Measuring and modeling surface sorption dynamics of organophosphate flame retardants on impervious surfaces

Use of Periodic Mesoporous Organosilica-Benzene Adsorbent for CO2 Capture to Reduce the Greenhouse Effect

The CO2 adsorption of a phenylene-bridged ordered mesoporous organosilica (PMO-benzene) was analyzed. The maximum capture capacity was 638.2 mg·g-1 (0 °C and 34 atm). Approximately 0.43 g would be enough to reduce the amount of atmospheric CO2 in 1 m3 to pre-industrial levels. The CO2 adsorption data were analyzed using several isotherm models, including Langmuir, Freundlich, Sips, Toth, Dubinin-Radushkevich, and Temkin models. This study confirmed the capability of this material for use in reversible CO2 capture with a minimal loss of capacity (around 1%) after 10 capture cycles. Various techniques were employed to characterize this material. The findings from this study can help mitigate the greenhouse effect caused by CO2.

Organophosphate Esters in Building Materials from China: Levels, Sources, Emissions, and Preliminary Assessment of Human Exposure

Source characteristics and health risks of indoor organophosphate esters (OPEs) are limited by the lack of knowledge on emission processes. This study attempted to integrate the contents and emissions of OPEs from indoor building materials to assess human health effects. Thirteen OPEs were investigated in 80 pieces of six categories of building materials. OPEs are ubiquitous in the building materials and ∑13OPE contents varied significantly (p < 0.05) from 72.8 ng/g (seam agent) to 109,900 ng/g (wallpaper). Emission characteristics of OPEs from the building materials were examined based on a microchamber method. Depending on the sample category, the observed initial area-specific emission rates of ∑13OPEs varied from 154 ng/m2/h (carpet) to 2760 ng/m2/h (wooden floorboard). Moreover, the emission rate model was developed to predict the release levels of individual OPEs, quantify source contributions, and assess associated exposure risks. Source apportionments of indoor OPEs exhibited heterogeneities in multiple environmental media. The joint OPE contribution of wallpaper and wooden floorboard to indoor dust was up to 94.8%, while latex paint and wooden floorboard were the main OPE contributors to indoor air (54.2%) and surface (76.1%), respectively. Risk assessment showed that the carcinogenic risks of tris(2-chloroethyl) phosphate (3.35 × 10-7) were close to the acceptable level (1 × 10-6) and deserved special attention.

Computational fluid dynamics analysis of a micro-scale chamber for measuring organic chemical emission parameters

Computational fluid dynamics simulations are used to model the velocity field and the transport of a passive scalar within a micro-scale chamber used to measure diffusional transport through various building materials. Comparisons of solutions obtained using a steady, laminar flow assumption with velocity measurements obtained from hot-wire anemometry show that the numerical method generally underpredicts the near surface velocity field. The results improve for higher flow rates and for carpeted test materials, modeled as a porous resistive layer. Calculations involving scalar transport within the upper chamber of the sampling device are performed for different flow rates and Schmidt numbers. The results are used to develop a model for the convective mass transfer coefficient, correlated as a function of the Reynolds and Schmidt numbers as well as the porosity of the carpet. This model is integrated into a steady-state mass transport model for predicting the diffusion of gaseous formaldehyde through various test materials. Predictions of diffusion and partition coefficients for vinyl flooring, gypsum wall board, and carpet are within the ranges of literature data. The results indicate that a perfectly mixed upper part of the sampling device is an adequate assumption.

Efficient removal of Tris(2-chloroethyl) phosphate by biochar derived from shrimp shell: Adsorption performance and mechanism study

Tris(2-chloroethyl) phosphate (TCEP) has been detected all over the world as a typical refractory organic phosphate, especially in groundwater. This work applied a calcium-rich biochar derived from shrimp shell as a low-cost adsorbent for TCEP removal. Based on the kinetics and isotherm studies, the adsorption of TCEP on biochar was monolayer adsorbed on a uniform surface, with SS1000 (the biochar was prepared at the carbonization temperature of 1000 °C) achieving the maximum adsorption capacity of 264.11 mg·g^-1. The prepared biochar demonstrated stable TCEP removal ability throughout a wide pH range, in the presence of co-existing anions, and in diverse water bodies. A rapid removal rate of TCEP was observed during the adsorption process. When the dosage of SS1000 was 0.2 g·L^-1, 95% of TCEP could be removed within the first 30 min. The mechanism analysis indicated that the calcium species and basic functional groups on the SS1000 surface were highly involved in the TCEP adsorption process.

A natural environmental chamber study on the emissions and fate of organophosphate esters in the indoor environment

In this study, we investigated the emission and fate of 9 organophosphate esters (OPEs) from a natural environment chamber, in which three environment matrices (i.e., air, dust, and window film samples) as well as three decoration materials (i.e., laminate flooring, latex paint, and nonwoven paper) were collected within gradient variation of room temperature and relative humidity. ΣAlkyl-OPEs and ΣCl-OPEs were the predominant classes in the three environment matrices, accounting - on average - for 98.7%, 99.8% and 99.3% of ΣOPEs in indoor dust, air and window film, respectively. TBOEP was the most abundant OPE in air, dust, and laminate flooring, respectively, while tris (2-chloro-isopropyl) phosphate (TCIPP) and tris (1,3-dichloro-2-propyl) phosphate (TDCIPP) in nonwoven paper and latex paint, respectively. The results showed that higher room temperature expedited the emission of OPEs to indoor air. However, the room temperature and relative humidity had no effect on the levels of OPEs in dust. The OPEs equilibrium time in indoor environment may be dependent on room temperature and relative humidity. The area specific emission rates (SERs) of the three materials were calculated, and an optimal expression based on the concept of mass balance model was constructed, preliminarily revealing a general relationship between OPEs source and sink effects in indoor environment.

Investigation on the Direct Transfer of SVOCs from Source to Settled Dust: Analytical Model and Key Parameter Determination

Settled dust is an important medium for semivolatile organic compound (SVOC) transport indoors. Understanding the mechanism of interaction between SVOCs and settled dust can greatly improve the exposure assessment. This study develops an analytical model to elucidate the mechanism of direct contact between SVOC sources and settled dust. The model incorporates the adsorption of SVOCs onto indoor surfaces, which was ignored in previous numerical models. Based on this model, a hybrid optimization method is applied to determine the key parameters of SVOC transport, i.e., the diffusion coefficient in the dust, the dust-air partition coefficient, and the chamber surface-air partition coefficient. Experiments of direct contact between SVOC source materials containing organophosphorus flame retardants (OPFRs) and settled dust were conducted in chambers. The key parameters were determined by performing curve fitting using data collected from the OPFR chamber tests and from the literature on phthalates. The reliability and robustness of the model and measurement method are demonstrated by the high fitting accuracy and sensitivity analysis. The obtained key parameters are more accurate than those from correlations in prior studies. Further analysis indicates that dust-air partition coefficient plays an important role and the adsorption effect on surfaces cannot be neglected for SVOC transport.

Sorption and migration of organophosphate flame retardants between sources and settled dust

Dust serves as a strong sink for indoor pollutants, such as organophosphorus flame retardants (OPFRs). OPFRs are semivolatile chemicals that are slow in emissions but have long-term effects in indoor environments. This research studied the emission, sorption, and migration of OPFRs tris(2-chloroethyl) phosphate, tris(1-chloro-2-propyl) phosphate, and tris(1,3-dichloro-2-propyl) phosphate, from different sources to settled dust on OPFR source surfaces and OPFR-free surfaces. Four sink effect tests and six dust-source migration tests, including direct contact and sorption tests were conducted in 53 L stainless steel small chambers at 23 °C and 50% relative humidity. OPFR emission concentrations, and sorption and migration rates were determined. The dust-air and dust-material partition coefficients were estimated based on the experimental data and compared with those from the literature obtained by empirical equations. They are in the range of 1.4 × 10⁷ to 2.6 × 10⁸ (dimensionless) for the dust-air equilibrium partition coefficients and 2.38 × 10^-3 to 0.8 (dimensionless) for the dust-material equilibrium partition coefficients. It was observed that the dust with less organic content and smaller size tended to absorb more OPFRs, but different dust did not significantly affect OPFRs emission from the same source to the chamber air. The dust-air partition favored the less volatile OPFRs in the house dust, whereas the emission from the source favored the volatile chemicals. Volatility of the chemicals had much less effect on dust-source partitioning than on dust-air partitioning. The results from this work improve our understating of the fate and mass transfer mechanisms between OPFRs sources, indoor air, surface, and dust.

Evaluation of a four-zone indoor exposure model for predicting TCPP concentrations in a low-energy test house

Numerous chemicals have been detected in indoor environments that have potential impacts on occupant health and comfort. However, due to limited resources, it's infeasible to assess indoor exposure of each chemical for all indoor conditions through measurements alone. Hence, indoor exposure models have been developed to predict time-varied exposure for a wide range of sources and chemicals under different conditions. The Indoor Environmental Concentrations in Buildings with Conditioned and Unconditioned Zones (IECCU) model was developed by the United States Environmental Protection Agency. This study evaluated the predictive ability of the IECCU by comparing airborne tris(1-chloro-2-propyl) phosphate (TCPP) concentrations measured from 2013 to 2018 in a test house to modeled predictions. Inputs to IECCU included building and environment (i.e., air zone configuration and geometry, interzonal airflow rates and air temperature in each zone), parameters for both source (spray polyurethane foam (SPF)) and sinks (gypsum and wallboard), and simulation conditions. Simulations were conducted using three sets of inputs. Simulation 1 and 2 differed in using quantified versus design inputs for temperatures and airflow rates. Simulation 1 and 3 differed in the configured air zones in the IECCU model. Given the best available inputs (Simulation 1), IECCU predicted basement concentrations that were generally higher but within a factor of three of the measurements. The basement prediction/measurement ratios for all three simulations ranged from 0.5 to 8.3 and the average was 2.9, while the predicted concentrations in the living zone were generally lower but still within an order of magnitude of the measurements. The prediction accuracy decreased with time. For Simulation 1, predicted basement concentrations were on average 1.4 times higher than measurements in 2013 and 2014. However, the ratio increased to 4.7 in 2018. The design inputs of Simulation 2 resulted in greater discrepancy between measurements and predictions than the measured inputs of Simulation 1. In addition, Simulation 2 did not capture diurnal variation as well as Simulation 1. Comparisons of Simulation 1 and 2 demonstrate the importance of using accurate temperature and airflow model inputs for more accurately predicting concentrations. Furthermore, a sensitivity analysis indicated that to improve the accuracy of IECCU predictions for TCPP emission from SPF, efforts are needed to accurately measure the mass transfer parameters for SPF, especially the SPF/air partition coefficient and the initial TCPP concentration in SPF.

Assessing Human Exposure to SVOCs in Materials, Products, and Articles: A Modular Mechanistic Framework

A critical review of the current state of knowledge of chemical emissions from indoor sources, partitioning among indoor compartments, and the ensuing indoor exposure leads to a proposal for a modular mechanistic framework for predicting human exposure to semivolatile organic compounds (SVOCs). Mechanistically consistent source emission categories include solid, soft, frequent contact, applied, sprayed, and high temperature sources. Environmental compartments are the gas phase, airborne particles, settled dust, indoor surfaces, and clothing. Identified research needs are the development of dynamic emission models for several of the source emission categories and of estimation strategies for critical model parameters. The modular structure of the framework facilitates subsequent inclusion of new knowledge, other chemical classes of indoor pollutants, and additional mechanistic processes relevant to human exposure indoors. The framework may serve as the foundation for developing an open-source community model to better support collaborative research and improve access for application by stakeholders. Combining exposure estimates derived using this framework with toxicity data for different end points and toxicokinetic mechanisms will accelerate chemical risk prioritization, advance effective chemical management decisions, and protect public health.

The influence of temperature on the emissions of organophosphate ester flame retardants from polyisocyanurate foam: Measurement and modeling

The material-phase diffusion coefficient (D_m) and material/air partition coefficient (K_ma) are the key parameters controlling the emissions of semivolatile organic compounds (SVOCs) from source materials. In indoor environments, air temperature is subject to change and can significantly affect the emission rates of SVOCs from building materials and consumer products. In this study, the emissions of organophosphate ester flame retardants (OPEFRs) from customized polyisocyanurate foam materials were measured in 44-mL microchambers at 23, 35, and 55 °C. The values of D_m and K_ma at different temperatures were determined. The results showed that the increase of temperature can significantly enhance the emissions of OPEFRs from the foam materials, and the emissions of OPEFRs were found to transfer from SVOC-type to volatile organic compound (VOC)-type with the increase of temperature. A correlation for OPEFRs between the steady-state emission rate and temperature and correlations between D_m, K_ma, and temperature were obtained. The research results shed light on the effect of temperature on the mechanisms governing emissions of SVOCs.

Measurements of Parameters Controlling the Emissions of Organophosphate Flame Retardants in Indoor Environments

Emission of semivolatile organic compounds (SVOCs) from source materials usually occurs very slowly in indoor environments due to their low volatility. When the SVOC emission process is controlled by external mass transfer, the gas-phase concentration in equilibrium with the material ( y₀) is used as a key parameter to simplify the source models that are based on solid-phase diffusion. A material-air-material (M-A-M) configured microchamber method was developed to rapidly measure y₀ for a polyisocyanurate rigid foam material containing organophosphate flame retardants (OPRFs). The emission test was conducted in 44 mL microchambers for target OPFRs, including tris(2-chloroethyl) phosphate (CASRN: 115-96-8), tris(1-chloro-2-propyl) phosphate (CASRN: 13674-84-5), and tris(1,3-dichloro-2-propyl) phosphate (CASRN: 13674-87-8). In addition to the microchamber emission test, two other types of tests were conducted to determine y₀ for the same foam material: OPFR diffusive tube sampling tests from the OPFR source foam using stainless-steel thermal desorption tubes and sorption tests of OPFR on an OPFR-free foam in a 53 L small chamber. Comparison of parameters obtained from the three methods suggests that the discrepancy could be caused by a combination of theoretical, experimental, and computational differences. Based on the y₀ measurements, a linear relationship between the ratio of y₀ to saturated vapor pressure concentration and material-phase mass fractions has been found for phthalates and OPFRs.