Mobility of contaminants in relation to dredging operations in a mesotidal estuary (Tagus estuary, Portugal)

Abstract

During the construction of a New Bridge over the Tagus estuary 2.5 million tons of sediments were dredged, part of this quantity being contaminated material. The extension and intensity of the water turbidity associated with dredging operating varied with the tidal conditions but the resuspended material collected near the bucket dredger did not present a concentration increment in metals and PCB, when compared to the estuarine suspended sediments. The calculated distribution coefficients suggest that some contaminants in solids near the dredger were not in equilibrium with the water. A 24-hour laboratory experiment demonstrated the complexity and quickness of anoxic sediments oxidation. In such a short period of time metals in the solids change their fractionation. A second laboratory simulation showed that mussels accumulate metals and PCB congeners when placed in turbid aerated water.

Biochemical endpoints on juvenile Solea senegalensis exposed to estuarine sediments: the effect of contaminant mixtures on metallothionein and CYP1A induction

“…Other research shows that organic contaminants have more complex desorption processes (e.g. due to hydrophobicity), still enhanced by turbation (Vale et al 1998;Hellou et al 2005). This information supports the presented data and confirms the importance of assay conditions during sediment tests.…”

Transport of branched tetraether lipids from the Tagus River basin to the coastal ocean of the Portuguese margin: consequences for the interpretation of the MBT'/CBT paleothermometer

“…2). Further, it has one of the largest estuaries in Europe, with an area of roughly 320 km 2 formed by several channels and islands (Vale et al, 1998) being connected to the sea by a relatively narrow channel (ca. 2 km width).…”

Predicting pollutant concentrations in the water column during dredging operations: Implications for sediment quality criteria

“…Regardless the economic importance of the dredging activities throughout the world, it has been shown that dredging causes serious impacts, threatening ecosystems and their biological communities, particularly in areas where dredged sediments are contaminated (Sturve et al, 2005;Vale et al, 1998). This contamination is a serious problem, because harbors are frequently located on urban and industrial coasts, within wave-protected areas, where the conditions for the accumulation of a myriad of contaminants are ideal.…”