Assessment of microplastics on the coastal urban waterways in a developing country: a spectrometric study

Microplastic pollution has become a significant environmental issue, especially in growing urban waterways of coastal regions. To investigate the sources, spatial distribution, ecological, and health effects of microplastics, water samples were collected from the coastal waterways that flow to the Bay of Bengal in Bangladesh. The concentration of microplastics was 181.11 ± 26.63 items/L. The size distribution was dominated by particles < 0.5 mm (70.34%), followed by 0.5-1 mm (21.85%). Transparent particles were most abundant (47.73%), followed by black (27.61%), while fibre-shaped particles were the dominant morphotypes (48.83%). Through Fourier Transform Infrared Spectrometer (FTIR) analysis, five polymer types were discovered in the water sample, including polyethylene, polyamide 6, polyamide 6,6, polyether-urethane, polyether-ester urethane, and alkyd resin. Principal component analysis (PCA) using six sites (S1-S6) showed a strong correlation between microplastic characteristics and sample sites. Water quality pollution index values indicated good to slightly polluted conditions at several locations. Redundancy analysis (RDA) based on 18 water samples (each sample with replicates) revealed a significant relationship between water quality parameters and microplastic characteristics (P < 0.05), except for abundance and size. This suggests that the microplastic distribution is strongly influenced by human activities in the study area. The Nemerow's pollution index (NPI), polymer hazard index (PHI), and potential ecological risk (PERI)- all ecological risk indicators show minor, moderate, and high categories of pollution due to microplastic exposure, where Sagordi Khal falls into the high-risk category. According to survey data, the main causes of microplastic pollution were improper trash disposal and high use of plastic bags, while 41.15% of respondents were unaware of the problem. Overall, the observed environmental pollution is strongly driven by anthropogenic behaviors, highlighting the human-driven nature of microplastic pollution in the study area.