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Measuring and modeling surface sorption dynamics of organophosphate flame retardants in chambers
Citation:
Liang, Y., X. Liu, AND M. Allen. Measuring and modeling surface sorption dynamics of organophosphate flame retardants in chambers. ASTM SVOC Workshop, New Orleans, LA, October 12, 2017.
Impact/Purpose:
The Frank R. Lautenberg Chemical Safety for the 21st Century Act, which amends the Toxic Substances Control Act (TSCA), expands the authority of U. S. EPA to obtain testing information for prioritizing or conducting risk evaluations on existing and new industrial chemicals and promote the use of alternative testing methodologies. There is a need for citable, consensus standards that EPA can guide industry to use when requesting chemical information for risk evaluation. This presentation will address the challenge for SVOC emission characterization and measurement of various SVOC emission parameters.
Description:
Understanding the sorption mechanisms for organophosphate flame retardants (OPFRs) on impervious surfaces is important to improve our understanding of the fate and transport of OPFRs in indoor environments. Langmuir and Freundlich models are widely adopted to describe sorption behaviors of indoor semivolatile organic compounds (SVOCs). The sorption process of SVOCs on surfaces involves heterogeneous (multilayer adsorption) and homogeneous (monolayer adsorption). In this study, we adopted Langmuir and Freundlich isotherms to characterize the adsorption/desorption dynamics of OPFRs on stainless steel surfaces and made comparisons between the two models through a series of empty chamber studies. The tests involve two types of stainless steel chambers (53-L small chambers and 44-mL micro chambers) using tris(2-chloroethyl)phosphate (TCEP) and tris(1-chloro-2-propyl)phosphate (TCPP) as target compounds. Test results show that the Freundlich model can better represent the adsorption/desorption process in the empty small chamber. Micro chamber test results show that both Langmuir and Freundlich models can well fit the measured gas-phase concentrations of OPFRs. We further apply the Freundlich model and the obtained parameters to predict the gas phase concentrations of OPFRs in a small chamber with an emission source. Comparisons between model predictions and measurements show the reliability and application of the sorption parameters.