| Processing Steps |
- Parameter or Variable: microplastic concentration (measured); Units: pieces/m3; Observation Category: in situ; Sampling Instrument: Metal scoop; Sampling and Analyzing Method: Sampling was conducted in July 2017 during periods without precipitation. Samples were collected from a square with each side of 0.5m length. To keep the sampled area constant, the study used a frame made of PVC tubes. From within the square, sand was collected from the surface using a metal scoop. The study tried to keep sampling depth as constant as possible at 1 cm. However, due to an irregular surface within the sampled square as well as human error, the sampling depth varied somewhat around 1 cm and may have reached a maximum of 2 cm depth in some places. Each sample therefore represents an area of 0.25 m2, or an estimated average volume of 0.0025 m3 but with some variation. Each transect’s starting point was at the fence on the top of the dune, and we then moved the frame with a constant distance of 2m towards the water line until the wet part of the intertidal zone was reached because wet sand cannot be sampled easily with our method. However, for transect number 3, the starting point was on the slope of the dune and not at the fence because of the dense vegetation in that area of the beach. This study used volume reduced sampling. The sand from each square was sieved through a sieve with 1mm mesh size (Endecotts test sieve). Thus, only the fraction≥1mm was kept for further analysis. During sampling, we removed large or obviously non-plastic items, e.g. shells, leaves, twigs, etc. Everything else was placed in zip-lock bags and brought to the laboratory. Before extraction of the plastic particles, all samples were dried in the oven at 50 °C for 24 h. For samples that contained a relatively low amount of material, potential plastic particles were collected visually without any further pre-treatment. Samples which contained a larger amount of material, especially sand grains, were subjected to density separation with saturated NaCl solution. This was achieved by placing the dry sample into an Erlenmeyer flask, adding a saturated NaCl solution, and then shaking the mixture vigorously for about 30 s. The supernatant was carefully poured through a sieve with 38 μm mesh size. This extraction procedure was repeated for at least three times or until the supernatant was free of visible floating particles. In order to test the reliability of this density separation procedure, the study conducted several recovery tests which demonstrated the reliability of this method. After density separation, the material from the supernatant was dried. Separately for each sample, we then extracted potential plastic particles visually under a Greenough stereo microscope. Due to the characteristic color, shape, and cleavage, most of the plastic particles were readily distinguished from non-plastic particles, such as stones, minerals, twigs, leaves, or shell fragments. All remaining particles which we could not identify as plastic or non-plastic during this step were then subjected to a test with diluted (5%) HCl solution. For this test, we dipped each potential plastic particle shortly into the HCl solution and observed the chemical reaction. All carbonaceous materials showed the typical bubbling from the release of CO2 during the reaction of the HCl with the carbonate ion CO3 2−. We treated all particles without or a different reaction as potential plastic particle. We sieved the potential plastic particles from each sample into the size classes ≥1 to<2 mm, ≥2 to<4 mm, ≥4 to<5 mm, and ≥5 mm. We counted the number of potential plastic particles for each sample and classified the particles according their size class, color, and shape.; Data Quality Method: Since access to spectroscopy equipment was time limited, we only examined the 268 potential microplastic particles which we had recovered from transect 2. Of these particles, 249 particles were analyzed with FTIR spectroscopy and 19 particles with Raman spectroscopy. In January and March 2018, we analyzed potential microplastic particles with the attenuated total reflection Fourier transform infrared (ATR-FTIR) microspectroscopy at the endstation BL14A1 of the National Synchrotron Radiation Research Center (NSRRC) in Taiwan. This method analyzes the chemical components based on the characteristic IR absorption of functional groups of plastic polymers. The endstation includes a FTIR spectrometer (IFS 66 v/S, Bruker, Ettlingen, Germany) equipped with an IR microscope (Hypersion 3000, Bruker, Ettlingen, Germany), coupled with a single reflection 20× ATR objective, which is an anvil shaped Ge crystal with an 80 μm contact area. The FTIR spectra of each plastic particle placed onto a filter paper were acquired with 512 scans and a resolution of 4 cm−1 in the spectral range of 4000–400 cm−1 by using the endstation of the ATR-FTIR microspectroscopy. We focused the infrared radiation into the Ge crystal of the ATR objective and contacted each plastic particle in order to acquire the FTIR spectrum of each individual plastic particle. In order to acquire an FTIR spectrum free of spectral interference from water and carbon dioxide in the atmosphere, the optical path of ATR-FTIR endstation was continuously purged with dry nitrogen evaporated from the LN Dewar (XL-100, TAYLOR-WHARTON, Theodore, AL, USA) during each FTIR data acquisition. We then compared the measured FTIR spectra from each particle with reference spectra from known plastic types which we collected from a variety of plastic objects made of different plastic types which were all unambiguously identified by their recycling codes. At least five specimens of each plastic type were measured with the FTIR spectrometer as described above to obtain representative spectra for each plastic type. We furthermore compared a particle's spectrum with those stored in a FTIR polymer spectrum library using the OPUS Software (OPUS 6.5; Bruker, Etlingen, Germany) and OMNIC software (OMNIC 9.2, 2012; Thermo-Fisher Scientific Inc., Waltham, MA, USA) to match spectra. In February 2018, we analyzed 19 particles with the Raman spectroscopy available at the Earth Science Department, Academia Sinica. We used a Raman microscope (Horiba Jobin Yvon) which employs a COHERENT 532 nm Sapphire laser with beam size of ~5 μm. The laser excited the sample so that the sample emits the Raman scattering and vibrational frequency shifts with a spectral resolution of approximately 2 cm−1. Again, we measured known plastic types to produce reference spectra which we then compared with the spectra of the measured particles..
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