Persistent free radicals in woodsmoke: an ESR spin trapping study

Understanding visible light and microbe-driven degradation mechanisms of polyurethane plastics: Pathways, property changes, and product analysis

The accumulation of polyurethane plastics (PU-PS) in the environment is on the rise, posing potential risks to the health and function of ecosystems. However, little is known about the degradation behavior of PU-PS in the environment, especially water environment. To address this knowledge gap, we investigated and isolated a degrading strain of Streptomyces sp. B2 from the surface of polyurethane coatings. Subsequently, a photoreactor was employed to simulate the degradation process of bio-based polyurethane (BPU) and petroleum-based polyurethane (PPU) under three conditions, including single microorganism (SM), single light exposure (SL), and combined light exposure/microorganism action (ML) in aqueous solution. The results indicated that PU-PS mainly relies on biodegradation, with the highest degradation rate observed after 28 d under SM condition (BPU 5.69 %; PPU 5.25 %). SL inhibited microbial growth and degradation, with the least impact on plastic degradation. Microorganisms colonized the plastic surface, secreting relevant hydrolytic enzymes and organic acids into the culture medium, providing a negative charge. The carbon chains were broken and aged through hydrogen peroxide induction or attack by oxygen free radicals. This process promoted the formation of oxidized functional groups such as OH and CO, disrupting the polymer's structure. Consequently, localized fragmentation and erosion of the microstructure occurred, resulting in the generation of secondary microplastic (MPs) particles, weight loss of the original plastic, increased surface roughness, and enhanced hydrophilicity. Additionally, BPU exhibited greater degradability than PPU, as microorganisms could utilize the produced fatty acids, which promoted their reproduction. In contrast, PPU degradation generated a large amount of isocyanate, potentially toxic to cells and inhibiting biodegradation. This study unveils the significant role of microorganisms in plastic degradation and the underlying degradation mechanisms of BPU, providing a novel strategy for polyurethane degradation and valuable information for comprehensive assessment of the behavior and fate of MPs in the environment.

Interactions between inhalable aged microplastics and lung surfactant: Potential pulmonary health risks

The relationship between microplastics (MPs) and human respiratory health has garnered significant attention since inhalation constitutes the primary pathway for atmospheric MP exposure. While recent studies have revealed respiratory risks associated with MPs, virgin MPs used as plastic surrogates in these experiments did not represent the MPs that occur naturally and that undergo aging effects. Thus, the effects of aged MPs on respiratory health remain unknown. We herein analyzed the interaction between inhalable aged MPs with lung surfactant (LS) extracted from porcine lungs vis-à-vis interfacial chemistry employing in-vitro experiments, and explored oxidative damage induced by aged MPs in simulated lung fluid (SLF) and the underlying mechanisms of action. Our results showed that aged MPs significantly increased the surface tension of the LS, accompanied by a diminution in its foaming ability. The stronger adsorptive capacity of the aged MPs toward the phospholipids of LS appeared to produce increased surface tension, while the change in foaming ability might have resulted from a variation in the protein secondary structure and the adsorption of proteins onto MPs. The adsorption of phospholipid and protein components then led to the aggregation of MPs in SLF, where the aged MPs exhibited smaller hydrodynamic diameters in comparison with the unaged MPs, likely interacting with biomolecules in bodily fluids to exacerbate health hazards. Persistent free radicals were also formed on aged MPs, inducing the formation of reactive oxygen species such as superoxide radicals (O2•-), hydrogen peroxide (HOOH), and hydroxyl radicals (•OH); this would lead to LS lipid peroxidation and protein damage and increase the risk of respiratory disease. Our investigation was the first-ever to reveal a potential toxic effect of aged MPs and their actions on the human respiratory system, of great significance in understanding the risk of inhaled MPs on lung health.

Sulfurization alters phenol-formaldehyde resin microplastics redox property and their efficiency in mediating arsenite oxidation

Microplastics weathering by various types of oxidants in the oxic environment and their interaction with environmental contaminants have drawn numerous scientific attention. However, the environmental fate of microplastics under a reducing environment has been largely unresolved. Herein, the change of physicochemical and redox properties of microplastics during the weathering under a sulfate-reducing environment and the interaction with arsenite were addressed. The sulfurization of phenol-formaldehyde resin microplastics under a sulfate-reducing environment generated smooth and porous particles with the induction of organic S species. Multiple spectroscopic results demonstrated thioether and thiophene groups formed by the substitute removal of O-containing functional groups. Moreover, the sulfurization process induced the reduction of carbonyl groups and oxidation of phenolic hydroxyl groups and resulted in the formation of semiquinone radicals. The O-containing functional groups contributed to microplastics redox property and As(III) oxidation while S-containing functional groups showed no obvious effect. The sulfurized microplastics had lower efficiency in mediating arsenite oxidation than the unsulfurized counterparts due to the decreased electron donating capacity. Producing hydrogen peroxides by electron-donating phenol groups and semiquinone radicals and the direct semiquinone radicals oxidation could mediate arsenite oxidation. The findings of this study help us understand the fate of microplastics in redox fluctuation interfaces.

Toxic effects and primary source of the aged micro-sized artificial turf fragments and rubber particles: Comparative studies on laboratory photoaging and actual field sampling

Numerous micro-sized artificial turf fragments (MATF) and rubber particles (MRP) are generated and accumulated during the use of the artificial playing field. However, attention has rarely been paid to the potential toxic effects of MATF and MRP on sportsmen. In this study, the active components and chemical composition of aged MATF and MRP derived from laboratory photoaging and actual field sampling were detected, and their effects on cytotoxicity were examined correspondingly. Laboratory photoaging significantly increased environmental persistent free radicals (EPFRs), reactive oxygen species (ROS) abundances and oxidative potential (OP) levels on MATF and MRP, but they have limited cytotoxicity. Unfortunately, in the actual field, aged MATF and MRP with higher heavy metals and polycyclic aromatic hydrocarbons (PAHs) contents exhibited markedly higher cytotoxicity with the survival rate of cells of 78 % and 26 % (p < 0.05), although they had lower EPFRs and ROS yields. Correlation analysis revealed that the cell viability was closely linked to heavy metals of MATF (p < 0.05), and to organic hydroperoxide (OHP), PAHs and heavy metals of MRP (p < 0.05). By systematically considering the above results, heavy metals and PAHs enriched on MATF and MRP from the surrounding environment played the important role in the cytotoxicity, which was different from conventional perspectives. Our findings demonstrate that MATF and MRP associated with an artificial turf field contain potent mixtures of pollutants and can, therefore, be relevant yet underestimated factors contributing to the health risks.

Formation of Environmentally Persistent Free Radicals on Microplastics under Light Irradiation

Microplastics (MPs) are presumed to be inert during aging under ambient conditions. In this study, four types of virgin MPs, including polystyrene (PS), phenol-formaldehyde resin (PF), polyethylene (PE), and polyvinyl chloride (PVC), were aged under simulated solar light irradiation. Surprisingly, several environmentally persistent free radicals (EPFRs), which are considered to be a type of emerging contaminant, were detected on the irradiated PS and PF, rather than PE and PVC, by electron paramagnetic resonance (EPR) spectroscopy. Depending on the photoaging duration time, the characteristic g-factors of the EPFRs produced on PS and PF were 2.0044-2.0049 and 2.0043-2.0044, respectively. The generated EPFRs on PS and PF decayed rapidly at the initial stage and then slowly disappeared with the elapsed aging time. Analyses by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR), and gel permeation chromatography (GPC) suggested that MPs might experience chemical chain scission, O₂/H₂O addition, and EPFR formation under the light irradiation. Accompanying with the formation of EPFRs, reactive oxygen species, such as O₂^•- and •OH, were also observed. The findings provide a novel insight to evaluate the potential hazards of MPs to organisms and ecosystems.

Current concepts in the pathophysiology and treatment of inhalation injury

The opinions or assertions contained herein are the private views of the author, and are not to be construed as official or as reflecting the official views of the Department of the Army or Department of Defense. Smoke inhalation injury occurs in about 10% of patients admitted to burn centres, and increases the mortality of burn patients by up to 20% over predictions based on age and burn size alone. The primary lesion in smoke inhalation injury is localized to the small airways, with alveolar injury and pulmonary oedema exercising a less prominent role during the initial phases. Injury incites a cascade of events that include ventilation-perfusion mismatch, secondary lung injury, systemic inflammation, impaired immune function, and pneumonia. The most important recent developments in the treatment of inhalation injury have included improved methods of pulmonary care targeted at the pathophysiology of the injury, such as high-frequency percussive ventilation and gentle mechanical ventilation.

Response of Steroid-Refractory Acute GVHD to α1-Antitrypsin

α1-Antitrypsin (AAT) is a serine protease inhibitor with anti-inflammatory, antiapoptotic, and immunomodulatory properties. It has therapeutic efficacy in animal models of autoimmune diseases, inflammatory disorders, and transplantation. In a phase I/II open-label single-center study, we administered AAT (Glassia; Baxalta/Kamada, New Ziona, Israel) as salvage therapy to 12 patients with steroid-refractory acute graft-versus-host disease (GVHD). AAT was given i.v. at 2 dose levels over a 15-day course. All patients had grades III or IV GVHD with stage 4 gut involvement. After treatment, plasma AAT levels increased in both cohorts and remained within 2 to 4 mg/mL for the duration of treatment. No clinically relevant toxicities attributable to AAT were observed. GVHD manifestations improved in 8 of 12 patients, and 4 responses were complete. Six patients (50%) were alive at last follow-up (>104 to >820 days). These findings show that AAT is well tolerated and has efficacy in the treatment of steroid-refractory severe acute GVHD. Further studies are warranted.

Wood smoke enhances cigarette smoke-induced inflammation by inducing the aryl hydrocarbon receptor repressor in airway epithelial cells

Our previous studies showed that cigarette smokers who are exposed to wood smoke (WS) are at an increased risk for chronic bronchitis and reduced lung function. The present study was undertaken to determine the mechanisms for WS-induced adverse effects. We studied the effect of WS exposure using four cohorts of mice. C57Bl/6 mice were exposed for 4 or 12 weeks to filtered air, to 10 mg/m(3) WS for 2 h/d, to 250 mg/m(3) cigarette smoke (CS) for 6 h/d, or to CS followed by WS (CW). Inflammation was absent in the filtered air and WS groups, but enhanced by twofold in the bronchoalveolar lavage of the CW compared with CS group as measured by neutrophil numbers and levels of the neutrophil chemoattractant, keratinocyte-derived chemokine. The levels of the anti-inflammatory lipoxin, lipoxin A4, were reduced by threefold along with cyclo-oxygenase (COX)-2 and microsomal prostaglandin E synthase (mPGES)-1 in airway epithelial cells and PGE2 levels in the bronchoalveolar lavage of CW compared with CS mice. We replicated, in primary human airway epithelial cells, the changes observed in mice. Immunoprecipitations showed that WS blocked the interaction of aryl hydrocarbon receptor (AHR) with AHR nuclear transporter to reduce expression of COX-2 and mPGES-1 by increasing expression of AHR repressor (AHRR). Collectively, these studies show that exposure to low concentrations of WS enhanced CS-induced inflammation by inducing AHRR expression to suppress AHR, COX-2, and mPGES-1 expression, and levels of PGE2 and lipoxin A4. Therefore, AHRR is a potential therapeutic target for WS-associated exacerbations of CS-induced inflammation.

Hydroxyl radical generation from environmentally persistent free radicals (EPFRs) in PM2.5

Hydroxyl radicals were generated from an aqueous suspension of ambient PM2.5 and detected utilizing 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap coupled with electron paramagnetic resonance (EPR) spectroscopy. Results from this study suggested the importance of environmentally persistent free radicals (EPFRs) in PM2.5 to generate significant levels of ·OH without the addition of H2O2. Particles for which the EPFRs were allowed to decay over time induced less hydroxyl radical. Additionally, higher particle concentrations produced more hydroxyl radical. Some samples did not alter hydroxyl radical generation when the solution was purged by air. This is ascribed to internal, rather than external surface associated EPFRs.

Environmentally persistent free radicals and their lifetimes in PM2.5

For the first time, an expansive study into the concentration and extended decay behavior of environmentally persistent free radicals in PM2.5 was performed. Results from this study revealed three types of radical decay-a fast decay, slow decay, and no decay-following one of four decay patterns: a relatively fast decay exhibiting a 1/e lifetime of 1-21 days accompanied by a slow decay with a 1/e lifetime of 21-5028 days (47% of samples); a single slow decay including a 1/e lifetime of 4-2083 days (24% of samples); no decay (18% of samples); and a relatively fast decay displaying an average 1/e lifetime of 0.25-21 days followed by no decay (11% of samples). Phenol correlated well with the initial radical concentration and fast decay rate. Other correlations for common atmospheric pollutants (ozone, NOx, SO2, etc.) as well as meteorological conditions suggested photochemical processes impact the initial radical concentration and fast decay rate. The radical signal in PM2.5 was remarkably similar to semiquinones in cigarette smoke. Accordingly, radicals inhaled from PM2.5 were related to the radicals inhaled from smoking cigarettes, expressed as the number of equivalent cigarettes smoked. This calculated to 0.4-0.9 cigarettes per day for nonextreme air quality in the United States.

Detection and separation of gas-phase carbon-centered radicals from cigarette smoke and diesel exhaust

Carbon-centered radicals were trapped from gas-phase cigarette smoke and diesel engine exhaust by reaction with a nitroxide, 3-amino-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (3AP). The resulting mixture of stable, diamagnetic adducts was derivatized with naphthalenedicarboxaldehyde (NDA) to produce highly fluorescent products. Derivatives were separated by high-performance liquid chromatography (HPLC), which revealed distinctly different suites of radicals present in the two systems. Integration of HPLC peaks gave approximately 22 ± 7 nmol of radicals per cigarette and 3 ± 1 nmol of radicals per liter of diesel engine exhaust. An estimated 8-10 different carbon-centered radical species are present in each system.

Assessment of oxidative stress in lungs from sheep after inhalation of wood smoke

To elucidate potential dose-dependent mechanisms associated with wood smoke inhalation injury, the present study evaluated antioxidant status and the extent of pulmonary injury in sheep after graded exposure to smoke. Adult, male sheep (n=4-5 per group) were anesthetized and received 0, 5, 10 or 16 units of cooled western pine bark smoke, corresponding to 0, 175, 350 and 560 s, respectively, of smoke dwell time in the airways and lung. Smoke was mixed at a 1:1 ratio with 100% O2 to minimize hypoxia. Plasma and expired breath samples were collected pre-smoke, and 6, 12, 18, 24, 36 and 48 h after smoke exposure. Sheep were euthanatized 48 h after smoke exposure and lung and airway sections were evaluated histologically for injury and biochemically for indices of oxidative stress. Plasma thiobarbituric acid reactive substances (TBARS) were 66 and 69% higher than controls after moderate and severe smoke exposure at 48 h, whereas total antioxidant potential was not statistically different among groups at any time after exposure. Lung TBARS showed a dose-dependent response to smoke inhalation and were approximately 2-, 3- and 4-fold higher, respectively, than controls after exposure to 5, 10 and 16 units of smoke. Lung myeloperoxidase (MPO) activity was also higher in smoke-exposed animals than controls, and MPO activity was markedly elevated (19- and 22-fold higher than controls in right apical and medial lobes) in response to severe smoke exposure. Smoke exposure also induced a dose-dependent injury to tracheobronchial epithelium and lung parenchyma. Taken together these data show that few indices of oxidative stress responded in a dose-dependent manner to graded doses of smoke inhalation, although most of the indices measured in lung were affected by the highest dose of smoke. Additional time course studies are necessary to determine whether these oxidants are a cause or a consequence of the airway and lung injury associated with exposure to wood smoke.

The toxicology of inhaled woodsmoke

In addition to developing nations relying almost exclusively upon biomass fuels, such as wood for cooking and home heating, North Americans, particularly in Canada and the northwestern and northeastern sections of the United States, have increasingly turned to woodburning as an alternate method for domestic heating because of increasing energy costs. As a result, the number of households using woodburning devices has increased dramatically. This has resulted in an increase in public exposure to indoor and outdoor woodsmoke-associated pollutants, which has prompted widespread concern about the adverse human health consequences that may be associated with prolonged woodsmoke exposure. This mini-review article brings together many of the human and animal studies performed over the last three decades in an attempt to better define the toxicological impact of inhaled woodsmoke on exposed children and adults; particular attention is given to effects upon the immune system. General information regarding occurrence and woodsmoke chemistry is provided so as to set the stage for a better understanding of the toxicological impact. It can be concluded from this review that exposure to woodsmoke, particularly for children, represents a potential health hazard. However, despite its widespread occurrence and apparent human health risks, relatively few studies have focused upon this particular area of research. More laboratory studies aimed at understanding the effects and underlying mechanisms of woodsmoke exposure, particularly on those individuals deemed to be at greatest risk, are badly needed, so that precise human health risks can be defined, appropriate regulatory standards can be set, and accurate decisions can be made concerning the use of current and new woodburning devices.

Oxidation of cysteamine induced by gas-phase radicals from combustion smoke of poly (methyl methacrylate)

In order to obtain fundamental knowledge on biological damage caused by the smoke from combustion of poly(methyl-methacrylate) (PMMA), we investigated the oxidation of cysteamine induced by PMMA smoke. We suggest that the long-lived and oxygen-centered radicals involved in PMMA smoke should play an important role in the oxidation of cysteamine. The mechanism for the oxidation of cysteamine by combustion smoke of PMMA was postulated as radical initiated chain reactions, taking into account the effect of pH, oxygen and radical concentrations.

Fluid resuscitation with deferoxamine hetastarch complex attenuates the lung and systemic response to smoke inhalation

BACKGROUND

We determined the effect of infusing the iron chelator deferoxamine complexed to hetastarch on the degree of lung dysfunction and systemic abnormalities produced by a severe smoke exposure.

METHODS

Adult sheep were given a smoke exposure under anesthesia that produced a peak carboxyhemoglobin between 40% and 45%. Twenty-eight sheep were studied; eight were given smoke alone and resuscitated with sufficient lactated Ringer's solution to maintain baseline hemodynamics. Seven sheep were given a bolus plus 1 ml/kg/hr of a 10% deferoxamine-hetastarch solution for resuscitation; five were given hetastarch alone. The response was compared with eight controls during a period of 24 hours.

RESULTS

Smoke alone and smoke with hetastarch resulted in a shunt fraction of greater than 25% and a 50% decrease in compliance, severe airway inflammation, mucosal slough, atelectasis, and some alveolar edema. Increased lipid peroxides measured as malondialdehyde were present in airway fluid. In addition, oxygen consumption increased by 100% early after injury, net 24-hour positive fluid balance was almost 3 L, and a significant increase occurred in liver lipid peroxidation. The group given deferoxamine had a significantly attenuated lung response, with only modest airway damage lung dysfunction, and minimal systemic changes including a net positive fluid balance of just over 1L and no liver lipid peroxidation.

CONCLUSIONS

An iron chelator deferoxamine complexed to hetastarch, given after a severe smoke exposure, significantly attenuates the airway and the systemic inflammatory (oxidant) injury, indicating free iron release and subsequent increased oxidant activity to be a major etiologic factor.

Effect of graded increases in smoke inhalation injury on the early systemic response to a body burn

OBJECTIVE

To study the early (first 24 hrs) effect of increasing lung exposure to smoke on the hemodynamic response to a modest body burn.

DESIGN

A prospective randomized study.

SETTING

Laboratory at a university medical center.

SUBJECTS

Thirty-two adult yearling female sheep.

INTERVENTIONS

Adult sheep (n = 32) were given an 18% of body surface burn; 24 sheep were then exposed to cotton toweling smoke using 12 breaths of a tidal volume of 5, 10, or 20 mL/kg. Animals were awakened, resuscitated to baseline oxygen delivery, and then killed at 24 hrs.

MEASUREMENTS AND MAIN RESULTS

Vascular pressure, cardiac output, and oxygen consumption and delivery were measured, as well as blood gases, lung and soft tissue lymph flow, and fluid balance. We found that a 5-mL/kg tidal volume smoke exposure x 12 breaths did not produce significant airway inflammation or alter the cardiopulmonary response to a burn alone. Oxygen consumption (VO2) remained at baseline and the net 24-hr positive fluid balance of 1.5 L was comparable to a burn alone. Increasing the smoke exposure to 10 mL/kg tidal volume, which produced a moderate airway injury, resulted in a significant increase in early fluid requirements, a 40% early increase in VO2, a doubling of positive fluid balance, as well as a marked increase in burn edema. However, gas exchange was not impaired. The 20-mL/kg tidal volume exposure resulted in an early 100% increase in VO2, a three-fold increase in fluid requirements at 1 to 4 hrs, compared with burn alone, in addition to a severe airway inflammation with mucosal slough and resulting impaired gas exchange.

CONCLUSIONS

The addition of a smoke exposure which produces airway inflammation and injury significantly increases early post burn systemic metabolic demands and fluid requirements, as well as the degree of burn edema and positive fluid balance compared with a burn alone. The magnitude of the accentuated response appears to correspond with the degree of airway inflammation and not with alveolar dysfunction.

Biological effects of cigarette smoke, wood smoke, and the smoke from plastics: the use of electron spin resonance

This review compares and contrasts the chemistry of cigarette smoke, wood smoke, and the smoke from plastics and building materials that is inhaled by persons trapped in fires. Cigarette smoke produces cancer, emphysema, and other diseases after a delay of years. Acute exposure to smoke in a fire can produce a loss of lung function and death after a delay of days or weeks. Tobacco smoke and the smoke inhaled in a burning building have some similarities from a chemical viewpoint. For example, both contain high concentrations of CO and other combustion products. In addition, both contain high concentrations of free radicals, and our laboratory has studied these free radicals, largely by electron spin resonance (ESR) methods, for about 15 years. This article reviews what is known about the radicals present in these different types of smokes and soots and tars and summarizes the evidence that suggests these radicals could be involved in cigarette-induced pathology and smoke-inhalation deaths. The combustion of all organic materials produces radicals, but (with the exception of the smoke from perfluoropolymers) the radicals that are detected by ESR methods (and thus the radicals that would reach the lungs) are not those that arise in the combustion process. Rather they arise from chemical reactions that occur in the smoke itself. Thus, a knowledge of the chemistry of the smoke is necessary to understand the nature of the radicals formed. Even materials as similar as cigarettes and wood (cellulose) produce smoke that contains radicals with very different lifetimes and chemical characteristics, and mechanistic rationales for this are discussed. Cigarette tar contains a semiquinone radical that is infinitely stable and can be directly observed by ESR. Aqueous extracts of cigarette tar, which contain this radical, reduce oxygen to superoxide and thus produce both hydrogen peroxide and the hydroxyl radical. These solutions both oxidize alpha-1-proteinase inhibitor (a1PI) and nick DNA. Because of the potential role of radicals in smoke-inhalation injury, we suggest that antioxidant therapy (such as use of an inhaler for persons brought out of a burning building) might prove efficacious.

Oxidants and the pathophysiology of burn and smoke inhalation injury

A skin burn is a common traumatic injury that results in both local tissue damage and a systemic mediator-induced response. There is evidence of both local and systemic oxidant changes manifested by lipid peroxidation in animal burn models and also in burned man. Both increased xanthine oxidase and neutrophil activation appear to be the oxidant sources. Animal studies have also demonstrated decreased burn edema, and also decreased distant organ dysfunction with the use of antioxidants, suggesting a cause-and-effect relationship, which needs to be tested in man. Smoke inhalation injury, a chemical injury to the airways caused by incomplete products of combustion, is frequently seen in conjunction with a body burn. Lipid peroxidation, both in lung and in distant organs, is also seen with this injury. The combined body burn and smoke inhalation injury lead to a marked increase in mortality rate and also an increase in the degree of generalized oxidant release and lipid peroxidation. Although data in man are limited, the available information, along with that from animal research on burns and smoke inhalation, indicates oxidants may well play a key role, and antioxidants may be of clinical therapeutic use.

Measurement of free radicals from smoke inhalation and oxygen exposure by spin trapping and ESR spectroscopy

Research in smoke inhalation has established that free radicals are produced from gases released during combustion and these species impair lung function. Using spin traps and their adducts in an animal model free radicals were measured. Various hyperbaric oxygen regimens were tested in an attempt to attenuate pulmonary damage caused by free radical reactions. Our data demonstrated that persistent oxygen- and carbon-centered free radicals are detectable in intravascular fluids after smoke inhalation. The smoke inhalation model showed however, clearing of spin trap adducts one hour after smoke exposure. Other researchers have found that when 100% oxygen is given at 1 atmosphere absolute (ATA) for 1 h, free radicals were not detectable. However, oxygen given at 2.5 ATA does produce detectable free radicals. With continued exposure at this pressure, the levels of free radicals increase for up to 60 min. This study suggests that the level of free radical induced oxygen toxicity may be a function of oxygen pressure and duration of oxygen exposure.

An epidemiologic study of cancer and other causes of mortality in San Francisco firefighters

To test the hypothesis that firefighter exposures may increase cancer risk, mortality rates were calculated for 3,066 San Francisco Fire Department firefighters employed between 1940 and 1970. Vital status was ascertained through 1982, and observed and expected rates, rate ratios (RR), and 95% confidence intervals (CI) were computed using United States death rates for comparison. The total number deceased (1,186) was less than expected and there were fewer cancer deaths than expected. However, there were significant excess numbers of deaths from esophageal cancer (12 observed, 6 expected), cirrhosis and other liver diseases (59 observed, 26 expected), and accidental falls (21 observed, 11 expected). There were 24 line-of-duty deaths, which were primarily due to vehicular injury, falls, and asphyxiation. Heart disease and respiratory disease deaths occurred significantly less often than expected. It was concluded that the increased risks of death from esophageal cancer and cirrhosis and other liver diseases may have been due to firefighter exposures, alcohol consumption, or interaction between alcohol and exposures. Because this was an older cohort and firefighter exposures have changed due to the increasing use of synthetic materials, it is recommended that the effects of modern-day exposures be further studied.

A comparison of the free radical chemistry of tobacco-burning cigarettes and cigarettes that only heat tobacco

Cigarette smoke contains free radicals both in the particulate matter (tar) and in vapor-phase smoke. Vapor-phase smoke decreases the activity of alpha-1-proteinase inhibitor (alpha 1PI) in vitro. The free radical content of the tar and vapor-phase smoke from a cigarette that heats rather than burns tobacco has been compared with data on a standard 1R4F cigarette. No radicals were detected in the tar from the new cigarette and radicals in its vapor-phase smoke are lower by more than 99% relative to the 1R4F standard cigarettes. The vapor-phase smoke from the new cigarette causes essentially no reduction of alpha 1PI activity in vitro. These findings support our previously published mechanisms for the production of radicals in tar and in vapor-phase smoke.