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Sunday, January 25, 2015

i-SVOC (2014): A Modern and Remarkable Advancement over AMEM

For me the best part about writing a blog is the networking and interaction with the colleagues.   After last week’s blog about an old but, I thought, still useful software tool (AMEM), I was contacted by Shen Tian, P.E., Environmental, Health and Safety Engineer at Bayer Material Science.   Shen advised that he had found and uses the EPA i-SVOC (2014) (Note: SVOC stands for Semi-Volatile Organic Compounds of which phthalates and flame retardants are prime examples). Shen advises that this model can do similar estimates of SVOC (e.g., flame retardant and phthalates) emitting from products (substrate).   Copying from the EPA web site on this program we are told:

“Computer program i-SVOC Version 1.0 is a Microsoft Windows-based application for dynamic modeling of the emissions, transport, sorption, and distribution of semi-volatile organic compounds (SVOCs) in the indoor environment. This program covers the following indoor media or compartments:
·         air,
·         sources,
·         sinks (i.e., sorption by interior surfaces),
·         contaminant barriers,
·         suspended particles, and
·         settled particles.”
 One can find and download the program and documentation   at:  http://www.epa.gov/nrmrl/appcd/mmd/i-sovc.html.  Shen went on in his email to discuss his experience with the model.   He notes that for the emission of SVOC from a plastic it depends on the following user inputs with I have copied and listed below:
  • D: diffusion coefficient of SVOC in the substrate,
  • Kma: partition coefficient of SVOC between solid and air,
  • ha: mass transfer coefficient in the air
  • C0: the initial SVOC concentration in the substrate. 

I have to admit I had not heard of the i-SVOC model so I downloaded it and installed it in my Window 8.1 laptop (reportedly, it will work on Windows 7 or XP as well).   My first impression of this program:  Holy Cow!   If AMEN is High School this is Graduate School!  It is a remarkable piece of freeware with a very slick interface that attempts to determine the time course and fate of an SVOC of concern in all the various compartments (sources, sinks, settled dust and airborne particulate matter) extant indoors.  The documentation was written by Dr. Zhishi Guo and is presented in a 2013, 80 page PDF file that downloads with the program.  I have known of Dr. Guo's work for many years and he is a brilliant modeler who has done outstanding work at the EPA in constructing and sharing many very useful and relatively user-friendly models.   The i-SVOC model was also reviewed and tested by some of the best technical minds working in this field.   By all indications, this is a first- rate model and program but it will require a significant level of study and time from anyone wishing to use it.  To make this task easier, a number of demo input files are provided with the download to help the new user.
In order to feed this model relative to its inputs, Shen Tian advises that the companion modeling program (PARAMS 1.0) from EPA can be used to estimate quite a few parameters required for input.    I went looking for this program and found at link at: (http://www.epa.gov/ordntrnt/ORD/NRMRL/appcd/mmd/PARAMS.zip); however, when I tried the link it was broken with the dreaded 404 error.   I am looking into reviving this link and will let you know what happens, if you like, via email correspondence.   If worst comes to worst I will get a copy of PARAM 1.0 and make it available to anyone who sends me a request at mjayjock@gmail.com.
In his work Shen reports that the most challenging part of using i-SVOC is the estimation of D since there has not been a lot of testing done on SVOC/pairs.  To help this particular gap he tells us that Liu and Guo et al recently published a testing method for estimating D and Kma in Atmospheric Environment 89 (2014) 76-84 , entitled:  Experimental method development for estimating solid-phase diffusion coefficients and material/air partition coefficients of SVOCs which he found helpful in filling the gap. 
In all, i-SVOC represents a remarkable accomplishment and resource for anyone doing this type of human exposure assessment of SVOC indoors.  I am indebted to Shen Tian for pointing us toward it.   If you have a need to perform this type of analysis, I believe that it would be well worth your effort to learn and use it.

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