Volatile organic compounds in the Scheldt estuary along the trajectory Antwerp–Vlissingen: concentration profiles, modelling and estimation of emissions into the atmosphere

During a two years sampling campaign, water samples were taken in the Scheldt estuary between Antwerp and Vlissingen over a 94 km trajectory in order to measure concentrations of 13 volatile chlorinated C1- and C2-hydrocarbons and monocyclic aromatic hydrocarbons. Averaged concentrations proved to be in the 8 (CCl4) to 189 ng•l−1 (tetrachloroethylene) range (n=72). Concentrations were compared to other estuarine concentration data and to marine concentration data of the adjacent southern North Sea. The increasing concentration profiles towards Antwerp for a number of chlorinated compounds was explained by inputs at and/or upstream of Antwerp. Dilution with marine water and water to air transfer downstream of Antwerp are considered as the main factors which contribute to the decrease in concentration towards open sea. In a second part, modelling and estimation of the water to air exchange transfer was carried out based on the water column concentrations, atmospheric concentration data and available air/water exchange models. Calculated volatilization rates were between 0.1 (CCl4) and 8.6 tonnes•year−1 (CHCl3). The significance of the amounts emitted was demonstrated by comparison with available data on anthropogenic emissions into surface waters.