Assessment of Heavy Metals, Microplastics Abundance, Pollution Level, and Contamination Risk in the Ganges Downstream

The degradation of aquatic ecosystems and their links to climate change had made microplastic (MP) contamination a significant environmental concern. The study evaluated the water quality and assessed the abundance, pollution level, and contamination risk of microplastics in the downstream of the Ganges. The analysis results revealed that biological oxygen demand, chemical oxygen demand, nitrate, and chromium levels slightly exceeded ECR-BD (2023) standards, reflecting mild pollution. Heavy metal analysis showed the following sequence of concentration: Fe > Cr > Cu > Ni > Pb > Zn > Mn > Cd, which increased gradually. Considering the water quality indices, the river water was moderately polluted. MP concentrations were higher in the pre-monsoon (17.7 particles/l) than in the post-monsoon (14.3 particles/l) season, with blue fibers <1 mm as the dominant forms. The identified MPs were polyethylene, polypropylene, polyethylene terephthalate, and polyvinyl chloride. The contamination factor (CF > 1) and the pollution load index (PLI > 1) indicated that the analyzed area was moderately contaminated with MPs. According to the study, the concentrations of Cr, Fe, and Cu increased with rising MP levels. Based on the co-occurrence of MPs and heavy metals, the Ganges River faced new ecological threats that needed to be addressed by tighter wastewater regulations, better plastic waste management, ongoing monitoring, and the implementation of transboundary policies to mitigate microplastic pollution.