Unregulated anthropogenic activities along Bangladesh's coastline have raised growing concerns over heavy metal contamination in aquatic ecosystems, yet sediment quality in coastal river systems remains critically understudied. This study investigated the concentration, seasonal variation, sources, and ecological risks of heavy metals in surface sediments of the Rabnabad River channel, a Bay of Bengal connected coastal system in Bangladesh. Sediment samples were collected from 16 sites during summer and winter and analyzed for copper (Cu), chromium (Cr), nickel (Ni), arsenic (As), cadmium (Cd), lead (Pb), and zinc (Zn). Heavy metal concentrations were significantly higher in winter, reflecting enhanced buildup under low-flow conditions. Spatial analysis revealed a marked contamination hotspot at site S7, situated near the power plant jetty. Pollution indices (e.g., geo-accumulation index, enrichment factor, pollution load index, and the Nemerow pollution index) indicated generally low contamination, except for pronounced anthropogenic enrichment of Cd. Sediment toxicity indices (e.g., multiple probable effect concentration quotients, toxic risk index, and total toxic units) suggested low toxic risk, although toxicity levels were relatively higher during winter. Ecological risk assessment (e.g., single metal risk index, ER and potential ecological risk index) identified Cd as the dominant contributor, with mean ER values of 348.7 in summer and 445.6 in winter, indicating a very high ecological risk, whereas the remaining metals posed negligible risk. Principal component analysis indicated that heavy metals are mainly influenced by anthropogenic sources, including coal-fired power plant, port activities, and agricultural practices, with Zn showing a comparatively distinct association with agricultural inputs.
Kormoker et al. (Mon,) studied this question.
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