The influence of weirs on microplastic fate in the riverine environment (case study: Jeneberang River, Makassar City, Indonesia)

The riverine environment is known as the main pathway of microplastic entering the ocean. Recent studies show that the barricading of water flow in the riverine environment can influence the microplastic load to the ocean. The Jeneberang River, which is located in Makassar City, is prone to microplastic pollution. There are three weirs located in this river as water barricades. The aim of this study was to measure the microplastic abundance upstream and downstream of each weir flow. Microplastics in the water compartment were measured using the volume-reduce towing method and were measured in the sediment compartment using a density separator method. The results show that microplastic abundance in the water prior to passing each weir was higher (1.43 – 3.19 item/m 3 ) compared by the flow after each weir (1.20 – 2.10 item/m 3 ). The same pattern was also apparent in the sediment compartment where the microplastic abundance prior to the weirs tended to be higher (28.33 – 56.67 item/kg DW) compared to the compartment after the weir (30.00 – 53.33 item/kg DW). Based on microplastic shape, there is no evidence that weirs in the Jeneberang River are blocking any specific shape of microplastic. In conclusion, weirs that are commonly found in the riverine environment could act as microplastic retention devices in the riverine environment.