Modelling the cycling of persistent organic pollutants (POPs) in the North Sea system: Fluxes, loading, seasonality, trends

The fate and cycling of two selected POPs is investigated for the North Sea system with an improved version of a fate and transport ocean model (FANTOM). The model uses atmospheric data from the EMEP MSC East POP model (Gusev et al., 2009), giving reasonable concentrations and seasonal distributions for the entire region, as opposed to the three observation stations that Ilyina et al. (2006) were limited to. Other model improvements include changes in the calculation of POP exchange between the water column and sediment.We chose to simulate the fate of two POPs with very different properties, γ-HCH and PCB 153. Since the fate and cycling of POPs are strongly affected by hydrodynamic processes, a high resolution version of the Hamburg Shelf Ocean Model (HAMSOM) was developed and utilised. Simulations were made for the period 1996–2005. Both models were validated by comparing results with available data, which showed that the simulations were of very satisfactory quality.Model results show that the North Sea is a net sink for γ-HCH and a net source to the atmosphere of PCB 153. Total masses of γ-HCH and PCB 153 in 2005 are reduced to 30% and 50%, respectively, of 1996 values.Storms resuspending bottom sediments into the water column mobilise POPs into the atmosphere and have the potential to deliver substantial loads of these POPs into Europe.

► The fate and cycling of two very different POPs is investigated for the North Sea.
► Model results show that the North Sea is a net sink for γ-HCH.
► Results show that the North Sea is a net source of PCB 153 to the atmosphere.
► POPs can be mobilised from bottom sediments into the atmosphere during winter storms.
► These events have the potential to deliver substantial loads of POPs into Europe.