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Developing a Visual Counting Method to Quantify Riverine Plastic Litter: A Case Study of Rivers in Semarang City, Indonesia

Indonesia has established a national action plan on marine plastic debris to tackle the issue of marine plastic debris. Because most of the marine plastic debris in Indonesia is likely due to mismanaged plastic waste, it is important to address the problem of riverine plastic river problem in Indonesia. The objectives of this study are to visually observe the condition of the river in terms of plastic pollution, to quantify plastic litter in the river, and to develop a visual counting model of plastic litter quantification. The visual counting of plastic debris (> 2.5 cm) method based on the European standard method was applied to a river in Indonesia. The main challenge was the high turbidity of the water that obstructed visual observation. The deployment of the fishing net was also not appropriate to collect debris. Most of the plastic debris was stranded on the riverbanks, indicating that the plastic flow was likely elevated due to runoff during the rainy season. Four types of plastic litter polymers were obtained, i.e., polyethylene terephthalate (PET), low-density polyethylene (LDPE), polypropylene (PP), and polystyrene (PS). The highest percentage of macroplastics is LDPE, which usually used as daily packaging (90%).