Urban drainage channels as a pathway for microplastics in riverine systems: A case study of Delhi, India

Abstract

Urban drainage channels act as significant routers of microplastics (MPs) originating from terrestrial to aquatic systems. In the present study, contamination of MPs (250–5,000 μm size) has been investigated in an interlinked urban aquatic system comprising Najafgarh drain, corresponding secondary drains, and Yamuna River in Delhi, India. A range of 100–4,300 MPs/m3 (pre-monsoon) and 100–6,700 MPs/m3 (post-monsoon) were detected in secondary drains, which meet the Najafgarh drain through its course in the city. Najafgarh drain showed an average abundance of 771 and 342 MPs/m3 during pre- and post-monsoon season, respectively. The discharge of microplastic (MP)-laden wastewater from the Najafgarh drain into the Yamuna River created a rise in MP abundance in the river at the drain's downstream location. Thus, revealing that secondary drains play a significant role in MP channelization to the Najafgarh drain and subsequently Yamuna River. White fragments were the dominant MP types in the study area. Chemical characterization revealed 11 types of MP polymers, with a predominance of polyethylene. Considering the knowledge gap in the MP database of interconnected urban aquatic systems in India, this study might help in providing baseline information and encourage more studies addressing the magnitude of this problem for predicting long-term environmental risks.