An Assessment of Mercury Loading in Core Sediments of Sunderban Mangrove Wetland, India (A Preliminary Report)

摘要

This is a preliminary report on total mercury (T_Hg) in core sediments (<63 μm particle size) of Sunderban mangrove wetland, northeastern part of the Bay of Bengal, India. Cold vapor atomic absorption spectrometry (CVAAS) was used for T_Hg determination. The concentration varies from 9.8 to 535.1 ppb (ngg−1). Results revealed variations over premonsoon and postmonsoon month at different core depth, as well as in studied three sampling stations, located at the site of three rivers: Hugli River (S₁), Matla River (S₂) and Bidyadhari River (S₃). Elevated concentration of T_Hg in subsurface layer (4–8 cm) of the core at S₂ is attributed to remobilization of mercury from deeper sediment (32–36 cm). Positive correlation is present between total Hg and clay content. Based on index of geoaccumulation (I_geo) and Effects-Range Low (ER-L) value (150 ppb) it is considered that the sediments are till now unpolluted. As a consequence, there is less chance of ecotoxicological risk to organisms living in studied sediments. Two statistical methods were applied to determine T_Hg anomalies. Box plot method showed one extreme and three outliers in S₁ at postmonsoon season. Two extremes were found at S₂ at 4–8 and at 32–36 cm in premonsoon period. In S₃ there was no anomaly by box plot method. MAD method was more sensitive than box plot method and T_Hg anomaly was detected at 12–16 cm in S₃ during postmonsoon season. The data reported are useful baselines for T_Hg in Sunderban mangrove wetland, India and would be of help in future sediment quality studies.