Sources and sinks of mercury in the coastal lagoon of Aveiro, Portugal

Abstract

Surface sediments collected from 67 locations throughout the Lagoon of Aveiro, Portugal and cores from five sites representing areas of heavy and moderate pollution from a chloralkali plant, slight pollution from sewage discharges, and unpolluted environments were analyzed for total mercury. The mercury concentration reached 180 mg kg −1 dry sediment in the most polluted core. Away from the areas affected by the discharges of the chloralkali plant, the mercury concentrations in the surface sediments were < 0.4 mg kg −1. The background concentration of mercury in the lagoon sediments is 0.14 mg kg −1, and in the sediments of the intertidal areas of the Atlantic beaches 0.065 mg kg −1. The most important contributor to the mercury content of the lagoon (estimated to be 80 tons) is the chloralkali plant, followed by sewage discharges, and natural sources. Most of the mercury is trapped in the sediments close to its source with gradients of 1000 mg/kg per kilometer and 500 mg/kg per meter depth.