Measurement and Modeling the Phase Partitioning of Organophosphate Esters Using Their Temperature-Dependent Octanol-Air Partition Coefficients and Vapor Pressures

Gas/particle partitioning of PCDD/Fs: Distributions and implications for available models

Polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) are semi-volatile organic compounds (SVOCs) existing in the atmosphere in the gas and particulate phase, remain persistent for a long time and pose a high risk to the environment and human health. In this study, PCDD/F measurements were made in an urban area between June 2022 and April 2023. In order to understand the fate of PCDD/Fs, the gas/particle (G/P) partitioning was studied. Although various models have been developed to determine the G/P partitioning of SVOCs, only logKp-logPL0, Junge-Pankow and Harner-Bidleman models are generally used for PCDD/Fs. In this study, nine different models (Junge-Pankow, Harner-Bidleman, Dachs-Eisenreich, Li-Ma-Yang, pp-LFER, mp-pp-LFER, QSPR, logKp-logPL0, logKp-logKOA) were employed to determine the G/P partitioning. To the best of our knowledge, pp-LFER, mp-pp-LFER and QSPR models were evaluated for PCDD/Fs for the first time in this study. In addition, the performance of the models within the equilibrium (EQ), non-equilibrium (NE) and maximum partitioning (MP) domain was investigated for PCDD/Fs for the first time in this study. Accordingly, models based on absorption in the EQ domain, adsorption in the NE domain and adsorption and absorption mechanisms in the MP domain were found to be effective in explaining the G/P transitions. It was determined that there is no equilibrium situation in the G/P partitioning. The Junge-Pankow, pp-LFER, Li-Ma-Yang and QSPR models under-predicted the particle fraction values while the other models showed a high prediction profile. The Li-Ma-Yang model showed the closest results to the measured particle fraction values, and it determined that deposition mechanisms are of non-negligible importance in the G/P partitioning of PCDD/Fs. One of the new models, the pp-LFER model, has shown remarkable success at high logKOA values. The mp-pp-LFER model, which overestimated the contribution of the adsorption mechanism, showed a very high prediction profile compared to the measured values.

Organophosphate flame retardants in air from formal e-waste recycling workshops in China: Size-distribution, gas-particle partitioning and exposure assessment

In order to understand the organophosphate flame retardants (OPFRs) pollution and evaluate the inhalation exposure risk in formal e-waste recycling facilities, the air concentrations, particle size distribution and gas-particle partitioning of OPFRs in four typical workshops were investigated. The total Σ15OPFR concentrations inside workshops were in the range of 64.7-682 ng/m3, with 5.80-23.4 ng/m3 in gas phase and 58.8-658 ng/m3 in particle phase. Triphenyl phosphate (TPHP) and tris(2-chloroisopropyl) phosphate (TCIPP) were main analogs, both of which contributed to 49.0-85.7% of total OPFRs. In the waste printed circuit boards thermal treatment workshop, the OPFRs concentration was the highest, and particle-bound OPFRs mainly distributed in 0.7-1.1 μm particles. The proportions of TPHP in different size particles increased as the decrease of particle size, while TCIPP presented an opposite trend. The gas-particle partitioning of OPFR analogs was dominated by absorption process, and did not reach equilibrium state due to continuous emission of OPFRs from the recycling activities. The deposition fluxes of OPFRs in respiratory tract were 65.7-639 ng/h, and the estimated daily intake doses of OPFRs were 8.52-76.9 ng/(kg·day) in four workshops. Inhalation exposure was an important exposure pathway for e-waste recycling workers, and deposition fluxes of size-segregated OPFRs were mainly in head airways region.

Archetypes of Spatial Concentration Variability of Organic Contaminants in the Atmosphere: Implications for Identifying Sources and Mapping the Gaseous Outdoor Inhalation Exposome

Whereas inhalation exposure to organic contaminants can negatively impact human health, knowledge of their spatial variability in the ambient atmosphere remains limited. We analyzed the extracts of passive air samplers deployed at 119 unique sites in Southern Canada between 2019 and 2022 for 353 organic vapors. Hierarchical clustering of the obtained data set revealed four archetypes of spatial concentration variability in the outdoor atmosphere, which are indicative of common sources and similar atmospheric dispersion behavior. "Point Source" signatures are characterized by elevated concentration in the vicinity of major release locations. A "Population" signature applies to compounds whose air concentrations are highly correlated with population density, and is associated with emissions from consumer products. The "Water Source" signature applies to substances with elevated levels in the vicinity of water bodies from which they evaporate. Another group of compounds displays a "Uniform" signature, indicative of a lack of major sources within the study area. We illustrate how such a data set, and the derived spatial patterns, can be applied to support the identification of sources, the quantification of atmospheric emissions, the modeling of air quality, and the investigation of potential inequities in inhalation exposure.

Temperature dependence of the rain-gas and snow-gas partition coefficients for nearly a thousand chemicals

Compared to the particle-gas partition coefficients (KPG), the rain-gas (KRG) and snow-gas (KSG) partition coefficients are also essential in studying the environmental behavior and fate of chemicals in the atmosphere. While the temperature dependence for the KPG have been extensively studied, the study for KRG and KSG are still lacking. Adsorption coefficients between water surface-air (KIA) and snow surface-air (KJA), as well as partition coefficients between water-air (KWA) and octanol-air (KOA) are vital in calculating KRG and KSG. These four basic adsorption and partition coefficients are also temperature-dependent, given by the well-known two-parameters Antoine equation logKXY = AXY + BXY/T, where KXY is the adsorption or partition coefficients, AXY and BXY are Antoine parameters (XY stand for IA, JA, WA, and OA), and T is the temperature in Kelvin. In this study, the parameters AXY and BXY are calculated for 943 chemicals, and logKXY can be estimated at any ambient temperature for these chemicals using these Antoine parameters. The results are evaluated by comparing these data with published experimental and modeled data, and the results show reasonable accuracy. Based on these coefficients, temperature-dependence of logKRG and logKSG is studied. It is found that both logKRG and logKSG are linearly related to 1/T, and Antoine parameters for logKRG and logKSG are also estimated. Distributions of the 943 chemicals in the atmospheric phases (gas, particle, and rain/snow), are illustrated in a Chemical Space Map. The findings reveal that, at environmental temperatures and precipitation days, the dominant state for the majority of chemicals is the gaseous phase. All the AXY and BXY values for logKSG, logKRG, and basic adsorption and partition coefficients, both modeled by this study and collected from published work, are systematically organized into an accessible dataset for public utilization.

Occurrence and Fate of Per- and Polyfluoroalkyl Substances (PFAS) in Atmosphere: Size-Dependent Gas-Particle Partitioning, Precipitation Scavenging, and Amplification

The concerns about the fate of per- and polyfluoroalkyl substances (PFAS) in the atmosphere are continuously growing. In this study, size-fractionated particles, gas, and rainwater samples were simultaneously collected in Shijiazhuang, China, to investigate the multiphase distribution of PFAS in the atmosphere. Perfluoroalkyl carboxylic acids (PFCAs) dominated the total concentration of PFAS in atmospheric media. A strong positive relationship (0.79 < R2 < 0.99) was observed between the concentration of PFCAs and organic matter fraction (fOM) in different particle size fractions, while no such relationship for perfluoroalkyl sulfonic acids (PFSAs) and fOM, suggesting fOM may be an important factor influencing the size-dependent distribution of PFCAs. Temperature played a key role in the gas-particle partitioning of PFAS, while it did not significantly affect their particle-size-dependent distribution. The associative concentration fluctuation of particle and particle-bound PFAS during precipitation suggested that precipitation scavenging was an important mechanism for the removal of PFAS from the atmosphere. Furthermore, temporary increases in atmospheric PFAS concentrations were observed during the precipitation. Fugacity ratios of PFAS in rainwater and gas phase (log fR/fG ranged between 2.0 and 6.6) indicated a strong trend for PFAS to diffuse from the rainwater to the gas phase during the precipitation, which may explain that the concentration of PFAS in the gas phase continued to increase even at the end of the precipitation.

Relationship between flame retardants and respiratory health- A systematic review and meta-analysis of observational studies

Chronic respiratory diseases are a dealing cause of death and disability worldwide. Their prevalence is steadily increasing and the exposure to environmental contaminants, including Flame Retardants (FRs), is being considered as a possible risk factor. Despite the widespread and continuous exposure to FRs, the role of these contaminants in chronic respiratory diseases is yet not clear. This study aims to systematically review the association between the exposure to FRs and chronic respiratory diseases. Searches were performed using the Cochrane Library, MEDLINE, EMBASE, PUBMED, SCOPUS, ISI Web of Science (Science and Social Science Index), WHO Global Health Library and CINAHL EBSCO. Among the initial 353 articles found, only 9 fulfilled the inclusion criteria and were included. No statistically significant increase in the risk for chronic respiratory diseases with exposure to FRs was found and therefore there is not enough evidence to support that FRs pose a significantly higher risk for the development or worsening of respiratory diseases. However, a non-significant trend for potential hazard was found for asthma and rhinitis/rhinoconjunctivitis, particularly considering urinary organophosphate esters (OPEs) including TNBP, TPHP, TCEP and TCIPP congeners/compounds. Most studies showed a predominance of moderate risk of bias, therefore the global strength of the evidence is low. The limitations of the studies here reviewed, and the potential hazardous effects herein identified highlights the need for good quality large-scale cohort studies in which biomarkers of exposure should be quantified in biological samples.

Occurrence, distribution, potential sources, and risks of organophosphate esters in fresh snow on Urumqi Glacier No. 1, eastern Tien Shan, China

Organophosphate esters (OPEs), extensively used as flame retardants, are widely detected in various regions and environments. The potential toxicity of OPEs has caused great concern in recent years. Based on the global distillation model, the Tien Shan glaciers, such as Urumqi Glacier No. 1, could be as a potential "sink" for OPEs. However, little is known about the concentration, distribution, potential sources, and ecological risks of OPEs in Tien Shan glaciers. In this study, fresh snow samples were collected at various altitudes on the Urumqi Glacier No. 1, eastern Tien Shan, China. The total concentrations of ten OPEs (Σ10OPEs) ranged from 116 to 152 ng/L. The most abundant OPE was tris-(2-chloroisopropyl) phosphate (TCIPP), contributing to 74 % of the total OPEs. Σ10OPEs, tri-n-butyl phosphate (TnBP), and TCIPP concentrations showed positive correlations with altitude, indicating the effect of cold condensation on OPEs deposition. Based on air mass back-trajectory analysis and principal component analysis, we found that emissions from both traffic and household products in indoor environment were the important sources, and OPEs on the Urumqi Glacier No. 1 might mainly originate from Europe. Our assessment also showed triphenyl phosphate (TPhP) posed a low ecological risk in snow. This is the first systematic study of OPEs on the Tien Shan glaciers.

Gas-particle partitioning of organophosphate esters in indoor and outdoor air and its implications for individual exposure

The extensive utilization of organophosphate esters (OPEs) has resulted in their widespread presence in the environment, raising concerns about potential human health risks. In this study, 13 OPEs were analyzed in both gas and particle phases as well as in indoor and outdoor atmospheric environments. Moreover, human exposure to OPEs were investigated within a university environment, focusing on forehead contact and individual PM2.5 inhalation. The results showed similar distribution patterns of OPEs indoors and outdoors, although higher concentrations were found indoors. The average atmospheric concentration of ∑OPEs (combining particle and gaseous OPEs) was 1575 pg/m3 in the outdoor environment and 6574 pg/m3 ∑OPEs in the indoor microenvironments. The overwhelming majority of OPEs exhibit a pronounced propensity to adsorb onto PM2.5 particles. Notably, the concentration of OPEs on the forehead differed significantly from that in the atmospheric environment, whereas individual PM2.5 exposure was consistent with the concentration of indoor PM2.5. Intriguingly, some OPEs with high octanol-water partition coefficient (log Kow) were not detected in the environment but found on human foreheads. Gas-particle partitioning was predicted using the Harner-Bidleman and Li-Ma-Yang models and the results were in agreement with the monitoring data for approximately half of the OPE monomers. Correlations between OPEs exposure and gas-particle partitioning were found to be more significant for novel OPEs. No non-cancer risk to humans through individual exposure to OPEs was identified via forehead exposure or inhalation. The previously unreported relationship between individual exposure and the environmental occurrence of traditional and novel OPEs demonstrated in this study highlights the importance of evaluating the potential health risks associated with actual OPE exposure.

Molecular Dynamics Simulation Prediction of the Partitioning Constants (KH, Kiw, Kia) of 82 Legacy and Emerging Organic Contaminants at the Water-Air Interface

The tendency of organic contaminants (OCs) to partition between different phases is a key set of properties that underlie their human and ecological health impacts and the success of remediation efforts. A significant challenge associated with these efforts is the need for accurate partitioning data for an ever-expanding list of OCs and breakdown products. All-atom molecular dynamics (MD) simulations have the potential to help generate these data, but existing studies have applied these techniques only to a limited variety of OCs. Here, we use established MD simulation approaches to examine the partitioning of 82 OCs, including many compounds of critical concern, at the water-air interface. Our predictions of the Henry's law constant (K_H) and interfacial adsorption coefficients (K_iw, K_ia) correlate strongly with experimental results, indicating that MD simulations can be used to predict K_H, K_iw, and K_ia values with mean absolute deviations of 1.1, 0.3, and 0.3 logarithmic units after correcting for systematic bias, respectively. A library of MD simulation input files for the examined OCs is provided to facilitate future investigations of the partitioning of these compounds in the presence of other phases.

Pollution profiles, influencing factors, and source apportionment of target and suspect organophosphate esters in ambient air: A case study in a typical city of Northern China

Organophosphate esters (OPEs) are attracting attention because they pose risks to biota, including humans. Little research has been performed into the environmental fates of OPEs in the atmosphere. Here, target/suspect OPEs were determined in 122 atmosphere samples (gas phase (n = 31), PM_2.5 (n = 30), PM₁₀ (n = 30), and total suspended particles (n = 31)) from a city in Northern China. Pollution profiles were established, influencing factors identified, and sources apportioned. We found 12 target OPEs and 29 suspect OPEs. The target and suspect OPE concentrations in the ambient air samples were 2.2-172.5 and 0.7-53.9 ng/m³, respectively. Tris(chloroethyl) phosphate, tris(1-chloro-2-propyl) phosphate, and tris(2,4-di-t-butylphenyl) phosphate were the dominant OPEs in all samples. The OPEs were not in equilibrium, indicated by a multi-parameter linear free energy relationship model. The air quality index and OPE concentrations significantly correlated, indicating that OPE pollution is often more serious during weather with worse air quality. The target and suspect screening strategy and a positive matrix factorization model allowed OPE sources to be apportioned, improving our understanding of OPE sources. The four dominant sources were (1) construction, (2) indoor emissions, (3) the plastic industry and industrial activities, and (4) traffic emissions, textiles, and foam products.

Novel quantitative structure activity relationship models for predicting hexadecane/air partition coefficients of organic compounds

Predicting the logarithm of hexadecane/air partition coefficient (L) for organic compounds is crucial for understanding the environmental behavior and fate of organic compounds and developing prediction models with polyparameter linear free energy relationships. Herein, two quantitative structure activity relationship (QSAR) models were developed with 1272 L values for the organic compounds by using multiple linear regression (MLR) and support vector machine (SVM) algorithms. On the basis of the OECD principles, the goodness of fit, robustness and predictive ability for the developed models were evaluated. The SVM model was first developed, and the predictive capability for the SVM model is slightly better than that for the MLR model. The applicability domain (AD) of these two models has been extended to include more kinds of emerging pollutants, i.e., oraganosilicon compounds. The developed QSAR models can be used for predicting L values of various organic compounds. The van der Waals interactions between the organic compound and the hexadecane have a significant effect on the L value of the compound. These in silico models developed in current study can provide an alternative to experimental method for high-throughput obtaining L values of organic compounds.

Insights into the Atmospheric Persistence, Transformation, and Health Implications of Organophosphate Esters in Urban Ambient Air

Transformation of organophosphate esters (OPEs) in natural ambient air and potential health risks from coexposure to OPEs and their transformation products are largely unclear. Therefore, a novel framework combining field-based investigation, in silico prediction, and target and suspect screening was employed to understand atmospheric persistence and health impacts of OPEs. Alkyl-OPE transformation products ubiquitously occurred in urban ambient air. The transformation ratios of tris(2-butoxyethyl) phosphate were size-dependent, implying that transformation processes may be affected by particle size. Transformation products of chlorinated- and aryl-OPEs were not detected in atmospheric particles, and atmospheric dry deposition might significantly contribute to their removal. Although inhalation risk of coexposure to OPEs and transformation products in urban ambient air was low, health risks related to OPEs may be underestimated as constrained by the identification of plausible transformation products and their toxicity testing in vitro or in vivo at current stage. The present study highlights the significant impact of particle size on the atmospheric persistence of OPEs and suggests that health risk assessments should be conducted with concurrent consideration of both parental compounds and transformation products of OPEs, in view of the nonnegligible abundances of transformation products in the air and their potential toxicity in silico.

Atmospheric Autoxidation of Organophosphate Esters

Organophosphate esters (OPEs), widely used as flame retardants and plasticizers, have frequently been identified in the atmosphere. However, their atmospheric fate and toxicity associated with atmospheric transformations are unclear. Here, we performed quantum chemical calculations and computational toxicology to investigate the reaction mechanism of peroxy radicals of OPEs (OPEs-RO₂^•), key intermediates in determining the atmospheric chemistry of OPEs, and the toxicity of the reaction products. TMP-RO₂^• (R₁) and TCPP-RO₂^• (R₂) derived from trimethyl phosphate and tris(2-chloroisopropyl) phosphate, respectively, are selected as model systems. The results indicate that R₁ and R₂ can follow an H-shift-driven autoxidation mechanism under low NO concentration ([NO]) conditions, clarifying that RO₂^• from esters can follow an autoxidation mechanism. The unexpected autoxidation mechanism can be attributed to the distinct role of the ─(O)₃P(═O) phosphate-ester group in facilitating the H-shift of OPEs-RO₂^• from commonly encountered ─OC(═O)─ and ─ONO₂ ester groups in the atmosphere. Under high [NO] conditions, NO can mediate the autoxidation mechanism to form organonitrates and alkoxy radical-related products. The products from the autoxidation mechanism have low volatility and aquatic toxicity compared to their corresponding parent compounds. The proposed autoxidation mechanism advances our current understanding of the atmospheric RO₂^• chemistry and the environmental risk of OPEs.

Polycyclic Aromatic Hydrocarbons in the Marine Atmosphere from the Western Pacific to the Southern Ocean: Spatial Variability, Gas/Particle Partitioning, and Source Apportionment

The spatial variability of polycyclic aromatic hydrocarbons (PAHs) in the marine atmosphere contributes to the understanding of the global sources, fate, and impact of this contaminant. Few studies conducted to measure PAHs in the oceanic atmosphere have covered a large scale, especially in the Southern Ocean. In this study, high-volume air samples were taken along a cross-section from China to Antarctica and analyzed for gaseous and particulate PAHs. The data revealed the spatial distribution, gas-particle partitioning, and source contributions of PAHs in the Pacific, Indian, and Southern Oceans. The median concentration (gaseous + particulate) of ∑₂₄PAHs was 3900 pg/m³ in the Pacific Ocean, 2000 pg/m³ in the Indian Ocean, and 1200 pg/m³ in the Southern Ocean. A clear latitudinal gradient was observed for airborne PAHs from the western Pacific to the Southern Ocean. Back trajectories (BTs) analysis showed that air masses predominantly originated from populated land had significantly higher concentrations of PAHs than those from the oceans or Antarctic continents/islands. The air mass origins and temperature have significant influences on the gas-particle partitioning of PAHs. Source analysis by positive matrix factorization (PMF) showed that the highest contribution to PAHs was from coal combustion emissions (52%), followed by engine combustion emissions (27%) and wood combustion emissions (21%). A higher contribution of PAHs from wood combustion was found in the eastern coastal region of Australia. In contrast, engine combustion emissions primarily influenced the sites in Southeast Asia.

Temperature and indoor environments

From the thermodynamic perspective, the term temperature is clearly defined for ideal physical systems: A unique temperature can be assigned to each black body via its radiation spectrum, and the temperature of an ideal gas is given by the velocity distribution of the molecules. While the indoor environment is not an ideal system, fundamental physical and chemical processes, such as diffusion, partitioning equilibria, and chemical reactions, are predictably temperature-dependent. For example, the logarithm of reaction rate and equilibria constants are proportional to the reciprocal of the absolute temperature. It is therefore possible to have non-linear, very steep changes in chemical phenomena over a relatively small temperature range. On the contrary, transport processes are more influenced by spatial temperature, momentum, and pressure gradients as well as by the density, porosity, and composition of indoor materials. Consequently, emergent phenomena, such as emission rates or dynamic air concentrations, can be the result of complex temperature-dependent relationships that require a more empirical approach. Indoor environmental conditions are further influenced by the thermal comfort needs of occupants. Not only do occupants have to create thermal conditions that serve to maintain their core body temperature, which is usually accomplished by wearing appropriate clothing, but also the surroundings must be adapted so that they feel comfortable. This includes the interaction of the living space with the ambient environment, which can vary greatly by region and season. Design of houses, apartments, commercial buildings, and schools is generally utility and comfort driven, requiring an appropriate energy balance, sometimes considering ventilation but rarely including the impact of temperature on indoor contaminant levels. In our article, we start with a review of fundamental thermodynamic variables and discuss their influence on typical indoor processes. Then, we describe the heat balance of people in their thermal environment. An extensive literature study is devoted to the thermal conditions in buildings, the temperature-dependent release of indoor pollutants from materials and their distribution in the various interior compartments as well as aspects of indoor chemistry. Finally, we assess the need to consider temperature holistically with regard to the changes to be expected as a result of global emergencies such as climate change.

Gas-particle partition and size-segregated distribution of flame retardants in indoor and outdoor air: Reevaluation on the role of fine particles in human exposure

In this study, we investigated the distribution of brominated and organophosphate flame retardants (BFRs and OPFRs) in the paired gaseous and nine size-segregated particulate samples collected from 8 typical indoor compartments and monthly outdoor in Xinxiang, China, respectively. For the indoor environments, total concentrations of FRs (Σ₁₉FRs) in bulk air ranged from 3.9 ng/m³ to 37.5 ng/m³, with that in children recreation center (37.5 ng/m³) and furniture store (28.7 ng/m³) showing highest levels. In the outdoor air, Σ₁₉FRs ranged from 3.1 ng/m³ to 13.6 ng/m³ among the 12 months, with that from late spring and summer being the highest. OPFRs had higher concentration than BFRs, with the total concentration of OPFRs accounting for 77%-99% of ∑₁₉FRs. TCIPP (tris(chloroiso-propyl) phosphate), TCEP (tris(2-chloroethyl) phosphate), TEP (triethyl phosphate) and DBDPE (decabromodiphenyl ethane), BDE-209 (decabromodiphenyl ether) were the predominant analogs. Specifically, BFRs tended to enrich in gas phase indoors and coarse particles (aerodynamic diameters >3.3 μm) outdoors, but OPFRs mainly distributed in coarse particles both indoors and outdoors. The size distribution patterns varied among FRs, with the higher volatile FRs (e.g., TCEP, TCIPP) distributed more uniformly across particulate size. Although the distribution patterns of FRs in air were driven by multiple factors, organic carbon and element carbon in particulate matter had an influence to a certain extent. Health risks from exposure to FRs were characterized via the hazard quotient approaches. The total noncarcinogenic risks of ∑₁₆FRs from inhalation were higher than that from air to skin transport, and the risks resulted from coarse particle-bound ∑₁₆FRs (>3.3 μm) and gas phase were both significantly higher than that from fine fraction (<3.3 μm) in all scenarios, implying that FRs in coarse particles should not be underestimated.

Effects of temperature and relative humidity on soil-air partition coefficients of organophosphate flame retardants and polybrominated diphenyl ethers

The soil-air partition coefficients (K_SA) of polybrominated diphenyl ethers (PBDEs) and organophosphate flame retardants (OPFRs) is important for determining their fate in soil and air media. However, K_SA values of OPFRs and PBDEs are not available from the current literature, and the effects of environmental factors such as temperature and relative humidity (RH) on K_SA values are not clear. In this study, a solid-phase fugacity meter was used to measure the K_SA values of PBDEs and OPFRs at different temperatures (25, 30, 35, 40, and 45 °C) and relative humidity (RH) conditions (<3 and 100% RH), the relationships between K_SA and octanol-air partition coefficients (K_OA) for OPFRs and PBDEs were analyzed. The results showed that an increase in temperature and RH resulted in a decrease of all K_SA values for PBDEs and OPFRs. Furthermore, the effects of RH on the soil-air partitioning behavior of PBDEs were larger than that of OPFRs. In addition, a significant correlation (p < 0.0001) was observed between log K_SA and log K_OA. The experimental K_SA values of OPFRs and PBDEs were quite different from the predicted K_SA, when calculated with their K_OA values. Overall, this study provides a better understanding for predicting the behavior and fate of OPFRs and PBDEs in soil-air systems.

Seasonal variation and deposition of atmospheric organophosphate esters in the coastal region of Shanghai, China

The coastal megacity Shanghai is located in the center of the Yangtze River Delta, a dominant flame retardants (FRs) production region in China, especially for organophosphate esters (OPEs). This prompted us to investigate occurrence and seasonal changes of atmospheric OPEs in Shanghai, as well as to evaluate their sources, environmental behavior and fate as a case study for global coastal regions. Atmospheric gas and particle phase OPEs were weekly collected at two coastal sites - the emerging town Lingang New Area (LGNA), and the chemical-industry zone Jinshan Area (JSA) from July 2016-June 2017. Total atmospheric concentrations of the observed OPEs were significantly higher in JSA (median of 1800 pg m^-3) than LGNA (median of 580 pg m^-3). Tris(1-chloro-2-propyl) phosphate (TCPP) was the most abundant compound, and the proportion of three chlorinated OPEs were higher in the particle phase (55%) than in the gas phase (39%). The year-round median contribution of particle phase OPEs was 33%, which changed strongly with seasons, accounting for 10% in summer in contrast to 62% in winter. Gas and particle phase OPEs in JSA exhibited significant correlations with inverse of temperature, respectively, indicating the importance of local/secondary volatilization sources. The estimated fluxes of gaseous absorption were almost 2 orders of magnitude higher than those of particle phase deposition, which could act as sources of organic phosphorus to coastal and open ocean waters.

Atmospheric deposition, seasonal variation, and long-range transport of organophosphate esters on Yongxing Island, South China Sea

The South China Sea (SCS), surrounded by developing countries/regions with a huge consumption of flame retardants, is generally contaminated by organophosphate esters (OPEs). However, studies on the occurrence, deposition and long-range atmospheric transport (LRAT) process over the SCS of OPEs compounds are still limited. In this work, 10 OPEs were measured in 100 atmospheric samples collected from Yongxing Island (YXI) in the SCS. The total OPEs concentrations ranged from 1508 to 1968 pg/m³ with 28.6-1416.9 pg/m³ in gas and 95.2-1066.2 pg/m³ in particle partition. The three chlorinated OPEs are present at higher concentrations than the other seven non-chlorinated OPEs. Most OPEs had clear seasonal variations that followed the order: spring>summer≈winter>autumn except for tri-isobutyl phosphate (TIBP) and tris-(2-ethylhexyl) phosphate (TEHP). The particle-bound fraction of the total OPEs had little seasonal variations with a mean value of 0.35. Comparing J-P model and Koa model, it was found that the gas/particle partition in the study area was in non-equilibrium condition. LRAT, controlled by seasonal wind direction, was the predominated factor that led to the seasonal variations of OPEs on YXI. The average daily deposition flux of total OPEs was 13.0 ng/m² with an annual total deposition of 15.06 g.

Quantum Chemical Calculation and Evaluation of Partition Coefficients for Classical and Emerging Environmentally Relevant Organic Compounds

Octanol/water (K_OW), octanol/air (K_OA), and hexadecane/air (K_HdA) partition coefficients are calculated for 67 organic compounds of environmental concern using computational chemistry. The extended CRENSO workflow applied here includes the calculation of extensive conformer ensembles with semiempirical methods and refinement through density functional theory, taking into account solvation models, especially COSMO-RS, and thermostatistical contributions. This approach is particularly advantageous for describing large and nonrigid molecules. With regard to K_OW and K_HdA, one can refer to many experimental data from direct and indirect measurement methods, and very good matches with results from our quantum chemical workflow are evident. In the case of the K_OA values, however, good matches are only obtained for the experimentally determined values. Larger systematic deviations between data computed here and available, nonexperimental quantitative structure-activity relationship literature data occur in particular for phthalic acid esters and organophosphate esters. From a critical analysis of the coefficients calculated in this work and comparison with available literature data, we conclude that the presented quantum chemical composite approach is the most powerful so far for calculating reliable partition coefficients because all physical contributions to the conformational free energy are considered and the structure ensembles for the two phases are generated independently and consistently.

Organophosphate esters in atmospheric particles and surface seawater in the western South China Sea

Seven organophosphate esters (OPEs) in atmospheric particles and surface seawater were observed during a cruise in the western South China Sea (SCS) in 2014. The median concentrations of ∑OPEs were 688 pg/m³ and 5.55 ng/L for particle and seawater samples, respectively. Total OPEs were dominated by tris(1-chloro-2-propyl) phosphate (TCPP) and tris(2-chloroethyl) phosphate (TCEP). The spatial distribution of OPEs indicates that the OPEs in particle phase were mainly influenced by the air masses originating from China, Indochina Peninsula and Malay Archipelago, showing the significant contribution of anthropogenic sources from these regions. Significant positive correlations between Tri-n-butylphosphate (TnBP) and organic carbon (P < 0.05) in particle phase over the western SCS suggests that it might be a potential tracer for the source regions of Indochina Peninsula and Malay Archipelago. The spatial distribution of OPEs in seawater was contributed by freshwater inputs associating with variations of human activities as well as salinity. Seawater pollution levels of OPEs in the eastern coast of Vietnam were increased compared to those measured in the northern SCS. The loadings of ∑OPEs transported to the vast area of western SCS vias atmospheric deposition and air-seawater gas exchange were estimated to be 59 tons/year and 105 tons/year, respectively. This work highlights the importance of transport processes and air-seawater interface behavior of OPEs in the oceanic area.

Probing Legacy and Alternative Flame Retardants in the Air of Chinese Cities

An increasing number of alternative flame retardants (FRs) are being introduced, following the international bans on the use of polybrominated diphenyl ether (PBDE) commercial mixtures. FRs' production capacity has shifted from developed countries to developing countries, with China being the world's largest producer and consumer of FRs. These chemicals are also imported with e-waste to China. Therefore, it is important to understand the current status of regulated brominated FRs, their phase-out in China, and their replacement by alternatives. In this study, a broad suite of legacy and alternative FRs, including eight PBDEs, six novel brominated FRs (NBFRs), two dechlorane plus variants (DP_S), and 12 organophosphate FRs (OPFRs) were evaluated in the air of 10 large Chinese cities in 2018. OPFRs are the most prevalent FRs in China, exhibiting a wide range of 1-612 ng/m³, which is several orders of magnitude higher than PBDEs (1-1827 pg/m³) and NBFRs (1-1428 pg/m³). BDE 209 and DBDPE are the most abundant compounds in brominated FRs (>80%). The North China Plain (NCP, excluding Beijing), Guangzhou, and Lanzhou appear to be three hotspots, although with different FR patterns. From 2013/2014 to 2018, levels of PBDEs, NBFRs, and DPs have significantly decreased, while that of OPFRs has increased by 1 order of magnitude. Gas-particle partitioning analysis showed that FRs could have not reached equilibrium, and the steady-state model is better suited for FRs with a higher log K_OA (>13). To facilitate a more accurate FR assessment in fine particles, we suggest that, in addition to the conventional volumetric concentration (pg/m³), the mass-normalized concentration (pg/g PM_2.5) could also be used.