Ppm Formaldehyde Vapor Research Articles

Nickel-Doped ZnO Porous Sea Urchin Nanostructures with Various Amounts of Oxygen Defects for Volatile Organic Compound Detection

Porous sea urchin-like nickel-doped ZnO with various nickel contents and high specific surface area were synthesized using a solution method followed by calcination. The nickel-doped ZnO products consisted of numerous porous nanoleaves. The Ni content in these products ranged from 5% to 20%. The Ni dopants in the ZnO lattice were verified by X-ray diffraction and X-ray photoelectron spectroscopy. The sensors based on nickel-doped ZnO sea urchins showed superior sensing performance for some volatile organic compounds (VOCs). ZnO sea urchins with 10% nickel doping exhibited the best gas-sensing performance, including a low working temperature, short response/recovery time, and high sensor response. In particular, the 10% Ni-doped ZnO sea urchin sensor exhibited a response of 84.4 with response/recovery times of 17/20 s towards 100 ppm formaldehyde vapor. These superior sensing behaviors were attributed mainly to a suitable Ni content with high content of oxygen defects, small nanocrystals, and a porous hierarchical structure with a high specific surface area.

Cross-Linked SnO2 Nanosheets Modified by Ag Nanoparticles for Formaldehyde Vapor Detection

Ag@SnO2 nanosheets were prepared through a hydrothermal method followed by heat treatment and a liquid reduction process. Many Ag nanoparticles (Ag NPs) were dispersed uniformly over the surface of the SnO2 nanosheets. The thickness of the SnO2 nanosheets was approximately 10 nm. After decoration with Ag NPs, the Ag@SnO2 nanosheet sensors exhibited improved gas-sensing behaviors compared to the pure SnO2 nanosheet sensor. The response of cross-linked SnO2 nanosheets decorated by Ag NP sensors for 100 ppm formaldehyde vapor was up to 101.4, which was double that (45.5) of the pure SnO2 nanosheet sensor. The response and recovery times of the Ag@SnO2 sensor were 21 s and 23 s, respectively. The Ag@SnO2 nanosheet sensors showed reasonable cycling stability, as demonstrated by testing with 100 ppm formaldehyde 10 times. The superior gas-sensing behaviors of the Ag@SnO2 sensor were due to the large specific surface area, cross-linked nanostructure, and synergistic effect of the Ag NPs with huge sensitizing active sites and numerous SnO2 nanosheets.

Effects of Occupational Formaldehyde Exposure on Passive Avoidance Conditioning and Anxiety Levels in Wistar rats

Background: Formaldehyde is a volatile organic compound widely used in industry and medical fields such as Anatomy and Pathology. Exposure to this chemical negatively affects the skin, mucous membrane, and respiratory system. It can pass through the blood-brain barrier, potentially causing neurotoxicity. According to studies, formaldehyde might be involved in memory impairment and the cognitive decline process in Alzheimer disease (AD). Objectives: This study aimed to simulate chronic occupational formaldehyde exposure in rats and study its impacts on passive avoidance conditioning and anxiety. Methods: Twenty-four adult male Wistar rats were divided into four groups of 6 rats each. After an adaptation period, the rats were exposed to 1, 2, and 3 ppm formaldehyde vapor in an exposure chamber, 6 hours per day for 7 days. The control group was exposed to saline. After the exposure period, a shuttle box for passive avoidance conditioning and an elevated plus-maze test for assessing anxiety levels were performed. The data were analyzed by 1-way ANOVA and Duncan’s multiple range test for group comparison in SPSS and SAS software. Results: In the shuttle box test, formaldehyde dose-dependently decreased escape-through latency and increased the percentage of dark compartment entries (P<0.0001). In the elevated plus maze test, the percentage of time spent in open arms decreased by increasing the dosage (P<0.0001). Conclusion: Based on these findings, formaldehyde exposure can negatively alter brain function and cause memory impairment and anxiety.

Chemiresistively sensitized SiOC structure for formaldehyde detection under thermal and pressure loading

Chemiresistive SiOC Negative Poisson's ratio structures for gas detection under thermal and pressure loading were constructed by vat photopolymerization and surface sensitization. Metal-organic framework-derived SnO2 nanocubes modification provided the structures with sensing capability, while the high deformation-resistant SiOC substrates protected the integrity and connectivity of the sensing layer. The resulting SnO2/SiOC sensing structures exhibited high selectivity to formaldehyde vapor and showed a response value of 3.6 to 100 ppm formaldehyde vapor. The structures also had a short sensing delay with the response and recovery times of 32 s and 41 s, respectively. Besides, the independent deformation of the units maintained the dimensional accuracy and avoided thermal fatigue failure of the structure at the working temperature by dispersing the thermal stress, at which the coefficient of thermal expansion reached 0.71 × 10−6/K, revealing a near-zero expansion behavior. Meanwhile, the mechanical performance can be adjusted by structure optimization, and the compressive strength and Young's modulus of the structure reached 51.25 MPa and 5.14 GPa, respectively. Taking advantage of the strengthened and self-adaptive design, the structure exhibited high load-carrying capacity and low thermal expansion performance, providing a facile strategy for highly stable gas detection under complex loading environments.

High specific surface area SnO2 prepared by calcining Sn-MOFs and their formaldehyde-sensing characteristics

In this study, micron-sized hollow hexagonal prisms of SnO2 have been successfully synthesized based on a metal-organic framework material, Sn-MOF. The structure, morphology and gas sensing performance of prepared products were investigated by XRD, SEM, BET, XPS, TEM, Raman, FTIR and gas-sensing measurements. The experimental results show that metal oxides with high specific surface area can be obtained by calcining metal-organic framework materials. Specifically, a sensor based on hollow hexagonal prisms of SnO2 exhibited high response value (882) and short response time (19 s) to 2 ppm formaldehyde vapor at an optimal temperature of 120 ℃. This could be due to its larger specific surface area (46.42 m2/g).

A formaldehyde gas sensor with improved gas response and sub-ppm level detection limit based on NiO/NiFe2O4 composite nanotetrahedrons

Formaldehyde is a hazardous indoor volatile organic pollutant, thus selective and precise detection at a low concentration level is crucial. In this paper, NiO/NiFe2O4 nanocomposites were prepared through a simple two-step hydrothermal route and their gas sensing performances were investigated. SEM and TEM results showed that the composite products were NiO nanotetrahedrons decorated with numerous separated NiFe2O4 nanoparticles on the outer layer surface. XPS characterization confirmed that the as formed NiFe2O4 exhibited a p-type conductivity due to the hole transfer between Ni3+ and Ni2+ and therefore p-p isotype heterojunctions formed in the composite products. The element ratio of Fe to Ni was optimized to gain higher gas-sensing performance through adjusting the feeding amount of Fe3+ in the synthesis process. As a consequence, the gas sensor based on the sample NiFe-0.008 showed the highest response of 33.3–200 ppm formaldehyde vapor at 240 °C and a low detection limit of 200 ppb. The composite sensor also showed short response/recovery time and good long term stability. The enhanced gas sensing properties to formaldehyde can be attributed to the unique tetrahedral morphology and p-p heterojunction structure, which can provide more active sites and significantly enlarge resistance variation. This work will provide a new perspective of p-p heterojunction for the practical application in formaldehyde gas sensor.

Enhanced formaldehyde gas sensing properties of La-doped SnO2 nanoparticles prepared by ball-milling solid chemical reaction method

Pure and La-doped SnO2 nanoparticles were synthesized by ball-milling solid chemical reaction method. The microstructure, morphologies and gas sensing properties of as-synthesized nanoparticles were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray, transmission electron microscope and gas-sensing measurement device. Compared with pure SnO2 sensor, La-doped SnO2 sensor exhibited excellent formaldehyde sensing properties at the optimum temperature of 240 °C. Among them, 3 at% La-doped SnO2 sensor showed the highest response of 31.5–50 ppm formaldehyde vapor, the response and recovery time were 5 and 26 s, respectively. Moreover, the relationships between response value and HCHO concentration, and the selectivity of pure and 3 at% La-doped SnO2 sensor were investigated. The result indicated that the 3 at% La-doped SnO2 sensor had high response, short response-recovery time and good selectivity to formaldehyde. Finally, the gas-sensing mechanism of SnO2 sensor were discussed.

Hyperplasia of the lymphoepithelium of NALT in rats but not in mice upon 28-day exposure to 15 ppm formaldehyde vapor

To investigate if local lymphoid tissues are a target of FA, nasopharynx-associated lymphoid tissues (NALT) and upper-respiratory tract-draining lymph nodes were examined in a 28-day inhalation study with FA vapor in Fischer-344 rats and B6C3F1 mice. Paraffin-embedded tissues were sectioned and stained with H&E or stained immunohistochemically for cell proliferation (BrdU incorporation). Light microscopy revealed simple hyperplasia of NALT lymphoepithelium of rats exposed to 15 ppm and an increased proliferation rate of the epithelial cells. Principal component (discriminant) analysis of rat NALT and lymph nodes data did not reveal other effects or effects at lower exposure levels. Mice tissues were not affected. It was concluded that hyperplasia of the lymphoepithelium of NALT of rats exposed to 15 ppm was the only distinct effect of FA vapor on local lymphoid tissues (NALT and lymph nodes) of Fischer-344 rats and B3C3F1 mice.

Effects of a single inhalative exposure to formaldehyde on the open field behavior of mice

The effects of formaldehyde on the explorative behavior and locomotor activity of mice after a single inhalative exposure were examined in an open field. Adult male mice were exposed to approximately 1.1 ppm, 2.3 ppm, or 5.2 ppm formaldehyde vapour for 2 hours and the open field test was carried out two hours after the end of exposure (trial 1) and repeated 24 hours thereafter (trial 2). The following behavioral parameters were quantitatively examined: numbers of crossed floor squares (inner, peripheral, total), sniffing, grooming, rearing, climbing, and incidence of fecal boli. The results of the first trial revealed that the motion activity was significantly reduced in all exposed groups. In the 1.1 ppm group, the frequency of rearing was reduced and that of floor sniffing increased. The exposure to the two higher formaldehyde concentrations caused a significant decrease in total numbers of floor squares crossed by the subjects, air sniffing, and rearing. The open field test on the next day (trial 2) showed that the frequencies of floor sniffing, grooming, and rearing in all formaldehyde groups were significantly altered. In the 2.5 ppm group, an increased incidence of fecal boli was observed. From the results obtained, we conclude that the exposure of male mice to formaldehyde vapour affects their locomotor and explorative activity in the open field, and that some open field parameters are still altered in the exposed animals even after 24 hours.

Immunohistochemical localization of p53, PCNA, and TGF-alpha proteins in formaldehyde-induced rat nasal squamous cell carcinomas.

Mutation of the p53 tumor suppressor gene is a common event in many human cancers and has been specifically associated with invasive squamous cell carcinoma of the human skin and respiratory tract. Alterations in the p53 gene have also been identified in certain rodent tumors, including formaldehyde-induced nasal squamous cell carcinomas. Overexpression of transforming growth factor-alpha (TGF-alpha) is associated with carcinomas of the head and neck and respiratory tract in human patients and formaldehyde-induced rat nasal squamous cell carcinomas. Sections of rat noses containing tumors and other formaldehyde-induced lesions from rats exposed to 15 ppm formaldehyde vapor were examined using immunohistochemical techniques to detect and identify potential relationships between the presence and distribution of p53, proliferating cell nuclear antigen (PCNA), and TGF-alpha proteins. The five tumors that had p53 mutations were for mutant p53 protein by immunohistochemistry and three of six tumors with no detected p53 mutations were also immunoreactive for p53 protein. The presence, pattern, and distribution of p53 staining in tissue sections depended on the morphology of the lesion. PCNA immunoreactivity was strikingly similar in pattern and distribution to p53 immunoreactivity. The pattern and distribution of immunoreactivity for TGF-alpha did not directly correlate with the other markers. Mutation of the p53 tumor suppressor gene may be an important step in the progression of formaldehyde-induced nasal carcinogenesis in the rat. This study demonstrated that immunohistochemistry is a useful tool for the identification of sites within tumors that might have p53 mutations.

Pulmonary Cytochrome P450 in Rats Exposed to Formaldehyde Vapor

The lungs of rats exposed to formaldehyde vapor, for 6 hr/day over 4 consecutive days, were examined for signs of injury and for changes in the level, or activity, of cytochrome P450. The animals were supplied with 10 ppm formaldehyde vapor generated, in two separate experiments, either from an aqueous solution of formaldehyde or from heated paraformaldehyde. All rats were exposed for 6 hr, on each of 4 consecutive days, and killed I day after the onset of the fourth period of exposure. The lung weights and gains in body weight of exposed animals were indistinguishable from those of their controls. Lungs from the formaldehyde-exposed animals did not show any signs of injury, even at the ultrastructural level. Bronchoalveolar lavage samples from exposed animals showed no increase in alkaline phosphatase or γ-glutamyl transpeptidase activity. The total concentration of cytochrome P450 in the lungs of exposed animals was similar to that found in their controls. The P450 activity of pulmonary microsomes from exposed animals was not significantly different from that obtained with samples from the control animals. These results indicate that repeated exposure to 10 ppm formaldehyde vapor does not injure the deep lung of rats and has no effect on the level of lung P450 or on its activity against substrates for the most common pulmonary forms of this enzyme.

Nasal tumours in rats after severe injury to the nasal mucosa and prolonged exposure to 10 ppm formaldehyde.

To study the significance of damage to the nasal mucosa for the induction of nasal tumours by formaldehyde in rats, a long-term inhalation study was conducted in which male rats with severely damaged or undamaged nose were exposed 6 h/day for 5 days/week to 0, 0.1, 1.0 or 10 ppm formaldehyde vapour for 28 months, or for 3 months followed by a 25-month observation period. The damage to the nasal mucosa was induced by bilateral intranasal electrocoagulation. The total number of rats used was 720, 480 with damaged and 240 with intact nose. Compound-related degenerative, inflammatory and hyperplastic changes of the nasal respiratory and olfactory mucosa were invariably observed when rats with intact nose were exposed to 10 ppm but not when exposed to 1.0 or 0.1 ppm formaldehyde. Nasal electrocoagulation increased the incidences of formaldehyde-induced rhinitis, hyper- and metaplasia of the respiratory epithelium, and degeneration and hyper- and metaplasia of the olfactory epithelium. In addition, exposure to 10 ppm formaldehyde for 28 months produced nasal squamous cell carcinomas in rats with damaged nose (15/58) but not in rats with intact nose. Three months of exposure to 10 ppm formaldehyde or exposure to 0.1 or 1.0 ppm formaldehyde for 28 months had no such effect. It was concluded that severe damage to the nasal mucosa may contribute to the induction of nasal tumours by formaldehyde.

Cytotoxic and adaptive effects in rat nasal epithelium after 3-day and 13-week exposure to low concentrations of formaldehyde vapour

To study in detail possible effects of low concentrations of formaldehyde on the nasal epithelium, Wistar rats were exposed to 0, 0.3, 1 and 3 ppm formaldehyde vapour for 6 h/day, 5 days/week during 3 days or 13 days or 13 weeks, using in vivo [ 3H]thymidine labeling for cell proliferation studies, and light and electron microscopy for detecting morphological effects. Compound related histopathological nasal changes varying from epithelial disarrangement to epithelial hyperplasia and sqyamous metaplasia were found in the 3 ppm group, and were restricted to a small area of the anterior part of the nose which is normally covered with respiratory epithelium. These changes were confirmed by electron microscopy and were not observed in the other groups. Increased cell turnover in the same anterior location confirmed high mitotic activity in the 3 ppm group after 3 days and 13 weeks of exposure. At a slightly more posterior level i n the nose a transient response in cell turnover was observed. After 3 days of exposure a nearly log-linear relationship was found between cell turnover and exposure concentration reaching a 10-fold increase in the 3 ppm group, and suggesting challenge of the mucociliary and/or regenerative defence systems not only at 3 ppm but also at 0.3 and 1 ppm. After 13 weeks of exposure mean turnover rates in all exposed groups were markedly lower than after 3 days, and the mean rates of the formaldehyde-exposed groups tended to be below that of the controls. The variation in turnover rate after 13 weeks had increased in a concentration related way, suggesting individual variation in adaptation. The most likely adaptive mechanism at this more posterior level of the nose seemed to be the mucociliary defence apparatus.

One-year inhalation toxicity study of formaldehyde in male rats with a damaged or undamaged nasal mucosa.

To study the effect of bilateral intranasal electrocoagulation damage on the susceptibility of rats to formaldehyde vapour, male Wistar rats with a damaged or undamaged nasal mucosa were exposed to atmospheres containing 0, 0.1, 1 or 10 ppm formaldehyde vapour during 6 h/day, 5 days/wk for 13 or 52 weeks. Electrocoagulation damage was induced in the anterior third part of the nose. The repair process followed the pattern of wound healing. Loss of turbinates and perforation of the septum were common irreversible findings. After 13 weeks basal cell hyperplasia and squamous metaplasia of the respiratory epithelium, and rhinitis were still visible. After 52 weeks effects attributable to electrocoagulation were slight basal cell hyperplasia and some rhinitis. Major formaldehyde-related adverse effects in the 10 ppm group not subjected to electrocoagulation included growth retardation, reduced urine production, and rhinitis accompanied by squamous metaplasia of the nasal respiratory epithelium. No adverse effects were seen at 0.1 or 1 ppm in rats with an intact nasal mucosa. The principal untoward effects of formaldehyde in electrocoagulation-treated rats seen after 13 and/or 52 weeks comprised increase in basal cell hyperplasia, squamous metaplasia of the nasal respiratory epithelium, damage to the olfactory epithelium at 10 ppm, and focal squamous metaplasia of nasal respiratory epithelium at 0.1 and 1 ppm.(ABSTRACT TRUNCATED AT 250 WORDS)

Nasal tumours in rats after short-term exposure to a cytotoxic concentration of formaldehyde

Male Wistar rats were exposed to 0, 10 or 20 ppm formaldehyde vapour for 4, 8 or 13 weeks (6 h/day; 5 days/week), and were then observed for periods up to 126 weeks. Transient growth retardation occurred in both test groups. Death rate was not noticeably affected by formaldehyde. Despite recovery periods of at most 126 weeks, the nasal respiratory and olfactory epithelium of many rats of the 20 ppm group exhibited non-neoplastic histopathological changes. Similar but much less severe changes of the respiratory epithelium were seen in a small number of rats of the 10 ppm group; the olfactory epithelium was not visibly affected in rats of this group. Nasal tumours considered to be induced by formaldehyde were seen only in the 20 ppm group and mainly in rats that had been exposed for 13 weeks, the incidence being 4.5% ( 6 132 ). These tumours comprised 3 squamous cell carcinomas, 1 carcinoma in situ and 2 polypoid adenomas, all originating from respiratory epithelium. It was concluded that rat nasal respiratory epithelium severely damaged by formaldehyde vapour often does not regenerate and in some cases develops tumours.

Subchronic (13‐week) inhalation toxicity study of formaldehyde in rats

Male and female albino Wistar rats were exposed to concentrations of 0, 1, 10 or 20 ppm formaldehyde vapour during 6 h/day, 5 days/wk for 13 weeks. Treatment-related changes observed at 20 ppm included in both sexes: stared coats, uncoordinated locomotion and excitation during the first 30 minutes of each exposure, yellowing of the fur, growth retardation, a decreased level of plasma protein, severe and extensive karatinized stratified squamous metaplasia of the nasal respiratory epithelium, and focal degeneration and squamous metaplasia occasionally accompanied by keratinization of the olfactory epithelium; in males only; increased activities of plasma aspartate amino transferase (ASAT), alanine amino transferase (ALAT) and alkaline phosphatase (ALP) and squamous metaplasia of the laryngeal epithelium. Lesions seen at 10 ppm included yellowing of the fur and moderate squamous metaplasia of the nasal respiratory epithelium. The only change observed in three out of twenty 1 ppm exposed animals that might or might not be treatment-related was minimal focal epithelial hyperplasia and squamous metaplasia of the respiratory epithelium lining the nasal septum and maxillary turbinates. No histopathological evidence of hepatotoxicity was detected in any of the formaldehyde-treated groups. An in vivo/in vitro cell proliferation study showed an increase in [3H]-thymidine labeling index of the respiratory epithelium lining the nasoturbinates of rats exposed to 10 or 20 ppm formaldehyde on three successive days, whereas at the 1 ppm level the labeling index was similar to that of controls. It was concluded that under the conditions of the present 13-week inhalation study, formaldehyde at concentrations up to 10 ppm was not hepatotoxic to rats. At the 20 ppm formaldehyde level, a slight effect on the liver of male rats cannot be completely excluded. The study was inconclusive with respect to 1 ppm formaldehyde being a cytotoxic or a no-cytotoxic effect level for the nasal epithelium.