Citation:

Liang, Y., X. Liu, AND M. Allen. Measuring and Modeling Surface Sorption Dynamics of Organophosphate Flame Retardants in Chambers. CHEMOSPHERE. Elsevier Science Ltd, New York, NY, 193:754-762, (2018).

Impact/Purpose:

SVOCs are widely used in industrial and consumer products. They are relatively persistent and can be transported within indoor environments and from indoor to outdoor environments. When an SVOC source is tested for emissions in an environmental chamber, interior walls of the chamber may adsorb substantial SVOCs from the air inside the chamber. Sorption by the walls of the chamber will cause underestimation of the emission rate and can be an error source for emissions testing. Poor understanding of SVOC adsorption by impermeable surfaces, such as stainless steel plates, has hindered the interpretation of chamber data for characterizing SVOC sources and sinks. In this study, both Langmuir and Freundlich isotherm models are used to characterize the adsorption/desorption dynamics of OPFRs on a stainless steel surface. Sorption parameters for OPFRs from chamber tests were obtained. It is the first time in the literature to report the Freundlich model parameters for OPFRs on stainless steel surfaces. The research results will reduce the uncertainties in the input parameters of SVOC models and substantially improve the accuracy of the parameter estimation methods leading to better risk assessments and management approaches. The method and data will support EPA OPPT flame retardants TSCA work plan, collaborative Federal Partnership (EPA, NIOSH, CPSC, NIST, OSHA, ASTDR, and NLM) Research on Spray Polyurethane Foam (SPF) Emission and ASTM International consensus methods for measuring and modeling emissions from SPF insulation and SVOCs.

Description:

Understanding the sorption mechanisms for organophosphate flame retardants (OPFRs) on impervious surfaces is important if we are to improve our understanding of the fate and transport of OPFRs in indoor environments. Traditional Langmuir and Freundlich models are widely adopted to describe the sorption behavior of indoor semivolatile organic compounds (SVOCs). In a real indoor environment, it is possible that the sorption process of SVOCs on surfaces is more heterogeneous (multilayer adsorption) than homogeneous (monolayer adsorption). Therefore, interpreting the sorption mechanisms of OPFRs on surfaces using Langmuir’s equation may not be accurate. In this study, we adopt both Langmuir and Freundlich isotherms to characterize the adsorption/desorption dynamics of OPFRs on a stainless steel surface and make comparisons between the two models through a series of empty chamber studies. The chamber 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 from empty small chamber test to predict the gas phase concentrations of OPFRs in a small chamber with an emission source. Comparisons between model predictions and measurement results show the reliability and application of the obtained sorption parameters.

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