Potential Ecological Risk and Characterization of Floating Microplastics in the Surface Water of a Highly Urbanized Large River in Southeast Asia

Microplastics (MPs) are widespread in aquatic environments and pose significant threats to ecosystems, wildlife, and human health. While MP pollution in water has received considerable attention, there is still limited understanding of its regional distribution, shapes, and associated risks. The Jamuna River, one of the largest freshwater ecosystems in Bangladesh, is increasingly contaminated by hazardous MPs, likely originating from industrial, domestic, hospital waste, and municipal sewage. This study aimed to investigate the abundance, distribution, characteristics, and ecological risks of MPs in the surface water of a highly urbanized large river in Southeast Asia. Water samples were collected from 30 sites along a 44 km stretch of the river during two periods: March to April (premonsoon) and July to August (monsoon). A total of 386 MPs were identified in the collected samples. The mean abundance of MPs in the surface water of the Jamuna River ranged from 0.01 to 0.15 MPs/L during the premonsoon season and from 0.01 to 0.13 MPs/L during the monsoon season. Approximately 79.78%-87.98% of the particles fell within the 100-1500 μm size range. The presence of polyethylene (31.60%-37.24%), polystyrene (PS) (6.71%-10.81%), and polyvinyl chloride (PVC) (5.64%-7.28%) contributed significantly to MP contamination, posing a high health hazard. Several risk assessment models were employed to evaluate the associated risks. The pollution load index (PLI) classified the contamination under risk Category I (minor pollution). Meanwhile, the polymer hazard index (PHI) values were 305.65 for the premonsoon season and 208.0 for the monsoon season, both indicating hazard Category IV ("danger" level). The potential ecological risk index (PERI) placed the Jamuna River surface water in the "extreme danger" risk category, with values of 2454.43 during the premonsoon and 1911.29 during the monsoon. The prevalence of high-hazard polymers such as PVC and PS suggests a potential risk of toxicological effects for aquatic organisms and humans through food web transfer. This baseline study provides valuable insights into the MP pollution of one of the country's major rivers. It may help improve our understanding of land-based MP inputs from inland water bodies severely impacted by anthropogenic activities.