A fate and transport ocean model for persistent organic pollutants and its application to the North Sea

An ocean model (FANTOM) has been developed to investigate the fate of selected persistent organic pollutants (POPs) in the North Sea. The main focus of the model is on quantifying the distribution of POPs and their aquatic pathways within the North Sea. Key processes are three-dimensional transport of POPs with ocean currents, diffusive air–sea exchange, wet and dry atmospheric depositions, phase partitioning, degradation, and net sedimentation in bottom sediments. This is the first time that a spatially resolved, measurements-based ocean transport model has been used to study POP-like substances, at least on the regional scale. The model was applied for the southern North Sea and tested by studying γ-HCH behaviour in sea water in the years 1995 to 2001. The model's structure and processes are described in details. Concentrations of γ-HCH and its fluxes between upper sediment, sea and atmosphere were modelled, based on discharge and emission estimates available through various monitoring programmes. Model results are evaluated against measurements. Modelled concentrations of γ-HCH in sea water are in good agreement with the observations; the spatial distribution and the downward trend in the entire North Sea are reproduced during the simulation period. The correlation between the model results and measurements is better during warmer seasons suggesting the importance of the temperature dependency of the air–sea exchange.