Decadal and spatial variation of Hg concentrations in sediments of a multi-stressor impacted estuary.

The present study has evaluated temporal and spatial mercury trends based on surficial sediment samples and Pb-dated sediment profiles. The obtained results show that there are areas close to the main bay's tributary rivers where the Hg content has doubled during the last 15 years and regions where it has decreased by a factor of 2, mainly the area close to the navigation channel, which is submitted to periodic dredging. In the inner part of the bay, the most contaminated region, mercury shows a strong association with sulfide. In the same region, based on the Pb results, it was possible to calculate the yearly increment on the Hg concentration in the surface sediment, 0.62 μg kg y to 0.29 μg kg y, according to the distance to the bay's main tributary rivers.