Materials and Methods
The research was conducted in Jaring Halus Village, Langkat Regency, North Sumatra Province, Indonesia. Data were collected from February to April 2017. The tools used were global position system (GPS), meter, sample bottle, tool box, core, lmxlm board, filter, shovel, digital camera and stationery.
Method of Macroplastic Survey
The macrodebric samples (>20 mm) were collected with transects (1 x 1 m) from each substation with the highest tidal boundaries and the lowest tidal boundaries divided into three sections . The macrodebric composition were grouped into plastics, fabrics, foams, Styrofoam, glass, metal, rubber and wood. Samples were collected into sacks and labeled. The items (to further explain the flakes) in each macrodebric group were collected macroplastic, dried, calculated and weighed. The parameters taken include the number of items (item nr2) and weight (g nr2) .
Method of Microplastic Survey
Sediment sampling (1 L) was performed with the core based on three stratified depths (0-30 cm). The core placement is performed on three sections (top, middle and bottom edge) at the substations at the highest tide and lows. The separation of microplastic particles (0.045-5 mm) from the sediments was carried out by several stages, namely (a) drying, (b) volume reduction, (c) separation of density, (d) filtration and (e) visual sorting. Drying was done with a 105°C oven for 72 hours. The dry-sediment volume reduction step was performed by filtration (5 mm in size) . The density separation step was carried out by mixing the dry sediment sample (1 kg) and the saturated NaCl (3 L) solution, and the mixture are stirred for 2 minutes .
Floating plastics were polystyrene, polyethylene and polypropylene. The filtration stage was carried out by filtering the supernatant (size 45 pm). Microplastic particles were visualized using a monocular microscope and grouped into four types, namely film, fiber, fragments and pellets. The parameters taken were density (particle/kg dry sediment) .
Sampling of Macrozoobenthos
A sampling of macrozoobenthos was done on the same plot/transect as macro- and microplastic retrieval. Macrozoobenthos were taken on each transect plot with a depth of 30 cm. All the substrate on the plot was removed with a shovel, then stored in a plastic bag for separation. The separation between macrozoobenthos and substrate was done in the field with the help of water and filter. Samples of macrozoobenthos that had been separated from the substrate were fed into a 70% alcohol-treated sample bottle to be identified in the laboratory.
The macroplastic abundance is calculated by the formula :
К = Macroplastic Abundance n = Number of Macroplastic (item/m3) w = Width of Sampling Area / = Length of Sampling Area
Microplastic abundance is calculated by the formula :
К = Microplastic Abundance N = Number of Microplastic (item/m3)
A = Sample Area of Sampling H = Depth of Sampling
Biota density of macrozoobenthos with formula :
К = Density
ni = Number of Individuals of a Type A = Area
Correlation analysis between macro- and microplastic to macrozoobenthos was done using Pearson correlation SPSS.