machine system (Candy Smart, model no. CS 1692D3-S) on a 15-minute cycle at 40 C and 1200 rpm. No detergents or softeners are added. The effluent is collected in a stainless-steel pressure vessel (Pope Scientific, Wisconsin, USA) and vacuum filtered through a 10 µm nylon membrane. This method yields fibres µm in length (IQR: µm) and 29 µm wide. A single wash (25 l effluent) produces approximately 200,000 fibres per 500 g blanket. The fibre material is currently undergoing certification as a reference material and will be available upon request. S6

7 Figure S4. Degradation of PA-6,6 in Protocol 1b; Replicate III during Phase 1 testing. The remainder of the PA-6,6 particles can be seen as small fragmented particulates floating in the reagent amongst the larger beads of other polymer types. Figure S5. Micrograph (10x) images of PET (a) and PC (b) particles before (top) and after (bottom) treatment with Protocol 3a. Surface degradation occurred as peeling on PET and the development of a matte texture on PC. S7

8 Figure S6. FT-IR analysis of the eight polymers (a-h) following treatment in the Phase 1 experiment. The untreated, control particles are represented by a thick grey line. The ATR accessory introduces interference associated with the diamond crystal that was used, indicated by the diamond exclusion zone. S8

9 Figure S7. FT-IR analysis of the degraded fragments from PP (a) following Protocol 1b treatment and PET (b) and PC (c) following Protocol 3b treatment. The outer layer which was affected by the treatments was carefully separated from the particle prior to analysis. The spectra of the control particles are represented by black lines and indicate the reference spectra for the corresponding particle. S9

10 Table S5. Extraction efficiencies of PET fibres when using 250 ml glass jars and 50 ml tubes to perform the density separation step. The extraction method was tested as 1) organic matter removal (OMR) followed by density separation, and 2) density separation followed by organic matter removal. Results are reported as the mean of the three replicates ± SD. OMR Density Density OMR 250 ml jars 50 ml tubes Sludge 75.6% ± 3.85% 85.6% ± 3.33% Soil 77.8% ± 3.85% 82.2% ± 3.85% Sludge 74.4% ± 8.39% 78.9% ± 5.09% Soil 75.6% ± 1.92% 83.3% ± 3.33% Table S6. Extraction efficiencies of the three spiked microplastic types: large PE beads (a), small PE beads (b), and PET fibres (c), associated with three extracts. PE beads (a,b) were extracted during the freshwater density extracts (1.0 g cm -3 ) and PET fibres (c) were only observed following subsequent high density extracts (1.8 g cm -3 ). The extractions were performed using 50 ml tubes. The method was tested as 1) organic matter removal (OMR) followed by density separation, and 2) density separation followed by organic matter removal. Results are reported as the mean of the three replicates ± SD. a. Large PE beads ( µm) OMR Density Density OMR Density Extract (1 g cm -3 ) Sludge 95.6% ± 7.77% 4.44% ± 7.77% 0 % Soil 95.6% ± 5.09% 4.44% ± 5.09% 0 % Sludge 91.1% ± 9.62% 1.11% ± 1.92% 1.11% ± 1.92% Soil 97.8% ± 1.92% 1.11% ± 1.92% 0 % b. Small PE beads ( µm) OMR Density Density OMR Density Extract (1 g cm -3 ) Sludge 91.1% ± 1.92% 5.56% ± 3.85% 0 % Soil 88.9% ± 5.09% 8.89% ± 6.94% 0 % Sludge 83.3% ± 16.7% 6.67% ± 11.5% 2.22% ± 3.85% Soil 85.6% ± 7.70% 8.89% ± 1.92% 1.11% ± 1.92% c. PET Fibres ( µm) Density Extract (1.8 g cm -3 ) OMR Density Density OMR Sludge 53.3% ± 3.33% 31.1% ± 5.09% 1.11% ± 1.92% Soil 46.7% ± 3.33% 32.2% ± 6.94% 3.33% ± 3.33% Sludge 52.2% ± 9.62% 22.2% ± 6.94% 4.44% ± 1.92% Soil 51.1% ± 1.92% 28.9% ± 1.92% 3.33% ± 3.33% S10