An estimation of industrial mercury stored in sediments of a confined area of the Lagoon of Aveiro (Portugal)

In the period from 1950 to 1994, most of the mercury discharged to the Lagoon of Aveiro was retained in the sediments of a small area of around 1.7 km2 (25.4 x 103 kg, about 77% of the total), which corresponds to the Estarreja Channel plus a basin named Laranjo Basin located downstream. In 1994, the mercury concentration in surface sediments of the area ranged from 2.3 to 343 μg g−1, with the highest values recorded near the industrial source of the metal. In places of the basin where the sedimentation rate could be considered uniform, the highest levels of Hg (35μg g−1) were recorded at depths around 40 cm, as result of reduction of the anthropogenic mercury input to the lagoon. Assuming an uniform sedimentation rate and a continuously low industrial input of mercury for the near future, the levels of Hg in the surface sediments would be less than 1 μg g−1 in 20 years. This may be considered the expected restoration time. The feasibility and consequences of several management options for this pollution problems is briefly presented.