Towards a systematic understanding of the dynamic fate of polychlorinated biphenyls in indoor, urban and rural environments

Are We Justified in Modeling Human Exposure to Chlorinated Paraffin Mixtures Using the Average Properties of Congeners and Homologues?

Concern over human exposure to chlorinated paraffin (CP) mixtures keeps increasing. The absence of a comprehensive understanding of how human exposure varies with the physicochemical properties of CP constituents has hindered the ability to determine at what level of aggregation exposure to CPs should be assessed. We answer this question by comparing exposure predicted with either a "complex" method that utilizes isomer-specific properties or "simplified" methods that rely on median properties of congener, homologue, or short-/medium-/long-chain CP groups. Our results demonstrate the wide range of physicochemical properties across CP mixtures and their dependence on molecular structures. Assuming unit emissions in the environment, these variances translate into an extensive disparity in whole-body concentrations predicted for different isomers, spanning ∼11 orders of magnitude. CPs with 13-19 carbons and 6-10 chlorines exhibit the highest human exposure potential, primarily owing to moderate to high hydrophobicity and slow environmental degradation and biotransformation. Far-field exposure is dominant for most CP constituents. Our study underscores that using average properties of congener, homologue, or S/M/LCCP groups yields results that are consistent with those derived from isomer-based modeling, thus offering an efficient and practical framework for future risk assessments and human exposure studies of CPs and other complex chemical mixtures.

Understanding the importance of atmospheric transformation in assessing the hazards of liquid crystal monomers

Liquid crystal monomers (LCMs), a group of synthetic chemicals released from liquid crystal devices such as televisions and smartphones, have recently been recognized as emerging contaminants due to their widespread occurrence in the environment and potential negative impacts on human health. Airborne LCMs can undergo atmospheric oxidation reactions to form various transformation products. Despite the certainty of atmospheric transformation chemistry, the knowledge about the hazard properties of transformation products remains largely unknown. Here, we perform an in silico model-based evaluation of the persistence, bioaccumulation potential, mobility, and toxicity of two representative LCMs, namely, 1-ethyl-4-(4-(4-propylcyclohexyl)phenyl)benzene and 4''-ethyl-2'-fluoro-4-propyl-1,1':4',1''-terphenyl, and their transformation products. We found that, among the investigated transformation products, 38% have overall persistence greater than the minimum of 331 days among the persistent organic pollutants regulated by the Stockholm Convention, 62% meet the bioaccumulation threshold of 1000 L kg-1 used by the United States Environmental Protection Agency, 44% are classified "mobile" according to the criterion used by the German Environmental Agency, and 58% have the potential to induce unacceptable toxic effects in aquatic organisms. Furthermore, we identified several transformation products with increased persistence, bioaccumulation potential, and mobility compared to their parent compounds. These findings not only offer insights for prioritizing LCM transformation products for future risk assessment, but also underscore the significance of considering atmospheric transformation in the evaluation of environmental risks posed by emerging contaminants, including LCMs.

Chemical Space Covered by Applicability Domains of Quantitative Structure-Property Relationships and Semiempirical Relationships in Chemical Assessments

A significant number of chemicals registered in national and regional chemical inventories require assessments of their potential "hazard" concerns posed to humans and ecological receptors. This warrants knowledge of their partitioning and reactivity properties, which are often predicted by quantitative structure-property relationships (QSPRs) and other semiempirical relationships. It is imperative to evaluate the applicability domain (AD) of these tools to ensure their suitability for assessment purpose. Here, we investigate the extent to which the ADs of commonly used QSPRs and semiempirical relationships cover seven partitioning and reactivity properties of a chemical "space" comprising 81,000+ organic chemicals registered in regulatory and academic chemical inventories. Our findings show that around or more than half of the chemicals studied are covered by at least one of the commonly used QSPRs. The investigated QSPRs demonstrate adequate AD coverage for organochlorides and organobromines but limited AD coverage for chemicals containing fluorine and phosphorus. These QSPRs exhibit limited AD coverage for atmospheric reactivity, biodegradation, and octanol-air partitioning, particularly for ionizable organic chemicals compared to nonionizable ones, challenging assessments of environmental persistence, bioaccumulation capability, and long-range transport potential. We also find that a predictive tool's AD coverage of chemicals depends on how the AD is defined, for example, by the distance of a predicted chemical from the centroid of the training chemicals or by the presence or absence of structural features.

A level IV fugacity-based multimedia model based on steady-state particle/gas partitioning theory and its application to study the spatio-temporal trends of PBDEs in atmosphere of northeast China

Particle/gas (P/G) partitioning can significantly affect the environmental behavior of atmospheric pollutants. In this study, we established a large-scale level IV fugacity-based multimedia model (the S-L4MF Model) based on the steady-state P/G partitioning theory. The spatial and temporal trends with the atmospheric contamination of polybrominated diphenyl ethers (PBDEs) in northeastern China under various climate conditions were simulated by the model. There is a reasonable agreement between the simulated and measured gaseous and particulate concentrations of 3 selected PBDE congeners (BDE-47, -99 and -209). For BDE-47, -99 and -209, 91.9 %, 94.8 % and 86.2 % of data points in the evaluation of the spatial trend, whereas 97.4 %, 98.2 % and 91.6 % of data points in the evaluation of the temporal trend, exhibit discrepancies between the modeled and measured data within 1 order of magnitude. The S-L4MF Model performed better than the other model with the same configuration but an equilibrium-state P/G partitioning assumption. The sensitivity and uncertainty analysis indicated that the air temperature and hexadecane-air partition coefficient were the dominant influencing factors on atmospheric concentrations. In addition, the model was successfully applied to study the inter-annual and seasonal variations of gaseous and particulate concentrations of the three PBDEs during 1971-2020 in Harbin, a northeastern Chinese city. Finally, we illustrated the potential to use the model to understand P/G partitioning behavior and the effects of snow and ice on atmospheric concentrations. In summary, the S-L4MF Model provided a powerful and effective tool for studying the environmental behavior of atmospheric organic pollutants, especially in cold regions.

Modeling sorption of environmental organic chemicals from water to soils

Reliable estimation of chemical sorption from water to solid phases is an essential prerequisite for reasonable assessments of chemical hazards and risks. However, current fate and exposure models mostly rely on algorithms that lack the capability to quantify chemical sorption resulting from interactions with multiple soil constituents, including amorphous organic matter, carbonaceous organic matter, and mineral matter. Here, we introduce a novel, generic approach that explicitly combines the gravimetric composition of various solid constituents and poly-parameter linear free energy relationships to calculate the solid-water sorption coefficient (Kd) for non-ionizable or predominantly neutral organic chemicals with diverse properties in a neutral environment. Our approach demonstrates an overall statistical uncertainty of approximately 0.9 log units associated with predictions for different types of soil. By applying this approach to estimate the sorption of 70 diverse chemicals from water to two types of soils, we uncover that different chemicals predominantly exhibit sorption onto different soil constituents. Moreover, we provide mechanistic insights into the limitation of relying solely on organic carbon normalized sorption coefficient (KOC) in chemical hazard assessment, as the measured KOC can vary significantly across different soil types, and therefore, a universal cut-off threshold may not be appropriate. This research highlights the importance of considering chemical properties and multiple solid constituents in sorption modeling and offers a valuable theoretical approach for improved chemical hazard and exposure assessments.

Emission and environmental distribution of decabromodiphenyl ethane (DBDPE) in China from 2006 to 2026: Retrospection, forecasting, and implications for assessment and management

Decabromodiphenyl ethane (DBDPE) is the main alternative to decabromodiphenyl ether (deca-BDE) in commercial use. However, there is increasing evidence show that DBDPE is a potential persistent organic pollutant, and it has been found ubiquitously in environmental media across China in recent years. Monitoring studies have not been able to determine the overall levels and temporal trends of DBDPE contamination in China, and have been unable to explain how emission patterns can affect their environmental distribution. Therefore, this study estimated the temporal variance of DBDPE emissions and environmental concentrations in five regions of China from 2006 to 2026 using the PROduction-To-EXposure (PROTEX) mass balance model. The results showed that Guangdong Province was the greatest DBDPE pollution hotspot in China due to emissions from plastics manufacturing and e-waste disposal; there was also severe pollution in Shandong Province, where almost all the DBDPE in China is produced. The DBDPE concentrations in indoor and outdoor environments increased substantially in all regions during 2006-2021. Furthermore, in Guangdong Province and Shandong Province, the ratio of indoor/outdoor air concentrations was greater than or close to 1, indicative of significant outdoor emission sources of DBDPE. In contrast, the ratios for the Beijing-Tianjin-Hebei region, East China, and Southwest China were below 1 due to the indoor use of electronic equipment containing DBDPE. The temporal trends of these ratios indicated that DBDPE contamination has gradually spread from high-concentration environments with strong emission sources to low-concentration environments. The outcomes of this study have important implications for the risk assessment of DBDPE use in China and can be used to establish contamination-mitigation actions.

Understanding inter-individual variability in short-chain chlorinated paraffin concentrations in human blood

Chlorinated paraffins (CPs), particularly short-chain CPs (SCCPs), have been reported in human blood with high detection frequency and often high variation among individuals. However, factors associated with and their contributions to inter-individual variability in SCCP concentrations in human blood have not been assessed. In this study, we first measured SCCP concentrations in 57 human blood samples collected from individuals living in the same vicinity in China. We then used the PROduction-To-Exposure model to investigate the impacts of variations in sociodemographic data, biotransformation rates, dietary patterns, and indoor contamination on inter-individual variability in SCCP concentrations in human blood. Measured ∑SCCP concentrations varied by a factor of 10 among individuals with values ranging from 122 to 1230 ng/g, wet weight. Model results show that age, sex, body weight, and dietary composition played a minor role in causing variability in ∑SCCP concentrations in human blood given that modeled ∑SCCP concentrations ranged over a factor of 2 - 3 correlated to the variations of these factors. In contrast, variations in the modeled ΣSCCP concentrations increased to factors of 6 and 8 when variability in biotransformation rates and indoor contamination were considered, respectively, indicating these two factors could be the most influential on inter-individual variability in SCCP concentrations in human blood.

Indoor partitioning and potential thirdhand exposure to carbonyl flavoring agents added in e-cigarettes and hookah tobacco

Flavoring agents added to the e-cigarettes and hookah tobacco have increased the attractiveness of novel nicotine products. Many widely used flavorings are carbonyls, which are toxic to humans. In an indoor environment, residents can be exposed to such harmful flavorings previously emitted to the surrounding environment, through a process termed thirdhand exposure. The recent discovery of a large volume of indoor reservoirs emphasizes the importance of indoor partitioning, which is responsible for thirdhand exposure. Indoor partitioning can be expressed with partitioning coefficients, such as Henry's law solubility constant (H). However, reliable H values for many key flavorings are currently lacking. To better understand their environmental behavior, this study experimentally determined the effective Henry's law constant (Hcps,eff) using the inert gas stripping (IGS) method. Further, the influence of the hydration process for target flavorings was quantified using proton nuclear magnetic resonance (¹H NMR) spectroscopy. We found that hydration of α-dicarbonyls (diacetyl and 2,3-pentanedione) enhanced their Hcps,eff from their intrinsic Henry's law constant (Hcps) by a factor of 3.52 and 2.88, respectively. The two-dimensional partitioning plots were employed to simulate the indoor phase distribution and evaluate the pathways of human exposure. Our findings show that the indoor partitioning of many harmful flavorings is highly sensitive to temperature and the size of indoor reservoirs, indicating that residents are likely to experience third-hand exposure.

A preliminary assessment of microplastics in indoor dust of a developing country in South Asia

Microplastics (MPs) pollution is an emerging global environmental concern. Considering the high fraction of time people spend indoors, the human population can be directly exposed to this contamination through indoor dust. This preliminary study evaluates MPs' abundance and human health risk assessment in the deposited indoor dust. A total of forty dust samples (n = 20) were collected from homes in two different cities (Pakistan) in steel mesh pouches using the vacuum cleaner. The identification and quantification of MPs were conducted with a stereo microscope, whereas the qualitative assessment was performed with Fourier transform infrared spectroscopy (FTIR). The US EPA parameters to calculate the human health risk assessment were used to determine MPs' risk per-day/month/year. Overall, microfibers were the dominant category, followed by microfilms, micro-fragments, and nurdles. The chemical categorization of MPs was revealed as polyester, polyethylene, copolymers of polypropylene, and polyurethane. In Lahore, an average abundance of 241.45 (items/m2) MPs were observed compared to Sahiwal, with 162.1 (items/m2). More than 90% of the identified MPs were microfibers, with higher detection frequency and abundance in Lahore than Sahiwal. The human health risk assessment revealed high exposure risk because of indoor MPs. Moreover, toddlers were more vulnerable as compared to adults at both low and high exposure risk scenarios. There is an imminent need to conduct in-depth risk assessment focusing on the respirable fraction of MPs.

Spatially resolved environmental fate models: A review

Spatially resolved environmental models are important tools to introduce and highlight the spatial variability of the real world into modeling. Although various spatial models have been developed so far, yet the development and evaluation of these models remain a challenging task due to several difficulties related to model setup, computational cost, and obtaining high-resolution input data (e.g., monitoring and emission data). For example, atmospheric transport models can be used when high resolution predicted concentrations in atmospheric compartments are required, while spatial multimedia fate models may be preferred for regulatory risk assessment, life cycle impact assessment of chemicals, or when the partitioning of chemical substances in a multimedia environment is considered. The goal of this paper is to review and compare different spatially resolved environmental models, according to their spatial, temporal and chemical domains, with a closer insight into spatial multimedia fate models, to achieve a better understanding of their strengths and limitations. This review also points out several requirements for further improvement of existing models as well as for their integration.

Emerging investigator series: the role of chemical properties in human exposure to environmental chemicals

One of the ultimate goals of environmental exposure science is to mechanistically understand how chemical properties and human behavior interactively determine human exposure to the wide spectrum of chemicals present in the environment. This comprehensive review assembles state-of-the-art knowledge of the role of partitioning, dissociation, mass transfer, and reactive properties in human contact with and absorption of organic chemicals via oral, dermal, and respiratory routes. Existing studies have revealed that chemicals with different properties vary greatly in mass distribution and occurrence among multiple exposure media, resulting in distinct patterns of human intake from the environment. On the other hand, these chemicals encounter different levels of resistance in the passage of intestinal, dermal, and pulmonary absorption barriers and demonstrate different levels of bioavailability, due to the selectivity of biochemical, anatomical and physiological structures of these absorption barriers. Moving forward, the research community needs to gain more in-depth mechanistic insights into the complex processes in human exposure, advance the technique to better characterize and predict chemical properties, generate and leverage experimental data for a more diverse range of chemicals, and describe better the interactions between chemical properties and human behavior.

Development and Evaluation of a Holistic and Mechanistic Modeling Framework for Chemical Emissions, Fate, Exposure, and Risk

BACKGROUND

Large numbers of chemicals require evaluation to determine if their production and use pose potential risks to ecological and human health. For most chemicals, the inadequacy and uncertainty of chemical-specific data severely limit the application of exposure- and risk-based methods for screening-level assessments, priority setting, and effective management.

OBJECTIVE

We developed and evaluated a holistic, mechanistic modeling framework for ecological and human health assessments to support the safe and sustainable production, use, and disposal of organic chemicals.

METHODS

We consolidated various models for simulating the PROduction-To-EXposure (PROTEX) continuum with empirical data sets and models for predicting chemical property and use function information to enable high-throughput (HT) exposure and risk estimation. The new PROTEX-HT framework calculates exposure and risk by integrating mechanistic computational modules describing chemical behavior and fate in the socioeconomic system (i.e., life cycle emissions), natural and indoor environments, various ecological receptors, and humans. PROTEX-HT requires only molecular structure and chemical tonnage (i.e., annual production or consumption volume) as input information. We evaluated the PROTEX-HT framework using 95 organic chemicals commercialized in the United States and demonstrated its application in various exposure and risk assessment contexts.

RESULTS

Seventy-nine percent and 97% of the PROTEX-HT human exposure predictions were within one and two orders of magnitude, respectively, of independent human exposure estimates inferred from biomonitoring data. PROTEX-HT supported screening and ranking chemicals based on various exposure and risk metrics, setting chemical-specific maximum allowable tonnage based on user-defined toxicological thresholds, and identifying the most relevant emission sources, environmental media, and exposure routes of concern in the PROTEX continuum. The case study shows that high chemical tonnage did not necessarily result in high exposure or health risks.

CONCLUSION

Requiring only two chemical-specific pieces of information, PROTEX-HT enables efficient screening-level evaluations of existing and premanufacture chemicals in various exposure- and risk-based contexts. https://doi.org/10.1289/EHP9372.

Human Chemical Exposure from Background Emissions in the United States and the Implication for Quantifying Risks from Marginal Emission Increase

The linear dose-response relationship has long been assumed in assessments of health risk from an incremental chemical emission relative to background emissions. In this study, we systematically examine the relevancy of such an assumption with real-world data. We used the reported emission data, as background emissions, from the 2017 U.S. National Emission Inventory for 95 organic chemicals to estimate the central tendencies of exposures of the general U.S. population. Previously published nonlinear dose-response relationships for chemicals were used to estimate health risk from exposure. We also explored and identified four intervals of exposure in which the nonlinear dose-response relationship may be linearly approximated with fixed slopes. Predicted rates of exposure to these 95 chemicals are all within the lowest of the four intervals and associated with low health risk. The health risk may be overestimated if a slope on the dose-response relationship extrapolated from toxicological assays based on high response rates is used for a marginal increase in emission not substantially higher than background emissions. To improve the confidence of human health risk estimates for chemicals, future efforts should focus on deriving a more accurate dose-response relationship at lower response rates and interface it with exposure assessments.

Polychlorinated biphenyls in indoor dust from urban dwellings of Lahore, Pakistan: Congener profile, toxicity equivalency, and human health implications

This study is the pioneer assessment of the PCBs in indoor dust particles (from air conditioners) of an urbanized megacity from South Asian. The ∑₃₅ PCB concentration ranged from 0.27 to 152.9 ng/g (mean: 24.84 ± 22.10 ng/g). The tri- and tetra-PCBs were dominant homologues, contributing 57.36% of the total PCB concentrations. The mean levels of Σ₈ -dioxin-like (DL), Σ₆ -indicator PCBs and WHO₂₀₀₅ -TEQ for DL-PCBs were 2.22 ± 2.55 ng/g, 9.49 ± 8.04 ng/g and 4.77 ± 4.89 pg/g, respectively. The multiple linear regression indicated a significant correlation of dusting frequency (p = 1.06 × 10-04) and age of the house (p = 1.02 × 10-06) with PCB concentrations in indoor environment. The spatial variation of PCB profile revealed relatively higher concentrations from sites near to illegal waste burning spots, electrical locomotive workshops, and grid stations. Human health risk assessment of PCBs for adults and toddlers through all three exposure routes (ie, inhalation, ingestion, and dermal contact) demonstrated that toddlers were vulnerable to high cancer risk (4.32 × 10^-04 ), while adults were susceptible from low to moderate levels of risk (3.16 × 10^-05 ). Therefore, comprehensive investigations for PCBs in the indoor settings, focusing particularly on the sensitive populations with relationship to the electronic devices, transformers, and illegal waste burning sites, are recommended.

Mass dose rates of particle-bound organic pollutants in the human respiratory tract: Implications for inhalation exposure and risk estimations

To date, little is known about the effective doses of airborne particulate matter (PM) and PM-bound hazardous organic components to the human respiratory tract (HRT). In the light of this, here we provide particle mass dose rates (dose per hour of exposure) of PM and a suite of PM-bound hazardous organic compounds in the HRT for two population age groups (adults & children). More specifically, the mass dose rates of PM and PM-bound polycyclic aromatic hydrocarbons (PAHs), nitrated-PAH (NPAHs), polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs) and polybrominated diphenyl ethers (PBDEs) were estimated at two urban sites using a multiple path particle dosimetry model. We find that, in most cases, the total mass doses are following similar variations across sites and seasons as their ambient total concentrations, however their distribution in the HRT is a function of the particle size distributions and the physiological parameters of each age group. More specifically, the majority of the deposited mass of PM and all the chemical components investigated was accumulated in the upper airways instead of the lungs. We further show that children, due to their different physiology, are more susceptible and receive larger fraction of the total mass doses in the deepest parts of the lungs compared to the adults' group. Comparing the traditional method for estimating the inhalation risk, which is based on the ambient concentration of pollutants, and a modified version using the mass dose in the HRT, we find that the former may overestimate the reported risks. The results presented here provide a novel dataset composed by previously undetermined doses of hazardous airborne particulate organic components in the HRT and demonstrate that alternative health risk estimation approaches may capture some variabilities that are traditionally overlooked.

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

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

Addressing uncertainty in mouthing-mediated ingestion of chemicals on indoor surfaces, objects, and dust

In indoor environments, humans ingest chemicals present as surface residues and bound to settled particles (dust), through mouthing hands (hand-to-mouth transfer) and objects (object-to-mouth transfer). Here, we introduce a novel modeling approach in support of systematic investigation into the mouthing-mediated ingestion of chemicals present in indoor environments. This model explicitly considers the indoor dynamics of dust and chemicals, building on mechanistic links with physicochemical properties of chemicals, features of the indoor environment, and human activity patterns. The evaluation of this model demonstrates that it satisfactorily reproduces chemical hand loadings and exposure data reported in the literature. We then use the evaluated model to investigate the response of mouthing-mediated ingestion to chemical partitioning between the gas phase and solid phases, expressed as the octanol-air partition coefficient (K_OA). Assuming a unit emission rate to the indoor environment, we find that low-volatility chemicals (with a K_OA greater than 10⁹) are more efficiently enriched in hand skin, resulting in higher mouthing-mediated ingestion than other compounds. For individuals living in a room with a typical level of dustiness, more than half of the chemical mass found in their hands comes from dust transfer, whereas more than half of the chemical mass ingested is the fraction present as residues on hands. We also use the new model to explore how the mouthing-mediated ingestion of chemicals is dependent on factors describing the indoor environment and human behavior. The model predicts that less frequent cleaning leads to higher accumulation of dust on indoor surfaces, thereby transferring more chemicals to hands and mouth in each contact. Introducing more dust into the room, but maintaining the same cleanup frequency, increases the dustiness of indoor surfaces, which promotes the transfer of relatively volatile chemicals (with a K_OA lower than 10⁹) to hands and mouth but decreases the transfer of chemicals with low volatility. More frequent hand contact with indoor surfaces increases both the hand loading and mouthing-mediated ingestion of chemicals, but the increases are more remarkable for adults than children because the higher surface contact frequency of children "saturates" hand loadings. An increase in handwashing frequency lowers the hand loading and mouthing-mediated ingestion of chemicals and this mitigating process is more prominent for relatively volatile chemicals. The new evaluated modeling approach can facilitate the prediction of mouthing-mediated ingestion for various age groups and the model predictions can be used to aid future fate and (bio)monitoring studies focusing on indoor contamination.

Evaluating consumer exposure to disinfecting chemicals against coronavirus disease 2019 (COVID-19) and associated health risks

Disinfection of surfaces has been recommended as one of the most effective ways to combat the spread of novel coronavirus (SARS-CoV-2) that causes coronavirus disease 2019 (COVID-19). However, overexposure to disinfecting chemicals may lead to unintended human health risks. Here, using an indoor fate and chemical exposure model, we estimate human exposure to 22 disinfecting chemicals on the lists recommended by various governmental agencies against COVID-19, resulting from contact with disinfected surfaces and handwashing. Three near-field exposure routes, i.e., mouthing-mediated oral ingestion, inhalation, and dermal absorption, are considered to calculate the whole-body uptake doses and blood concentrations caused by single use per day for three age groups (3, 14, and 24-year-old). We also assess the health risks by comparing the predicted whole-body uptake doses with in vivo toxicological data and the predicted blood concentrations with in vitro bioactivity data. Our results indicate that both the total exposure and relative contribution of each exposure route vary considerably among the disinfecting chemicals due to their diverse physicochemical properties. 3-year-old children have consistent higher exposure than other age groups, especially in the scenario of contact with disinfected surfaces, due to their more frequent hand contact and mouthing activities. Due to the short duration of handwashing, we do not expect any health risk from the use of disinfecting chemicals in handwashing. In contrast, exposure from contact with disinfected surfaces may result in health risks for certain age groups especially children, even the surfaces are disinfected once a day. Interestingly, risk assessments based on whole-body uptake doses and in vivo toxicological data tend to give higher risk estimates than do those based on blood concentrations and in vitro bioactivity data. Our results reveal the most important exposure routes for disinfecting chemicals used in the indoor environment; they also highlight the need for more accurate data for both chemical properties and toxicity to better understand the risks associated with the increased use of disinfecting chemicals in the pandemic.

Degradation mechanism of biphenyl and 4-4'-dichlorobiphenyl cis-dihydroxylation by non-heme 2,3 dioxygenases BphA: A QM/MM approach

Biphenyl 2,3-dioxygenase (BphA), a Rieske-type and first enzyme in the aerobic degradation process, plays a key role in the metabolizing process of biphenyl/polychlorinated biphenyl aromatic pollutants in the environment. To understand the catalytic mechanism of biphenyl 2,3-dioxygenase, the conversions leading to the cis-diols are investigated by means of quantum mechanics/molecular mechanics (QM/MM) method. A hydroperoxo-iron (III) species is involved in the enzyme-catalyzed reaction. Herein, we explored the direct reaction mechanism of hydroperoxo-iron (III) species with biphenyl and 4-4'-dichlorobiphenyl. The reaction process involves an epoxide intermediate, it could develop into a carbocation intermediate, and ultimately evolve into a cis-diol product. The important roles of several residues during the dioxygenation process were highlighted. This study may provide theoretical support for further directed mutations and enzymatic engineering of BphA, as well as promote the development of degrading environmentally persistent biphenyl/polychlorinated biphenyl aromatic contaminants.

Concentrations and accumulation rates of polychlorinated biphenyls in soil along an urban-rural gradient in Shanghai

This study proposed an in situ soil experimental system to quantify concentration and accumulation rates of polychlorinated biphenyl (PCB) congeners in the soil in a rural-urban fringe and correlated them with multiple variables in the area. Variables, including road density, normalized difference vegetation index (NDVI), distance to the nearest highway and industrial area from the soil experimental sites, land-use impact index, population density, population change index (PCI), total population, and percentage of water area, were used to explain the concentration of different PCB congeners in soil during the experimental period. A proportion of 40.1%, 22.6%, 56.9%, and 34.3% accumulation rates of PCB8, PCB18, PCB28, and PCB118, respectively was explained by industrial developments, using stepwise linear regression analysis. NDVI was used to explain 33.6%, 61.5%, 49.1%, and 53.2% accumulation rates of PCB44, PCB101, PCB187, and PCB180, respectively. Filtering and transferring of airborne organic pollutants from atmosphere to soil by forests or tree stands and farmlands were all NDVI-related factors that affected the concentrations and accumulation rates of PCB congeners in soil. The traffic-related particle deposition might be the reason why the concentrations and accumulation rates of PCB congeners in soil were affected by road density. The findings can help quantitatively understand urbanization and the associated environmental effects. Graphic abstract.

Determination of the Polychlorinated Biphenyls Distribution in Different Fat Tissues of Cattle by Age and Gender

Polychlorinated biphenyls (PCBs), which cause environmental pollution, are found in animal-based fatty foods. Due to their long half-life and lipophilic properties, they can accumulate in the fat tissues of cattle. The study was conducted to compare the PCB levels (PCB28, 52, 101, 118, 138, 153, and 180) in the different fat tissues (muscle, liver, kidney, spinal cord, lung, back fat, perihepatic fat, and perirenal fat) of cattle by age and gender. This information is also useful to evaluate the exposure risks for different bovine edible tissues. Therefore, 15 female and 15 male cattle under 24 months of age and 15 female and 15 male cattle over 24 months of age were used, and 480 samples were analyzed for target PCBs using gas chromatography-mass spectrometry. Of all the samples, two (50.2 µg/kg in perihepatic fat and 51.1 µg/kg in kidney) were found above the maximum residue limit; these samples were taken from the animals in the elderly female group (over 24 months). There were more PCBs in cattle older than 2 years. Muscle, kidney, and perihepatic fat presented higher PCB concentrations than other tissues, and perirenal fat presented lower PCB concentrations than other tissues. PCB101, PCB153, and PCB138 were found to have the highest contribution to the PCB concentration. Thus, it is concluded that perihepatic fat, muscle, or kidney should be sampled, particularly in routine residue monitoring, and specifically analyzed for PCB101, PCB153, and PCB138.

Clarifying Temporal Trend Variability in Human Biomonitoring of Polybrominated Diphenyl Ethers through Mechanistic Modeling

Human biomonitoring data collected from individuals of the same age sampled in different years provide within-age temporal trends, which are often employed to evaluate the effectiveness of chemical regulatory policies. For polybrominated diphenyl ethers (PBDEs), this within-age temporal trend has been observed to vary between congeners and age groups. We systematically explore the mechanisms responsible for such variability through simulating human exposure via multiple exposure pathways to PBDEs released from multiple lifecycle stages. Our simulation indicates that, after new use of PBDEs is banned, emissions to the outdoor environment from use and waste disposal outlast those to the indoor environment from the indoor use phase, leading to slower decline rates in the contamination of food items sourced from the outdoor environment than that from indoors. Compared with indoor exposure pathways, the consumption of contaminated food contributes more to the exposure (i) to more hydrophobic, recalcitrant congeners, and (ii) of adults than children, which results in slower rates of decline in the within-age temporal trend of those congeners and in adults. The within-age temporal trend is influenced to a lesser extent by the elimination of PBDEs from the human body, e.g., differences in biotransformation potential of congeners, growth dilution, and pre- and postnatal exposures by children.

Polycyclic aromatic hydrocarbons, polychlorinated biphenyls and legacy and current pesticides in indoor environment in Australia - occurrence, sources and exposure risks

Paired indoor air and floor dust samples were collected from residential houses and offices (n = 28) in two Australian cities in 2015. For the air samples, a modified passive air sampler (PAS) was used to collect semi-volatile organic compounds (SVOCs) in gaseous phase and airborne particles simultaneously. Sampling rates (R) of the PAS for gaseous SVOCs ranged from 0.69 to 3.4 m³ sampler^-1 day^-1. Out of the 33 analytes, 22, 14 and 17 compounds were detected (above the method detection limit) in over 50% of air, airborne particles and floor dust samples respectively. The highest median level in air, airborne particles and floor dust was observed for phenanthrene (2.0 ng m^-3), permethrin (8800 ng g^-1) and permethrin (5100 ng g^-1) respectively. Among polychlorinated biphenyl (PCB) congeners, with few exceptions, the largest contribution was from 3,3'-dichlorobiphenyl (PCB11) for both indoor air and floor dust samples. In these houses and offices, the indoor level of polycyclic aromatic hydrocarbons (PAHs) was mainly influenced by ambient (outdoor) air. Primary sources of PCBs were from within indoor environments and generally older houses have higher concentrations in air. Among pesticides, hexachlorobenzene in indoor environments appeared to be due to transfer from outdoor sources whereas chlordanes and pyrethroids were associated with past and current household application respectively. Compared to data from other countries/regions, concentrations of chlordanes, chlorpyrifos and pyrethroids in indoor air and dust samples from Australia were among the highest whereas PCB and PAH levels were among the lowest. The sum of estimated daily intakes (EDIs) via inhalation and dust contact and ingestion were calculated. The highest median value of EDI was observed for permethrin at 2.8 (for adults) and 74 ng kg^-1 day^-1 (for toddlers), which are <0.15% of the U.S. EPA reference dose.

Photochemical formation of hydroxylated polychlorinated biphenyls (OH-PCBs) from decachlorobiphenyl (PCB-209) on solids/air interface

In this work, the photochemical transformation of decachlorobiphenyl (PCB-209) on the surface of several solid particles were systematically evaluated under simulated solar irradiation. The degradation kinetics of PCB-209 were first investigated using silica as a model aerosol particulate. It was found that PCB-209 photodegradation was enhanced at small silica particle size, low surface coverage and low humidity. Electron paramagnetic resonance (EPR) analysis and radicals quenching experiments demonstrated that hydroxyl radicals contributed to PCB-209 degradation. Stepwise hydrodechlorination, hydroxyl addition and cleavage of the CC bridge bond were mainly observed in the reaction process, leading to the formation of lower chlorinated PCBs, hydroxylated PCBs (OH-PCBs) and chlorophenols. Based on density functional theory (DFT) calculation, the dissociation energy of the CCl bond requires 354.81-359.79 kJ/mol energy that corresponds to a wavelength of less than 322 nm. And the minimum activation energy of OH radicals attack on PCB-209 is only 18.12 kJ/mol. Photochemical transformation of PCB-209 can also occur on the surface of natural particles, but the rates were inhibited as compared to silica. The hydroxylation and hydrodechlorination products of PCB-209 were detected in all natural particles. This study would make significant contribution to understanding the fate of PCBs in solids/air interface.

How are Humans Exposed to Organic Chemicals Released to Indoor Air?

Humans are exposed to organic chemicals released to indoor air through near-field exposure routes such as air inhalation and nondietary dust ingestion as well as far-field exposure routes such as consumption of food. Here, we explore the relative importance of near- and far-field exposure routes and its variability between chemicals, age groups, and subpopulations, by modeling aggregate human exposure to indoor-released chemicals with diverse partitioning behavior and degradability. Our model results indicate that if chemicals are assumed to be perfectly persistent, dietary and nondietary ingestion dominates human exposure to hydrophobic chemicals of relatively low volatility (with an octanol-air partition coefficient K_OA > 10^6.5 and an octanol-water partition coefficient K_OW < 10¹¹), whereas inhalation of indoor air dominates human exposure to volatile chemicals. Other exposure routes, for example, dermal absorption and drinking water, make a relatively small contribution to human exposure. Reduced chemical persistence in environmental media and biota lowers the contribution of dietary ingestion. For most chemicals other than those with a K_OA between 10⁹ and 10¹² and a K_OW between 10⁶ and 10⁹ (e.g., polybrominated diphenyl ethers), the relative importance of near- and far-field exposure routes is primarily governed by chemical partitioning and degradability rather than age- and population-dependent human exposure factors.

Toward Sustainable Environmental Quality: Priority Research Questions for North America

Anticipating, identifying, and prioritizing strategic needs represent essential activities by research organizations. Decided benefits emerge when these pursuits engage globally important environment and health goals, including the United Nations Sustainable Development Goals. To this end, horizon scanning efforts can facilitate identification of specific research needs to address grand challenges. We report and discuss 40 priority research questions following engagement of scientists and engineers in North America. These timely questions identify the importance of stimulating innovation and developing new methods, tools, and concepts in environmental chemistry and toxicology to improve assessment and management of chemical contaminants and other diverse environmental stressors. Grand challenges to achieving sustainable management of the environment are becoming increasingly complex and structured by global megatrends, which collectively challenge existing sustainable environmental quality efforts. Transdisciplinary, systems-based approaches will be required to define and avoid adverse biological effects across temporal and spatial gradients. Similarly, coordinated research activities among organizations within and among countries are necessary to address the priority research needs reported here. Acquiring answers to these 40 research questions will not be trivial, but doing so promises to advance sustainable environmental quality in the 21st century. Environ Toxicol Chem 2019;38:1606-1624. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Global Historical Stocks and Emissions of PBDEs

The first spatially and temporally resolved inventory of BDE28, 47, 99, 153, 183, and 209 in the anthroposphere and environment is presented here. The stock and emissions of PBDE congeners were estimated using a dynamic substance flow analysis model, CiP-CAFE. To evaluate our results, the emission estimates were used as input to the BETR-Global model. Estimated concentrations were compared with observed concentrations in air from background areas. The global (a) in-use and (b) waste stocks of ∑₅BDE(28, 47, 99, 153, 183) and BDE209 are estimated to be (a) ∼25 and 400 kt and (b) 13 and 100 kt, respectively, in 2018. A total of 6 (0.3-13) and 10.5 (9-12) kt of ∑₅BDE and BDE209, respectively, has been emitted to the atmosphere by 2018. More than 70% of PBDE emissions during production and use occurred in the industrialized regions, while more than 70% of the emissions during waste disposal occurred in the less industrialized regions. A total of 70 kt of ∑₅BDE and BDE209 was recycled within products since 1970. As recycling rates are expected to increase under the circular economy, an additional 45 kt of PBDEs (mainly BDE209) may reappear in new products.

Advancements in Life Cycle Human Exposure and Toxicity Characterization

BACKGROUND

The Life Cycle Initiative, hosted at the United Nations Environment Programme, selected human toxicity impacts from exposure to chemical substances as an impact category that requires global guidance to overcome current assessment challenges. The initiative leadership established the Human Toxicity Task Force to develop guidance on assessing human exposure and toxicity impacts. Based on input gathered at three workshops addressing the main current scientific challenges and questions, the task force built a roadmap for advancing human toxicity characterization, primarily for use in life cycle impact assessment (LCIA).

OBJECTIVES

The present paper aims at reporting on the outcomes of the task force workshops along with interpretation of how these outcomes will impact the practice and reliability of toxicity characterization. The task force thereby focuses on two major issues that emerged from the workshops, namely considering near-field exposures and improving dose–response modeling.

DISCUSSION

The task force recommended approaches to improve the assessment of human exposure, including capturing missing exposure settings and human receptor pathways by coupling additional fate and exposure processes in consumer and occupational environments (near field) with existing processes in outdoor environments (far field). To quantify overall aggregate exposure, the task force suggested that environments be coupled using a consistent set of quantified chemical mass fractions transferred among environmental compartments. With respect to dose–response, the task force was concerned about the way LCIA currently characterizes human toxicity effects, and discussed several potential solutions. A specific concern is the use of a (linear) dose–response extrapolation to zero. Another concern addresses the challenge of identifying a metric for human toxicity impacts that is aligned with the spatiotemporal resolution of present LCIA methodology, yet is adequate to indicate health impact potential.

CONCLUSIONS

Further research efforts are required based on our proposed set of recommendations for improving the characterization of human exposure and toxicity impacts in LCIA and other comparative assessment frameworks. https://doi.org/10.1289/EHP3871.

Revisiting the Contributions of Far- and Near-Field Routes to Aggregate Human Exposure to Polychlorinated Biphenyls (PCBs)

The general population is exposed to polychlorinated biphenyls (PCBs) by consuming food from far-field contaminated agricultural and aquatic environments, and inhalation and nondietary ingestion in near-field indoor or residential environments. Here, we seek to evaluate the relative importance of far- and near-field routes by simulating the time-variant aggregate exposure of Swedish females to PCB congeners from 1930 to 2030. We rely on a mechanistic model, which integrates a food-chain bioaccumulation module and a human toxicokinetic module with dynamic substance flow analysis and nested indoor-urban-rural environmental fate modeling. Confidence in the model is established by successfully reproducing the observed PCB concentrations in Swedish human milk between 1972 and 2016. In general, far-field routes contribute most to total PCB uptake. However, near-field exposure is notable for (i) children and teenagers, who have frequent hand-to-mouth contact, (ii) cohorts born in earlier years, e.g., in 1956, when indoor environments were severely contaminated, and (iii) lighter chlorinated congeners. The relative importance of far- and near-field exposure in a cross-section of individuals of different age sampled at the same time is shown to depend on the time of sampling. The transition from the dominance of near- to far-field exposure that has happened for PCBs may also occur for other chemicals used indoors.