Influence of monsoon season on heavy metal composition of Hooghly River estuary sediments, West Bengal, India

The sediments of Ganga estuary, Hooghly River in India, were assayed for the effect of monsoon season on heavy metal loads over 2014-2017, a time frame never investigated before. As, Co, Cr, Cu, Pb, Zn, correlated with Mn, r 0.70-0.83, and Fe, r 0.70-0.76, meaning bounding to amorphous and/or crystallized iron and manganese oxyhydroxides. Pb and U were highly correlated, r of 0.86, and this may be likely linked to the important presence of the fertilizer industry. Ni instead had a negative correlation with the other metals indicating a different provenience. During the monsoon season, it was observed a significant increase in the number of metals significantly correlated with Mn, Fe, and Al, r of 0.80-0.86, due likely to weathering of transported continental detritus. All metals, except Ni, were significantly correlated with silt, r 0.73-0.83, which together with Mn, Fe and Al, is responsible for the increased transport of metals under monsoon period. Temporal trends of metals and ecological risk indexes split over two periods after the 2015 monsoon. The geo-accumulation index of As decreased from 3.82 to 1.14 and that of Ni increased from 2.74 to 3.99. On the overall the geo-accumulation index, enrichment factor, and pollution load indexes were several folds higher than those from the literature. Ni was the most threatening element for the aquatic ecosystem being above TEL and ERM quality guidelines by 100 and 98.9 %.