Towards a systematic understanding of the dynamic fate of polychlorinated biphenyls in indoor, urban and rural environments.

Indoor environments and urban areas are hubs of chemical stocks and emissions, which contaminate those indoor and urban areas as well as the surrounding rural areas. Here, we introduce a newly developed nested multimedia indoor-urban-rural chemical fate model, coupled with a substance flow analysis, aiming to provide an integrated and dynamic understanding of the mass distribution, concentrations, and major pathways of contaminants within and between indoor, urban and rural environments. The model is applied to simulate the emissions, transport and fate of polychlorinated biphenyl (PCB) congeners 28 and 153 in the Western Baltic drainage basin over time. Whereas >90% of PCBs were used in the urban outdoor environment, the model indicates that ~80% of emissions occurred indoors because of higher emission factors in open-end usage. Atmospheric advection is highly effective in transporting the bulk of the PCBs emitted indoors to urban (>85%) and rural (>75%) environments. The rural environment is identified as the main locale for accommodating (>80%) and removing (>50%) the emitted PCBs. Contamination of exposure-relevant compartments in the rural environment is anticipated to decrease slower than, and thus outlast, that in the indoor environment, which implies an increasing importance of the food chain accumulation in overall human exposure to PCBs over time. Our model demonstrates that, whereas the indoor environment contains an insignificant fraction of the total emissions remaining in the regional environment, it experiences orders of magnitude higher concentrations than the rural environment. Therefore, while including indoor and urban environments in modeling influences little the modeled overall chemical fate on a regional scale, it strongly affects modeling the human exposure associated with multimedia concentrations.