PT17 Assessment and Remediation of Mercury Contaminated Sites
Exhibit Hall
8:00 AM - Tuesday
(PT268) The pathway of mercury in contaminated waters determined by association with organic carbon.
Canário, J.1, Vale, C.1, Nogueira, M.1, 1 National Institute for Agronomy and Fisheries Research - IPIMAR, Lisboa, Portugal, Portugal
ABSTRACT- The Tagus estuary is one of the largest estuaries in Europe (320 km2) with several longitudinal channels in the central bay. The North Channel has been contaminated by mercury during several years, as shown by the vertical distribution of Hg concentrations in sediments. At the present time suspended particulate matter still contains high Hg levels due to resuspension of contaminated bottom sediments and eventually industrial emissions. Because the hydrodynamic and the suspended particulate matter field are greatly influenced by the tide, the export of Hg by the two end-members of the North Channel is difficult to estimate by a simple mass balance. Reactive dissolved mercury (HgR), non-reactive dissolved mercury (HgNR), particulate mercury (HgP), dissolved organic carbon (DOC), particulate organic carbon (POC), salinity and other interpretative parameters were determined in water samples collected in the North Channel and in adjacent areas during four campaigns in 2002 and 2003. Higher concentrations of both dissolved and particulate Hg in the North Channel raise the possibility of Hg being exported to other areas of the estuary by the tidal excursion. This hypothesis was confirmed by the increases of HgR with salinity and HgNR with DOC, along a longitudinal axis paralleling the North Channel. Apparently, mercury escaping this channel is progressively complexed by several ligands (eg. Cl-, OH-, DOC). Near the estuarine mouth values decreased reflecting dilution with clean seawater. Moreover the HgP:POC ratio also increased seaward, suggesting mixing with enriched particles escaped from the North Channel or incorporation of dissolved mercury species in river-derived particles or particles exported from the maximum turbidity zone. These results suggest that pathway of anthropogenic mercury in contaminated waters may be identified by their enrichment in organic matter, both in dissolved and particulate fraction.
Key words: organic carbon, mercury, water, particles