**3. Methodology**

#### **3.1 Sampling**

To have a representative sample, samples were collected from beaches that were not developed and prepared for recreational purposes. The sand of recreational beaches usually is replaced or cleaned on regular basis. Therefore, it is recommended to sample from the original uncleaned sand. Moreover, low tide (LTZ) and high tide (HTZ) zones must exist and be identifiable in the sampling site to achieve our sampling objective. Northing and easting coordinates were recorded for each sample using global positioning system (GPS). Six samples were collected from each beach of which three samples were from the high tide zone (HTZ), and three from the low tide zone (LTZ). A wooden quadrat with 50× 50 cm was used for sampling with a small metal shovel. After removing the

debris and other liters, the top 5 cm sediment within the quadrat was collected in a metal bucket, weighted, and covered with foil aluminum. Then, 2 kg of each sample was filtered through 5, and 0.5 mm mesh-size stainless steel sieves. The remaining sand in between the sieves was collected in labeled glass bottles and sent to the lab for the next steps.

### **3.2 Sample preparation**

The density separation method was used to separate microplastic from the sand. Sodium Chloride salt (NaCl) was added gradually to a beaker filled with distilled water. The beaker was placed under a magnetic stirrer for continuous stirring. NaCl was added to the distilled water up to saturation point when the salt is not dissolving in the water anymore. To confirm the density of the brine, the weight of 1 L of brine was measured which was around 1.18 g/cm3 . Sand samples were extracted from the glass bottles into a stainless-steel container using a stainless-steel spoon and distilled water to make sure all the samples is collected. Brine was filtered through 100 μm mesh and then added to the containers using a volume equal to two to three times the sand volume to submerge the sample. Sand then was stirred for 5 minutes to allow light components like microplastics to float. The container then was covered with aluminum foil and kept for 24 hours to settle. After 24 hours, the brine in the samples along with the supernatant material was filtered through 100 μm stainless-steel mesh. The materials caught in the mesh were then washed using distilled water into a glass beaker. Then, the collected materials in the beaker were filtered using a 47 mm Whatman glass microfiber filter, ceramic funnel, and electric vacuum pump. Glass microfiber filter was then kept in a glass petri dish to dry and covered with aluminum foil.
