Towards a nested multimedia fate, transport and bioaccumulation model for the Nordic region

Most empirical monitoring programs on organic contaminants, including POPs, typically target a specific area, country or region. The Nordic region, including remote Arctic areas such as Svalbard, is probably among the more well studied regions with respect to the empirical occurrence of organic contaminants within various ecosystems. Yet, gaps remain in our understanding of the link between sources and exposures in this region, including how source-exposure relationships may vary in space and time, for individual contaminants
and across abiotic and biotic compartments. As POPs are global pollutants, sources affecting Nordic regions
could both be distant and/or of more local origin. Furthermore, the persistence of POPs implies that current
exposures could be a result of both historical as well as recent emissions. This calls for regional modelling
strategies which are global in context yet dynamic, reflecting both the possible mobility and life-time of
relevant contaminants. Here, we introduce the first version of an integrated fate, transport and exposure model for the Nordic region (Nordic Exposure Model - NEM). The point of departure for NEM are three existing models, notably BETR-Global, ACC-Human and CoZMo-POP2. In contrast to these models, theNEM model reflects the hypothesis that accurate predictions of organic contaminant exposures call for
increasing resolution with increasing proximity (in space and time) to a study region of interest. Hence, NEM is being developed as a nested model, consisting of (up to) five different gridded model domains, simulated in sequence: Global (30ºx120º Lat/Long) > Northern Hemisphere (30ºx30º) > Europe (15ºx15º) > Northern Europe (7.5ºx7.5º) > Nordic region (3.75ºx3.75º). Chemical transport between neighbouring grid cells may occur by air, fresh water and seawater. Chemical inflow from the outside world and into a given domain (except the initial global domain), is based on simulations of the preceding domain. The physical environment within a given grid cell within NEM includes up to 10 different compartments (upper and lower atmosphere, broadleaf and needleleaf canopies, forest soil, uncultivated soil, agricultural soil, fresh water, fresh water sediment and marine water). The NEM model also includes the opportunity to simulate bioaccumulation in the human food-chain within a user-defined grid cell, allowing relationships between sources and biotic exposures in a specific receptor to be evaluated. Here, an overview of the initial version of NEM will be given, along with initial results using PCBs (polychlorinated biphenyls) as an example. Plans for further development, evaluation and opportunities for future applications will be presented.