Microplastics pollution and risk assessment in two urban rivers and an associated water treatment plant in Bangladesh

Abstract

Microplastics (MPs) are considered emerging contaminants because they can potentially harm wildlife and humans. MPs in freshwater environments, especially in urban rivers, are less documented than those in marine habitats. This study examined the abundance, types, and distribution of MPs by collecting five (5) surface water samples from both the Buriganga and Shitalakshya rivers, in triplicate. Additionally, two (2) water samples were obtained from a nearby drinking water treatment plant (DWTP), also in triplicate. We further assessed the risks associated with microplastic contamination by calculating the pollution load index of the twelve sampling sites. The mean concentration of MPs in the Buriganga and Shitalakshya rivers was 12.4 p/L and 11.5 p/L, respectively; the MPs are mostly of transparent color (69%), in the shape of microfilms (71%), and < 1 mm in size (>90%). The DWTP showed similar microplastic concentrations in the inlet (8.7 particles/L) and outlet (7.3 particles/L), with no statistically significant difference (one-way ANOVA; p > 0.05). Polypropylene and polyethylene were identified as the most prevalent polymer kinds through analysis of infrared spectra, and the carbonyl index suggested that particles had undergone aging. A novel approach was taken to compute the pollution load index (PLI), which was subsequently employed for estimating the associated ecological risk. The Buriganga and Shitalakshya river waters were categorized as risk category Ⅳ and risk category Ⅲ, indicating the river waters are intermediately and seriously polluted, respectively. Policymakers and researchers are expected to take the findings of this study into cognizance and act accordingly to reduce the plastic loads of these two rivers.