Inhalation exposure pathways for polybrominated diphenyl ethers : a source to human receptor model for semivolatile organic compounds
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Many chemicals off-gas or leech into indoor environments from sources such as consumer products, furnishings, and building materials. An understanding of the pathways from the sources to human exposure is vital in order to implement control strategies and lower exposure. Objects containing Brominated flame retardants (BFRs), one class of semivolatile organic compounds (SVOCs), burn more slowly during combustion. BFRs, especially polybrominated diphenyl ethers (PBDEs), are used in electronic devices including casings and circuit boards. Heat from internal circuitry increases the BFR vapor pressure and the partition coefficient, enhancing its transport out of the substrate and into the indoor environment. In this work, a computer tower in an office setting provides a case study to examine the emissions of, and exposure to, PBDEs. the case of a computer tower, the cooling fan increases the mass transfer coefficient, further increasing emissions. During computer use, the emission rate of PBDEs from the interior of the case is more than double the emission rate from the exterior of the case due to elevated internal temperatures and higher mass transfer due to the cooling fan. The concentration of PBDEs in the room air increases 40 - 80% for every 5°C increase inside the computer case, depending on the PBDE congener. Such enhanced emissions are a concern since recent studies have shown adverse health effects of PBDEs on human health. The major contributions of this work are: A model was developed that is useful for SVOC emissions for various heat and mass transfer situations, including diffusion through the slab and convective boundary conditions on each side of the slab, which may be simplified if the situation warrants; A systematic propagation of the uncertainties and variability of the model parameters was accomplished by using a Monte Carlo method for the input of the parameters into the model; A polydisperse indoor particle distribution was used as a sink, identifying the size-discretized particle phase PBDE concentration; An exposure assessment showed that the inhalation pathway for PBDEs in the gas and particulate phases is relevant and that the particulate phase exposure is dominant.