MERCURY IN THE SANTA CRUZ CHANNEL, NE BRAZIL - A POTENTIAL RISK

Abstract

This work evaluated the level of mercury contamination in a mangrove system (Santa Cruz Channel) a couple of years after Hg discharge into its main tributary (Botafogo River) ceased, as well as the role of mangrove sediments as sinks or secondary sources of mercury whiting the system and/or to coastal areas. Mangrove oysters, suspended matter and sediment cores representing different compartments of the Channel and seasonal and tidal stages were analyzed. Mercury concentrations was 0.27-2.21 ppm (dry mass DM) in mangrove oysters; 0.04-6.20 ppm in total sediment (DM) and 0.3-20.5 ppm in relation to the grain size fraction <63 μm. Mercury concentrations in suspended matter were between 0.43-5.56 ppm (DM), corresponding to 4-175 ngL-1 particulate mercury. Results corroborates the importance of fine and organic-rich matter for the accumulation of mercury but also indicated that mangrove sediments do not function as a long-term trap for Hg. Instead, mercury is remobilized from the sediments, presumably as bioavailable species. As the export to coastal areas is small, a large portion of the remobilized Hg probably cycles within the system or is released into the air. Both processes represent a considerable risk for aquatic organisms and humans exposed to the mercury.