Risk of papillary thyroid carcinoma and nodular goiter associated with exposure to semi-volatile organic compounds: A multi-pollutant assessment based on machine learning algorithms

BACKGROUND

Exposure to semi-volatile organic compounds (SVOCs) may link to thyroid nodule risk, but studies of mixed-SVOCs exposure effects are lacking. Traditional analytical methods are inadequate for dealing with mixed exposures, while machine learning (ML) seems to be a good way to fill the gaps in the field of environmental epidemiology research.

OBJECTIVES

Different ML algorithms were used to explore the relationship between mixed-SVOCs exposure and thyroid nodule.

METHODS

A 1:1:1 age- and gender-matched case-control study was conducted in which 96 serum SVOCs were measured in 50 papillary thyroid carcinoma (PTC), 50 nodular goiters (NG), and 50 controls. Different ML techniques such as Random Forest, AdaBoost were selected based on their predictive power, and variables were selected based on their weights in the models. Weighted quantile sum (WQS) regression and Bayesian kernel machine regression (BKMR) were used to assess the mixed effects of the SVOCs exposure on thyroid nodule.

RESULTS

Forty-three of 96 SVOCs with detection rate >80 % were included in the analysis. ML algorithms showed a consistent selection of SVOCs associated with thyroid nodule. Fluazifop-butyl and fenpropathrin are positively associated with PTC and NG in single compound models (all P < 0.05). WQS model shows that exposure to mixed-SVOCs was associated with an increased risk of PTC and NG, with the mixture dominated by fenpropathrin, followed by fluazifop-butyl and propham. In the BKMR model, mixtures showed a significant positive association with thyroid nodule risk at high exposure levels, and fluazifop-butyl showed positive effects associated with PTC and NG.

CONCLUSION

This study confirms the feasibility of ML methods for variable selection in high-dimensional complex data and showed that mixed exposure to SVOCs was associated with increased risk of PTC and NG. The observed association was primarily driven by fluazifop-butyl and fenpropathrin. The findings warranted further investigation.

An integrated non-targeted and targeted analysis approach for identification of semi-volatile organic compounds in indoor dust

Household dust contains a wide variety of semi-volatile organic compounds (SVOCs) that may pose health risks. We developed a method integrating non-targeted analysis (NTA) and targeted analysis (TA) to identify SVOCs in indoor dust. Based on a combined use of gas and liquid chromatography with high-resolution mass spectrometry, an automated, time-efficient NTA workflow was developed, and high accuracy was observed. A total of 128 compounds were identified at confidence level 1 or 2 in NIST standard reference material dust (SRM 2585). Among them, 113 compounds had not been reported previously, and this suggested the value of NTA in characterizing contaminants in dust. Additionally, TA was done to avoid the loss of trace compounds. By integrating data obtained from the NTA and TA approaches, SVOCs in SRM 2585 were prioritized based on exposure and chemical toxicity. Six of the top 20 compounds have never been reported in SRM 2585, including melamine, dinonyl phthalate, oxybenzone, diheptyl phthalate, drometrizole, and 2-phenylphenol. Additionally, significant influences of analytical instruments and sample preparation on NTA results were observed. Overall, the developed method provided a powerful tool for identifying SVOCs in indoor dust, which is necessary to obtain a more complete understanding of chemical exposures and risks in indoor environments.

Derivation and application of indoor air screening values for inhalation exposure to semi-volatile organic compounds

Semi-volatile organic compounds (SVOCs) are being increasingly studied in indoor air. The absence of health-based inhalation exposure guidelines for most SVOCs impedes the interpretation of indoor air concentrations from a health risk context. To accelerate the derivation of screening values for a large number of SVOCs, a tiered framework was developed to evaluate and adjust published hazard assessments for SVOCs to calculate benchmarks relevant for evaluation of inhalation risk. Inhalation screening values were derived for 43 SVOCs considered in this study, most of which required extrapolation from oral exposure guidelines. The screening values were compared to published SVOC concentrations in homes in Canada to evaluate the potential health risks of chronic exposure to SVOCs in indoor residential environments. SVOCs that could be prioritized for further evaluation were dibutyl phthalates (DBP), di(2-ethylhexyl) phthalate (DEHP) and polybrominated diphenyl ethers (PBDEs). The framework could be applied more broadly in the future to derive screening values for other non-traditional indoor air contaminants with limited inhalation hazard data or assessments.

Wearable Passive Samplers for Assessing Environmental Exposure to Organic Chemicals: Current Approaches and Future Directions

PURPOSE OF REVIEW

We are continuously exposed to dynamic mixtures of airborne contaminants that vary by location. Understanding the compositional diversity of these complex mixtures and the levels to which we are each exposed requires comprehensive exposure assessment. This comprehensive analysis is often lacking in population-based studies due to logistic and analytical challenges associated with traditional measurement approaches involving active air sampling and chemical-by-chemical analysis. The objective of this review is to provide an overview of wearable passive samplers as alternative tools to active samplers in environmental health research. The review highlights the advances and challenges in using wearable passive samplers for assessing personal exposure to organic chemicals and further presents a framework to enable quantitative measurements of exposure and expanded use of this monitoring approach to the population scale.

RECENT FINDINGS

Overall, wearable passive samplers are promising tools for assessing personal exposure to environmental contaminants, evident by the increased adoption and use of silicone-based devices in recent years. When combined with high throughput chemical analysis, these exposure assessment tools present opportunities for advancing our ability to assess personal exposures to complex mixtures. Most designs of wearable passive samplers used for assessing exposure to semi-volatile organic chemicals are currently uncalibrated, thus, are mostly used for qualitative research. The challenge with using wearable samplers for quantitative exposure assessment mostly lies with the inherent complexity in calibrating these wearable devices. Questions remain regarding how they perform under various conditions and the uncertainty of exposure estimates. As popularity of these samplers grows, it is critical to understand the uptake kinetics of chemicals and the different environmental and meteorological conditions that can introduce variability. Wearable passive samplers enable evaluation of exposure to hundreds of chemicals. The review presents the state-of-the-art of technology for assessing personal exposure to environmental chemicals. As more studies calibrate wearable samplers, these tools present promise for quantitatively assessing exposure at both the individual and population levels.

Measurement methods and impact factors for the key parameters of VOC/SVOC emissions from materials in indoor and vehicular environments: A review

The emissions of volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs) from indoor building and vehicle cabin materials can adversely affect human health. Many mechanistic models to predict the VOC/SVOC emission characteristics have been proposed. Nowadays, the main obstacle to accurate model prediction is the availability and reliability of the physical parameters used in the model, such as the initial emittable concentration, the diffusion coefficient, the partition coefficient, and the gas-phase SVOC concentration adjacent to the material surface. The purpose of this work is to review the existing methods for measuring the key parameters of VOCs/SVOCs from materials in both indoor and vehicular environments. The pros and cons of these methods are analyzed, and the available datasets found in the literature are summarized. Some methods can determine one single key parameter, while other methods can determine two or three key parameters simultaneously. The impacts of multiple factors (temperature, relative humidity, loading ratio, and air change rate) on VOC/SVOC emission behaviors are discussed. The existing measurement methods span very large spatial and time scales: the spatial scale varies from micro to macro dimensions; and the time scale in chamber tests varies from several hours to one month for VOCs, and may even span years for SVOCs. Based on the key parameters, a pre-assessment approach for indoor and vehicular air quality is introduced in this review. The approach uses the key parameters for different material combinations to pre-assess the VOC/SVOC concentrations or human exposure levels during the design stage of buildings or vehicles, which can assist designers to select appropriate materials and achieve effective source control.

Surface-dependent gas equilibrium of semi-volatile organic compounds on glass, wood, and polyurethane foam using SPME-GC/MS

The surface-dependent evaporation behavior of phthalates as semi-volatile organic compounds (SVOCs) on glass, wood, and polyurethane foam (PUF) was investigated. Three phthalates of di-2-ethylhexyl phthalate (DEHP), butyl benzyl phthalate (BBP), and dibutyl phthalate (DBP) were studied to compare the amount of gases vaporized from their surfaces. A 10 mL silicate glass vial was used to compare the gas equilibrium of the phthalates after 2 h. The gases accumulated in the air were transferred to a solid-phase microextraction (SPME) column and analyzed by gas chromatography-mass spectrometry (GC-MS). As correlated with the physicochemical properties of the phthalates, including molecular weights and vapor pressure, the surface-air partition coefficients (K_sa) were found to be in the range of 10¹-10⁵ m, 10⁶-10⁷ m, and 10⁷-10⁹ m on glass, wood, and PUF, respectively, implying that a significant amount of phthalates are retained on wood and PUF surfaces as compared to glass, and only a trace amount of phthalates can be volatilized into the air, especially the less volatile DEHP. The three-dimensional (3D) morphologies of glass and wood were also examined using a white-light interferometric surface profile microscope and an atomic force microscope (AFM). In contrast to smooth glass surfaces within the sub-micrometer vertical range, the wood surfaces exhibited uneven irregular structures at a height of 5-30 μm. The rough wood surfaces were found to adsorb substantial amounts of gases to prevent the effective volatilization of phthalates into the air, especially the low molecular DBP. Our results imply that wood and PUF surfaces may be superior to glass surfaces in storage and reduction of phthalates in the air, especially DBP.

Predicting the emissions of VOCs/SVOCs in source and sink materials: Development of analytical model and determination of the key parameters

The emissions of volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs) from indoor materials pose an adverse effect on people's health. In this study, a new analytical model was developed to simulate the emission behaviors for both VOCs and SVOCs under ventilated conditions. Based on this model, we further introduced a hybrid optimization method to accurately determine the key parameters in the model: the initial emittable concentration, the diffusion coefficient, the material/air partition coefficient, and the chamber surface/air partition coefficient (for SVOCs). Experiments for VOC emissions from solid wood furniture were performed to determine the key parameters. We also evaluated the hybrid optimization method with the data of flame retardant emissions from polyisocyanurate rigid foam and VOC emissions from a panel furniture in the literature. The correlation coefficients are high during the fitting process (R² = 0.92-0.99), demonstrating effectiveness of this method. In addition, we observed that chemical properties could transfer from SVOC-type to VOC-type with the increase of temperature. The transition temperatures from SVOC-type to VOC-type for the emissions of tris(2-chloroethyl) phosphate (TCEP) and tris(1-chloro-2-propyl) phosphate (TCIPP) were determined to be about 45 ℃ and 35 ℃, respectively. The present study provides a unified modelling and methodology analysis for both VOCs and SVOCs, which should be very useful for source/sink characterization and control.

Particle/gas partitioning for semi-volatile organic compounds (SVOCs) in Level III multimedia fugacity models: Gaseous emissions

Atmospheric transport is a global-scale process that moves semi-volatile organic compounds (SVOCs) rapidly from source regions to remote locations, where these chemicals have never been produced or used. Particle/gas (P/G) partitioning of SVOCs during atmospheric transport governs wet and dry deposition, and thereby controls the efficiency and scope of long-range atmospheric transport and fate for these sorts of compounds. Previous work has shown that the assumption of steady state between particulate and gaseous phases in the atmosphere leads to model results that more closely match observations especially for compounds that strongly favor the particulate phase. Here, the practical application of steady-state P/G partitioning in the atmosphere in multimedia fugacity models is presented in greater detail. A method is developed whereby the fugacity of a chemical in the particle-phase is set equal to that in the gaseous phase (a pseudo equilibrium) but still maintains steady state of the chemical between air and aerosols in the atmosphere. This procedure greatly simplifies the application of multimedia fugacity models. Using this approach, a condition of steady state between air and aerosols is developed and applied in a Level III six-compartment six-fugacity model, which becomes a much simpler Level III six-compartment four-fugacity model. This newly-developed model is then applied to data observed during a monitoring program.

Particle/gas partitioning for semi-volatile organic compounds (SVOCs) in level III multimedia fugacity models: Both gaseous and particulate emissions

Multimedia fugacity models have long been used to address the fate of toxic organic chemical emissions by providing a quantitative account of the sources, transport processes, and sinks. Recently, we have examined three level-III fugacity models (E4F (equilibrium six-compartment four-fugacity), S6F (steady-state six-compartment six-fugacity) and S4F (steady-state six-compartment four-fugacity) Models), in the context of their performance set against real-world data, and their practicality of application. Here, we discuss how the balance between gaseous and aerosol phases of emissions assumed for initial conditions affects the different model outcomes. Our results show that the S6F Model predictions closely match those of the S4F Model when chemical emissions are entirely in the gas-phase. As the particulate proportion of the emission increases, the S6F Model predictions diverge from those of the S4F Model and approach those of the E4F Model. Once the particulate portion reaches 100%, the S6F and E4F Models produce identical results: an internally inconsistent system where chemicals are not in a steady state between air and aerosols, and mass balance for both air and aerosols is not achieved. Thus, in terms of practicality, internal consistency, chemical mass balance and agreement with observations, the S4F Model is clearly the best choice.

Volatile and Semi-Volatile Organic Compounds May Help Reduce Pollinator-Prey Overlap in the Carnivorous Plant Drosophyllum lusitanicum (Drosophyllaceae)

Most carnivorous plants show a conspicuous separation between flowers and leaf-traps, which has been interpreted as an adaptive response to minimize pollinator-prey conflicts which will reduce fitness. Here, we used the carnivorous subshrub Drosophyllum lusitanicum (Drosophyllaceae) to explore if and how carnivorous plants with minimal physical separation of flower and trap avoid or reduce a likely conflict of pollinator and prey. We carried out an extensive field survey in the Aljibe Mountains, at the European side of the Strait of Gibraltar, of pollinating and prey insects of D. lusitanicum. We also performed a detailed analysis of flower and leaf volatile and semi-volatile organic compounds (VOCs and SVOCs, respectively) by direct thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) to ascertain whether this species shows different VOC/SVOC profiles in flowers and leaf-traps that might attract pollinators and prey, respectively. Our results show a low overlap between pollinator and prey groups as well as clear differences in the relative abundance of VOCs and SVOCs between flowers and leaf-traps. Coleopterans and hymenopterans were the most represented groups of floral visitors, whereas dipterans were the most diverse group of prey insects. Regarding VOCs and SVOCs, while aldehydes and carboxylic acids presented higher relative contents in leaf-traps, alkanes and plumbagin were the main VOC/SVOC compounds detected in flowers. We conclude that D. lusitanicum, despite its minimal flower-trap separation, does not seem to present a marked pollinator-prey conflict. Differences in the VOCs and SVOCs produced by flowers and leaf-traps may help explain the conspicuous differences between pollinator and prey guilds.

Biomarkers of exposure to SVOCs in children and their demographic associations: The TESIE Study

Semi-volatile organic compounds (SVOCs) are used extensively in consumer and personal care products; electronics; furniture; and building materials and are detected in most indoor environments. As a result, human exposure to mixtures of SVOCs is wide-spread. However, very few studies have measured biomarkers of exposure to multiple SVOC classes, and exposure determinants have not been thoroughly explored, particularly for young children. In this study, we investigated biomarkers of exposure to SVOCs among children (age 3-6 years), who may experience higher exposures and be more susceptible to adverse health outcomes than other age groups. We enrolled 203 participants in the Toddlers Exposure to SVOCs in Indoor Environments (TESIE) study (181 provided urine samples and 90 provided serum samples).We quantified 44 biomarkers of exposure to phthalates, organophosphate esters (OPEs), parabens, phenols, antibacterial agents and per- and polyfluoroalkyl substances (PFASs); we detected 29 of the 44 biomarkers in >95% of samples, and many biomarkers were detected at higher median concentrations than those previously reported in the U.S. general population. Demographic characteristics were associated with differences in concentrations. In general, non-Hispanic white race and higher maternal education were associated with lower concentrations, even after adjusting for other potential confounding variables. Our results suggest that outdoor temperature at the time of biospecimen collection may be a particularly important and under-evaluated predictor of biomarker concentrations; statistically significant relationships were observed between 10 biomarkers and outdoor temperature at the time of collection. A complex correlation structure was also observed among the biomarkers assessed. By and large, statistically significant correlations between biomarkers of exposure to phthalates, parabens, phenols, and OPEs were positive. Conversely, although PFASs were positively correlated with one another, they tended to be negatively correlated with other biomarkers where significant associations were observed. Taken together, our results provide evidence that the assessments of SVOC-associated health impacts should focus on chemical mixtures.

Multi-component determination of atmospheric semi-volatile organic compounds in soils and vegetation from Tarragona County, Catalonia, Spain

Tarragona County (Spain) is home to the most important chemical/petrochemical industrial complex in Southern Europe, which raises concerns about the presence and effects of the numerous environmental contaminants. In order to assess the levels and patterns of five classes of semi-volatile organic compounds (SVOCs) - polycyclic aromatic hydrocarbons (PAHs), synthetic musks (SMs), polychlorinated biphenyls (PCBs), brominated flame retardants (BFRs) and one organochlorine pesticide, hexachlorobenzene (HCB), 27 samples of soil and vegetation (Piptatherum L.) from different areas (petrochemical, chemical, urban/residential, and background) of Tarragona County were analysed. The results show that PAHs levels in soils ranged from 45.12 to 158.00ng/g and the urban areas presented the highest concentrations, mainly associated with the presence of a nearby highway and several roads with heavy traffic. PAHs levels in vegetation samples ranged from 42.13 to 80.08ng/g, where the greatest influence came from the urban and petrochemical areas. In the case of SMs, levels in soils and vegetation samples ranged from 5.42 to 10.04ng/g and from 4.08 to 17.94ng/g, respectively, and in both cases, background areas (at least 30km away from the main SVOCs emission sources) showed the highest levels, suggesting an influence of the personal care products derived from beach-related tourism in the coast. PCBs (from 6.62 to 14.07ng/g in soils; from 0.52 to 4.41ng/g in vegetation) prevailed in the chemical area in both matrices, probably associated with the presence of two sub-electrical stations located in the vicinities. In general terms, BFRs and HCB values recorded in soil and vegetation samples were quite similar between matrices and sampling areas.

Using long-term air monitoring of semi-volatile organic compounds to evaluate the uncertainty in polyurethane-disk passive sampler-derived air concentrations

Much effort has been made to standardise sampling procedures, laboratory analysis, data analysis, etc. for semi volatile organic contaminants (SVOCs). Yet there are some unresolved issues in regards to comparing measurements from one of the most commonly used passive samplers (PAS), the polyurethane foam (PUF) disk PAS (PUF-PAS), between monitoring networks or different studies. One such issue is that there is no universal means to derive a sampling rate (R_s) or to calculate air concentrations (C_air) from PUF-PAS measurements for SVOCs. C_air was calculated from PUF-PAS measurements from a long-term monitoring program at a site in central Europe applying current understanding of passive sampling theory coupled with a consideration for the sampling of particle associated compounds. C_air were assessed against concurrent active air sampler (AAS) measurements. Use of "site-based/sampler-specific" variables: R_s, calculated using a site calibration, provided similar results for most gas-phase SVOCs to air concentrations derived using "default" values (commonly accepted R_s). Individual monthly PUF-PAS-derived air concentrations for the majority of the target compounds were significantly different (Wilcoxon signed-rank (WSR) test; p < 0.05) to AAS regardless of the input values (site/sampler based or default) used to calculate them. However, annual average PUF-PAS-derived air concentrations were within the same order of magnitude as AAS measurements except for the particle-phase polycyclic aromatic hydrocarbons (PAHs). Underestimation of PUF-derived air concentrations for particle-phase PAHs was attributed to a potential overestimation of the particle infiltration into the PUF-PAS chamber and underestimation of the particle bound fraction of PAHs.