Metal-Catalyzed Formation of Organic Pollutants Intermediated by Organic Free Radicals.

Metal compounds play important roles in the formation of organic pollutants during thermal-related processes. However, the metal-catalyzed predominant organic pollutants have not previously been characterized nor have any detailed catalytic mechanisms been clarified. Here, we preciously distinguished the multiple organic free radical intermediates on metal catalyst surfaces during the organic pollutant formation through laboratory and theoretical studies. Differences between the organic free radical intermediate species, concentrations, and formation mechanisms under the catalysis of different metal compounds were investigated. The results were verified mutually with the differed characteristics of organic pollutant products. CuO predominantly catalyzed the formation of highly chlorinated phenoxy radical intermediates and dioxins. High proportions of semiquinone radicals and oxygen-containing derivatives were found on ZnO surfaces. Differently, methyl-substituted phenoxy radicals and long-chain products formed on Al2O3 surfaces. The results will be instructive for the target emission control of priority organic pollutants during thermal-related processes rich in different metal compounds.

Comprehensive Evaluation of Dietary Exposure and Health Risk of Polychlorinated Naphthalenes.

Intake from food is considered an important route of human exposure to polychlorinated naphthalenes. To our knowledge, several studies have quantified dietary exposure but only in European countries and measuring only a few of the 75 congeners. In addition, the influence of source diversity on human exposure has seldom been assessed. We analyzed 192 composite food samples composed of 17,280 subsamples from 24 provinces in China to measure the concentrations of polychlorinated naphthalenes and estimate their daily intake and potential health risks on a national scale. The estimated cancer risk was in the range of 6.8 × 10-8 to 4.6 × 10-7. We compared our findings for 75 congeners with reports in the literature that quantified only 12 congeners. We estimate that these 12 congeners contribute only approximately 4% to the total mass daily intake of polychlorinated naphthalenes and 70% to the total toxic equivalent quantity, indicating underestimation of dietary exposure. The contributions of combustion-associated congeners to the total concentrations of polychlorinated naphthalenes were in the range of 31-52%, suggesting that the ongoing unintentional release of these compounds from industrial thermal processes is an important factor in polychlorinated naphthalene contamination and human exposure in China.

Insights into the Formation and Profile of Chlorinated Polycyclic Aromatic Hydrocarbons during Chlorobenzene and Chloroethylene Manufacturing Processes.

Chlorinated polycyclic aromatic hydrocarbons including chlorinated naphthalenes and congeners with three to five rings are ubiquitous atmospheric pollutants. Congener profiles and formation mechanisms from typical chemical manufacturing have not been researched extensively. We measured the concentrations of 75 chlorinated naphthalenes and 18 chlorinated polycyclic aromatic hydrocarbons in raw materials, intermediates, products, and bottom residues from chemical plants producing monochlorobenzene and chloroethylene by different techniques. The findings confirmed that these chemical manufacturing processes are newly identified sources of atmospheric emissions of these compounds. More-chlorinated naphthalenes were formed from chloroethylene production than from monochlorobenzene production, which could be explained by the higher temperatures in the former process. Successive chlorination appeared to be an important formation pathway of polychlorinated naphthalenes according to their congener profiles and was supported by quantum chemical calculations of electrophilic chlorination on various positions of naphthalene. Chlorinated polycyclic aromatic hydrocarbons were more likely to be formed during the production of monochlorobenzene than chloroethylene. Moreover, we suggested that ring rearrangement and ring coupling are important transformation reactions between polychlorinated naphthalenes and chlorinated polycyclic aromatic hydrocarbons.

Risk evaluation of environmentally persistent free radicals in airborne particulate matter and influence of atmospheric factors.

Environmentally persistent free radicals (EPFRs) was considered unrecognized composition of air pollutants and might help explain the long-standing medical mystery of why non-smokers develop tobacco-related diseases like lung cancer. EPFRs in airborne fine particulate matter (PM2.5) can induce oxidative and DNA damage when inhaled. We assessed the inhalation risk of EPFRs in PM2.5 and factors influencing this risk in Beijing as a large city with frequent haze events. The average concentration of EPFRs in PM2.5 was 6.00 × 1017 spins/m3 in spring, autumn, and winter; lower concentrations were recorded in the summer. To estimate the daily inhalation risk of EPFRs in PM2.5, we used the equivalent EPFRs in cigarette tar. The average daily inhalation exposure of EPFRs in PM2.5 was estimated to be the equivalent of 33.1 cigarette tar EPFRs per day (range: 0.53-226.9) during both haze and non-haze days. The major factors influencing EPFR concentrations in the atmosphere were precipitation and humidity, which reduced airborne concentrations. Levels of PM2.5 and carbon monoxide were positively correlated with EPFR concentrations. The health risks of inhaling airborne EPFRs could be significant and should be recognized and quantified.

Brominated dioxins and furans in a cement kiln co-processing municipal solid waste.

A field study and theoretical calculations were performed to clarify the levels, profiles, and distributions of polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs) in a cement kiln co-processing solid waste, with a focus on the PBDF formation mechanism. The raw materials contributed greatly to input of PBDD/Fs into the cement kiln. The PBDD/F concentrations in the raw materials were much higher than those in particle samples from different process stages in the cement kiln. The PBDD/F concentrations in the clinkers were 1.40% of the concentrations in the raw materials, which indicated that the high destruction efficiencies for PBDD/Fs by cement kiln. PBDD/F distribution patterns in particle samples collected from different process stages indicated the cement kiln backend was a major site for PBDD/F formation. PBDFs with high levels of halogenation, such as heptabrominated furans (HpBDF), were the dominant contributors to the total PBDD/F concentrations and accounted for 42%-73% of the total PBDD/F concentrations in the particle samples. Our results showed that co-processing of municipal solid waste in a cement kiln may influence the congener profile of PBDD/Fs, especially for the higher halogenated PBDD fraction. In addition, there were significant correlations between the decabromodiphenyl ether and heptabrominated furan concentrations, which is an indicator of transformation from polybrominated diphenyl ethers to PBDD/Fs. Theoretical calculations were performed and demonstrated that elimination of HBr and Br2 from polybrominated diphenyl ethers were the dominant formation pathways for PBDD/Fs. These pathways differed from that for polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs).

Free radical mechanisms of ammonium sulfate as intensively used industrial materials on suppressing organic pollutants.

Organic free radicals are critical intermediates for the generation and inhibition of organic pollutants during industrial processes. Clarifying the free radical mechanism of pollutant inhibition is significant for their efficient control. Ammonium sulfate is intensively used in industrial materials to suppress organic pollutants. In this study, organic free radical intermediate species in metal-catalyzed reactions inhibited by ammonium sulfate were identified using continuous-wave electron paramagnetic resonance (EPR) spectroscopy, providing direct evidence for the free radical mechanisms of organic pollutants inhibition. The transverse (T2) and longitudinal (T1) relaxation time variations catalyzed by different metal catalysts in the presence of ammonium sulfate were compared using pulsed-wave EPR. Consequently, after the addition of ammonium sulfate, the observed increase in T2 suggests that ammonium sulfate leads to radical concentration reduction. A decrease in the T1 relaxation time suggests the enhanced interaction between organic radicals and metals, which is an obstacle to subsequent radical reactions. Therefore, ammonium sulfate dominantly changed the free radical intermediates species, concentrations, and their reactivity, and then inhibited the organic pollutants formations. The inhibition mechanisms of ammonium sulfate on metal-catalyzed pollutants were then proposed combining EPR analysis, X-ray characterization, and high-resolution mass spectrometry screening. As a result, (1) occupying the active sites of metal catalysis and (2) inhibiting free radical intermediates are the two main intrinsic inhibition mechanisms of ammonium sulfate. The findings provide new perspectives on the efficient inhibition of organic pollutants in industrial processes involving various metal catalysts.

Linking industrial emissions and dietary exposure to human burdens of polychlorinated naphthalenes.

Relationships between toxic pollutant emissions during industrial processes and toxic pollutant dietary intakes and adverse health burdens have not yet been quantitatively clarified. Polychlorinated naphthalenes (PCNs) are typical industrial pollutants that are carcinogenic and of increasing concern. In this study, we established an interpretable machine learning model for quantifying the contributions of industrial emissions and dietary intakes of PCNs to health effects. We used the SHapley Additive exPlanations model to achieve individualized interpretability, enabling us to evaluate the specific contributions of individual feature values towards PCNs concentration levels. A strong relationship between PCN dietary intake and body burden was found using a robust large-scale PCN diet survey database for China containing the results of the analyses of 17,280 dietary samples and 4480 breast milk samples. Industrial emissions and dietary intake contributed 12 % and 52 %, respectively, of the PCN burden in breast milk. The model quantified the contributions of food consumption and industrial emissions to PCN exposure, which will be useful for performing accurate health risk assessments and developing reduction strategies of PCNs.

Formation of persistent free radicals from epigallocatechin Gallate in tea processing and their implications on DNA damage and cell cytotoxicity.

Tea is widely consumed in both beverages and food. Epigallocatechin gallate (EGCG) is the most crucial active ingredient in tea. Currently, knowledges on transformation processes of EGCG during tea processing are lacking. Understanding the chemical reactions of EGCG and its products during tea processing is important for assessing the safety of tea-containing food. Here, we revealed the formation of persistent free radicals (PFRs) from EGCG under the influence of heating and light irradiation, which was substantiated with evidence. These PFRs exhibited stability for >30 min in simulated gastric fluid. Furthermore, we observed potential effects of these PFRs on DNA damage and cell cytotoxicity in vitro. By combining electron paramagnetic resonance spectrometer with Fourier transform ion cyclotron resonance mass spectrometry, we elucidated the pathways involved in free radical formation. These findings are expected to contribute to a comprehensive understanding of free radical chemistry in tea-containing food.

Unexpected hydroxyl radical production in brewed tea under sunlight.

Tea is one of the world's most popular and widely consumed beverages. It is a common pastime to enjoy a cup of tea in the sunshine. However, little attention has been given to understanding the possible photochemical reactions occurring beneath the calm surface of brewed tea. Epigallocatechin gallate (EGCG), which is widely used in food and beverages, is the most significant active ingredient found in tea. In this study, we investigated the presence of free radicals in both an aqueous EGCG solution and brewed tea under simulated sunlight conditions. To our surprise, we unexpectedly observed the production of hydroxyl radicals (•OH) in brewed tea. It was found that sunlight irradiation played a critical role in the formation of •OH, independent of the presence of metal ions. Furthermore, we demonstrated that the •OH generated from the EGCG aqueous solution induced cell cytotoxicity and DNA damage in vitro. Considering the crucial role of •OH in various fields, including human health and the environment, it is important to further explore the practical implications of •OH production in brewed tea under sunlight. In summary, our study unveils the unexpected formation of •OH in brewed tea and emphasizes the significance of sunlight-induced reactions. The observed cytotoxic and DNA-damaging effects of •OH emphasize the importance of understanding the potential health consequences associated with tea consumption. Further research in this area will contribute to a better understanding of the broader implications of •OH production in brewed tea under sunlight.

Free radical mechanism of toxic organic compound formations from o-chlorophenol.

Organic free radical intermediates are pivotal to our understanding of toxic chemicals formation from chlorophenols that widely exist in thermal processes. However, in most cases, multiple free radical intermediates exist and produce complex spectra that are hard to deconvolute. Identification of free radical intermediates is the current difficulty for detailed formation mechanisms of toxic products from chlorophenols. In this study, a universal bottom-up method was developed to identify the organic free radical intermediates. Candidate organic free radicals were firstly speculated according to the critical parameters obtained from experimental electron paramagnetic resonance (EPR) spectra and the calculated bond dissociation energies of precursors. Their theoretical spectra were then used retrospectively to justify the accordance with the experimental EPR spectra. Identification of the organic free radicals provides straightforward evidence for the formation pathways of pollutants from chlorophenol. Internal factors influencing formation of radical intermediates and the toxic products were also studied, including the ortho effect of the precursor, spin densities of the organic free radical intermediates, and steric hindrance effects of the molecular intermediates. In combination of the experimental results and theoretical calculations, detailed formation mechanisms of toxic pollutants intermediating by organic free radicals from thermal oxidation of chlorophenol were strongly evidenced.

Bridging the Energy Benefit and POPs Emission Risk from Waste Incineration.

Incineration has been the globally controversial and concerned method of solid waste disposal. Energy recovery and volume reduction are the benefits from waste incineration, but risk due to release of persistent organic pollutants is the major public concern in the world. In this study, the emission of organic pollutants including dioxins and polychlorinated naphthalenes from solid waste incineration in China was comprehensively evaluated, and a relationship between energy benefit and pollutant emission was firstly established. The results show that production of medical and industrial waste was smaller than that of municipal waste but yielded comparable or even higher emission of dioxins. The energy benefit-to-emission index for organic pollutants (EBEIOP) for evaluation of solid waste management on a local or regional scale was proposed. Significant correlations between net energy benefit and pollutant emission for provinces with higher EBEIOP values were found. Furthermore, higher EBEIOP values were associated with economic factors while lower values were influenced by emission from incineration of medical and industrial waste. We suggest that an EBEIOP value of ≥60 can serve as a reference for "profitable" solid waste management, assisting decision making during energy benefit and environmental risk assessment.

Formation of environmentally persistent free radicals from thermochemical reactions of catechol.

In many anthropogenic activities, catechol as a widespread organic chemical could be released and also environmentally persistent free radicals (EPFRs) can be unintentionally formed. However, the underlying links between EPFRs and the role of catechol as an important precursor are not well understood. In this study, EPFR formation from catechol during heating was monitored online by electron paramagnetic resonance spectroscopy. It was found that catechol can produce significant amounts of EPFRs via thermochemical reactions. The EPFR species formed from catechol on metal oxides were oxygen-centered phenoxy and semiquinone radicals. Their half-lives were evaluated to be in the range of 113-909 h. The promotional effects of CaO and CuO on EPFR formation from catechol were stronger than that of Fe2O3. The promotional abilities and underlying mechanisms of various metal oxides in EPFR formation were clarified by X-ray photoelectron spectroscopy. Significant EPFR formation was observed during the cooling stage of a heating reaction system when CaO was used as the reaction medium. The obtained knowledge on the formation of EPFRs from catechol and the key factors involved will enable better control of the formation of EPFRs from anthropogenic activities.

Assessment of personal exposure to environmentally persistent free radicals in airborne particulate matter.

Environmentally persistent free radicals (EPFRs) are a type of emerging contaminants. The EPFR species in airborne particulate matter are similar to carcinogenic tar paramagnetic species in cigarettes that can cause DNA damage. However, understanding on daily EPFR exposure levels and risks are lacking currently. We used personal aerosol exposure monitors worn by volunteers to assess EPFR exposure in a spatio-temporal, non-static manner. Daily individual exposure to EPFRs for urban residents in Beijing, China ranged from 1.11 × 1017 to 7.42 × 1017 spins/m3 during the heating period (winter) and from 4.79 × 1014 to 7.76 × 1016 spins/m3 during the non-heating period (summer). Carbon-centered radicals were dominant in winter, while oxygen-centered radicals were dominant in summer because of higher atmospheric oxidizing capacity contributing to oxidation reactions. Coal combustion in winter is a key influencing factor in EPFR exposure levels. An intuitional assessment was used to evaluate the inhalation risks of EPFRs by converting their concentrations in inhaled particulate matter to equivalents in cigarettes smoked. The assessment concluded that one urban resident may, on average, inhale the equivalent of 46 cigarettes per day in EPFRs. The health risks of these free radicals, especially during winter, should be researched in depth.

Photoinduced formation of persistent free radicals, hydrogen radicals, and hydroxyl radicals from catechol on atmospheric particulate matter.

Catechol is speculated to be a potential precursor of environmentally persistent free radicals (EPFRs) in the atmosphere. EPFRs absorbed on PM2.5 have attracted public attention because their toxicity is similar to cigarette smoke. In this study, we found that catechol could produce EPFRs, which were oxygen-centered phenoxy and semiquinone radicals. These free radical species had half-lives of up to 382 days. CaO, CuO, and Fe2O3 markedly promoted EPFR formation from catechol. The valence states of Cu and Fe changed during the photochemical reactions of catechol but no valence state changed for Ca. Alkaline nature of CaO is possibly the key for promoting the free radical formations through acid-base reactions with catechol. In addition to hydroxyl free radicals, hydrogen free radicals and superoxide anions formed from the photochemical reactions of catechol were first discovered. This is of concern because of the adverse effects of these free radicals on human health.

Polychlorinated naphthalenes in human milk: Health risk assessment to nursing infants and source analysis.

Polychlorinated naphthalenes are teratogenic environmental contaminants. Mother milk is the most important food for nursing infants. The World Health Organization actively promotes breastfeeding for its immunological, psychological, and economic advantages. We firstly measured concentrations of polychlorinated naphthalenes in human milk from 19 provinces in China and estimated their potential health risks to nursing infants and their possible sources. Concentrations ranged from 211.07 to 2497.43 pg/g lipid. The high prevalence of highly toxic hexachlorinated naphthalenes (Hexa-CN66/67) in human milk samples indicated a higher health risk in the sampling areas. Cancer risk posed to nursing infants was not significant, but potential non-carcinogenic adverse health effects were suggested and should be emphasized in some sampling areas. Unintentional emission of polychlorinated naphthalenes from industries that employ thermal processes appears to be the main source for PCNs in human milk in most sampling areas. Correlation analysis also suggested PCNs as impurities in polychlorinated biphenyl mixtures as a previously unrecognized source of polychlorinated naphthalenes in human milk.