Seasonal assessment of trace element contamination in intertidal sediments of the meso-macrotidal Hooghly (Ganges) River Estuary with a note on mercury speciation.

The spatial and seasonal distribution of trace elements (TEs) (n=16) in surficial sediment were examined along the Hooghly River Estuary (~175km), India. A synchronous elevation of majority of TEs concentration (mgkg) was encountered during monsoon with the following descending order: Al (67070); Fe (31300); Cd (5.73); Cr (71.17); Cu (29.09); Mn (658.74); Ni (35.89). An overall low and homogeneous concentration of total Hg (T=17.85±4.98ngg) was recorded in which methyl mercury (MeHg) shared minor fraction (8-31%) of the T. Sediment pollution indices, viz. geo-accumulation index (I) and enrichment factor (EF) for Cd (I=1.92-3.67; EF=13.83-31.17) and Ba (I=0.79-5.03; EF=5.79-108.94) suggested high contamination from anthropogenic sources. From factor analysis it was inferred that TEs primarily originated from lithogenic sources. This study would provide the latest benchmark of TE pollution along with the first record of MeHg in this fluvial system which recommends reliable monitoring to safeguard geochemical health of this stressed environment.