Allantoin ameliorates amyloid ß-peptide-induced memory impairment by regulating the PI3K/Akt/GSK-3ß signaling pathway in rats.

Alzheimer's disease (AD) is a brain disease that causes problems in memory, thinking, and behavior. Allantoin has been shown to have antioxidant, anti-inflammatory, and neuroprotective effects. In this study, we aimed to investigate the effect and mechanism of action of allantoin on AD-related memory impairment. We investigated the effect of allantoin on an amyloid ß1-42 peptide (Aß1-42)-induced AD model in rats and evaluated its memory-enhancing effect using the Morris water maze test. Pathological changes in the hippocampus and cortex were examined by hematoxylin-eosin staining. The expression of the phosphorylated Tau protein and PI3K/Akt/GSK-3ß signaling pathway was analyzed by western blotting. The results of the water maze test showed that after treatment with allantoin, the rats could reduce their swimming time and travel distances to find the platform. Allantoin treatment also increased the time spent in the quadrant in which the platform was located. Histological assessment showed that Aß1-42 could cause morphological alterations in nerve cells in the hippocampal CA1 region, and that allantoin could repair the damage to these cells. Western blotting revealed that allantoin treatment increased the expression of p-PI3K, p-Akt, and p-GSK-3ß and decreased p-Tau in the hippocampus and cortex of rats. These effects were inhibited by LY294002. These findings showed that allantoin could improve cognitive impairment in Aß1-42-induced rats by activating the PI3K/Akt/GSK-3ß signaling pathway to reduce abnormal hyperphosphorylation of Tau. Thus, allantoin may be a potential therapeutic agent for neurodegenerative diseases.

A model-based validation study of postoperative complications with considerations on operative timing.

BACKGROUND: Surgery is a highly technical procedure relying on high mental acuity and manual dexterity. The possibility that surgical outcomes and post-operative complications could be subject to influence by fatigue and/or circadian rhythms in surgeons has been investigated with inconsistent results. METHODS: We conducted a retrospective study to assess the significance of operative timing on classifying surgical complications using an interpretable machine learning approach. We trained various linear, generative as well as tree models on the surgical record data collected from a university-affiliated, tertiary teaching hospital in China by performing parameter tuning using grid search cross-validation for optimizing the F1 score. RESULTS: The results indicated that XGBoost was the best-performing model overall and its feature importance was shown to provide insight into possible timing-related associations with postoperative complications. We observed that the duration of surgery acted as the strongest indicator, and while surgery initiated at night (between 9 pm and 7 am) also ranked higher on the feature importance scale, it bore less significance than other factors such as the patient's age, gender, and type of surgery performed. CONCLUSIONS: We showed that surgical records could be used to demonstrate that operative timing might affect the occurrence of postoperative complications, but only in a relatively mild way while potentially entangling with multiple factors.

Association between weight change during initial chemotherapy and clinical outcome in dogs with multicentric lymphoma.

The majority of the known prognostic factors in dogs with lymphoma have been evaluated before treatment commences or at the time of diagnosis. Prognostic factors evaluated during the initial phase of treatment are less described but may provide important clinical information. In this retrospective study, 82 canine lymphoma patients were categorized according to the weight change between diagnosis and after 5 weeks of chemotherapy. Dogs that gained greater than 5% or lost greater than 5% of initial body weight were categorized as increased- or decreased-weight groups, respectively. Those in which weight changed less than 5% were categorized as the maintained-weight group. The median progression-free survival (PFS) in the increased-weight group, maintained-weight group and decreased-weight group was 226, 256 and 129 days, respectively. The decreased-weight group had significantly shorter PFS than the increased and maintained groups (P = .023, P = .003, respectively). The median survival time (ST) in the increased-weight group, maintained-weight group and decreased-weight group was 320, 339 and 222 days, respectively. There was no significant difference in ST among the three groups (P = .128). In Cox-regression results, weight change group and initial body weight were significant risk factors associated to PFS (P = .007, P = .001, respectively) while only patient's initial body weight was a significant risk factor to ST (P = .013). In conclusion, evaluation of initial body weight and weight changes over time can provide valuable information regarding PFS and ST in dogs with multicentric lymphoma.

Postoperative sufentanil intravenous patient-controlled analgesia within the first 24 hours: a retrospective study.

BACKGROUND: Intravenous patient-controlled analgesia (IV-PCA) is recommended for postoperative systemic analgesia by the American Pain Society. As there is no efficacy advantage and a higher probability of adverse events, routine basal infusion of opioids is not recommended for opioid-naïve adults. However, the opioids referred to in postoperative pain management guidelines were mainly morphine. Nowadays, sufentanil is widely used in postoperative acute pain management. In this retrospective study, we evaluated and compared the analgesic effect, PCA use, as well as adverse events among different basal infusions with sufentanil-based postoperative PCA. METHODS: The data of 322 eligible postoperative patients who received sufentanil-based IV-PCA from January 2018 to December 2019 were collected in this study. According to the settings of background infusions, patients were allocated to 3 groups: 2, 1, or 0.5 mL/hour. The primary endpoint was PCA attempts and successful delivery. We also evaluated the occurrence of adverse events associated with sufentanil-based PCA and the intensity of postoperative pain using the Numeric Rating Scale (NRS). RESULTS: PCA attempts, successful deliveries, total volume of PCA and patient NRS scores were significantly different between the 3 groups (P<0.05). Through pairwise comparison, there was only a statistical difference between the 2 mL/hour and the 0.5 mL/hour group in PCA attempts, successful deliveries, and total volumes of PCA. There were no statistical differences in adverse events between groups (P>0.05). CONCLUSIONS: We found that a smaller background infusion with sufentanil required more bolus infusions and a higher total volume of PCA within 24 hours after surgery. However, NRS scores were higher in the smaller background infusion group. Our results highlight the need for further studies to optimize doses for sufentanil IV-PCA basal infusions, which will also provide useful information to enhance the quality of pain control in the future.

Erratum to Transperitoneal versus extraperitoneal robot-assisted laparoscopic radical prostatectomy on postoperative hepatic and renal function.

[This corrects the article DOI: 10.21037/gs-20-533.].

Transperitoneal versus extraperitoneal robot-assisted laparoscopic radical prostatectomy on postoperative hepatic and renal function.

Background: In this retrospective study, we evaluated the effect of two approaches of robotic-assisted laparoscopic radical prostatectomy (RALP). The first approach was pneumoperitoneum via transperitoneal (TP-RALP), and the second approach was extraperitoneal (EP-RALP) on visceral function. We aimed to provide clinical evidence for the perioperative safety with RALP and to help the surgical team choose an appropriate approach for those with hepatic or renal insufficiency. Methods: One hundred and fifty-seven eligible prostate cancer patients from 2015 to 2019 were included in this study. The postoperative related laboratory tests were compared between transperitoneal and extraperitoneal. The primary endpoint was hepatic and renal function. We also evaluate the intraoperative amount of bleeding, the length of postoperative hospital stays, the occurrence of postoperative complications (lymphatic leakage, bleeding, and infection), and the prostate-specific antigen (PSA). Results: Postoperative total bilirubin and bound bilirubin in both groups were significantly increased, while total protein, albumin, globulin, urea, and uric acid were significantly decreased (P<0.05). The total protein, albumin, and globulin are significantly higher in the EP-RALP group than in the TP-RALP group (P<0.05) postoperatively. There are no statistical differences in estimated glomerular filtration rate (eGFR) and creatinine clearance (CCR) between these two groups, postoperatively. Conclusions: RALP had a significant effect on hepatic function after both TP-RALP and EP-RALP approaches, while the latter showed a lesser extent. Our results suggested that pneumoperitoneal pathways have significant effects on protein consumption. Thus, we should require a more cautious choice of surgical approaches when it comes to patients with impaired hepatic function or under risk of hepatic malfunction.

Polybrominated diphenyl ethers in various atmospheric environments of Taiwan: their levels, source identification and influence of combustion sources.

In this study, ambient air samples from different atmospheric environments were examined for both PBDE and PCDD/F characteristics to verify that combustion is a significant PBDE emission source. The mean ± SD atmospheric PBDE concentrations were 165 ± 65.0 pg Nm(-3) in the heavy steel complex area and 93.9 ± 24.5 pg Nm(-3) in the metals complex areas, 4.7 and 2.7 times higher than that (35.3 ± 15.5 pg Nm(-3)) in the urban areas, respectively. The statistically high correlation (r=0.871, p<0.001) found between the atmospheric PBDE and PCDD/F concentrations reveals that the combustion sources are the most likely PBDE emission sources. Correspondence analysis shows the atmospheric PBDEs of the heavy steel and metals complex areas are associated with BDE-209, -203, -207, -208, indicative of combustion source contributions. Furthermore, the PBDEs in urban ambient air experience the influence of the evaporative releases of the commercial penta- and octa-BDE mixtures, as well as combustion source emissions. By comparing the PBDE homologues of indoor air, urban ambient air, and stack flue gases of combustion sources, we found that the lighter brominated PBDEs in urban ambient air were contributed by the indoor air, while their highly brominated ones were from the combustion sources, such as vehicles. The developed source identification measure can be used to clarify possible PBDE sources not only for Taiwanese atmosphere but also for other environmental media in other countries associated with various emission sources in the future.

Emission estimation and congener-specific characterization of polybrominated diphenyl ethers from various stationary and mobile sources.

Here we show that combustion sources, including waste incinerators, metallurgical processes, power-heating systems and so on, are also important emitters of polybrominated diphenyl ethers (PBDEs) to the atmosphere. Geometric mean PBDE concentrations in the stack flue gases of the combustion sources ranged from 8.07 to 469 ng/Nm3. The sinter plants (24.7 mg/h), electric arc furnaces (EAFs) (11.3 mg/h) and power plants (50.8 mg/h) possessed the largest PBDE emission rates, which were several orders higher than those of the other reported sources. The occurrences of the PBDEs in the flue gases of the power plants and vehicles, as well as their PBDE concentrations statistically highly correlated with combustion-originated PCDD/Fs, revealing that PBDEs should be the products of combustion. The ranking of major PBDE emission sources in Taiwanese PBDE inventory for combustion sources was power plants (30.85 kg/year), vehicles (14.9 kg/year) and metallurgical processes (5.88 kg/year).

Establishment of a fluorescence resonance energy transfer-based bioassay for detecting dioxin-like compounds.

Dioxins comprise a group of compounds which contain a double aromatic ring-like structure. They are among the most prevalent and toxic environmental pollutants. Accumulation of dioxins in human tissues poses a potential threat to human health. Currently, analytical chemical procedures dominate dioxin-detection protocols. In this study, we established a fluorescence resonance energy transfer (FRET)-based dioxin-detection bioassay. Aryl hydrocarbon receptor (AHR) and AHR nuclear translocator (ARNT) fused-cyan fluorescent protein (CFP) and -yellow fluorescent protein (YFP) constructed were transiently co-transfected into rat hepatoma cell line, H4IIEC3 cells. Our results showed that no FRET signals were detected in AHR-CFP- and ARNT-YFP-transfected H4IIEC3 cells. However, dioxin treatments upregulated FRET signals in these transfected cells in a dose-dependent manner. This work highlighted the potential of FRET technique in the detection of dioxin-like compounds.

Validation of the CALUX bioassay as a screening and semi-quantitative method for PCDD/F levels in cow's milk.

The objectives of this study were first to set up and validate the quality criteria of the Xenobiotic Detection Systems-chemical activated luciferase gene expression (CALUX) bioassay for the analysis of cow's milk samples spiked with polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). The application of this bioassay was then tested by analyzing 28 commercially available pasteurized milk samples and comparing the data with the reference method for PCDD/F analysis. The CALUX criteria from the U.S. EPA and the European Union (EU) were calculated from 16 replaced spiked milk (SM) samples and 8 performance evaluation (PE) samples to validate the CALUX bioassay system. The CALUX bioassay criteria included control chart for quality control (QC) standards, recovery efficiency, and data comparability. The control chart for QC standards were both within the micro+/-2sigma range. The recovery efficiencies ranged from 60.4% to 106% with an average of 79.9% (relative standard deviation (RSD): 20.7%). The mean of data comparability (i.e., relative percent difference, RPD) between CALUX bioassay and high-resolution gas chromatography and high-resolution mass spectrometry (HRGC/HRMS) was 19.0% for SM samples. For the PE samples, Pearson's correlation coefficient between CALUX and the HRGC/HRMS method was 0.953. The high correlation shows that the CALUX system is suitable as a screening method and a semi-quantitative method to analyze the PCDD/F concentration in milk samples. Next, the validated CALUX bioassay was applied to measure 28 commercially available pasteurized milk samples. These milk samples were also analyzed with the HRGC/HRMS method to compare the analysis data from two different methods. There is no false negative sample when applying the bioassay to pasteurized milk and PE samples as a screening method and a semi-quantitative method. The present study indicates that CALUX is a powerful bioassay method for screening a large number of milk samples.

Influence of start-up on PCDD/F emission of incinerators.

This study aims to evaluate the influence of start-up on polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) concentration in the stack flue gas of incinerators and its contributing PCDD/F emission. The PCDD/F emission of the first sample among three consecutive stack flue gas samples of five intermittent incinerators, which sampled at a stable combustion condition after start-up, is 2-3 times higher than the mean of the others. For verifying the PCDD/F characteristics of incinerators during start-up, one continuous MSWI was investigated for two years. The elevated PCDD/F emissions of the MSWI during start-up could reach 96.9 ng I-TEQN m(-3) and still maintained a high PCDD/F emission (40 times higher than the Taiwan emission limit) even 18 h after the injection of activated carbon, indicating the memory effect. Taking the MSWI for example, which consists of four incinerators, the estimated annual PCDD/F emission from normal operational conditions was 0.112 g I-TEQ. However, one start-up procedure can generate approximately 60% of the PCDD/F emissions for one whole year of normal operations. And the PCDD/F emission, which is the result of the start-ups of four incinerators, was at least two times larger than that of a whole year's normal operations, without consideration for the PCDD/F emission contributed by the long lasting memory effect.

Cancer patients' preferences for communication of unfavourable news: an Asian perspective.

It is important to understand cancer patients' preferences for communication as it impacts on how unfavourable news should be delivered in such a way as not to demoralize the patients while at the same time maintain good doctor-patient relationships. However, few studies have been undertaken in the Asian countries. This study aims to determine the preferences of cancer patients regarding the disclosure of unfavourable news in an Asian population in Singapore. Two hundred cancer patients at the National Cancer Centre, Singapore, completed a Measure of Patients' Preferences (MPP) questionnaire on how they would like their physicians to tell them unfavourable news about their condition. The patients rated the content and context of the communication as well as the physicians' characteristics on a five-point Likert scale. Items that scored the highest mostly related to physicians' expertise and content of the interaction, while those relating to the supportive aspects scored the lowest. Gender was significantly associated with scores on the support subscale of the MPP such that women reported that the supportive elements were more important than the men did. No other demographic and medical characteristics were associated with patients' preferences. Exploratory factor analysis yielded two main factors, which accounted for 79.38% of the common variance. Patients' preferences in our local Asian population are fairly similar to those obtained from other studies conducted in the West, despite possible socio-cultural differences such as the use of euphemisms.

Dry deposition of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in ambient air.

The PCDD/Fs in the ambient air associated with concentration and dry deposition flux of four seasons were characterized in rural area. The mean PCDD/F concentrations were 0.342, 0.221, 0.675, 0.741 pg m(-3) and the mean I-TEQ values were 0.027, 0.016, 0.024, 0.063 pg m(-3) in spring, summer, fall and winter, respectively. Ambient air in winter was higher by a factor of 3.4 and 3.9 for PCDD/F concentration and I-TEQ, respectively, than in summer. The study area is located in a Tropical region. Hence, domestic heating is not found in this area and is not responsible for the elevated winter concentration in comparison to other studies. A smooth plate with a sharp leading edge that is pointed into the wind by a wind vane was used for measuring dry deposition flux of PCDD/Fs. Atmospheric dry deposition fluxes of total PCDD/Fs were 140, 116, 137, and 207 pg m(-2)day(-1) in spring, summer, fall, and winter, respectively, and averaged approximately 150 pg m(-2)day(-1). The total dry deposition flux was found to decrease as the temperature increased. Calculated dry deposition velocities of total PCDD/Fs were 0.45, 0.52, 0.32 and 0.39 cm s(-1) in spring, summer, fall, and winter, respectively, and averaged 0.42 cm s(-1).

Photodegradation of tetra- and hexachlorodibenzo-p-dioxins.

This study examined the direct photolysis and photocatalytic processes for 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) and 1,2,3,6,7,8-hexachlorodibenzo-p-dioxin (1,2,3,6,7,8-HxCDD). The photocatalytic procedure was performed on the TiO2 film under irradiation with 365 nm UV and the compounds were immobilized on TiO2/solid phase. No 2,3,7,8-substituted PCDD/Fs products were detected in photocatalytic process under the experimental conditions. The reaction rate constants were 0.3256 h-1 for 2,3,7,8-TCDD (2000 ng) in UV/TiO2 reaction, 0.2474 h-1 for 1,2,3,6,7,8-HxCDD (2000 ng) in UV/TiO2 reaction and 0.0666 h-1 for 1,2,3,6,7,8-HxCDD (50 ng) under direct UV irradiation. For 1,2,3,6,7,8-HxCDD (50 ng) in a UV/TiO2 reaction, the degradation is too fast to determine the reaction rate. The photocatalytic process was faster than direct photolysis for the same chlorinated PCDDs, and the rate decreased with increasing PCDDs quantity. The photocatalytic rate of the PCDDs decreased with increasing chlorination extent. The confirmed intermediates of 1,2,3,6,7,8-HxCDD in direct photolysis, 1,2,3,7,8-PeCDD and 2,3,7,8-TCDD both were formed by the loss of a longitudinal chlorine nearest the oxygen atom. The quantity of 1,2,3,7,8-PeCDD and toxic equivalency quantity (TEQ) declined after 10 h of UV irradiation. The proposed dechlorination pathway of 1,2,3,6,7,8-HxCDD was via 1,2,3,7,8-PeCDD to 2,3,7,8-TCDD. Formation of trace concentrations of 1,2,3,4,7,8-hexachlorodibenzo-p-dioxin (1,2,3,4,7,8-HxCDD) and 1,2,3,7,8,9-hexachlorodibenzo-p-dioxin (1,2,3,7,8,9-HxCDD) from 1,2,3,6,7,8-HxCDD appears to be a minor side reaction.

Emissions of polychlorinated dibenzo-p-dioxins and dibenzofurans from stack gases of electric arc furnaces and secondary aluminum smelters.

This study investigates the emissions of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) from four electric arc furnaces (EAFs) and eight secondary aluminum smelters (secondary ALSs) in Taiwan. The mean PCDD/F International-Toxicity Equivalents (I-TEQ) concentrations in the stack gases of these EAFs and secondary ALSs are 0.28 ng I-TEQ/Nm3 (relative standard deviation [RSD]= 100%) and 3.3 ng I-TEQ/Nm3 (RSD = 260%), respectively. The high RSDs, especially for those obtained from secondary ALSs, could be caused by the intrinsic differences in their involved feeding materials, furnace operating conditions, and air pollution control devices. The mean I-TEQ emission factor of PCDD/Fs for EAFs (1.8 microg I-TEQ/tonne-feedstock) is lower than that for secondary ALSs (37 microg I-TEQ/tonne-feedstock). This result might be because the involved furnace temperatures for secondary ALSs (650-750 degrees C) are lower than those for EAFs (1600-1700 degrees C), resulting in the deterioration of the combustion condition, leading to the formation of PCDD/Fs during the industrial process. This study found that the total PCDD/F emissions from EAFs (20 g I-TEQ/yr) and secondary ALSs (18 g I-TEQ/yr) are approximately 27, 53, and approximately 24, 49 times higher than those from municipal solid waste incinerators (MSWIs; 0.74 g I-TEQ/yr) and medical waste incinerators (MWIs; 0.37 g I-TEQ/yr), respectively; while those are 44 and 40% of total PCDD/F emission from sinter plants (45 g I-TEQ/ yr), respectively. Considering a more stringent emission limit has been applied to waste incinerators (0.1 ng I-TEQ/Nm3) in Taiwan lately, the results suggest that the control of the emissions from metallurgical processes has become the most important issue for reducing the total PCDD/F emission from industrial sectors to the ambient environment.

Photodegradation of polychlorinated dibenzo-p-dioxins: comparison of photocatalysts.

1,2,3,6,7,8-hexachlorodibenzo-p-dioxin (1,2,3,6,7,8-HxCDD) and octachlorodibenzo-p-dioxin (OCDD) were photocatalytically degraded using immobilized TiO(2), ZnO and SnO(2) films under ultraviolet (UV) with the wavelength between 300 and 450 nm. The specific surface areas of TiO(2), ZnO and SnO(2) powders were calculated as 54.2, 4.6 and 4.8 m(2)/g, and the band gap energies were determined to be 3.17, 2.92 and 4.13 eV, respectively. The light source used had wavelengths between 300 and 450 nm, and the main wavelength was approximately 365 nm; hence, the smaller quantum efficiency of SnO(2) with wider band gap due to poor utilization of the UV light was expected. X-ray diffraction (XRD) revealed that sintered photocatalysts at 400 degrees C did not alter their characteristics. The first-order rate constants of OCDD in UV/TiO(2), UV/ZnO and UV/SnO(2) were 5.30, 0.74 and 0.28 h(-1), respectively; those of 1,2,3,6,7,8-HxCDD in UV/ZnO and UV/SnO(2) were 3.28 and 3.19 h(-1), respectively. As expected, photodegradation rates declined as the number of chlorine atoms increased. Due to the low dosage (50 ng) of target compounds used, the amounts of Cl(-) and total organic carbon were too small for quantification. No 2,3,7,8-substituted congeners was identified during the photodegradation, and the UV/photocatalyst treatment might offer an effective treatment for PCDDs.

Source identification of PCDD/Fs for various atmospheric environments in a highly industrialized city.

This study set out to identify possible PCDD/F emission sources for different atmospheric environments in a highly industrialized city located in southern Taiwan. We collected stack flue gas samples from five main stationary emission sources of the municipal solid waste incinerators (MSWIs), medical waste incinerators (MWIs), electric arc furnaces (EAFs), secondary aluminum smelters (ALSs), and sinter plants to assess the characteristics of their PCDD/F emissions. For mobile sources, congener profiles reported in U.S. EPA's database for unleaded gas-fueled vehicles (UGFV) and diesel-fueled vehicles (DFV) were directly adopted owing to lack of local data. The congener profiles of the 2,3,7,8-substituted PCDD/Fs were selected as the signatures of these PCDD/F emission sources. We conducted PCDD/F samplings on atmospheric environments of four categories, including background, residential area, traffic area, and industrial area. Through PCA and cluster analyses, we found that traffic areas were most influenced by PCDD/F emissions from UGFV and DFV, while those of industrial areas were mainly influenced by metallurgical facilities and MWIs. The above results were further examined by using the methodology of the indicatory PCDD/Fs. We confirmed that traffic areas were contributed by traffic sources, but industrial areas were simply affected by metallurgical facilities rather than MWIs. In conclusion, besides the use of PCA and cluster analyses, the methodology of the indicatory PCDD/Fs should be conducted for further validation in order to prevent misjudgment.

Effect of chlorine content in feeding wastes of incineration on the emission of polychlorinated dibenzo-p-dioxins/dibenzofurans.

This study attempts to clarify the effects of chlorine content in waste on the formation mechanisms of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in full scale incinerators by proposing and using the principal component analysis (PCA) to compare the congener profiles of PCDD/Fs in the stack flue gases of 17 emission sources, including incinerators and vehicles. Four incinerators, among these 17 emission sources, were sampled and analyzed in this study, and the data for the other 13 emission sources were selected from previous studies. These 17 emission sources can be classified into four categories, including medical waste incinerators (MWIs, H1-H5), municipal solid waste incinerators (MSWIs, M1-M8), vehicle fuel combustion (unleaded gas-fueled vehicles, UGFV; diesel-fueled vehicles, DFV, n = 2) and polyvinylchloride (PVC) facility vent combustors (PVC1 and PVC2, n = 2). PCA was conducted for these emission sources with the fractions of 17 2,3,7,8-congeners in the stack flue gases as variables to clarify the effect of chlorine content in feeding wastes on the emission of PCDD/Fs. From the results of PCA, we extrapolated that the threshold value of the chlorine content was at 0.8-1.1%, and the formation mechanisms of PCDD/Fs are influenced first by whether the chlorine content in the feeding waste is over or below the threshold value then by other factors, which furnaces or APCDs represent. When the chlorine level in the waste is below the threshold value at 0.8-1.1%, the formation of PCDDs dominates, probably because the chlorine is used to chlorinate the non-substituted phenol to produce chlorophenols, which are important precursors for PCDDs. rather than chlorinate the dibenzofuran. While the chlorine level in the waste exceeds this threshold (0.8-1.1%), the rates of formation of PCDFs increase faster than those of PCDDs, probably because the chlorine content in the waste contributes to the deterioration of combustion conditions, and many products of incomplete combustion (PICs) like PAHs, will grow to a substantial level. When PCDD/Fs are formed from PAHs, the formation rates of PCDFs are higher than those of PCDDs.

Characterizing the emissions of polychlorinated dibenzo-p-dioxins and dibenzofurans from crematories and their impacts to the surrounding environment.

This study was set out to characterize PCDD/F emissions from crematories and assess their impacts on the surrounding environment. Two crematories located in southern Taiwan were investigated, including the one (C1) with no air pollution control device installed and the other (C2) installed with a bag filter. Results show the mean PCDD/F emissions (11% oxygen) from the stacks of Cl and C2 were 2.36 and 0.322 ng I-TEQ Nm(-3), respectively. The mean emission factors for C1 and C2 were 13.6 and 6.11 microg I-TEQ body(-1), respectively. The removal efficiency of the bag filter on PCDD/Fs was 55.1%. The estimated PCDD/F emission rate for all crematories in Taiwan was 0.838 g I-TEG yr(-1) accounting for 227% and 112% of the annual emissions from all medical waste incinerators and municipal waste incinerators, respectively. The above results indicate that PCDD/F emissions from crematories were quite significant. To assess the impact of PCDD/F emissions from a crematory to the surrounding environment, ambient air samples were collected from the downwind site of C1 with the maximum ground concentration. We found the estimated maximum ground concentration at the downwind site of C1 (= 0.521 pg I-TEQ Nm(-3)) was much higherthan thatfound atthe background, rural area, residential area, urban area, and industrial area (= 0.006, 0.023, 0.052, 0.093, and 0.190 pg I-TEG Nm(-3), respectively). The above results suggestthat PCDD/F emissions from a crematory did significantly affect its surrounding environment. In conclusion, a proper control strategy should be taken immediately in order to eliminate PCDD/F emissions from crematories.

Emissions of polychlorinated dibenzo-p-dioxins and dibenzofurans from stack flue gases of sinter plants.

This study investigated four sinter plants, classified into two categories--with selective catalytic reduction (SCR) (S1, S2 and S3) and without SCR (S4) as its air pollution control device. Polychlorinated dibenzofurans (PCDFs) are dominant in the stack flue gases of sinter plants with and without SCR. The polychlorinated dibenzofurans/polychlorinated dibenzo-p-dioxins (PCDFs/PCDDs) ratio exceeds 1 extremely. The degree of chlorination of the sinter plant without SCR is towards hepta and hexa congeners while that of the sinter plant with SCR is towards penta and hexa congeners. PCDD/Fs are indeed decomposed (75.5% and 69% on ng and ng TEQ bases, respectively) and not only reduced in degree of chlorination. The overall concentration in the stack flue gas of sinter plants with SCR (7.97-14.1 ng/Nm(3); 0.995-2.06 ng TEQ/Nm(3)) is lower than that of the sinter plant without SCR (28.9 ng/Nm(3); 3.10 ng TEQ/Nm(3)). In Taiwan, based on the emission factors of 0.970 microg TEQ/ton-feedstock (sinter plants with SCR) and 3.13 microg TEQ/ton-feedstock (sinter plant without SCR), the annual PCDD/F emission of 44.7 g TEQ/year from sinter plants is 60 and 121 times higher than those from municipal solid waste incinerators (0.750 g TEQ/year) and MWIs (0.369 g TEQ/year). These results show that sinter plants have become the dominating PCDD/F emission source since tighter emission limits have been applied to incinerators.