Integrate Experiments and Models to Estimate Exposure – (1) Building Fumigation and (2) Elemental Mercury Spill

February 22, 2010 - 12:00pm
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Models that predict exposure concentrations in the indoor and outdoor air can be improved by experiments designed to validate or calibrate the models. This presentation will showcase two examples where experiments and models are integrated to estimate exposure concentrations. One example is the use of methyl bromide as fumigant at food processing facilities. Field studies were conducted at three mill sites that are representative of typical industry practices in terms of size, operation, and fumigation protocol. Concentrations of methyl bromide inside the mills and outdoors were monitored using real-time instruments and time-integrated samples. Emissions of methyl bromide from the fumigated mills to the outdoors were calculated during the treatment and aeration phases. The emission rates were input in an air dispersion model to predict the ambient concentrations. Comparison with measurements shows that the complex layout of mill sites is a challenge for modeling emissions and dispersion. Methods developed from this analysis can be applied to calculate buffer zone needed during fumigation to ensure the safety of workers and bystanders. The second example of integrating experiments and models to estimate exposure is an elemental mercury spill case. Elemental mercury was spilled onto roads from a truck leaving a gold mine in South America. Villagers collected the spilled elemental mercury and took it home. Efforts to recover the spill began the next day, but were unsuccessful until 1 week later when a reward was offered for the return of spilled mercury. Indoor and outdoor sampling of elemental mercury concentrations occurred about 10 days after the spill. To reconstruct the exposure concentrations of the villagers, an experimental room was built with a compacted dirt floor typical of that area. Elemental mercury were placed in the room and manipulated according to descriptions of the villagers. Emission fluxes were quantified under different environmental conditions based on the measured real-time concentrations. Exposures of the villagers were estimated while at homes, in schools, and outdoors. Exposure predictions were in the expected range when compared with the mercury concentrations measured in urine samples from the villagers. For more information about this seminar, please contact: Mike Sohn(510) 486-7610

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