Storage and export of mercury from a contaminated bay (Ria de Aveiro,Portugal)

Mercury has been determined in water, suspended particulate matter (SPM)and sediments (solid fraction and pore water) collected in a heavilycontaminated confined area (Largo do Laranjo) of the Ria de Aveiro.Mercury has been analysed in seabass (Dicentrarchus labrax) capturedin several locations of the lagoon. The levels of mercury in water and SPMin the contaminated sampled places fluctuated daily with the tide (from 10to 53 ng.dm^-3 and 3.5 to 26 g.g^-1, respectively),indicating the export at the tidal rhythm. Bottom sediments exhibitedhigher concentrations, the maximum (48 g.g^-1) occurringnear the anthropogenic source at depths corresponding to the periods ofhigher industrial discharges. Mercury concentrations in pore waters (max.80 ng.dm^-3) exceed the values found in the water column and werehigher at depths where Acid Volatile Sulphides (AVS) presented broadmaximums. This implies a remobilization at anoxic conditions. However theexport across the sediment-water interface predicted through moleculardiffusion is low (between 1 to 4 × 10^-3 ng.cm^-2.h^-1) incomparison to the industrial input. The anthropogenic mercury appears tobe rapidly accumulated in seabass, a predator fish that enter seasonally inLargo do Laranjo.