| Processing Steps |
- Parameter or Variable: microplastic concentration (measured); Units: items/m3; Observation Category: in situ; Sampling Instrument: net - plankton net; Sampling and Analyzing Method: Hangzhou Bay, located in the east coast of China, is a funnel-shaped tidal estuary of Qiantang River and widely opens eastwards in East China Sea. This bay receives massive riverine influx from Qiantang River. The entire sampling region is relatively shallow, having the seawater depth of <15 m. Hangzhou Bay is the hub of anthropogenic activity of some developed cities (e.g., Hangzhou and Shanghai), industrial districts, and mariculture regions. Hydrological conditions in Hangzhou Bay are greatly influenced by the tide from East China Sea and the inflow of Qiantang River. All samples were collected during two cruises between September and November 2020 in Hangzhou Bay. Each sampling campaign was conducted during the neap tide under calm weather conditions. Some artificial lagoon areas close to the northern Hangzhou Bay were avoided for sampling. Hydrologic conditions, including seawater temperature, pH, and dissolved oxygen of seawater were measured. Seawater samples were collected at 26 sites in Hangzhou Bay using a standard plankton net (mesh-aperture 0.30 mm, mouth diameter 65 cm, length 2.2 m) equipped with a flowmeter (MultiNet; HYDRO-BIOS, Germany. At each sampling station, the net was horizontally towed in the surface of seawater (0–3.5 m) at approximately 2.5 knots for 20 min. After towing, microplastic (MPs) retained by a collector equipped at the bottom of the net were flushed into glass bottles with pure water, and then stored at -20◦C until MP extraction. Sediment samples were collected at the same site as the seawater samples. In total, 3–5 individual sediment subsamples (top 5 cm layer; 350 g per subsample) were collected using grab samplers (Wildco Ponar®; Yulee, FL, USA), and then completely mixed to obtain a pooled sediment sample. Prepared sediment samples were wrapped with the aluminum foil and kept at -20◦C until MP extraction. Seawater samples were treated as follows; briefly, collected seawater samples were sequentially filtered with 5.5 mm and 0.33 mm sieves. The MPs retained on 0.33 mm sieves were rinsed three times with 100 mL of pure water, and then transferred to 500-mL glass beakers. After that, 200 mL of 10 % sodium hydroxide (NaOH) was added to the individual glass beakers, and then heated at 60 ◦C for 48 h. After digestion, these solutions were filtered with glass microfiber filters (GF/F, 0.45 μm; Whatman, UK) and a vacuum pump. These filters containing MP items were individually wrapped with aluminum foils, dried at 60 ◦C for 24 h, and then used for further analysis. MP abundance in seawater samples were reported as items/m3 of seawater. Sediment samples were extracted for MPs as follows; briefly, sediment samples were dried at 65 ◦C for 72 h, until reaching the constant weight, and then 50 g of sediment samples (n= 3) in dry weight (dw) were completely mixed with 500 mL of ZnCl2 solution (1.7 g/cm3) in glass beakers, followed by shake at 120 rpm for 20 min and sedimentation for 24 h. After that, the supernatant ZnCl2 solutions containing MPs were transferred to clean glass beakers, in which 15 mL of 30 % H2O2/pure water was added, and shaken at 200 rpm for 24 h to degrade the organic matter. These digested solutions were filtered through 0.45 μm glass microfiber filters (GF/F, Whatman ™; UK), and dried at ambient temperature for further analysis. Potential MPs were visually examined using the optical microscopy (Olympus BX53; Tokyo, Japan) to determine the shape (e.g., fiber, fragment, and film) and color of MPs. Plastic and natural fibers were separated based on their morphological characteristics and physical response features. The size of particle was measured along their longest length, using the Olympus cellSens software. Chemical composition of MPs, including microplastic-like objects, was accurately identified using Fourier-transform infrared spectroscopy (FT-IR, Nicolet™ iN™10 MX; Thermo-Fisher Scientific, MA. USA), operated under the transmittance mode. For large MPs, after recording their size, color, and shape information, they were carefully retrieved from the filter and squashed by the tableting machine before analysis. The spectrum range was set at 650–4000 cm-1 with the resolution of 8 cm-1. Obtained spectrum of samples was matched with that in the OMNIC™ Specta library, and objects with their spectrum at the matching degree of >70 % were identified as MPs.; Data Quality Method: Several measures were applied to minimize the potential MP contamination during the whole MP analysis procedures. Sampling tools and glassware were rinsed several times with pure water, and then dried before use. No plastic consumables were used in sample collection and extraction processes. Filters, laboratory consumables, and solutions were always covered with aluminum foils during the sample extraction process. Latex gloves and cotton laboratory coats were worn during the sampling and MP extraction period. Prior to use, all glass microfiber filters were rinsed with pure water, and then heated at 400 ◦C for 12 h. Procedural blanks were analyzed along with every ten real samples to examine the possible MP contamination. Each procedural blank always contained <2 fiber MPs, which were subtracted from real samples. Recovery tests were performed to evaluate the efficiency of current MP extraction methods. Ash samples (10 g each; n = 5) prepared through calcinating sediment at 750 ◦C for 10 h were spiked with 6 types of raw MPs, including PE, PP, PS, polyester, PET, and PVC. After that, these fortified samples were analyzed with the methods used for seawater, sediment, and organism samples. Results showed that the mean recoveries of spiked MPs were 92–97 %, and 95–98 %, for the extraction methods of seawater, and sediment, samples, respectively..
- Parameter or Variable: microplastic concentration (measured); Units: items kg-1 d.w.; Observation Category: in situ; Sampling Instrument: Sediment grab sampler.
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