Advancements in Assays for Micro- and Nanoplastic Detection: Paving the Way for Biomonitoring and Exposomics Studies.

Although plastic pollution and exposure to plastic-related compounds have received worldwide attention, health risks associated with micro- and nanoplastics (MNPs) are largely unknown. Emerging evidence suggests MNPs are present in human biofluids and tissue, including blood, breast milk, stool, lung tissue, and placenta; however, exposure assessment is limited and the extent of human exposure to MNPs is not well known. While there is a critical need to establish robust and scalable biomonitoring strategies to assess human exposure to MNPs and plastic-related chemicals, over 10,000 chemicals have been linked to plastic manufacturing with no existing standardized approaches to account for even a fraction of these exposures. This review provides an overview of the status of methods for measuring MNPs and associated plastic-related chemicals in humans, with a focus on approaches that could be adapted for population-wide biomonitoring and integration with biological response measures to develop hypotheses on potential health effects of plastic exposures. We also examine the exposure risks associated with the widespread use of chemical additives in plastics. Despite advancements in analytical techniques, there remains a pressing need for standardized measurement protocols and untargeted, high-throughput analysis methods to enable comprehensive MNP biomonitoring to identify key MNP exposures in human populations. This review aims to merge insights into the toxicological effects of MNPs and plastic additives with an evaluation of analytical challenges, advocating for enhanced research methods to fully assess, understand, and mitigate the public health implications of MNPs.

Thermal Decomposition Mechanism of Tetraethylsilane by Flash Pyrolysis Vacuum Ultraviolet Photoionization Mass Spectrometry and DFT Calculations: The Competition between ß-Hydride Elimination and Bond Homolysis.

Thermal decomposition of tetraethylsilane was investigated at temperatures up to 1330 K using flash pyrolysis vacuum ultraviolet photoionization mass spectrometry. Density functional theory and transition state theory calculations were performed to corroborate the experimental observations. Both experimental and theoretical evidence showed that the pyrolysis of tetraethylsilane was initiated by Si-C bond fission to the primary reaction products, triethylsilyl (SiEt3) and ethyl radicals. In the secondary reactions of the triethylsilyl radical, at lower temperatures, the ß-hydride elimination pathway (producing HSiEt2) was found to be more favored than its competing reaction channel, Si-C bond fission (producing :SiEt2); as the temperature further increased, the Si-C bond fission reaction became significant. Other important secondary reaction products, such as EtHSi═CH2 (m/z = 72), H2SiEt (m/z = 59), and SiH3 (m/z = 31) were identified, and their formation mechanisms were also proposed.

Mechanism of Thermal Decomposition of Hydroxyacetone: A Flash Pyrolysis Vacuum Ultraviolet Photoionization Time-of-Flight Mass Spectrometry and Density Functional Theory Study.

The thermal decomposition mechanism of hydroxyacetone from 850 to 1390 K was examined by using flash pyrolysis vacuum ultraviolet photoionization time-of-flight mass spectrometry combined with density functional theory calculation. The results showed that keto-enol tautomerisms could occur prior to the thermal decomposition of hydroxyacetone. The decomposition pathways of hydroxyacetone and its isomer, 2-hydroxypropanal were characterized. The thermal decomposition reactions started at about 950 K. The homolysis reactions related to the cleavage of the CCO-CCOH bond of hydroxyacetone and 2-hydroxypropanal, as well as CH3 loss of hydroxyacetone, dominated the initial decomposition reactions. The subsequent decompositions of the radical intermediates generated by the initial homolysis decompositions were the major secondary decomposition reactions. The formation pathways of small molecules, such as H2, CH4, H2O, and HCHO, were proposed to proceed via molecular elimination reactions facilitated by the active α-H atoms. These elimination reactions were not negligible at high temperatures above 1230 K.

A Mechanistic Study of Thermal Decomposition of 1,1,2,2-Tetramethyldisilane Using Vacuum Ultraviolet Photoionization Time-of-Flight Mass Spectrometry.

Thermal decomposition of 1,1,2,2-tetramethyldisilane was performed by flash pyrolysis in a SiC microreactor in the temperature range from 295 to 1340 K, followed by molecular beam sampling and vacuum ultraviolet photoionization mass spectrometry analysis. Density functional theory investigations on the energetics of reactants, intermediates, and products were carried out to support the experimental observations. Energetics for 1,1,2,2-tetramethyldisilane initiation decomposition reactions and important secondary reactions were calculated. Dimethylsilane, dimethylsilyl radicals, dimethylsilylene, trimethylsilane, and tetramethyldisilene were determined as the primary reaction products in the initiation thermal decompositions of 1,1,2,2-tetramethyldisilane. Further decomposition reactions of tetramethyldisilene, such as production of dimethylsilene (m/z = 72) and eventually SiC3H4 (m/z = 68) fragments, were examined. Other products from secondary reactions of dimethylsilane and dimethylsilylene such as SiC2H2-6 and SiCH0-4 were also observed. The comprehensive pyrolysis mechanism of 1,1,2,2-tetramethyldisilane was proposed.

Thermal and Catalytic Decomposition of 2-Hydroxyethylhydrazine and 2-Hydroxyethylhydrazinium Nitrate Ionic Liquid.

To develop chemical kinetics models for the combustion of ionic liquid-based monopropellants, identification of the elementary steps in the thermal and catalytic decomposition of components such as 2-hydroxyethylhydrazinium nitrate (HEHN) is needed but is currently not well understood. The first decomposition step in protic ionic liquids such as HEHN is typically the proton transfer from the cation to the anion, resulting in the formation of 2-hydroxyethylhydrazine (HEH) and HNO3. In the first part of this investigation, the high-temperature thermal decomposition of HEH is probed with flash pyrolysis (<1400 K) and vacuum ultraviolet (10.45 eV) photoionization time-of-flight mass spectrometry (VUV-PI-TOFMS). Next, the investigation into the thermal and catalytic decomposition of HEHN includes two mass spectrometric techniques: (1) tunable VUV-PI-TOFMS (7.4-15 eV) and (2) ambient ionization mass spectrometry utilizing both plasma and laser ionization techniques whereby HEHN is introduced onto a heated inert or iridium catalytic surface and the products are probed. The products can be identified by their masses, their ionization energies, and their collision-induced fragmentation patterns. Formation of product species indicates that catalytic surface recombination is an important reaction process in the decomposition mechanism of HEHN. The products and their possible elementary reaction mechanisms are discussed.

Thermal decomposition of cyclohexane by flash pyrolysis vacuum ultraviolet photoionization time-of-flight mass spectrometry: a study on the initial unimolecular decomposition mechanism.

Thermal decomposition of cyclohexane at temperatures up to 1310 K was performed using flash pyrolysis coupled with vacuum ultraviolet (118.2 nm) photoionization time-of-flight mass spectrometry. The experimental results revealed that the major initiation reaction of cyclohexane decomposition was C-C bond fission leading to the formation of 1,6-hexyl diradical. The 1,6-hexyl diradical could isomerize to 1-hexene and decompose into ˙C3H7 + ˙C3H5 and ˙C4H7 + ˙C2H5. The 1,6-hexyl diradical could also undergo direct dissociation; the C4H8 fragment via the 1,4-butyl diradical intermediate was observed, serving as evidence of the 1,6-hexyl diradical mechanism. Quantum chemistry calculations at UCCSD(T)/cc-pVDZ level of theory on the initial reaction pathways of cyclohexane were performed and found to be consistent with the experimental conclusions. Cyclohexyl radical was not observed as an initial intermediate in the pyrolysis. Benzene was produced from sequential H2 eliminations of cyclohexane at high temperatures.

Ultraviolet Photodissociation Dynamics of the Cyclohexyl Radical: The H-Atom Product Channel.

The ultraviolet (UV) photodissociation dynamics of the jet-cooled cyclohexyl (c-C6H11) radical is studied using the high-n Rydberg atom time-of-flight (HRTOF) technique. The cyclohexyl radical is produced by the 193 nm photodissociation of chlorocyclohexane and bromocyclohexane and is examined in the photolysis wavelength region of 232-262 nm. The H-atom photofragment yield (PFY) spectrum contains a broad peak centered at 250 nm, which is in good agreement with the UV absorption spectrum of the cyclohexyl radical and assigned to the 3p Rydberg states. The translational energy distributions of the H-atom loss product channel, P(ET)'s, are bimodal, with a slow (low ET) component peaking at ∼6 to 7 kcal/mol and a fast (high ET) component peaking at ∼44-48 kcal/mol. The fraction of the average translational energy in the total excess energy, ⟨fT⟩, is in the range of 0.16-0.25 in the photolysis wavelength region of 232-262 nm. The H-atom product angular distribution of the slow component is isotropic, while that of the fast component is anisotropic with an anisotropy parameter of ß ≈ 0.5-0.7. The bimodal product translational energy and angular distributions indicate two dissociation pathways to the H + C6H10 products in cyclohexyl. The high-ET anisotropic component is from a repulsive, prompt dissociation on a repulsive potential energy surface coupling with the Rydberg excited states to produce H + cyclohexene. The low-ET isotropic component is consistent with the unimolecular dissociation of hot radical on the ground electronic state after internal conversion from the Rydberg states. The similarity of the photodissociation dynamics of the cyclohexyl radical to the previously studied small linear and branched alkyls expands on the understanding of the dissociation dynamics of alkyl radicals to include larger cyclic alkyl radicals.

Investigating Exposure and Hazards of Micro- and Nanoplastics During Pregnancy and Early Life (AURORA Project): Protocol for an Interdisciplinary Study.

BACKGROUND: Micro- and nanoplastics (MNPs) are emerging pollutants of concern with ubiquitous presence in global ecosystems. MNPs pose potential implications for human health; however, the health impacts of MNP exposures are not yet understood. Recent evidence suggests that MNPs can cross the placental barrier, underlying the urgent need to understand their impact on reproductive health and development. OBJECTIVE: The Actionable eUropean ROadmap for early-life health Risk Assessment of micro- and nanoplastics (AURORA) project will investigate MNP exposures and their biological and health effects during pregnancy and early life, which are critical periods due to heightened vulnerability to environmental stressors. The AURORA project will enhance exposure assessment capabilities for measuring MNPs, MNP-associated chemicals, and plastic additives in human tissues, including placenta and blood. METHODS: In this interdisciplinary project, we will advance methods for in-depth characterization and scalable chemical analytical strategies, enabling high-resolution and large-scale toxicological, exposure assessment, and epidemiological studies. The AURORA project performs observational studies to investigate determinants and health impacts of MNPs by including 800 mother-child pairs from 2 existing birth cohorts and 110 women of reproductive age from a newly established cohort. This will be complemented by toxicological studies using a tiered-testing approach and epidemiological investigations to evaluate associations between maternal and prenatal MNP exposures and health perturbations, such as placental function, immune-inflammatory responses, oxidative stress, accelerated aging, endocrine disruption, and child growth and development. The ultimate goal of the AURORA project is to create an MNP risk assessment framework and identify the remaining knowledge gaps and priorities needed to comprehensively assess the impact of MNPs on early-life health. RESULTS: In the first 3 years of this 5-year project (2021-2026), progress was made toward all objectives. This includes completion of recruitment and data collection for new and existing cohorts, development of analytical methodological protocols, and initiation of the toxicological tiered assessments. As of September 2024, data analysis is ongoing and results are expected to be published starting in 2025. CONCLUSIONS: As plastic pollution increases globally, it is imperative to understand the impact of MNPs on human health, particularly during vulnerable developmental stages such as early life. The contributions of the AURORA project will inform future risk assessment. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): DERR1-10.2196/63176.

Flash pyrolysis vacuum ultraviolet photoionization mass spectrometry of cycloheptane: A study of the initial decomposition mechanism.

Thermal decomposition of cycloheptane was studied using flash pyrolysis coupled with vacuum ultraviolet (118.2 nm) single photon ionization time-of-flight mass spectrometry at temperatures ranging from 295 K to 1380 K. C-C bond breaking of cycloheptane leading to the 1,7-heptyl diradical was considered as the initiation step. The 1,7-heptyl diradical could readily isomerize to 1-heptene and decompose into several fragments, with dissociation to •C4H9 and •C3H5 as the predominant product channel. The 1,7-heptyl diradical could undergo direct dissociation, as evidenced by the production of the C5H10 species. Quantum chemistry calculations at UCCSD(T)/cc-pVDZ//UB3LYP/cc-pVDZ level of theory on the initial reaction pathways of cycloheptane were also carried out to support the experimental observations. Other possible initiation channels, as well as some secondary reaction products, were also identified.