An Assessment of Mercury Loading in Core Sediments of Sunderban Mangrove Wetland, India

This is a preliminary report on total mercury (THg) in core sediments (\63 lm particle size) of Sunderban mangrove wetland, northeastern part of the Bay of Bengal, India. Cold vapor atomic absorption spectrometry (CVAAS) was used for THg determination. The concentration varies from 9.8 to 535.1 ppb (ngg). 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 THg 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 (Igeo) 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 THg 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 THg anomaly was detected at 12–16 cm in S3 during postmonsoon season. The data reported are useful baselines for THg in Sunderban mangrove wetland, India and would be of help in future sediment quality studies.