Abundance and Characteristics of Microplastics in Urban Canals: A Case Study In Dhaka City

Abstract

Microplastic pollution is an emerging global environmental challenge with significant implications for aquatic ecosystems and human health. This study focuses on the urban canals of Dhaka city, Bangladesh, where the abundance and characteristics of microplastics remain largely unexplored. The research problem lies in the lack of comprehensive data on how urban canals contribute to microplastic pollution in peripheral rivers, thereby exacerbating ecological risks. Prior studies have primarily concentrated on larger water bodies, leaving a critical gap in understanding the role of smaller canals as conduits for microplastics. The main objectives of this research were to investigate the occurrence and characteristics of microplastics in urban canals of Dhaka, evaluate the environmental and ecological risks associated with microplastic pollution, and assess the loading of microplastics into connected peripheral rivers. These objectives aim to bridge the knowledge gap and provide actionable insights for policymakers to devise effective plastic waste management strategies. The research adopted a systematic design encompassing field sampling, laboratory analysis, and data interpretation. Five canals—Kallayanpur, Norail, Gobindapur, Digun, and Abdullahpur— were selected for their strategic connections to the Balu, Buriganga, and Turag rivers. Sampling was conducted during the dry season to ensure higher microplastic concentrations, with water and sediment samples collected from urban areas, connecting channels, and canal-river junctions. Laboratory methodologies included vacuum pump filtration for water samples, oven drying for sediment samples, density separation using zinc chloride solutions, and visual and spectroscopic analysis for microplastic identification and quantification. Quality assurance measures adhered to NOAA guidelines to ensure reliability and minimize contamination. The findings revealed that microplastics were present in all sampled canals, with higher concentrations observed in sediment samples compared to water samples. The average concentration in water samples ranged from 13 to 185 items per liter, while sediment samples exhibited 81 to 594 items per kilogram. Among the canals, Digun recorded the highest microplastic concentration in water samples due to industrial discharges, whereas Abdullahpur had the highest sediment concentrations, attributed to stagnant flow and water retention. The dominant microplastic shapes included fibers (55% in water and 22.99% in sediment), films (18.62% in water and 43.1% in sediment), and fragments. Microplastics predominantly ranged in size from 0.1 millimeters to 1 millimeter, with transparent particles accounting for the largest proportion. These findings highlight significant spatial variability influenced by land use and human activities. The study concludes that urban canals in Dhaka serve as critical pathways for microplastics, facilitating their transfer to peripheral rivers and contributing to broader environmental pollution. The implications underscore the urgent need for targeted waste management policies, improved industrial effluent treatment, and public awareness campaigns to mitigate microplastic pollution. Future research should explore seasonal variations, microplastic weathering processes, and their combined ecological impacts, while assessing the risks to human health and biodiversity. This study provides a foundational framework for addressing microplastic pollution in urban waterways, offering insights for environmental management in rapidly urbanizing regions worldwide.