Effect of Bromine Substitution on Human Dermal Absorption of Polybrominated Diphenyl Ethers

Penetration pathways, influencing factors and predictive models for dermal absorption of exobiotic molecules: A critical review

This review provides a comprehensive summary of the skin penetration pathways of xenobiotics, including metals, organic pollutants, and nanoparticles (NPs), with a particular focus on the methodologies employed to elucidate these penetration routes. The impacts of the physicochemical properties of exogenous substances and the properties of solvent carriers on the penetration efficiencies were discussed. Furthermore, the review outlines the steady-state and transient models for predicting the skin permeability of xenobiotics, emphasizing the models which enable realistic visualization of pharmaco-kinetic phenomena via detailed geometric representations of the skin microstructure, such as stratum corneum (SC) (bricks and mortar) and skin appendages (hair follicles and sebaceous gland units). Limitations of published research, gaps in current knowledge, and recommendations for future research are highlighted, providing insight for a better understanding of the skin penetration behavior of xenobiotics and associated health risks in practical application contexts.

Factors impacting human exposure to legacy and emerging contaminants in residential dust in Beijing, China: Characteristics of indoor microenvironment

Exposure to indoor dust is of concern since dust may be contaminated by various toxic chemicals and people spend considerable time indoors. Factors impacting human exposure risks to contaminants in indoor dust may differ from those affecting the loadings of contaminants, but the dominant factors have not yet been well clarified. In this study, the occurrence, human exposure, and related influencing factors of several classes of legacy and emerging contaminants in residential dust across Beijing were investigated, including per- and polyfluoroalkyl substances (PFASs) and three types of flame retardants (FRs), i.e., organophosphate esters (OPEs), polybrominated diphenyl ethers (PBDEs), and novel halogenated FRs (NHFRs). OPEs (median: 3847 ng/g) were the most abundant group, followed by PBDEs (1046 ng/g) and NHFRs (520 ng/g). PFASs (14.3 ng/g) were one to two orders of magnitude lower than FRs. The estimated daily intakes of these contaminants were relatively higher for toddlers than other age groups, with oral ingestion being the main exposure pathway compared with dermal contact. Higher human exposure risks were found in new buildings or newly finished homes due to the elevated intake of emerging contaminants (such as OPEs). Furthermore, higher risks were also found in homes with wooden floors, which were mainly associated with higher levels of PFASs, chloroalkyl and alkyl OPEs, compared with tile floors. Citizens in the urban area also showed higher exposure risks than those in the suburban area. The quantity of household appliances and finishing styles (simple or luxurious) showed an insignificant impact on overall human exposure risks despite their significant effect on the levels of some of the dust contaminants. Results in this study are of importance in understanding human exposure to the co-existence of multiple contaminants in indoor dust.

A review of occurrence, bioaccumulation, and fate of novel brominated flame retardants in aquatic environments: A comparison with legacy brominated flame retardants

Novel brominated flame retardants (NBFRs) have been developed as replacements for legacy brominated flame retardants (BFRs) such as polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecanes (HBCDs). The prevalence of NBFRs in aquatic environments has initiated intense concerns that they resemble to BFRs. To comprehensively elucidate the fate of NBFRs in aquatic environments, this review summarizes the physico-chemical properties, distribution, bioaccumulation, and fates in aquatic environments. 1,2-bis(2,3,4,5,6-pentabromophenyl) ethane (DBDPE) as the major substitute for PBDEs is the primary NBFR. The release from industrial point sources such as e-waste recycling stations is the dominant way for NBFRs to enter the environment, which results in significant differences in the regional distribution of NBFRs. Sediment is the major sink of NBFRs attributed to the high hydrophobicity. Significantly, there is no decreasing trend of NBFRs concentrations, while PBDEs achieved the peak value in 1970-2000 and decreased gradually. The bioaccumulation of NBFRs is reported in both field studies and laboratory studies, which is regulated by the active area, lipid contents, trophic level of aquatic organisms, and the log KOW of NBFRs. The biotransformation of NBFRs showed similar metabolism patterns to that of BFRs, including debromination, hydroxylation, methoxylation, hydrolysis, and glycosylation. In addition, NBFRs show great potential in trophic magnification along the aquatic food chain, which could pose a higher risk to high trophic-level species. The passive uptake by roots dominates the plant uptake of NBFRs, followed by acropetal and basipetal bidirectional transportation between roots and leaves in plants. This review will provide the support to understand the current pollution characteristics of NBFRs and highlight perspectives for future research.

Determination of potential dermal exposure rates of phosphorus flame retardants via the direct contact with a car seat using artificial skin

Dermal exposure to phosphorus flame retardants (PFRs) has received much attention as a major alternative exposure route in recent years. However, the information regarding dermal exposure via direct contact with a product is limited. In addition, in the commonly used dermal permeability test, the target substance is dissolved in a solvent, which is unrealistic. In this study, a dermal permeability test of PFRs in three car seats was performed using artificial skin. The PFR concentrations in the car seats are 0.12 wt% tris(2-chloroethyl) phosphate (TCEP), 0.030-0.25 wt% tris(2-chloroisopropyl) phosphate (TCPP), 0.15 wt% triphenyl phosphate (TPhP), 0.89 wt% cresyl diphenyl phosphate (CsDPhP), 0.074 wt% tricresyl phosphate (TCsP), and 0.46-4.7 wt% diethylene glycol bis [di (2-chloroisopropyl) phosphate (DEG-BDCIPP). The mean skin permeation rates for a contact time of 24 h are 14 (TCEP), 5.4-160 (TCPP), 0.67 (CsDPhP), 0.38 (TPhP), and 3.3-58 ng cm-2 h-1 (DEG-BDCIPP). The concentrations of TCsP in receptor liquid were lower than the limit of quantification at the contact time of 24 h. The skin permeation rates were significantly affected by the type of car seat (e.g., fabric or non-fabric). The potential dermal TCPP exposure rate for an adult via direct contact with the car seat during the average daily contact time (1.3 h), which was the highest value assessed in this study, was estimated to be 16,000 ng kg-1 day-1, which is higher than that related to inhalation and dust ingestion reported as significant exposure route of PFRs in previous studies. These facts reveal that dermal exposure associated with direct contact with the product might be an important exposure pathway for PFRs.

Assessment of human dermal absorption of flame retardant additives in polyethylene and polypropylene microplastics using 3D human skin equivalent models

To overcome ethical and technical challenges impeding the study of human dermal uptake of chemical additives present in microplastics (MPs), we employed 3D human skin equivalent (3D-HSE) models to provide first insights into the dermal bioavailability of polybrominated diphenyl ether (PBDEs) present in MPs; and evaluated different factors influencing human percutaneous absorption of PBDEs under real-life exposure scenario. PBDEs were bioavailable to varying degrees (up to 8 % of the exposure dose) and percutaneous permeation was evident, albeit at low levels (≤0.1 % of the exposure dose). While the polymer type influenced the release of PBDEs from the studied MPs to the skin, the polymer type was less important in driving the percutaneous absorption of PBDEs. The absorbed fraction of PBDEs was strongly correlated (r2 = 0.88) with their water solubility, while the dermal permeation coefficient Papp of PBDEs showed strong association with their molecular weight and logKOW. More sweaty skin resulted in higher bioavailability of PBDEs from dermal contact with MPs than dry skin. Overall, percutaneous absorption of PBDEs upon skin contact with MPs was evident, highlighting, for the first time, the potential significance of the dermal pathway as an important route of human exposure to toxic additive chemicals in MPs.

A comprehensive assessment of external exposure to persistent halogenated organic pollutants for residents in an e-waste recycling site, South China

Human skin wipes from 30 participants, air, dust, and food items were collected from a former electronic waste site in South China to provide a comprehensive understanding of residents' exposure to halogenated flame retardants (HFRs) and polychlorinated biphenyls (PCBs). The total concentration of halogenated organic pollutants (HOPs) in the dust, air, food and skin wipes ranged 240-25000 ng/g, 130-2500 pg/m3, 0.08-590 ng/g wet weight, and 69-28000 ng/m2, respectively. Wild fish, vegetables, and air were dominated by PCBs, whereas dust, livestock, and poultry were dominated by HFRs. The HOP concentrations were several orders of magnitude higher in local foodstuffs than in market foodstuffs. The chemical composition on the forehead was remarkably different from that on the hand. The importance of different exposure routes depends on the residents' food choices, except decabromodiphenyl ethane (DBDPE). For residents who consumed a 100-foot diet (mainly egg) and local wild fish, diet ingestion overwhelmed other exposure routes, and PCBs were mainly contributed by fish and HFRs by egg. For residents who consumed market food, the dermal absorption of most PCB congeners and dust ingestion of highly brominated flame retardants were relatively prominent. Inhalation was found to be a crucial route for pentabromoethylbenzene (PBEB).

Methods for the characterisation of dermal uptake: Progress and perspectives for organophosphate esters

Organophosphate esters (OPEs) are a group of pollutants that are widely detected in the environment at high concentrations. They can adversely affect human health through multiple routes of exposure, including dermal uptake. Although attention has been paid to achieving an accurate and complete quantification of the dermal uptake of OPEs, existing evaluation methods and parameters have obvious weaknesses. This study reviewed two main categories of methodologies, namely the relative absorption (RA) model and the permeability coefficient (PC) model, which are widely used to assess the dermal uptake of OPEs. Although the PC model is more accurate and is increasingly used, the most important parameter in this model, the permeability coefficient (Kp), has been poorly characterised for OPEs, resulting in considerable errors in the estimation of the dermal uptake of OPEs. Thus, the detailed in vitro methods for the determination of Kp are summarised and sorted. Furthermore, the commonly used skin membranes are identified and the factors affecting Kp and corresponding mechanisms are discussed. In addition, the experimental conditions, conclusions, and available data on Kp values of the OPEs are thoroughly summarised. Finally, the corresponding knowledge gaps are proposed, and a more accurate and sophisticated experimental system and unknown Kp values for OPEs are suggested.

Update of the risk assessment of polybrominated diphenyl ethers (PBDEs) in food

The European Commission asked EFSA to update its 2011 risk assessment on polybrominated diphenyl ethers (PBDEs) in food, focusing on 10 congeners: BDE-28, -47, -49, -99, -100, -138, -153, -154, -183 and ‑209. The CONTAM Panel concluded that the neurodevelopmental effects on behaviour and reproductive/developmental effects are the critical effects in rodent studies. For four congeners (BDE-47, -99, -153, -209) the Panel derived Reference Points, i.e. benchmark doses and corresponding lower 95% confidence limits (BMDLs), for endpoint-specific benchmark responses. Since repeated exposure to PBDEs results in accumulation of these chemicals in the body, the Panel estimated the body burden at the BMDL in rodents, and the chronic intake that would lead to the same body burden in humans. For the remaining six congeners no studies were available to identify Reference Points. The Panel concluded that there is scientific basis for inclusion of all 10 congeners in a common assessment group and performed a combined risk assessment. The Panel concluded that the combined margin of exposure (MOET) approach was the most appropriate risk metric and applied a tiered approach to the risk characterisation. Over 84,000 analytical results for the 10 congeners in food were used to estimate the exposure across dietary surveys and age groups of the European population. The most important contributors to the chronic dietary Lower Bound exposure to PBDEs were meat and meat products and fish and seafood. Taking into account the uncertainties affecting the assessment, the Panel concluded that it is likely that current dietary exposure to PBDEs in the European population raises a health concern.

Exploring Route-Specific Pharmacokinetics of PFAS in Mice by Coupling in Vivo Tests and Physiologically Based Toxicokinetic Models

BACKGROUND

Oral ingestion, inhalation, and skin contact are important exposure routes for humans to uptake per- and polyfluoroalkyl substances (PFAS). However, nasal and dermal exposure to PFAS remains unclear, and accurately predicting internal body burden of PFAS in humans via multiple exposure pathways is urgently required.

OBJECTIVES

We aimed to develop multiple physiologically based toxicokinetic (PBTK) models to unveil the route-specific pharmacokinetics and bioavailability of PFAS via respective oral, nasal, and dermal exposure pathways using a mouse model and sought to predict the internal concentrations in various tissues through multiple exposure routes and extrapolate it to humans.

METHODS

Mice were administered the mixed solution of perfluorohexane sulfonate, perfluorooctane sulfonate, and perfluorooctanoic acid through oral, nasal, and dermal exposure separately or jointly. The time-dependent concentrations of PFAS in plasma and tissues were determined to calibrate and validate the individual and combined PBTK models, which were applied in single- and repeated-dose scenarios.

RESULTS

The developed route-specific PBTK models successfully simulated the tissue concentrations of PFAS in mice following single or joint exposure routes as well as long-term repeated dose scenarios. The time to peak concentration of PFAS in plasma via dermal exposure was much longer (34.1-83.0 h) than that via nasal exposure (0.960 h). The bioavailability of PFAS via oral exposure was the highest (73.2%-98.0%), followed by nasal (33.9%-66.8%) and dermal exposure (4.59%-7.80%). This model was extrapolated to predict internal levels in human under real environment.

DISCUSSION

Based on these data, we predict the following: PFAS were absorbed quickly via nasal exposure, whereas a distinct hysteresis effect was observed for dermal exposure. Almost all the PFAS to which mice were exposed via gastrointestinal route were absorbed into plasma, which exhibited the highest bioavailability. Exhalation clearance greatly depressed the bioavailability of PFAS via nasal exposure, whereas the lowest bioavailability in dermal exposure was because of the interception of PFAS within the skin layers. https://doi.org/10.1289/EHP11969.

New brominated flame retardant decabromodiphenyl ethane (DBDPE) in water sediments: A review of contamination characteristics, exposure pathways, ecotoxicological effects and health risks

As an alternative to polybrominated diphenyl ethers (PBDEs), decabromodiphenyl ethane (DBDPE) has become one of the most important new brominated flame retardants (NBFRs). However, little is known about whether this emerging contaminant may has an environmental fate similar to PBDEs. Sediments are the main sink for DBDPE in the aqueous phase. Worldwide concentration data, since it was first found in sediments to date, have been collated, and the following conclusions have been drawn. (1) DBDPE concentrations in sediments have increased rapidly, often with a higher risk of contamination in source discharge areas. Compared with other countries, DBDPE contamination in China is more severe, especially in Guangdong Province, which is closely related to its being an e-waste dismantling area. (2) The amount of DBDPE in surface sediments has exceeded that of legacy brominated flame retardants (BFRs), and data recorded in sediment cores also corroborate that DBDPE is replacing decabromodiphenyl ether (BDE-209) as one of the most dominant NBFRs in the environment. (3) The exposure pathways of DBDPE include dietary intake, air or indoor dust intake, cutaneous absorption and endogenous exposure. For sediments, dietary exposure and endogenous exposure pathways need to be considered. Sediment DBDPE can enter the human body through bioenrichment such as contaminated seafood and the food chain. (4) DBDPE can exhibit neurotoxicity, thyrotoxicity, reproductive and developmental toxicity, hepatotoxicity and oxidative stress in organisms. Long-term DBDPE exposure may increase hyperthyroidism risk and inhibit normal cells activity. This review focuses on the distribution characteristics and exposure risks of DBDPE in global water sediments, providing a strong reference for environmental management and related legal policy formulation. The next steps are to focus on continuous source monitoring, process control and sediment clean-up of DBDPE. The development of sustainable water management options for waste microplastics (MPs) and e-waste spiked with DBDPE is a priority.

Percutaneous Penetration of Liquid Crystal Monomers (LCMs) by In Vitro Three-Dimensional Human Skin Equivalents: Possible Mechanisms and Implications for Human Dermal Exposure Risks

Liquid crystal monomers (LCMs) are indispensable materials in liquid crystal displays, which have been recognized as emerging persistent, bioaccumulative, and toxic organic pollutants. Occupational and nonoccupational exposure risk assessment suggested that dermal exposure is the primary exposure route for LCMs. However, the bioavailability and possible mechanisms of dermal exposure to LCMs via skin absorption and penetration remain unclear. Herein, we used EpiKutis 3D-Human Skin Equivalents (3D-HSE) to quantitatively assess the percutaneous penetration of nine LCMs, which were detected in e-waste dismantling workers' hand wipes with high detection frequencies. LCMs with higher log K_ow and greater molecular weight (MW) were more difficult to penetrate through the skin. Molecular docking results showed that ABCG2 (an efflux transporter) may be responsible for percutaneous penetration of LCMs. These results suggest that passive diffusion and active efflux transport may be involved in the penetration of LCMs across the skin barrier. Furthermore, the occupational dermal exposure risks evaluated based on the dermal absorption factor suggested the underestimation of the continuous LCMs' health risks via dermal previously.

Polybrominated diphenyl ethers (PBDEs) in household dust: A systematic review on spatio-temporal distribution, sources, and health risk assessment

Much attention has been paid on polybrominated diphenyl ethers (PBDEs) in household dust due to their ubiquitous occurrences in the environment. Based on the data from 59 articles sampled from 2005 to 2020, we investigated the spatio-temporal distribution, sources, and health risk of 8 PBDE homologues in household dusts worldwide. BDE-209 is the predominant PBDE in household dusts, followed by BDE-99 and BDE-47. The total concentrations of PBDEs (∑₈PBDEs) are found to be high in household dusts sampled from 2005 to 2008 and show a significant decline trend from 2009 to 2016 (p < 0.05) and a little upward tendency from 2017 to 2020. The concentrations of PBDEs in household dusts vary greatly in different countries of the world. The use of penta-BDE is the main source of three to five bromo-biphenyl ether monomers contributing 17.4% of ∑₈PBDEs, while BDE-209 and BDE-183 are derived from the use of household appliances contributing 82.6% of ∑₈PBDEs. Ingestion is the main exposure route for adults and toddlers, followed by dermal contact. The values of hazard index (HI) exposed to PBDEs in household dusts are all less than 1 for both adults and toddlers, indicating a low non-cancer risk. The incremental lifetime cancer risks (ILCRs) of BDE-209 are less than 10^-6 for both adults and toddlers, suggesting a negligible risk. However, the total carcinogenic risk of toddlers is higher than that of adults, indicating that much attention should be paid to toddlers exposed to BDE-209 in household dust.

Insights into the Dermal Absorption, Deposition, and Elimination of Poly- and Perfluoroalkyl Substances in Rats: The Importance of Skin Exposure

Humans are frequently exposed to poly- and perfluoroalkyl substances (PFASs) via direct skin contact with personal care and consumer products containing them. Here, we used a rat model to estimate the dermal penetration efficiency of 15 representative PFASs. After 144 h post-dosing, 4.1-18.0 and 5.3-15.1% of the applied PFASs in the low (L) and high (H) groups, respectively, were absorbed into the rats. PFAS absorption and permeation were parabolically associated with the perfluorinated carbon chain length (C_F), peaking for perfluoroheptanoic acid (PFHpA). The lipid-rich stratum corneum of the skin barrier substantially suppressed the penetration of less hydrophobic short-chain PFASs, whereas the water-rich viable epidermis and dermis served as obstacles to hydrophobic long-chain PFAS permeation. However, the renal clearance (CL_renal) of the target PFAS decreased with increasing C_F, suggesting that urinary excretion is crucial to eliminate less hydrophobic short-chain PFASs. Notably, the peak times of PFASs in the systemic circulation of rats (8-72 h) were remarkably longer than those after oral administration (1-24 h). These results suggest that dermal penetration can be long-lasting and contribute considerably to the body burden of PFASs, especially for those with moderate hydrophobicity due to their favorable skin permeation and unfavorable urinary excretion.

Dermal uptake: An important pathway of human exposure to perfluoroalkyl substances?

Per- and polyfluoroalkyl substances (PFAS) have been produced and used in a broad range of products since the 1950s. This class, comprising of thousands of chemicals, have been used in many different products ranging from firefighting foam to personal care products and clothes. Even at relatively low levels of exposure, PFAS have been linked to various health effects in humans such as lower birth weight, increased serum cholesterol levels, and reduced antibody response to vaccination. Human biomonitoring data demonstrates ubiquitous exposure to PFAS across all age groups. This has been attributed to PFAS-contaminated water and dietary intake, as well as inadvertent ingestion of indoor dust for adults and toddlers. In utero exposure and breast milk have been indicated as important exposure pathways for foetuses and nursing infants. More recently, PFAS have been identified in a wide range of products, many of which come in contact with skin (e.g., cosmetics and fabrics). Despite this, few studies have evaluated dermal uptake as a possible route for human exposure and little is known about the dermal absorption potential of different PFAS. This article critically investigates the current state-of-knowledge on human exposure to PFAS, highlighting the lack of dermal exposure data. Additionally, the different approaches for dermal uptake assessment studies are discussed and the available literature on human dermal absorption of PFAS is critically reviewed and compared to other halogenated contaminants, e.g., brominated flame retardants and its implications for dermal exposure to PFAS. Finally, the urgent need for dermal permeation and uptake studies for a wide range of PFAS and their precursors is highlighted and recommendations for future research to advance the current understanding of human dermal exposure to PFAS are discussed.

A nationwide survey of 20 legacy brominated flame retardants in indoor dust from China: continuing occurrence, national distribution, and implication for human exposure

Despite the restrictions on polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecanes (HBCDDs), these chemicals are still ubiquitous environmental pollutants. In this study, we measured the concentrations and profiles of 17 PBDE congeners and 3 HBCDD isomers in indoor dust samples collected from 23 provinces and cities across China. The summed concentrations of PBDEs (Σ₁₇PBDEs) ranged from 4.19 to 817 ng/g, with an average of 171 ± 184 ng/g. BDE-209 was the most abundant congener. The concentrations of HBCDDs ranged from 6.65 to 1335 ng/g, with an average of 236 ± 324 ng/g. Unlike commercial HBCDD formulations, α-HBCDD was the predominant isomer in the indoor dust samples analyzed. Geographical distributions showed that the concentrations of PBDEs and HBCDDs varied significantly among different regions. Higher PBDE and HBCDD levels were observed in samples from eastern coastal and economically developed regions. Further, we estimated the daily intakes of PBDEs and HBCDDs through the routes of dust ingestion and dust dermal absorption for different age groups. Dust dermal absorption is an unneglectable exposure pathway to PBDEs and HBCDs for the Chinese population. Among the age groups, infants had the highest exposure via dust dermal absorption, and toddlers had the highest exposure via dust ingestion. Compared with the threshold values, the exposure doses of PBDEs and HBCDDs are unlikely to pose significant health concerns for both infants and adults in China. This is the first national survey of PBDEs and HBCDDs in indoor dust samples across China after the restriction.

Dermal uptake of chlorinated organophosphate flame retardants via contact with furniture fabrics; implications for human exposure

The chlorinated organophosphate flame retardants (Cl-PFRs): tris-(2-chloroethyl)-phosphate (TCEP), tris-(1-chloro-2-propyl)-phosphate (TCIPP) and tris-(1,3-dichloropropyl)-phosphate (TDCIPP), have been widely used in upholstered furniture despite their carcinogenic potential. Although Cl-PFRs are mainly added to furniture foam, they are present in the fabrics likely due to migration from the foam. While several studies have assessed human exposure to Cl-PFRs via different pathways, no information exists on dermal uptake of these chemicals through contact with fabrics. In the current study, dermal absorption of TCEP, TCIPP and TDCIPP from 3 UK domestic furniture fabrics was experimentally assessed for the first time using in vitro 3D-human skin equivalents (EpiSkin™) under different real-life exposure scenarios. Results revealed all 3 target Cl-PFRs were dermally bioavailable to varying degrees (3.5%-25.9% of exposure dose) following 24 h contact with the studied fabrics. Estimated permeability coefficients (K_P, cm h^-1) showed TCEP had the highest percutaneous penetration potential followed by TCIPP, then TDCIPP. Further investigation revealed human dermal uptake of Cl-PFRs can be influenced by several factors including: the specific physicochemical properties of the compound, the type of exposure matrix, the exposure dose and the degree of skin hydration at the point of contact. Exposure assessment revealed UK adults and toddlers can be exposed to 20.4 and 14.1 ng TCIPP/kg bw/day via contact with furniture fabrics in summer, which is higher than international average exposures via inhalation and dust ingestion for adults and dietary exposure for toddlers. Therefore, risk assessment studies for Cl-PFRs and future replacements should consider dermal contact with consumer products (e.g. furniture fabrics) as a potential significant human exposure pathway.

Occurrence, Distribution, and Human Exposure of Emerging Liquid Crystal Monomers (LCMs) in Indoor and Outdoor Dust: A Nationwide Study

Liquid crystal monomers (LCMs) are a class of emerging, persistent, bioaccumulative, and toxic organic pollutants. They are detected in various environmental matrixes that are associated with electronic waste (e-waste) dismantling. However, their occurrence and distribution in indoor and outdoor dust on a national scale remain unknown. In this study, a dedicated target analysis quantified a broad range of 60 LCMs in dust samples collected across China. The LCMs were frequently detected in indoor (n = 48) and outdoor dust (n = 97; 37 sampled concomitantly with indoors dust) from dwellings, and indoor dust from cybercafés (n = 34) and phone repair stores (n = 22), with median concentrations of 41.6, 94.7, 106, and 171 ng/g, respectively. No significant spatial difference was observed for the concentrations of the total LCMs among distinct geographical regions (p > 0.05). The median daily intake values of the total LCMs via dust ingestion, dermal contact, and inhalation were estimated at 1.50 × 10^-2, 2.90 × 10^-2, and 8.57 × 10^-6 ng/kg BW/day for adults and 1.47 × 10^-1, 1.22 × 10^-1, and 2.18 × 10^-5 ng/kg BW/day for children, respectively. These estimates suggested higher exposure risks for children and indicated that dust ingestion and dermal contact significantly contribute to the human intake of LCMs. The microenvironmental pollution levels of LCMs together with the potential exposure risks associated with some of these chemicals are of concern for human health.

Electronic-Waste-Driven Pollution of Liquid Crystal Monomers: Environmental Occurrence and Human Exposure in Recycling Industrial Parks

Liquid crystal monomers (LCMs) in liquid crystal displays (LCDs) may be released into the environment, especially in electronic waste (e-waste) recycling industrial parks with a high pollution risk. However, little has been known about the environmental release and human exposure to LCMs until now. Herein, a total of 45 LCMs were detected in LCDs of commonly used smartphones and computers by high-resolution mass spectrometry with suspect screening analysis. Fluorinated biphenyls and their analogs were the dominant LCMs. Based on available standards of the screening results and previous studies, 55 LCMs were quantified in samples from an e-waste recycling industrial park in Central China. The LCMs were frequently detected in outdoor dust (n = 43), workshop #1 indoor dust (n = 53), and hand (n = 43) and forehead wipes (n = 43), with median concentrations of 6950 ng/g, 67,400 ng/g, 46,100 ng/m², and 62,100 ng/m², respectively. The median estimated daily intake values of the LCMs via dust ingestion and dermal absorption were 48.3 and 16.5 ng/kg body weight/day, respectively, indicating a high occupational exposure risk of these compounds. In addition, 16 LCMs were detected in the serum of eight elderly people (≥60 years old) with over 5 years of experience in e-waste dismantling operations, resulting in a total concentration range of 3.9-26.3 ng/mL.

Identifying Dermal Uptake as a Significant Pathway for Human Exposure to Typical Semivolatile Organic Compounds in an E-Waste Dismantling Site: The Relationship of Contaminant Levels in Handwipes and Urine Metabolites

Dermal exposure to semivolatile organic compounds (SVOCs) has recently attracted widespread attention; understanding these exposures is particularly important for people whose skin is frequently exposed to different pollution surfaces. In this study, handwipes were collected from exposed occupational workers and local residents near a typical electronic waste (e-waste) dismantling area; urine samples were also sampled. The wipes were analyzed for three typical SVOCs: polybrominated diphenyl ethers (PBDEs), polycyclic aromatic hydrocarbons (PAHs), and organophosphate flame retardants (OPFRs). The median levels of PAHs, OPFRs, and PBDEs in handwipes from e-waste dismantlers were 96.0, 183, and 238 ng, respectively. The analytes were higher in the handwipes collected from workers than those from residents, indicating that they were subjected to greater dermal exposure during primitive e-waste dismantling activities. Among the three SVOCs, the strongest correlation was found between triphenyl phosphate (TPhP) in handwipes and diphenyl phosphate (DPhP) in paired urine; the next strongest correlations were between PAHs and PBDEs and their corresponding urinary metabolites. The results showed that TPhP contributed the highest exposure to e-waste dismantlers via dermal exposure. Our research highlights the importance of dermal exposure to TPhP, which should be considered in future exposure risk assessments.

A review of the success and challenges in characterizing human dermal exposure to flame retardants

Since organic flame retardants (FRs) have several industrial applications, they have been largely detected in environmental and biological samples, and humans have been highly exposed to them. Although the effects of oral and inhaled FRs have been well studied, dermal exposure to them has only recently been pointed out as a potential route of human exposure. Consequently, the effects of FRs on the skin and secondary target organs have been poorly investigated. This review article summarizes the main findings regarding dermal exposure to FRs, points the limitation of the published studies, and suggests future perspectives for better understanding of how dermal exposure to FRs impacts the human health. This review lists some gaps that must be filled in future studies, including characterization of the bioavailable fraction and assessment of exposure for new FRs, to establish their physiological significance and to improve the development of 3D dermal tissue for more reliable results to be obtained.

Percutaneous penetration and dermal exposure risk assessment of chlorinated paraffins

The widespread occurrence of chlorinated paraffins (CPs) in environmental matrices has resulted in a high frequency exposure to CPs via dermal contact. To quantitatively estimate percutaneous penetration of CPs, Episkin® human skin equivalents (HSE) was applied as an in vitro model to evaluate the mechanism of percutaneous penetration of CPs. The co-exposure of CPs mixtures to HSE showed that about 11.7% and 10.2% of short-chain CPs (SCCPs) and medium-chain CPs (MCCPs) could penetrate the HSE and enter the receptor fluid, while no long-chain CPs (LCCPs) (C>17) were able to penetrate the HSE during the 36-h assay period. The experimentally obtained permeability coefficient (K_p) values for CPs were significantly (p < 0.01) negatively correlated with their log octanol-water partition coefficient (log K_ow). Furthermore, 24 participants were recruited to assess direct human dermal exposure to CPs in China with the total CPs collected onto hand wipes and forehead wipes being 96,600 and 30,400 ng/person, respectively. The proportion of total SCCPs and MCCPs intake via dermal penetration (skin area investigated in this study) accounting for 2.0% of the total intake of CPs. Considering the total skin surface of human body is around 20 times of the area studied, the total intake of CPs through dermal penetration could be a significant exposure pathway.

Chlorinated paraffins and tris (1-chloro-2-propyl) phosphate in spray polyurethane foams - A source for indoor exposure?

In this study, we investigated chemical additives present in new and used spray polyurethane foams (SPFs) and assessed the dermal transfer through direct contact. This first study shows that cured do-it-yourself spray one-component SPFs (OCFs) often contain chlorinated paraffins (C₁₄-C₃₇), and tris (1-chloro-2-propyl) phosphate (TCIPP), ranging 0.2-50%, and 0.9-30% w/w, respectively. Six OCFs contained CP levels ranging 22-50% w/w, whereas nine OCFs used for similar applications only contained CP levels ranging 2-17% w/w. It is unclear if the combination CPs/TCIPP is meant to improve the flame retardancy of products, and could suggest an unnecessary use of high CPs/TCIPP concentrations in OCFs. The two-component SPFs (TCFs) contained only TCIPP with levels ranging from 7.0% to 9.0%. The CPs and TCIPP were easily transferred from cured OCFs to the hands. Levels up to 590 µg per hand for CPs and up to 2.7 µg per hand for TCIPP were found. After end-of-life, it is challenging to recycle used SPFs. They may, therefore, end up at landfills where the TCIPP/CPs may leach into the environment. Therefore, further investigation is needed to assess potential exposure risks associated with general and occupational use, and the impact of landfill leaching on the environment.

Polybrominated diphenyl ethers in indoor and outdoor dust from Southeast Asia: An updated review on contamination status, human exposure, and future perspectives

Contamination status, potential emission sources, environmental fate, and human exposure risk of polybrominated diphenyl ethers (PBDEs) are reviewed for indoor and outdoor dust from Southeast Asian countries, under an international comparison point of view. PBDEs have been widely detected in house, workplace, car, and road dust samples collected from Indonesia, Philippines, Singapore, Thailand, and Vietnam. The highest PBDE levels up to hundreds of μg/g were found in settled dust from some e-waste processing areas in Thailand and Vietnam. Concentrations of PBDEs in house, car, and road dust from this region were generally lower than those reported in China and Western developed countries. BDE-209 was the most predominant congener in almost all analyzed samples, reflecting the widespread application of materials and products treated with commercial deca-BDE mixtures in this region. The market demand and application rate of commercial PBDE mixtures in Southeast Asia were lower than those documented for other regions in the world. As a result, PBDE contamination levels in the environments (e.g., indoor and outdoor dust) and associated risks in these countries were not significantly high. However, more attention should be paid to informal processing activities and management strategies for modern wastes such as e-waste, plastics, and end-of-life vehicles. There exist several knowledge gaps about spatiotemporal trends, potential sources, risk assessment, inventory, management, and legislation regarding PBDEs in dust from this region, which should be filled by additional comprehensive, detailed studies with relevant inter-country/regional monitoring schemes.

Brominated and phosphate flame retardants from interior and surface dust of personal computers: insights into sources for human dermal exposure

It remains unclear whether internal or external sources play the more significant role in flame retardant (FR) contamination of surface dust from personal computers (PCs), which may lead to bias on dermal exposure assessment of FRs. In the present study, the occurrence and profiles of several brominated and phosphate FRs were measured in the interior dust, and the upper surface (keyboard) and bottom surface (bottom cover) wipes of PCs. BDE 209 (639 ng/g), decabromodiphenyl ethane (DBDPE, 885 ng/g), and triphenyl phosphate (TPHP, 1880 ng/g) were the most abundant chemicals in interior PC dust, while tris(2-chloroisopropyl) phosphate (TCIPP), TPHP, and DBDPE were dominant on both surfaces of PCs. No significant correlation between interior dust and both PC surfaces was observed for concentrations of most FRs except BDE 183. Different sources of FRs for interior and surface dust of PCs were further revealed by principal component analysis (PCA). FRs from external sources, rather than emission from inner PC components, are likely the main contributor for FR profiles on PC surfaces. Exposure assessment results demonstrated a minor contribution from PC dermal contact, compared with hand-to-mouth uptake, to total exposure. The applicability of surface wipes to assess dermal exposure to FR-treated products needs to be further investigated.

Impact of Nonylphenols and Polyhalogenated Compounds in Follicular Fluid on the Outcome of Intracytoplasmic Sperm Injection

Endocrine-disrupting chemicals (EDCs) interfere with the mammalian hormone system and alter its endo- and paracrine regulation. The goal of the present study was to examine the presence of 14 EDCs, including the technical mixture of nonylphenols and Mirex, in human follicular fluid (FF) and to find a potential correlation between endocrine active substances and a possible impact on female fertility. Furthermore, potential sources of EDC exposition regarding patients' lifestyle and socioeconomic factors were investigated. Human FF was collected from a total of 210 women undergoing intracytoplasmic sperm injection-treatment cycles because of male subfertility. The presence of EDCs was analyzed using gas chromatography coupled with mass spectrometry. Thirteen of the 14 investigated EDCs were present in every FF sample; compounds with the highest concentrations in FF were nonylphenol and Mirex. Nearly all kinds of EDCs led to significantly reduced maturation and fertilization rate. No significant influence of EDC concentration on the clinical pregnancy rate was observed for neither of the analyzed EDCs. Patients who obtained their clothes and textiles at fashion discounters displayed a higher amount of EDCs in their FF. In contrast, patients' residential area, source of food products, and nicotine or caffeine consumed were not associated with EDC accumulation. Clinicaltrials.gov NCT01385605 (11 July 2011).

Human exposure to halogenated and organophosphate flame retardants through informal e-waste handling activities - A critical review

Informal electrical and electronic waste (e-waste) handling activities constitute a potentially important source of halogenated (HFRs) and organophosphate flame retardants (OPFRs) to the environment and humans. In this review, two electronic databases (ScienceDirect and Web of Science Core Collection) were searched for papers that addressed this topic. A total of 82 relevant studies (including 72 studies selected from the two databases and 10 studies located from the references of the first 72 selected studies) were identified that reported on human external and internal exposure to HFRs and OPFRs arising as a result of informal e-waste handling activities. Compared to the general population, higher levels of external exposure (i.e., inhalation, ingestion, and dermal absorption) and internal exposure (i.e., blood serum, hair, breast milk, urine, and other human matrices) to HFRs and OPFRs were identified for e-waste recyclers and residents inhabiting e-waste dismantling and recycling zones, especially for younger adults and children. Food intake and dust ingestion were the dominant exposure pathways for the majority of brominated flame retardants (BFRs) and dechlorane plus (DP); while inhalation was identified as the most significant pathway of human exposure to OPFRs in informal e-waste sites. The majority of research to date has focused on China and thus future studies should be conducted in other regions such as Africa and South Asia. Other suggested foci of future research are: examination of exposure via dermal contact with e-waste, dietary exposure of local populations to OPFRs, confirmation of the existence of and cause(s) of the higher body burdens of females compared with males amongst populations impacted by informal e-waste handling, and characterisation of exposure of such populations to chlorinated paraffins.

Computational simulation associated with biological effects of alkyl organophosphate flame retardants with different carbon chain lengths on Chlorella pyrenoidosa

The environmental safety of flame retardants has attracted growing attention. Alkyl organophosphorus flame retardants (OPFRs) have been prevalently applied, but the potential risk and the structure effects of different alkyl chain lengths OPFRs on aquatic microalgae remain unknown. This study investigated the biological response of five alkyl-OPFRs to Chlorella pyrenoidosa by computational simulation together with biological approaches. The reduced docking energy had a significantly positive correlation (R² = 0.9) with the cell inhibition alongside the incremental chain length of alkyl-OPFRs. Molecular docking simulations suggested that the toxicity of alkyl-OPFRs would be highly correlated to their molecular structures. Coincidently, the reactive oxygen species, superoxide dismutase and malondialdehyde were triggered by 85%, 92% and 155% (based on the control group), after exposure to the longest chain length tributyl phosphate (TBP_C12), respectively. Furthermore, combining the ultrastructure scrutiny with the photosynthesis analysis, TBP_C12 was also found to significantly inhibit the chlorophyll biosynthesis (43%) and restrain the photosynthetic efficiency (26%) when compared with the control group. Overall, this is the first study to comprehensively reveal the biological effects of different alkyl-OPFRs on microalgae via the combination of computational simulation and cellular responses, providing a novel insight into targeted predicting the aquatic ecological risks of OPFRs.

First insight into polybrominated diphenyl ethers in car dust in Turkey: concentrations and human exposure implications

The presence of polybrominated diphenyl ethers (PBDEs) in the car is due to their use as a flame retardant additive in various car components such as dashboard, plastic parts, seat and headliner cushion foams, insulated cables, and electronic circuits. Ingestion of dust inadvertently or dermal contact to dust are significant pathways of human exposure to pollutants including PBDEs. There are no studies documenting presence of car dust associated flame retardants in Turkey. In the current study, a total of 13 PBDEs congeners were investigated in 62 car dust samples collected from Bursa province of Turkey using glass-fiber filters and a vacuum cleaner. Results of the study showed that congener concentrations were within the range of <MDL-40198 ng/g and PBDE-209, major component of commercial deca-BDE, showed the highest concentration among the targeted congeners. Assessment of exposure to analyzed PBDEs via inadvertent dust ingestion and skin contact showed toddlers are exposed to these chemicals approx. 10 times higher compared to adults. Hazard quotient (HQ) values calculated based on total exposure (ingestion + dermal contact) and were < 1 for both adults and toddler indicated that exposure to car dust-associated PBDEs through ingestion and skin contact does not pose any health risks for human in Bursa.

Cytotoxic Screening and Transcriptomics Reveal Insights into the Molecular Mechanisms of Trihexyl Phosphate-Triggered Hepatotoxicity

Mounting evidence shows that organophosphate flame retardants (OPFRs), especially aryl- and halogenated-OPFRs, exert various adverse health effects on living organisms. This study evaluated the hepatotoxic effect of trihexyl phosphate (THP) as a long-chain alkyl-OPFR on human hepatocyte cells (LO2) and mouse hepatocyte cells (AML12) by performing screening of cytotoxicity in vitro. In combination with transcriptomic analysis, toxicological mechanisms in vitro were further investigated. Results showed that THP triggered hepatotoxicity in vitro by altering four signaling pathways: endoplasmic reticulum (ER) stress, apoptosis, cell cycle, and the glycolysis signaling pathway. Exposure of LO2 and AML12 liver cells to THP (25 μg/mL) significantly induced ER stress-mediated apoptosis and cell cycle arrest. Meanwhile, downregulation of glycolysis caused the blockage of energy metabolism. Furthermore, the high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (HPLC-Q-TOF-MS/MS) revealed that much of THP was absorbed into the cells and displayed stability in the two liver cell lines. In vivo assays using a mouse model demonstrated that exposure to THP at 400 mg/kg induced the ballooning degeneration of hepatocytes in liver tissue, whereas exposure to THP at 800 mg/kg caused acute liver injury with high alanine aminotransferase levels. This study provides novel insights into the impact of THP on hepatotoxicity in vitro and in vivo and uncovers the underlying toxicological mechanisms, which may serve as a guide for further ecological risk assessment and reasonable application of alkyl-OPFRs.

Facile synthesis of tubular magnetic fluorinated covalent organic frameworks for efficient enrichment of ultratrace polybrominated diphenyl ethers from environmental samples

Polybrominated diphenyl ethers (PBDEs), known as the most widely used brominated flame retardant, have received great public concern due to its hidden environment and health problems. Development of highly selective and sensitive analytical approaches for enrichment and detection of ultratrace PBDEs are in high demand. Conventional sample pretreatment techniques usually require tedious procedures, long time, and excessive consumption of solvent and sample, thus hindering ultrasensitive detection of PBDEs. To address this issue, we first reported a simple room-temperature approach for synthesis of tubular magnetic fluorinated covalent organic frameworks (MCNT@TAPB-TFTA). The introduction of fluorine atoms played multiple roles in improving the frameworks' hydrophobicity and the adsorption capabilities for PBDEs. Combined with atmospheric pressure gas chromatography-tandem mass spectrometry (APGC-MS/MS), several crucial parameters of magnetic solid-phase extraction (MSPE) including adsorbent dosage, adsorption time, pH, ion strength, the eluent, elution time and elution frequencies were examined in detail. The optimal method exhibited wide linear ranges (0.01-500 ng/L), low limit of detections (LODs, 0.0045-0.018 ng/L), good correlation coefficients (r ≥ 0.9977), and high enrichment factors (EFs, 1425-1886 folds) for eight PBDEs. Furthermore, this proposed method could be successfully applied to sensitive determination of ultratrace PBDEs in environmental samples, demonstrating the promising potential of the MCNT@TPAB-TFTA as an adsorbent in sample pretreatment.

Exposure pathways, levels and toxicity of polybrominated diphenyl ethers in humans: A review

Polybrominated diphenyl ethers (PBDEs) are extensively used as brominated flame retardants (BFRs) in different types of materials, which have been listed as Persistent Organic Pollutants (POPs) by the Stockholm Convention in 2009 and 2017. Due to their ubiquities in the environment and toxicities, PBDEs have posed great threat to both human health and ecosystems. The aim of this review is to offer a comprehensive understanding of the exposure pathways, levels and trends and associated health risks of PBDEs in human body in a global scale. We systematically reviewed and described the scientific data of PBDE researches worldwide from 2010 to March 2020, focusing on the following three areas: (1) sources and human external exposure pathways of PBDEs; (2) PBDE levels and trends in humans; (3) human data of PBDEs toxicity. Dietary intake and dust ingestion are dominant human exposure pathways. PBDEs were widely detected in human samples, especially in human serum and human milk. Data showed that PBDEs are generally declining in human samples worldwide as a result of their phasing out. Due to the common use of PBDEs, their levels in humans from the USA were generally higher than that in other countries. High concentrations of PBDEs have been detected in humans from PBDE production regions and e-waste recycling sites. BDE-47, -153 and -99 were proved to be the primary congeners in humans. Human toxicity data demonstrated that PBDEs have extensively endocrine disruption effects, developmental effects, and carcinogenic effects among different populations.

Flame retardants, dioxins, and furans in air and on firefighters' protective ensembles during controlled residential firefighting

INTRODUCTION

Structure fires that involve modern furnishings may emit brominated flame retardants (BFRs) and organophosphate flame retardants (OPFRs), as well as brominated and chlorinated dioxins and furans, into the environment.

OBJECTIVES

The goal of this study was to quantify the airborne and personal protective equipment (PPE) contamination levels of these compounds during controlled residential fires in the U.S., and to evaluate gross-decontamination measures.

METHODS

Bulk-sampling was done to confirm the presence of flame retardants (FRs) in the furnishings used in 12 controlled residential structure fires. Area air samples were collected during the fires and PPE wipe samples were collected from the firefighters' turnout jackets and gloves after firefighting. For each fire, half of the jackets were decontaminated and the other half were not.

RESULTS

Of the BFRs and OPFRs measured in air during the fire period, decabromodiphenyl ether (BDE-209) and triphenyl phosphate (TPP) were the most abundant, with medians of 15.6 and 408 µg/m³, respectively, and were also detected during overhaul. These and several other BFRs and OPFRs were measured on PPE. Some gloves had contaminant levels exceeding 100 ng/cm² and were generally more contaminated than jackets. Air and surface levels of the brominated furans appeared to be higher than the chlorinated dioxins and furans. Routine gross decontamination appeared to reduce many of the BFR contaminants, but results for the OPFRs were mixed.

CONCLUSIONS

Structure fires are likely to result in a variety of FRs, dioxins, and furans into the environment, leading to PPE contamination for those working on the fireground. Firefighters should wear self-contained breathing apparatus during all phases of the response and launder or decontaminate their PPE (including gloves) after fire events.

Measuring exposure of e-waste dismantlers in Dhaka Bangladesh to organophosphate esters and halogenated flame retardants using silicone wristbands and T-shirts

Silicone (polydimethylsiloxane or PDMS) wristbands and cotton T-shirts were used to assess the exposure of e-waste recyclers in Dhaka, Bangladesh to polybrominated diphenyl ethers (PBDEs), novel brominated flame retardants (NBFRs), dechlorane plus (DPs), and organophosphate esters (OPEs). The median surface-normalized uptake rates of PBDEs, NBFRs, DPs, and OPEs were 170, 8.5, 4.8, and 270 ng/dm²/h for wristbands and 5.4, 2.0, 0.94, and 23 ng/dm²/h for T-shirts, respectively. Concentrations of Tris(2-chloroethyl) phosphate (TCEP), Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP), Tri-m-cresyl phosphate (TmCP), Bis(2-ethlyhexyl) tetrabromophthalate (BEH-TEBP), and Dechlorane plus (DPs) in wristbands were significantly correlated with those in T-shirts. Wristbands accumulated ~7 times more mass than T-shirts, especially of compounds expected to be mainly in the gas phase. We introduce the silicone "sandwich" method to approximate the easily releasable fraction (ERF) from T-shirts, hypothesized to be related to dermal exposure. ERFs varied from 6 to 75% of total chemical accumulated by T-shirts and were significantly negatively correlated with compounds' octanol-air partition coefficient (log K_oa). The median daily exposure doses via dermal transfer from the front of the T-shirt to the front body trunk were 0.32, 0.13, 0.11, and 9.1 ng/kg-BW/day for PBDEs, NBFRs, DPs, and OPEs, respectively. The evidence of e-waste recycler exposure to flame retardants in this low income country, lacking protective personal equipment, calls for measures to minimize their exposure and for chemical management regulations to consider exposures to chemicals in waste products.

Organophosphate compounds, polybrominated diphenyl ethers and novel brominated flame retardants in European indoor house dust: Use, evidence for replacements and assessment of human exposure

52 pollutants including organophosphate flame retardants and plasticizers (OPs), polybrominated diphenyl ethers (PBDEs) and novel brominated flame retardants (NBFRs) were evaluated in household dust from Belgium, Italy and Spain. Pollutant pattern was dominated by ∑OPs (12.8 μg/g; median) followed in decreasing order by ∑PBDEs (229 ng/g), decabromodiphenyl ethane (DBDPE, 130 ng/g), 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE, 1.35 ng/g), hexabromobenzene (HBB, 0.28 ng/g) and finally pentabromoethylbenzene (PBEB, 0.03 ng/g). Country differences and substitution of regulated chemicals by unregulated ones were explored. Results clearly reflected a decrease in c-penta and c-octaBDE commercial mixtures, which are mainly substituted by OPs, BTBPE and PBEB. On the other hand, c-decaBDE concentrations increased in Spanish case. However, positive correlations with its proposed substitute (DBDPE) and recent restricted policies make it possible to assume that this trend will change in the coming years. On the basis of the relationship between pollutants, house characteristics and inhabitant habits, potential sources were studied. Finally, data obtained were used to determine estimated daily intakes (EDI) via house dust ingestion and dermal absorption for toddlers and adults at central and upper percentiles. Calculated EDI levels even at worst case scenario were below available reference dose (RfD) values in all cases.

A Review of Environmental Occurrence, Fate, and Toxicity of Novel Brominated Flame Retardants

Use of legacy brominated flame retardants (BFRs), including polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCD), has been reduced due to adverse effects of these chemicals. Several novel brominated flame retardants (NBFRs), such decabromodiphenyl ethane (DBDPE) and bis(2,4,6-tribromophenoxy) ethane (BTBPE), have been developed as replacements for PBDEs. NBFRs are used in various industrial and consumer products, which leads to their ubiquitous occurrence in the environment. This article reviews occurrence and fate of a select group of NBFRs in the environment, as well as their human exposure and toxicity. Occurrence of NBFRs in both abiotic, including air, water, dust, soil, sediment and sludge, and biotic matrices, including bird, fish, and human serum, have been documented. Evidence regarding the degradation, including photodegradation, thermal degradation and biodegradation, and bioaccumulation and biomagnification of NBFRs is summarized. The toxicity data of NBFRs show that several NBFRs can cause adverse effects through different modes of action, such as hormone disruption, endocrine disruption, genotoxicity, and behavioral modification. The primary ecological risk assessment shows that most NBFRs exert no significant environmental risk, but it is worth noting that the result should be carefully used owing to the limited toxicity data.

Higher health risk resulted from dermal exposure to PCBs than HFRs and the influence of haze

To investigate the influence of haze on human dermal exposure to a series of halogenated flame retardants (HFRs) and polychlorinated biphenyls (PCBs), paired forehead wipes were collected from 46 volunteers (23 males, 23 females) using gauze pads soaked in isopropyl alcohol under heavy and light haze pollution levels. The median levels of ∑₂₇HFRs and ∑₂₇PCBs in all 92 samples were 672 and 1300ng/m², respectively. Decabromodiphenyl ether (BDE-209) (171ng/m²) and decabromodiphenylethane (DBDPE) (134ng/m²) were the dominant components of HFRs, indicating that dermal exposure may also be the significant pathway for non-volatile compounds. PCB-37 contributed the most to ∑₂₇PCBs, with a median concentration of 194ng/m², followed by PCB-60 (141ng/m²). Generally, PBDE, PCB and DD (dehalogenated derivatives of DPs) levels on the foreheads of female participants (291, 1340, 0.92ng/m²) were higher (p=0.037, 0.001, and 0.031, respectively) than those of male participants (226, 989, and 0.45ng/m²). A significant difference (p=0.001) in PCBs was found between light (1690ng/m²) and heavy (996ng/m²) haze pollution conditions. Nevertheless, HFR levels under heavy (median=595ng/m², ranging from 295 to 1490ng/m²) and light haze pollution conditions (ranging from 205 to 1220ng/m² with a median of 689ng/m²) did not show significant differences (p=0.269). The non-carcinogenic health risk resulting from dermal exposure to ∑₈HFRs and ∑₂₇PCBs was 8.72×10^-5 and 1.63×10^-2, respectively, raising more concern about populations' exposure to PCBs than HFRs.

Concentrations of Brominated Flame Retardants in Indoor Air and Dust from Ireland Reveal Elevated Exposure to Decabromodiphenyl Ethane

Concentrations of decabromodiphenyl ethane (DBDPE), 13 polybrominated diphenyl ethers (PBDEs), and hexabromocyclododecane (HBCDD) were measured in indoor air and dust collected from Irish homes, cars, offices, and primary schools during 2016-2017. Median concentrations of DBDPE in air (88 pg/m³) and dust (6500 ng/g) significantly exceed those previously reported internationally, with concentrations highest in offices and schools, suggesting that DBDPE is widely used in Ireland. Median concentrations of BDE-209 in air (340 pg/m³) and dust (7100 ng/g) exceed or are within the range of concentrations reported recently for the same microenvironments in the U.K., and exceed those reported in many other countries. Concentrations of BDE-209 in cars exceeded significantly (p < 0.05) those in other microenvironments. HBCDD was detected in all dust samples (median: 580 ng/g), and in 81% of air samples (median: 24 pg/m³) at concentrations similar to those reported recently for the U.K. and elsewhere. Estimates of exposure to DBDPE of Irish adults (92 ng/day) and toddlers (210 ng/day) as well as to BDE-209 (220 ng/day and 650 ng/day for adults and toddlers, respectively) substantially exceed those reported for the U.K. population. Moreover, our estimates of exposure of the Irish population to Σtrideca-PBDEs exceed previous estimates for Ireland via dietary exposure.

Exposure of Canadian electronic waste dismantlers to flame retardants

Exposure of e-waste workers to eight halogenated and five organophosphate ester flame retardant chemicals (FRs) was studied at a Canadian e-waste dismantling facility. FR concentrations were measured in air and dust samples collected at a central location and at four work benches over five-24 hour periods spanning two weeks. The highest concentrations in air from workbenches were of BDE-209 (median 156 ng m^-3), followed by Tris(2-chloroethyl) phosphate (TCEP, median 59 ng m^-3). Dust concentrations at the workbenches were higher than those measured at the central location, consistent with the release of contaminated dust during dismantling. Dust concentrations from the workbenches were also dominated by BDE-209 (median 96,300 ng g^-1), followed by Triphenyl phosphate (TPhP, median 47,000 ng g^-1). Most FRs were in coarse particles 5.6-18 μm diameter and ~30% were in respirable particles (<~3 μm). Exposure estimates indicated that dust ingestion accounted for 63% of total FR exposure; inhalation and dermal absorption contributed 35 and 2%, respectively. Some air and dust concentrations as well as some estimated exposures in this formal facility in a high-income country exceeded those from informal e-waste facilities located in low and middle income countries. Although there is demonstrated toxicity of some FRs, FR exposure in the e-waste industry has received minimal attention and occupational limits do not exist for most FRs.

Concentrations of brominated and phosphorous flame retardants in Finnish house dust and insights into children's exposure

Brominated and phosphorous flame retardants (BFRs, PFRs) are added to household and consumer products to reduce their flammability. Some FRs are persistent in the environment and may have adverse health effects. As exposure indoors contributes significantly to total exposure, we wanted to estimate the exposure of children (3 years of age) through dust ingestion, inhalation, and dermal absorption. We measured 17 BFRs and 10 PFRs in indoor dust, predicted their respective concentrations in the indoor air and assessed children's exposure. Among the BFRs, decabromodiphenyl ether (BDE-209) had highest median level in the dust (411 ng/g) followed by decabromodiphenyl ethane (DBDPE, 119 ng/g) and bis-ethylhexyl tetrabromophthalate (BEH-TEBP, 106 ng/g). Among the PFRs, trisbutoxyethyl phosphate (TBOEP) had the highest concentration (11100 ng/g) followed by tris(2-chloroisopropyl) phosphate (TCIPP, 1870 ng/g) and triphenyl phosphate (TPHP, 773 ng/g). FR concentration in air predicted from dust concentrations were within the interquartile range of experimental data for 10/13 of BFRs and 4/8 of PFRs compared. Dust ingestion was the major route of exposure (75-99%) for higher molecular weight BFRs, TBOEP and phenyl based PFRs (73-77%). Inhalation was important for volatile BFRs like pentabromobenzene (PBB 71%) and pentabromotoluene (PBT 52%) and dermal exposure for volatile chlorinated PFRs (TCEP 84%, TCIPP 77%). Margins of Exposure (MoE) were calculated as the ratio of total exposure to oral Reference Dose (RfD). MoEs were lowest for TCEP (220), TBOEP (240) and TCIPP (830), and > 1000 for all other FRs. These MoEs imply no risk for Finnish children by the studied FRs.

Field evaluation of sequential hand wipes for flame retardant exposure in an electronics recycling facility

Flame retardants have been associated with endocrine disorders, thyroid disruption, reproductive toxicity, and immunological interference. Through dismantling and recycling electronics and electric products, flame retardants can be released into the air and settle on work surfaces which may lead to dermal exposure. Hand wipe sampling is commonly used to evaluate dermal exposure. This study assesses the removal efficiency of wipes on the hands of recycling employees, and to compare the efficacy of two common surface wipe sampling materials. We used three sequential hand wipes and quantified the percentage of flame retardants that was removed by each hand wipe in the sequence. Two common wipe materials (gauze and twill) were used to compare the ability to remove flame retardants. The wipes were collected from 12 employees at a U.S. electronics recycling facility immediately at the end of their shift, prior to washing their hands. Results show that although the first wipe removed the highest median percent of the sum of the three wipes for most flame retardants, there was a wide range of the percentages of total individual flame retardants removed by both gauze (4%-98%) or twill hand wipe (1%-89%). Approximately half of the flame retardants a high percentage (>50%) removed by the second and third wipes. This suggests that a single wipe is not sufficient to characterize the extent of dermal contamination. The average of the total amount of flame retardants removed by twill wipes was greater than the average using gauze, but the difference was not statistically significant.

Amplification effect of haze on human exposure to halogenated flame retardants in atmospheric particulate matter and the corresponding mechanism

The health impact of haze is of great concern; however, few air quality studies have investigated trace pollutant contamination in the air. Size-segregated atmospheric particles (nine size fractions derived from PM₁₀) were collected in dwelling (indoor) and traffic (outdoor) environments in Xinxiang, China, during light pollution conditions (air quality index (AQI), 60-90) and heavy pollution conditions (AQI, 350-550), and they were analysed for halogenated flame retardants (HFRs), including polybrominated diphenyl ethers (PBDEs), novel brominated flame retardants (NBFRs) and Dechlorane Plus (DP) isomers. HFR occurrence levels generally decreased in the order of PBDEs > NBFRs > DPs. The total mean abundance ratios of heavy pollution/light pollution were 4.0, 2.9, 4.4 and 3.6 for PBDEs, NBFRs, DPs and HFRs, respectively. Meteorological conditions played distinctive roles in the HFR distribution in the air. Apparent differences were found for the particle size distribution of HFRs under light and heavy pollution conditions. In general, for adults, the estimated hazard quotient (HQ) and incremental lifetime cancer risk (ILCR_BDE-209) values were approximately 1.7 × 10^-2 and 9.3 × 10^-9 in heavy pollution conditions, respectively, which were significantly higher than those in light pollution conditions (1.8 × 10^-3 and 2.1 × 10^-9, respectively).

Estimation of Exposure to Organic Flame Retardants via Hand Wipe, Surface Wipe, and Dust: Comparability of Different Assessment Strategies

This study aimed to investigate the exposure of three occupational populations (i.e., office worker, taxi drivers, and security guards) to flame retardants by comparing different sampling approaches (i.e., hand wipe, surface wipe, and dust). Hand wipe samples were collected from 68 participants from three populations in Beijing, China. Dust and/or surface wipes were also sampled from their respective occupational workplaces. Ten phosphorus flame retardants (PFRs), two novel brominated flame retardants (NBFRs) and eight polybrominated diphenyl ethers (PBDEs) were analyzed. BDE209, decabromodiphenylethane (DBDPE), tris(chloropropyl) phosphate isomers (∑TCPP), tris(2-chloroethyl) phosphate (TCEP) and triphenyl phosphate (TPHP) were detected in at least 95% of the samples, collectively accounting for over 90% of the total concentrations in each type of samples. Concentrations and composition profiles of flame retardants differed in hand wipes of the three populations with summed level of all target compounds (∑FRs) ranked as taxi drivers > office workers > security guards. Most FRs in hand wipes were significantly correlated with those in surface wipes, whereas the correlations between hand wipes and dust are weak. Estimated exposure to FRs via dust ingestion and dermal absorption for each population varied when using different types of samples for exposure assessment, suggesting the importance of sampling strategy selection. Estimation via hand wipes indicated that taxi drivers were subjected to greater exposure to PFRs among three populations, while office workers were subjected to greater BFR exposure. Our data suggest hand wipes have the potential of being standardized into a noninvasive method for evaluating human exposure to environmental contaminants across different populations.

Dermal contact with furniture fabrics is a significant pathway of human exposure to brominated flame retardants

Despite extensive application in consumer products and concerns over their adverse health effects, how external exposure to brominated flame retardants (BFRs) contributes to their human body burdens is not yet fully understood. While recent studies focused on inadvertent indoor dust ingestion and diet as potential major pathways of exposure, dermal uptake has been largely overlooked. We provide the first experimentally-based assessment of dermal uptake of BFRs via contact with indoor dust and flame-retarded furniture fabrics. Results reveal substantial uptake from furniture fabrics (e.g. 8.1 ng pentaBDE/kg bw/day for adults in summer), exceeding the overall adult intake of pentaBDE estimated previously via other exposure pathways. For HBCDs, despite the low absorption fraction (<2.5%) from the studied fabrics, the estimated dermal uptake of UK adults and toddlers (101 and 76.9 ng/kg bw/day) exceed the reported average daily intakes of 7.9 and 43.0 ng/kg bw/day for these UK age groups. Conversely, uptake from dust was low (0.05 and 0.19 ng pentaBDE/kg bw/day for adults and toddlers, respectively), indicating previous pharmacokinetic approaches may have overestimated the significance of this route. Future exposure and risk assessment studies should consider dermal contact with treated products as a significant pathway of human exposure to BFRs and related chemicals.

Occupational exposure to polybrominated diphenyl ethers (PBDEs) and other flame retardant foam additives at gymnastics studios: Before, during and after the replacement of pit foam with PBDE-free foams

Coaches spend long hours training gymnasts of all ages aided by polyurethane foam used in loose blocks, mats, and other padded equipment. Polyurethane foam can contain flame retardant additives such as polybrominated diphenyl ethers (PBDEs), to delay the spread of fires. However, flame retardants have been associated with endocrine disruption and carcinogenicity. The National Institute for Occupational Safety and Health (NIOSH) evaluated employee exposure to flame retardants in four gymnastics studios utilized by recreational and competitive gymnasts. We evaluated flame retardant exposure at the gymnastics studios before, during, and after the replacement of foam blocks used in safety pits with foam blocks certified not to contain several flame retardants, including PBDEs. We collected hand wipes on coaches to measure levels of flame retardants on skin before and after their work shift. We measured flame retardant levels in the dust on window glass in the gymnastics areas and office areas, and in the old and new foam blocks used throughout the gymnastics studios. We found statistically higher levels of 9 out of 13 flame retardants on employees' hands after work than before, and this difference was reduced after the foam replacement. Windows in the gymnastics areas had higher levels of 3 of the 13 flame retardants than windows outside the gymnastics areas, suggesting that dust and vapor containing flame retardants became airborne. Mats and other padded equipment contained levels of bromine consistent with the amount of brominated flame retardants in foam samples analyzed in the laboratory. New blocks did not contain PBDEs, but did contain the flame retardants 2-ethylhexyl 2,3,4,5-tetrabromobenzoate and 2-ethylhexyl 2,3,4,5-tetrabromophthalate. We conclude that replacing the pit foam blocks eliminated a source of PBDEs, but not 2-ethylhexyl 2,3,4,5-tetrabromobenzoate and 2-ethylhexyl 2,3,4,5-tetrabromophthalate. We recommend ways to further minimize employee exposure to flame retardants at work and acknowledge the challenges consumers have identifying chemical contents of new products.

Exposure to brominated and organophosphate ester flame retardants in U.S. childcare environments: Effect of removal of flame-retarded nap mats on indoor levels

We assessed exposure to 39 brominated and 16 organophosphate ester flame retardants (FRs) from both dust and indoor air at seven childcare centres in Seattle, USA, and investigated the importance of nap mats as a source of these chemicals. Many childcare centres serving young children use polyurethane foam mats for the children's naptime. Until recently, the vast majority of these mats sold in the United States contained flame-retarded polyurethane foam to meet California Technical Bulletin 117 (TB117) requirements. With the 2013 update of TB117, allowing manufacturers to meet flammability standards without adding FRs to filling materials, FR-free nap mats have become widely available. We conducted an intervention study by actively switching out FR-treated nap mats with FR-free nap mats and measuring FR levels in indoor air and dust before and after the switch-out. The predominant FRs found in dust and indoor air were 2-ethylhexyl tetrabromobenzoate (EHTBB) and tris(1-chloro-2-propyl) phosphate (TCIPP), respectively. Nap mat samples analysed from four of the six centres contained a Firemaster^® mixture, while one mat was predominantly treated with tris(1,3-dichloroisopropyl) phosphate (TDCIPP) and the other contained no detectable target FRs. After replacement, there was a significant decrease (p = 0.03-0.09) in median dust concentrations for bis(2-ethylhexyl) tetrabromophthalate (BEHTBP), EHTBB, tris(4-butylphenyl) phosphate (TBPP), and TDCIPP with reductions of 90%, 79%, 65%, and 42%, respectively. These findings suggest that the nap mats were an important source of these FRs to dust in the investigated childcare environments and that a campaign of swapping out flame-retarded mats for FR-free ones would reduce exposure to these chemicals. While calculated exposure estimates to the investigated FRs via inhalation, dust ingestion, and dermal absorption were below established reference dose values, they are likely underestimated when considering the toddlers' direct contact to the mats and personal cloud effects.

Brominated flame retardants in black plastic kitchen utensils: Concentrations and human exposure implications

Concerns exist that restricted brominated flame retardants (BFRs) present in waste polymers may have, as a result of recycling, inadvertently contaminated items not required to meet flame retardancy regulations (e.g. plastic kitchen utensils). To investigate the extent to which kitchen utensils are contaminated with BFRs and the potential for resultant human exposure, we collected 96 plastic kitchen utensils and screened for Br content using a hand-held X-ray fluorescence (XRF) spectrometer. Only 3 out of 27 utensils purchased after 2011 contained detectable concentrations of Br (≥3μg/g). In contrast, Br was detected in 31 out of the 69 utensils purchased before 2011. Eighteen utensils with Br content higher than 100μg/g, and 12 new utensils were selected for GC-MS analysis of BFRs. BFRs targeted were polybrominated diphenyl ethers (PBDEs) BDE-28, 47, 99, 100, 153, 154, 183 and 209, and novel BFRs (NBFRs) pentabromoethylbenzene (PBEB), 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EH-TBB), 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), bis(2-ethylhexyl)-3,4,5,6-tetrabromo-phthalate (BEH-TEBP) and decabromodiphenyl ethane (DBDPE). The ability of XRF to act as a surrogate metric of BFR concentration was indicated by a significant (Spearman coefficient=0.493; p=0.006) positive relationship between Br and ΣBFR concentration. Measurements of ΣBFRs were always exceeded by those of Br. This may be due partly to the presence of BFRs not targeted in our study and also to reduced extraction efficiency of BFRs from utensils. Of our target BFRs, BDE-209 was the most abundant one in most samples, but an extremely high concentration (1000μg/g) of BTBPE was found in one utensil. Simulated cooking experiments were conducted to investigate BFR transfer from selected utensils (n=10) to hot cooking oil, with considerable transfer (20% on average) observed. Estimated median exposure via cooking with BFR contaminated utensils was 60ng/day for total BFRs. In contrast, estimated exposure via dermal contact with BFR-containing kitchen utensils was minimal.

Legacy and novel brominated flame retardants in interior car dust - Implications for human exposure

Brominated flame retardants (BFRs) are organobromine compounds with an inhibitory effect on combustion chemistry tending to reduce the flammability of products. Concerns about health effects and environmental threats have led to phase-out or restrictions in the use of Penta-, Octa- and Deca-BDE technical formulations, increasing the demand for Novel BFRs (NBFRs) as replacements for the banned formulations. This study examined the occurrence of legacy and NBFRs in the dust from the interior of private cars in Thessaloniki, Greece, aged from 1 to 19 years with variable origin and characteristics. The determinants included 20 Polybrominated Diphenyl Ethers (PBDEs) (Di-to Deca-BDEs), four NBFRs such as Decabromodiphenylethane (DBDPE), 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (TBB), and bis(2-ethylhexyl)-3,4,5,6-tetrabromophthalate (TBPH), three isomers of hexabromocyclododecane (HBCD), and tetrabromobisphenol A (TBBPA). The concentrations of ∑₂₀PBDE ranged from 132 to 54,666 ng g^-1 being dominated by BDE-209. The concentrations of ∑₄NBFRs ranged from 48 to 7626 ng g^-1 and were dominated by DBDPE, the major substitute of BDE-209. HBCDs ranged between <5 and 1745 ng g^-1, with alpha-HBCD being the most prevalent isomer Finally, the concentrations of TBBPA varied from <10 to 1064 ng g^-1. The concentration levels and composition profiles of BFRs were investigated in relation to the characteristics of cars, such as year of manufacture, country of origin, and interior equipment (type of car seats, electronic and electrical components, ventilation, etc.). The average daily intakes of selected BFRs (BDE-47, BDE-99, BDE-153, BDE-209, TBB, BTBPE, TBPH, DBDPE, HBCDs and TBBPA) via ingestion and dermal absorption were estimated for adults and toddlers. The potential health risk due to BFRs was found to be several orders of magnitude lower than their corresponding reference dose (RfD) values.

Polyhalogenated compounds (chlorinated paraffins, novel and classic flame retardants, POPs) in dishcloths after their regular use in households

Dishcloths are routinely used in the clean-up process following daily kitchen activities and are thus subject to contamination commensurate with their frequent use. Here we analyzed dishcloths for the occurrence of polyhalogenated compounds after 14days of use in household kitchens. Analysis of 19 dishcloths revealed the presence of 29 polyhalogenated contaminants with total mean/median concentrations of 6,900/3,600ng/dishcloth, respectively. The spectrum featured classic and novel halogenated flame-retardants (HFRs) like polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCD), decabromodiphenyl ethane (DBDPE), pentabromoethylbenzene (PBEB), chlordene plus and dechlorane plus, as well as typical chloropesticides and background contaminants (e.g. hexachlorobenzene (HCB), p,p'-dichlorodiphenyldichloroethene (p,p'-DDE), polychlorinated biphenyls (PCBs) and lindane). The individual dishcloths showed highly variable fingerprints of polyhalogenated compounds. If present, medium-chain chlorinated paraffins (MCCPs) were by far the most prominent compound class with up to 55,400ng/dishcloth. Without consideration of chlorinated paraffins, the mean concentration of other polychlorinated compounds (270ng/dishcloth) was generally one order of magnitude lower than the mean concentration of brominated flame retardants (BFRs) (1,700ng/dishcloth). Our study verified that a wide range of polyhalogenated compounds is readily available in the kitchen environment. Furthermore, dishcloths are ordinarily handled without gloves or hand protection, given the observed concentrations of polyhalogenated compounds in dishcloths, such handling may serve as an additional exposure pathway for human users. Evaluation of this thesis was supported by conduction of a dermal uptake assessment.