Dataset: Low-density microplastics (LD-MPs) in seven recreational parks of Al Ain, UAE isolated by density flotation method (DFM)
Description
The LD-MPs from 104 soil samples collected from seven different recreational parks of Al Ain, UAE were isolated by DFM using saturated sodium chloride solution (1.2 g/cm3). A total of 10, 701 g of soil samples were processed for this study (Loc_Info_Micp_count.xlsx). Prior to extraction and isolation of MPs, the 10 ± 0.1 g of each sample were dried at 40 degrees Celsius for 24 hr and then filtered using a stack of 8" dm stainless steel sieves with aperture of 5 mm and 1mm. An aliquot of 5 ± 0.1 g were subjected for DFM. After that, the sample was filtered using a Whatman glass microfiber filter to separate LD-MPs from the liquid. The filter was then viewed under stereomicroscope. The physical characteristics of LD-MPs, such as size, color, and shape, were noted (Loc_info_Micp_count.xlsx). Microplastic concentration were determined and expressed as particles per kg of samples (Micp_conc_per_sampling_site.xlsx; Table 8). Statistical data of isolated LD-MPs sizes were computed (Stat_data_of_LD-MPs_size.xlsx; Table 9). The study also tried to correlate the LD-MPs concentrations with soil pH and moisture content. Results showed that there is a negative correlation in MPs concentrations and the two selected soil properties suggesting potential negative effects in soil health (Stat_data_soil_pH_moisture_content.xlsx; Tables 10 & 11). FTIR analyses were conducted to initially determine the possible polymers present in the isolated LD-MPs (SFig3_FTIR). Polymers identified were possibly polyethylene, polypropylene, polyethylene terephthalate, or polyvinyl chloride. These results found that the presence of LD-MPs in urban recreational parks might contribute to impending environmental negative effects.
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Soil samples were taken from seven recreational parks in Al Ain, UAE using a sterile stainless-steel sample probe (HiHydro, T-style, 12 inch). A total of 10,701 g (n=104) of soil samples were gathered. and GPS were recorded (Garmin e Trex®10). Each sample was placed in a brown paper bag (29 × 9.2 × 5 cm) and transported immediately to the laboratory for further analysis. For microplastic extraction, each sample (10.0 ± 0.1 g) was dried at 40°C for 24 h. Then, filtered through a stack of 8" dm stainless-steel sieves (GlenammarTM) with apertures of 5 mm and 1 mm, followed by the density flotation method (DFM) with saturated NaCl solution (1.2 g/cm3). An aliquot of 5.0 ± 0.1 g from each filtered sample was placed in a clean Erlenmeyer flask, added with 50 mL saturated NaCl solution and stirred for 30 min. After rinsing, the flask was left undisturbed for 48 h. The liquid portion contains LD-MPs. The liquid was siphoned, transferred into a clean beaker, and filtered by a vacuum filtration system. The filter paper used was a glass microfiber filter (Whatman® pore size 1.2 µ, 4.7 cm), and the filtration process was performed twice. To verify LD-MPs, residues on the filter were brushed onto a glass Petri dish using a sable series 16 (Winsor & Newton) paintbrush (no.3) with weasel hairs to prevent contamination. The dish was viewed under a stereomicroscope (AmScopeTM) at a magnification of 40×. A hot needle test (De Witte et al., 2014) was performed for isolation of suspected LD-MPs. Controls were low-density polyethylene (LDPE) microbeads and cotton fibers. Each plastic particle was photographed and measured using ImageJ 1.53t Java 1.8.0_345 (64-bit). The isolated LD-MPs were subjected to visual color identification using the 120-palette code (SFig2). Descriptive statistical analysis was performed to summarize the measurements and observe microplastic color. Kruskal-Wallis test was performed to analyze microplastic concentration and size distribution between sampling sites. Representative LD-MPs were subjected to spectroscopic analysis using FTIR spectrometer (Thermo Nicolet Nexus 470 FTIR, USA) and equipped with DTGS detector. To measure soil pH, distilled water extraction was performed using a benchtop pH meter (Denver Instrument, Basic pH meter 13183). To measure moisture content, each sample was weighed (5.0 ± 0.1 g) before air-drying then placed in a hot-air oven at 105°C until a constant mass was achieved. The moisture content was measured using the formula: moisture content [%] = (wt. of sample before oven drying ˗ wt. of sample after oven drying / wt. of sample before oven drying) *100. A simple linear regression was used to evaluate the correlation of soil pH and moisture content to the number of LD-MPs, while the Kruskal-Wallis test was performed to determine if there were significant difference between sampling sites in terms of the LD-MPs concentration. Spike-recovery experiment was conducted to ensure the accuracy of DFM.