Legacy and emerging flame retardants (FRs) in the urban atmosphere of Pakistan: Diurnal variations, gas-particle partitioning and human health exposure

Cellular and physiological mechanisms of halogenated and organophosphorus flame retardant toxicity

Flame retardants (FRs) are chemical substances used to inhibit the spread of fire in numerous industrial applications, and their abundance in modern manufactured products in the indoor and outdoor environment leads to extensive direct and food chain exposure of humans. Although once considered relatively non-toxic, FRs are demonstrated by recent literature to have disruptive effects on many biological processes, including signaling pathways, genome stability, reproduction, and immune system function. This review provides a summary of research investigating the impact of major groups of FRs, including halogenated and organophosphorus FRs, on animals and humans in vitro and/or in vivo. We put in focus those studies that explained or referenced the modes of FR action at the level of cells, tissues and organs. Since FRs are highly hydrophobic chemicals, their biophysical and biochemical modes of action usually involve lipophilic interactions, e.g. with biological membranes or elements of signaling pathways. We present selected toxicological information about these molecular actions to show how they can lead to damaging membrane integrity, damaging DNA and compromising its repair, changing gene expression, and cell cycle as well as accelerating cell death. Moreover, we indicate how this translates to deleterious bioactivity of FRs at the physiological level, with disruption of hormonal action, dysregulation of metabolism, adverse effects on male and female reproduction as well as alteration of normal pattern of immunity. Concentrating on these subjects, we make clear both the advances in knowledge in recent years and the remaining gaps in our understanding, especially at the mechanistic level.

Evaluation of the oral bioaccessibility of legacy and emerging brominated flame retardants in indoor dust

Indoor dust is the main source of human exposure to brominated flame retardants (BFRs). In this study, in vitro colon-extended physiologically-based extraction test (CE-PBET) with Tenax as a sorptive sink was applied to evaluate the oral bioaccessibility of twenty-two polybrominated diphenyl ethers (PBDEs) and seven novel BFRs (NBFRs) via indoor dust ingestion. The mean bioaccessibilities of two NBFRs pentabromotoluene (PBT) and 1,2-Bis(2,4,6-tribromophenoxy) ethane (BTBPE) were first proposed, reaching 36.0% and 26.7%, respectively. In order to maintain homeostasis of the gastrointestinal tract, 0.4 g Tenax was added in CE-PEBT, which increased BFRs bioaccessibility by up to a factor of 1.4-1.9. The highest bioaccessibility of legacy PBDEs was tri-BDEs (73.3%), while 2-ethylhexyl-tetrabromo-benzoate (EHTBB), one of penta-BDE alternatives, showed the highest (62.2%) among NBFRs. The influence of food nutrients, liquid to solid (L/S) ratio, and octanol-water partition coefficient (Kow) on bioaccessibility was assessed. The oral bioaccessibility of BFRs increased with existence of protein or carbohydrate while lipid did the opposite. The bioaccessibilities of PBDEs and NBFRs were relatively higher with 200:1 L/S ratio. PBDEs bioaccessibility generally decreased with increasing LogKow. No significant correlation was observed between NBFRs bioaccessibility and LogKow. This study comprehensively evaluated the bioaccessibilities of legacy and emerging BFRs via dust ingestion using Tenax-assisted CE-PBET, and highlighted the significance to fully consider potential influencing factors on BFRs bioaccessibility in further human exposure estimation.

Emission and gas-particle partitioning characteristics of atmospheric halogenated and organophosphorus flame retardants in decabromodiphenyl ethane-manufacturing functional areas

The emission and gas-particle partitioning characteristics in various functional areas of production lines are still unknown. However, flame-retardant manufacturing activities are the primary emission source of flame retardants. Thus, fine particles and gases were investigated in three functional areas of a decabromodiphenyl ethane production line, i.e., polybrominated diphenyl ethers (PBDEs), novel brominated flame retardants (NBFRs), dechlorane plus (DPs), and organophosphorus flame retardants (OPFRs) in a flame-retardant manufacturing factory. High levels of PBDEs (8.02 × 10³-4.16 × 10⁴ pg/m³), NBFRs (6.05 × 10³-1.92 × 10⁵ pg/m³), and DPs (89.5-5.20 × 10³ pg/m³) were found in various functional areas, suggesting manufacturing activities were a primary emission source. In contrast, OPFRs were derived from long-range transport or other non-industrial sources. Varied concentrations of PBDEs, NBFRs, and DPs were observed in different production lines, higher in the reaction zone area than others. As the predominant compounds, decabromodiphenyl ether, decabromodiphenyl ethane, syn-DP, and tris(chloropropyl) phosphate accounted for 54.7%, 89.3%, 93.4%, and 34.7% of PBDEs, NBFRs, DPs, and OPFRs, respectively. Three models were used to predict the gas-particle partitioning of the halogenated flame retardants emitted from manufacturing activities. The Li-Jia Empirical Model predicted the gas-particle partitioning behavior well. This research shows that the adsorption-desorption process of the halogenated flame retardants between the gaseous and particulate phases did not reach equilibrium.

Partitioning behavior-oriented health risk assessment on internal organophosphorus flame retardants exposure

Though the partitioning behavior of organophosphorus flame retardants (OPFRs) has been recognized in vitro incubation assay, health risk assessment on those internal exposure with or without partitioning indexes in human blood is still unclear. In this study, nine commonly used OPFRs were quantified in 96 pairs of plasma and blood cell samples from Chinese volunteers. Non-carcinogenic and carcinogenic risk (CR) assessment building upon two distinct scenarios were conducted and compared. The dominant OPFRs in both plasma and blood cells were TBEP, TBP and TPHP. TCEP was the most enriched compound in plasma with F_plasma nearly to 1.0 (0.92), followed by TCPP, TBEP, TPHP, TBP and TEHP (from 0.61 to 0.76). The partitioning behavior of TCP in plasma was equivalent to blood cells with F_plasma at 0.50. When fully considered the F_plasma, the estimated average daily intake (DI) of ∑OPFRs (638.44 ng/kg BW/day) reached nearly 1.48-fold higher than the conventional calculation (dividing the concentration of plasma (C_plasma) by a factor of 2.0). Accordingly, we found the average hazard quotation (index) of TBP, TPHP and ∑OPFRs was underrated 1.50-fold when neglected the partitioning behaviors. Notably, the average CR of TCEP exceeded 10^-6 at the highest concentration (1.19 × 10^-6 ng/mL in plasma) only when the F_plasma was introduced. These data conjointly demonstrated that most of the DI levels and the corresponding risk index of OPFRs would be underestimated without factoring F_plasma into calculation, especially for those of low plasma partitioning. To our best knowledge, this study initially uncovered the gap between introducing F_plasma and dividing C_plasma by 2.0 during health risk assessment on internal OPFRs exposure.

The coupling between biological pump export and air-water exchange of organophosphate esters in a subtropical water environment

Organophosphate esters (OPEs) are well-known persistent organic pollutants with their ubiquitous environmental presence and adverse ecological and human health impacts. To study the transport and fate of OPEs in a subtropical environment, nine OPE compounds were analyzed in the gas phase (air samples), dissolved phase (water samples), and plankton samples collected over one year from or in the vicinity of an urban lake in Guangzhou, South China. The mean concentrations of ∑₉OPEs were 2.93 ± 1.68 ng/m³ in the air, 455 ± 236 ng/L in the dissolved phase, 81.3 ± 41.2 ng/L in phytoplankton, and 4.79 ± 1.94 ng/L in zooplankton. Although the compositional profiles of OPEs varied among different media, tris (1-chloro-2-propyl) phosphate (TCPP) was the predominant OPE in most samples. Less hydrophobic OPEs such as TCPP and tris (2-chloroethyl) phosphate (TCEP) had lower bioaccumulation potential in the lake. The biological pump export played an important role in eliminating OPEs from the surface water, with fluxes ranging from 30.5 to 361 ng/m²/d. The more phytoplankton biomass in surface water, the greater the role of the biological pump. The fugacity fractions and air-water exchange fluxes suggested that TCPP and tris (1,3-dichloro-2-propyl) phosphate (TDCP) would enter the urban lake by gaseous deposition. Nevertheless, the lake acted as an important "secondary source" for TCEP and triphenyl phosphate (TPhP). The bio-pump might influence the air-water exchange processes of OPEs.

Distribution of flame retardants among indoor dust, airborne particles and vapour phase from Beijing: spatial-temporal variation and human exposure characteristics

The occurrence and distribution of 10 brominated flame retardants (BFRs) and 10 organophosphate flame retardants (OPFRs) were investigated in indoor dust, total suspended particles (TSP), and vapour phase from offices (n = 10), homes (n = 9), and day-care centres (n = 10) in Beijing, China. Three types of samples were collected biweekly from one office and one home over a year to examine temporal trends. BFRs in dust significantly correlated with those in TSP, while OPFRs significantly correlated among all three matrices. In addition, BFRs in dust (ng/g) and TSP (pg/m³) exhibited similar temporal trends with higher levels in the cold season, whereas OPFRs in TSP and vapour phase (pg/m³) showed similar temporal trends with higher levels in the warm season. The geometric mean concentrations of BFRs and OPFRs in the three matrices from the above mentioned three types of indoor microenvironments were used for exposure and health risk estimation, and ∑₇OPFRs showed much higher hazard index (HI) values than ∑₁₀BFRs for all subpopulations, and inhalation of OPFRs was a major risk source. With the volatility of flame retardants (FRs) decreasing, the contribution of dust ingestion and dermal absorption showed an increasing trend, and the contribution of inhalation exhibited a gradual decreasing trend, which implied the dominant exposure pathway to FRs is strongly related to the vapour pressure (25 °C, Pa) of these substances. Using a single type of microenvironment or the collection of samples at a single point in time can lead to overestimation or underestimation of overall exposure and risk for people to some extent. The correlations of FRs in dust, TSP, and vapour phase from indoor microenvironments, as well as their temporal trends were first reported in this study, which will provide a basis for more accurate FR exposure assessments in the future.

Comprehensive analysis of emerging flame retardants, a risk factor to prostate cancer?

Among man-made chemicals, flame retardants have caused great environmental concerns. Several studies in recent years have investigated potential sources of flame retardants, environmental distribution, exposure to wild animals and humans and toxicity. However, studies focusing on the prediction of toxicity of flame retardants are limited. Herein, toxicological and tumor databases were applied to evaluate the potential correlation between emerging flame retardants (EFRs) and tumors. Further analysis also showed that EFRs may be associated with prostate cancer (PCa). After constructing an EFR-related prognostic prediction model, it was established that EFR-related genes showed a strong prognostic predictive value among PCa patients. In addition, compared with the clinical characteristics model (including age, Gleason score, prostate-specific antigen level, T stage and N stage), a prognostic predictive model-based risk score demonstrated a better predictive value of PCa. The AUC of the 31-gene prognostic signature at 1, 3 and 5 years was 0.843, 0.824 and 0.819, respectively. In addition, the AUC of the risk score, Gleason score, age, PSA level, T stage and N stage were 0.843, 0.637, 0.414, 0.490, 0.668 and 0.517, respectively. Our analysis provides a comprehensive map of EFR interaction genes and demonstrated a new direction for environmentally hazardous materials and diseases.

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.

Pollution profiles and human health risk assessment of atmospheric organophosphorus esters in an e-waste dismantling park and its surrounding area

Recycling e-waste has been recognized as an important emission source of organophosphate triesters (tri-OPEs) and organophosphate diesters (di-OPEs), but the presence of di-OPEs in atmosphere has not been studied. Herein, tri-OPEs and di-OPEs in atmosphere of an e-waste dismantling park and surrounding area in South China were monitored for three consecutive years. Thirteen tri-OPEs and seven di-OPEs were identified. In 2017, 2018, and 2019, tri-OPE concentrations in e-waste dismantling park were 1.30 × 10⁸, 4.60 × 10⁶, and 4.01 × 10⁷ pg/m³, while di-OPE concentrations were 1.14 × 10³, 1.10 × 10³, and 0.35 × 10³ pg/m³, respectively, which were much higher than the surrounding area. Tri-OPEs and di-OPEs generated during e-waste dismantling affected surrounding area through diffusion. Triphenyl phosphate (TPhP) and diphenyl phosphate (DPhP) were the predominant congeners of tri-OPEs and di-OPEs, respectively. Additionally, TPhP concentration was extremely higher than other tri-OPEs, so TPhP could be used as an indicator of e-waste dismantling. Spearman correlation analysis showed significant correlations between DPhP and TPhP (R² = 0.53, p < 0.01), bis-(1-chloro-2-propyl) phosphate (BCIPP) and tris(2-chloropropyl) phosphate (TCIPP) (R² = 0.49, p < 0.01), as well as dibutyl phosphate (DBP) and tributyl phosphate (TBP) (R² = 0.53, p < 0.01), indicating that they had the same source. Further, non-carcinogenic risk of them to people via inhalation was acceptable and non-carcinogenic risk of tri-OPEs decreased year by year in surrounding area.

Occurrence, potential sources and risks of organophosphate esters in the high-elevation region, Tibet, China

Organophosphate esters (OPEs) are widely used flame retardants that are frequently released into the environment, causing potential harm to humans and ecosystems. Tibet is located on the Tibetan Plateau, known as the "roof of the world", but the occurrence of OPEs in Tibet remains unclear. This is the first report of the occurrence, potential sources and risks of 12 OPEs in water, soil, sediment and snow from Xainza, a typical town at high-elevation in Tibet (average elevation = 4700 m). Ten OPEs were observed, with ∑OPE concentrations of 46.45-1744.73 ng/L in surface water, 29.74-73.85 ng/g in soil, and 13.30-32.23 ng/g in sediment. Moreover, the mean ∑OPE concentration in snow was 413.90 ng/L. Tris (2-chloroethyl) phosphate (TCEP) and tris (2-chloroisopropyl) phosphate (TCPP) were the main OPEs in surface water and snow, while 2-ethylhexyl diphenyl phosphate (EHDPP) was dominant in soil and sediment. Local human activities and long-distance atmospheric transport may be the main sources of OPEs in Xainza. The assessment of ecological risk indicated that EHDPP in soil poses potential risk. The occurrence of OPEs in Xainza showed that more attention should be paid to persistent organic pollutants in high-elevation regions.

Approach to Predicting the Size-Dependent Inhalation Intake of Particulate Novel Brominated Flame Retardants

The risk of human exposure to particulate novel brominated flame retardants (NBFRs) in the atmosphere has received increasing attention from scientists and the public, but currently, there is no reliable approach to predict the intake of these compounds on the basis of their size distribution. Here, we develop a reliable approach to predict the size-dependent inhalation intake of particulate NBFRs, based on the gas/particle (G/P) partitioning behavior of the NBFRs. We analyzed the concentrations of eight NBFRs in 363 size-segregated particulate samples and 99 paired samples of gaseous and bulk particles. Using these data, we developed an equation to predict the G/P partitioning quotients of NBFRs in particles in different size ranges (K_Pi) based on particle size. This equation was then successfully applied to predict the size-dependent inhalation intake of particulate NBFRs in combination with an inhalation exposure model. This new approach provides the first demonstration of the effects of the temperature-dependent octanol-air partitioning coefficient (K_OA) and total suspended particle concentration (TSP) on the intake of particulate NBFRs by inhalation. In an illustrative case where TSP = 100 μg m^-3, inhalation intake of particulate NBFRs exceeded the intake of gaseous NBFRs when log K_OA > 11.4.

Size distribution and inhalation exposure of airborne particle-bound polybrominated diphenyl ethers, new brominated flame retardants, organophosphate esters, and chlorinated paraffins at urban open consumption place

At present, the global urban population has exceeded half of the total population and is still on the rise. Urban air pollution has attracted much attention, but most of the research focuses on typical pollution sources and indoor environment. This study reports the occurrence characteristics of particle-bound polybrominated diphenyl ethers (PBDEs), new brominated flame retardants (NBFRs), organophosphate esters (OPEs), short-chain chlorinated paraffins (SCCPs), and medium-chain chlorinated paraffins (MCCPs) at urban open consumption place. Among those pollutants detected in this study, the level of CPs was generally higher than other urban outdoor environments, and even higher than few indoor environments, such as house in Guangzhou (China) and Stockholm (Sweden). The size distributions of PBDEs and NBFRs exhibited bimodal peaks and that of SCCPs presented a unimodal peak, whereas no obvious trend was observed for OPEs or MCCPs. Additionally, the results of calculating the deposition fluxes of target pollutants in various regions based on the size distribution confirmed that total deposition was dominated by deposition in the head airways and alveolar region, and inhalation exposure in the current environment poses no significant health risk. Both discrepancy of the spatial distribution and principal component analysis indicated that sources of these organic pollutants may be related to the type of stores. Various construction and decoration materials might have been responsible for the high concentrations of OPEs and CPs, and thus, these materials require further analysis.

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.

Brominated flame retardants (BFRs) in PM2.5 associated with various source sectors in southern China

The present study investigates legacy and novel brominated flame retardants (BFRs) in atmospheric PM2.5 associated with various urban source sectors in a city and electronic waste (e-waste) recycling facilities in southern China. The concentrations of polybrominated diphenyl ethers (PBDEs) and novel BFRs (∑2NBFRs) at the urban industrial park (UIP) sites varied greatly from 22.0 to 105 pg m-3 and from to 29.7 to 459 pg m-3, respectively, and higher concentrations were generally found at sites involving industrial sectors of electronics, plastics, and machinery. Their spatial variations at other urban potential source sites were small suggesting a lack of strong point emissions. The levels of PBDEs and ∑2NBFRs at the e-waste facilities (220-2356 pg m-3 and 83.6-569 pg m-3) were significantly higher and did not temporally decline, indicating that improvement in e-waste recycling techniques does not significantly reduce emissions of PBDEs. NBFRs dominated the BFRs at the urban sites (55% on average), while PBDEs were still dominant (78%) at the e-waste sites. PBDE congener profiles in PM2.5 were substantially different from those in commercial mixtures. The congener profiles as well as their correlations suggested frequent formation of lower brominated PBDEs from degradation of highly brominated congeners in this region, which became appreciable due to the reduced emissions. The significant correlations among the lower brominated congeners also reflected similar environmental behaviors due to similar physicochemical properties.