Tidal export of particulate mercury from the most contaminated area of Aveiroʹs Lagoon, Portugal

Mercury pollution is a regional problem in the Aveiroʹs Lagoon. During 4 decades, a remote branch (Estarreja Channel) has received a discharge of mercury from a chlor-alkali plant, that is spread in the Laranjo Basin. Of special interest is the dispersion of mercury from these areas to the Lagoon. This work is a first attempt to quantify the net flux of particulate mercury from the most contaminated basin (Laranjo). Measurements of current intensity, suspended particulate matter and particulate mercury were carried out at two sampling stations over a spring tidal cycle, in April 1994. Based on a mass balance calculation at two stations, at the end of Estarreja Channel (F1) and near the outlet of Laranjo Basin (F2), the net tidal fluxes of particulate anthropogenic mercury were estimated: 0.4 g of mercury enter the Laranjo Basin and 94.5 g of particulate mercury escape the Basin. These results indicate that mercury from the most contaminated area continues to be dispersed, predominantly through the particulate fraction, to the rest of the Lagoon.