Coupling of metal fractionation with sediment quality in Mandovi and Zuari rivers, estuaries, and adjoining coastal area of Goa: Constrains on environmental risk
Date
2025Author
Vudamala, K.
Deep, S.S.
Ray, D.
Chinnadurai, K.
Anil, K.
Kocherla, M.
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Study was conducted to assess the variability of bulk loads and speciation of toxic metals in surface sediment in relation to the basic sediment characters along fresh-water, estuarine zones of the rivers Mandovi, Zuari, and adjacent coastal areas of Goa, India. The distributions of sediment parameters like texture, total organic carbon (TOC), total nitrogen (TN), heavy metals (e.g. Cu, Ni, Cr, and Pb) contents and their speciation were investigated. Results indicated that variable metal concentrations were observed across fluvial, estuarine, and coastal sites, with certain metal such as Cr showing higher levels at three environments. The Cr and Ni concentrations in estuarine and coastal sediments exceeded the ERL (81?mg?kg?1 for Cr, 20.9?mg?kg?1 for Ni) and TEL (52.3?mg?kg?1 for Cr) values, indicating ecological concern, although they remained below the ERM values in most cases. To assess the possible ecological risks, the speciation of those metals was investigated, and it showed the majority (42�94?%)of total metals were associated with residual silicic fraction of all sediment samples. This suggests the silicic materials in sediments; which usually originate through erosion of terrestrial rocks in the catchment areas could be the main host of those toxic metals. Due to their immobile nature, metals trapped within silicate structures are generally not exchangeable with water and are considered less bioavailable; however, these residual fractions may still pose ecological risks to benthic organisms through direct sediment interaction or ingestion. A notable portion (9�49?%) was also bound to organic matter, especially in estuarine and coastal sediments, while smaller amounts were associated with Fe-Mn oxides (2.5�14.5?%) and the exchangeable fraction (<5?%). Therefore, even the bulk contents of toxic metals in sediments exceed limits of standard sediment quality guidelines; the relative association of toxic metals with different sedimentary components is an important factor for ultimate toxicity assessment.
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