Polychlorinated Dibenzo-p-dioxins And Dibenzofurans Research Articles

Low-Temperature NH3-SCR Technology for Industrial Application of Waste Incineration: An Overview of Research Progress

Selective catalytic reduction of nitrogen oxides with NH3 (NH3-SCR) was investigated deeper and deeper with poisoning factors such as H2O, SO2, heavy metals, etc. In order to remove the reheating process before the SCR reactor, the application trend of NH3-SCR technology in the non-power industry is concentrated on the condition of low temperature even ultra-low temperature. The present study summarizes the research process of SO2 and H2O resistance of NH3-SCR catalysts under low temperatures related to the working conditions of municipal solid waste incineration plants. In detail, the effects of a high content of H2O and low concentration of SO2 are reviewed. Other factors such as heavy metals, alkali, or alkaline earth metals in the reaction system, synergistic removal of NOx, polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) are addressed. Finally, the catalytic performance of assembled monolithic catalysts and pilot-scale experiments are also analyzed for the possibility of industrial application. Hopefully, in view of the questions outlined in this study, valuable insights could be taken into consideration for the development of NH3-SCR in waste incineration.

Health risks and sources of PCDD/Fs and PCBs residue in cultured crabs

The Chinese mitten crab (Eriocheir sinensis) holds significant importance as a popular aquaculture food source; however, there are concerns about its potential contamination with polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs) from both food and aquatic environment. To assess the associated health risks and identify potential sources of contamination in crabs, a comprehensive investigation was conducted, including a total of 70 samples from the crab food web. The results demonstrated that crabs predominantly exhibited elevated concentrations of PCBs and dl-PCBs, with mean concentrations of 12 207 ± 11 962 pg g-1 and 554 ± 203 pg g-1, respectively, while PCDD/Fs concentrations were comparatively lower at 20 ± 17 pg g-1. The accumulation of PCBs in crabs significantly surpassed that of PCDD/Fs. The material balance of PCDD/Fs and PCBs in the crab food web was estimated, indicating that sediments and feeds likely constitute the two primary sources of PCDD/Fs and PCBs in crabs. The monthly intake of PCDD/Fs and PCBs through crab consumption accounted for 30% of the dietary intake, which was well below the provisional tolerable monthly intake (PTMI) limit. The weekly intake of PCDD/Fs and PCBs for adults consuming one crab (100 g) does not pose health risks and the recommended weekly intake of white crabmeat and brown crabmeat is 443 g and 21 g, respectively.

Modification of activated carbon to enhance the absorption of PCDD/F and dl-PCBs emissions in flue gas in South Africa

Activated carbon (AC) adsorption is commonly used for polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) removal from flue gas. However, the AC available in the market predominantly possesses a substantial specific surface area and numerous micropores leading to significant variations in their adsorption characteristics. In this study, three types of activated carbon (AC) impregnated with different activating agents, namely K2CO3, KOH, and H3PO4 were evaluated for their effectiveness in removing PCDD/Fs and dl-PCBs compounds. For dl-PCBs, AC impregnated with H3PO4 resulted in a substantial reduction of PCB concentrations with an impressive 98% reduction achieved. Impregnation with KOH proved even more effective attaining a remarkable 99% reduction. In contrast, impregnation with K2CO3 while still effective achieved a slightly lower reduction rate of 95%. For PCDD/F, LACH3PO4 showed selectivity in achieving high reductions across both CDD and CDF congeners however proved effective in reducing the ∑PCCDF from 403.94 ng/Nm3 to 3.463 ng/Nm3 and ∑TEQ from 41.34 ng I-TEQ/Nm3 to 0.35 ng I-TEQ Nm3. LACKOH proved effective in reducing the ∑PCCDF from 540.45 ng/Nm3 to 0.25 ng/Nm3 and ∑TEQ from 57.42 ng I-TEQ/Nm3 to 0.12 ng I-TEQ Nm3 obtaining the overall removal efficiency of 99.5%. While the LACKOH injections were successful in the absorption of PCDD/Fs from the gas phase, it was observed that certain PCDD/F congeners became desorbed and entrapped within the ash necessitating further treatment of the ash residue. The ash underwent a thermal treatment first at 300 °C and 500 °C. The thermal treatment at 500 °C achieved a remarkable degradation of 99.7% removal efficiency rendering the ash and residue safe for disposal in a landfill site.Graphical

Robust online monitoring system for PCDD/Fs in a full-scale MSWI by Deans switch: Efficiently separation and purification

Existing online monitoring system for polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), technically named Thermal Desorption-Gas Chromatography-Tunable Laser Ionization-Time of Flight Mass Spectrometry (TD-GC-TLI-TOFMS), has been applied in several incinerators in China. TD-GC-TLI-TOFMS can realize rapid detection of PCDD/Fs emissions from incineration sources. However, the long-term measurement of unclean flue gas will pollute the instruments in TD-GC-TLI-TOFMS, and interfere with the peak output of the target 1,2,4-trichlorobenzene (1,2,4-TrCBz). In this study, Deans switch (DS) was utilized for the first time in an online monitoring system for PCDD/Fs to separate 1,2,4-TrCBz signal from impurity signals, which improved the anti-interference capability of the system. Laboratory standard gas experiments showed that after adding a DS device between GC and TLI pulse valve, when the pressure set in DS was 4 psi and switched before or near the peak output of 1,2,4-TrCBz, the change of 1,2,4-TrCBz signal intensity was minimal. The impurities near the target peak were removed, and TLI-TOFMS was highly stable during continuous measurement. Moreover, the maximum intensity peak time of 1,2,4-TrCBz was stable after using DS in different switching time intervals. When connecting DS to TD-GC-TLI-TOFMS for field validation on the tail flue gas of a municipal solid waste incinerator (MSWI), results showed that a better 1,2,4-TrCBz signal could be obtained with a 69.52 % reduction of impurity peaks at the moments closer to the target peak. Furthermore, DS improved the sensitivity of the system to low concentration variations of 1,2,4-TrCBz in the flue gas. The robust system developed in this study can be better applied to incineration factories with poor combustion or suboptimal purification technology, facilitating online PCDD/Fs monitoring.

Dietary exposure to metals/metalloids and persistent organic pollutants in Spanish preschool and primary school children

Diet is a primary source of pollutant exposure. Given children's vulnerability to their effects, this study assessed dietary intake of metals/metalloids and different persistent organic pollutants in children in Tarragona (Spain), compared it with the health-based guideline values (HBGV), and identified the main dietary sources. The analysis included 533 preschoolers and 443 primary school children from the EPINED and ECLIPSES studies. Dietary intake of cadmium (Cd), methylmercury (MeHg), lead (Pb), inorganic arsenic (inAs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), dioxin-like polychlorinated biphenyls (DL-PCBs), and non-dioxin-like polychlorinated biphenyls (NDL-PCBs) was estimated using validated food frequency questionnaires and a database from the Catalan Agency for Food Safety. Preschoolers and primary school children exceeded the relevant reference value for InAs and DL-PCBs. Only preschoolers exceeded the limit for MeHg and PCDD/Fs. Cd, Pb, and NDL-PCBs intakes did not exceed the limits in either age group. Salted cereals/potatoes were the main source of InAs; fish for MeHg and DL-PCBs; and milk/yogurt for PCDD/Fs, followed by white fish in preschoolers and fatty fish in primary school children. The findings highlight that dietary exposure to some pollutants poses a significant risk to these children, emphasizing the need for public health policies to reduce pollutants in their diets.

Environmental Levels of PCDD/Fs near Cement Plants in Catalonia, Spain. An Update of Human Health Risks

Cement production is an important industrial activity that generates large amounts of pollutants, including, among others, polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). These environmental contaminants are persistent and bioaccumulative, potentially causing serious adverse effects on human health, including cancer. The present paper was aimed at providing an update of the environmental concentrations of PCDD/Fs around various cement plants located in Catalonia, Spain. The non-carcinogenic and the carcinogenic risks associated to PCDD/Fs exposure were also assessed for the population living near the facilities. According to the present results, the environmental burdens of PCDD/Fs were highly dependent on the surroundings, rather than the technical specifics characteristics of each facility. Thus, higher concentrations were found near cement plants located in urban areas, where other emission sources (e.g., heavy traffic, domestic heating, etc.) may be present. The surveillance studies showed long-term stable concentrations in air, while PCDD/Fs levels in soil and vegetation were more variable. Although inhalation was the most relevant pathway of environmental exposure, the main uptake of PCDD/Fs occurs -in general- via dietary intake. Cancer risks were higher for people living near cement plants in urban areas than in rural environments, but at levels that are considered as acceptable by international regulations. In turn, the non-carcinogenic risks suggest a low concern, as the hazard quotient was <1. Long-term surveys conducted in Catalan cement plants indicate that these facilities, which are periodically (every two years) monitored, should not be of concern for human health, in terms of PCDD/F exposure.

Unveiling the competitive mechanism between SO2 and PCDD/Fs on activated carbon adsorption

In municipal solid waste incineration (MSWI) plants, activated carbon (AC) adsorption is the key technique for eliminating Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from flue gases. This research thoroughly investigates the potential competitive adsorption between SO2 and PCDD/Fs and examines how adsorption at the center and the edge of the AC layer impacts the adsorption process. The findings show a decline in the removal efficiency of PCDD/Fs from 86.8 % to 84.2 % and further to 74.4 % when using SO2 pre-treated (AC-A3) and H2SO4-impregnated (AC-B2) activated carbon, respectively. Multiple characterization methods reveal that sulfur elements occupy active sites within the inner pores of the activated carbon, reducing the availability of its pore structure, particularly affecting microporous more than mesoporous structures. DFT calculations suggest that the π-π EDA effect facilitates the adsorption of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD), whereas dispersion force drive SO2 adsorption. Comparisons among various oxygenated functional groups show that the organic acid anhydride (CO-CO) has better adsorption selectivity toward TCDD and less adsorption to SO2. This study provides a novel perspective on the adsorption mechanisms of PCDD/Fs on AC and the competitive dynamics of sulfur in the flue gas.

Calcium oxide adsorption of gas phase PCDD/Fs and its impact on the adsorption properties of activated carbon

Calcium oxide (CaO), utilized in semi-dry/dry desulfurization systems at municipal solid waste incineration (MSWI) plants, demonstrates some capability to remove polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). This study assessed the gas-phase PCDD/F removal performance of CaO, activated carbon (AC) and CaO-AC mixtures. Alone, CaO achieved removal efficiencies of only 31.9% for mass and 50.8% for I-TEQ concentration. However, CaO-AC mixtures exhibited significantly higher efficiencies, reaching 96.0% and 92.5% for mass and I-TEQ concentrations, respectively, surpassing those of AC alone, which were 74.7% and 58.5%. BET analysis indicated that CaO's limited surface area and pore structure are major constraints on its adsorption performance. Density functional theory (DFT) calculations revealed that the π-π electron donor-acceptor (EDA) interaction enhances the adsorption between AC and PCDD/F, with adsorption energies ranging from −1.02 to −1.24 eV. Additionally, the induced dipole interactions between CaO and PCDD/F contribute to adsorption energies ranging from −1.13 to −1.43 eV. Moreover, with increasing chlorination levels, PCDD/F molecules are more predisposed to accept electron transfers from the surfaces of AC or CaO, thereby facilitating adsorption. The calculation for mixed AC and CaO showed that CaO modifies AC's properties, enhancing its ability to adsorb gas phase PCDD/Fs, with the higher adsorption energy and more electrons transfer, aligning with gas phase PCDD/Fs adsorption experiments. This study provides a comprehensive understanding of how CaO influences the PCDD/F adsorption performance of AC.

Insight into the inhibition mechanisms of Ca-, N-, S-containing compounds on persistent organic pollutant formation from the thermal reaction of anthracene on copper chloride

Four inhibitors (CaO, CaS, CH4N2S, and (NH4)2SO4) were employed to inhibit the formation of multiple unintentional persistent organic pollutants (POPs) and environmentally persistent free radicals (EPFRs) using anthracene as a precursor, with CuCl2 serving as both a transition metal catalyst and chlorine source. The inhibition mechanisms were elucidated in terms of chlorine immobilization, catalyst deactivation, and free radical regulation. The inhibition efficiency of the four inhibitors on polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), and polychlorinated naphthalenes (PCNs) ranged from 64.7 % to 98.4 %, with the corresponding inhibition rates on toxic equivalency quantity ranging from 86.3 % to 99.7 %. The distribution of homologs shifted towards less chlorinated species, indicating effective suppression of chlorination. Calcium- and nitrogen-containing compounds consumed chlorine sources by forming CaCl2, CaClOH, and NH4Cl, while sulfur-containing compounds deactivated catalysts by forming CuSO4. EPFRs derived from anthracene were identified as carbon-centered anthracene-type and anthraquinone-type radicals. Positive correlations were observed between POPs and EPFRs concentrations, suggesting the pivotal role of organic free radicals as intermediates in POPs formation. Anthraquinones derived from anthracene underwent decomposition, recombination and chlorination, leading to the formation of PCDD/Fs and PCBs. The addition of inhibitors reduced EPFRs concentrations by 74.2–95.1 %. Sulfur- and nitrogen-containing inhibitors generated radicals that attacked POPs precursors and intermediates, forming heteroatomic compounds and inhibiting POPs formation. These findings enhanced the understanding of the source control mechanisms of POPs and provided theoretical and technical support for the synergistic inhibition of POPs and EPFRs in industrial thermal processes.

Polychlorinated dibenzo-p-dioxin and dibenzofuran contamination of free-range eggs: estimation of the laying hen’s soil ingestion based on a toxicokinetic model, and human consumption recommendations

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) are ubiquitous in the environment. The main route of human exposure is through food consumption. Soil contamination can be problematic for sanitary safety depending on the usage of the soil, such as farming. In case of environmental soil contamination with PCDD/Fs, hen’s eggs may be contaminated due to soil ingestion by hens. For this reason, it is important to understand the parameters that influence eggs’ contamination when hens are raised in contaminated areas. After the discovery of a contaminated area in Lausanne (Switzerland), we collected hens’ eggs from ten domestic-produced eggs and one farm. Based on PCDD/F measurements of eggs and soil, and a toxicokinetic model, we estimated individual hen’s soil intake levels and highlighted appropriate parameters to predict the dose ingested. Recommended weekly consumption for home-produced eggs was calculated based on the tolerable weekly intake proposed by EFSA in 2018. The most important parameter to assess the soil ingestion does not seem to be the soil coverage by vegetation but rather the hen’s pecking behaviour, the latter being difficult to estimate objectively. For this reason, we recommend using a realistic soil ingestion interval to assess the distribution of egg PCDD/F concentration from free-range hens reared on contaminated soil. The addition of soil contamination in the toxicokinetic model can then be used to recommend to the general population weekly consumption of eggs. The consumption by adults of free-range eggs produced on land with soil containing >90 ng toxic-equivalent (TEQ)/kg dry soil should be avoided. Even with a low level of soil contamination (1–5 ng TEQ/kg dry soil), we would recommend consuming not more than 5 eggs per week for adults and no more than 2 eggs for children below 4 years old.

Mixture analysis of associations between environmental and workplace toxins and liver damage and telomere length, stratified by race/ethnicity

This study aimed to identify the worst “bad actors” in mixtures of pollutants contributing to liver damage and shorter telomeres in the U.S. population, using Weighted Quantile Sum (WQS) modeling with stratification by race/ethnicity. We conducted a comprehensive cross-sectional analysis of mixtures of pollutants in National Health and Nutrition Examination Survey datasets: a) 33,979 adults with blood levels of cadmium (Cd), lead (Pb), and mercury, including subsets with measurements of per-/polyfluoroalkyl substances (PFAS), and polychlorinated biphenyls (PCBs)/polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs); and b) 7360 adults with measurements of telomeres, Cd, and Pb. Multivariable-adjusted WQS regression examined associations between WQS mixture indices and liver injury [alanine aminotransferase (ALT)-elevation], advanced liver-fibrosis (LF), and telomere length. WQSmetal indices were associated with advanced-LF in all racial/ethnic groups. The top contributor was Cd in the total population and in non-Hispanic Whites (NHW), while Pb was the top contributor in non-Hispanic Blacks (NHB). The WQSmetal-PCB-PCDD/F index was associated with ALT-elevation, with PCB126, Cd and Pb as main contributors; the odds ratio (OR) per decile was 1.50 (95%CI, 1.26-1.78), while the OR per decile of the WQSmetal-PFAS index was 1.03 (95%CI, 0.98-1.05), not significant. WQSmetal indices were associated with shorter telomeres. Cd was main contributor associated with advanced-LF in NHW, while Pb was the major bad actor in NHB, suggesting that NHB may be especially susceptible to Pb toxicity. Metals were associated with shorter telomeres. Metal and PCB/PCDD/F mixtures were associated with ALT-elevation. Heavy metals and organic chemicals may contribute to liver-related morbidity and healthcare disparities.

Unveiling respiratory health risks: PCDD/Fs adhering to particulate matter (PM10 and PM2.5) in Bien Hoa City, Dong Nai, Vietnam

This study investigates the concentrations of atmospheric aerosol particles (PM, including PM2.5 and PM10), as well as the presence and distribution of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in ambient air in Bien Hoa City (Dong Nai province, Vietnam) during the dry and rainy seasons in 2023. The concentrations of 7 PCDDs and 10 PCDFs congeners in PM10 or PM2.5 were determined using gas chromatography-mass spectrometry (GC-MS). The results show that the concentration of PM10 and PM2.5 were 54.7 ± 9.4 µg/m3, 65.3 ± 7.6 µg/m3, and 39.6 ± 7.9 µg/m3, 58.9 ± 12.6 µg/m3, in the rainy season and dry season, respectively. This reveals that while only PM2.5 concentration levels in the dry seasonexceed national ambient air quality standards, but all of PM2.5 concentration levels consistently exceeded WHO guidelines. The study highlights the dominance of PM2.5 and its adverse health implications, as evidenced by the PM2.5/PM10 ratio (0.74 and 0.85 for the rainy and dry seasons, respectively) and its association with worse air quality. Analysis of PCDD/Fs concentrations in PM samples demonstrates their comparable levels in both seasons, with OCDD being the most abundant species. Furthermore, the study estimates the toxic equivalency (TEQ) of PCDD/Fs and assesses health risks, revealing a potentially high cancer risk from exposure to these pollutants, particularly PM2.5 under WHO2005-TEQ. Several PCDD/Fs- WHO2005-TEQ congeners exhibit higher concentration levels in PM2.5 compared to PM10, suggesting differential particulate matter dynamics and potential environmental implications. These findings underscore the urgent need for mitigation strategies to alleviate air pollution and reduce associated health risks in the dioxin hotspot of Vietnam.

Accumulation Rate, Depuration Kinetics, and Tissue Distribution of Polychlorinated Dibenzo-p-Dioxins and Dibenzofurans (PCDD/Fs) in Suckler Ewes (Ovis aries).

Understanding the transfer of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in farm animals is essential for ensuring food safety, but such information for suckler ewes (Ovis aries) has been lacking. This work quantifies the accumulation, tissue distribution, and depuration kinetics of PCDD/Fs in these animals. Six suckler ewes (EXP group) were exposed to PCDD/Fs through contaminated hay (2.3-12.7 ng toxic-equivalent kg-1 dry matter) and then allowed to depurate by switching to noncontaminated hay from 29 days of lactation. Four control ewes were fed continuously with noncontaminated hay. At different time points covering depuration, weaning and slaughter, PCDD/F analysis of milk (three time points), blood and sternal adipose tissue (five time points), Longissimus thoracis muscle, liver, and empty body homogenate at slaughter (188 days of depuration) was performed. A relevant PCDD/F bioaccumulation was observed from oral intake in milk and adipose tissue (biotransfer factors of 1.24 and 1.06 day kg-1 lipids for the sum toxic-equivalent, respectively) in the EXP ewes, especially for penta- and hexa-chlorinated congeners. The EXP ewes' adipose tissue started at 10-fold the EU maximum level (ML) and showed depuration below the ML after 130 days. Specific PCDD/F accumulation in the ewe liver was observed, especially for dibenzofurans. These toxicokinetic data can inform recommendations to ensure the chemical safety of sheep food products.

Regulatory compliance of PCDD/F emissions by a municipal solid waste incinerator. A case study in Sant Adrià de Besòs, Catalonia, Spain

Despite incineration is an important emission source of toxic pollutants, such as heavy metals and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), it is still one of the most widely used methods for the management of municipal solid waste. The current paper summarizes the results of a 20-year follow-up study of the emissions of PCDD/Fs by a municipal solid waste incinerator (MSWI) in Sant Adrià de Besòs (Catalonia, Spain). Samples of ambient air, soils and herbage were periodically collected near the facility and the content of PCDD/Fs was analyzed. In the last (2017) survey, mean levels in soil were 3.60 ng WHO-TEQ/kg (range: 0.40–10.6), being considerably higher than the mean concentrations of PCDD/Fs in soil samples collected near other MSWIs in Catalonia. Moreover, air PCDD/F concentrations were even higher than those found in a previous (2014) survey, as they increased from 0.026 to 0.044 pg WHO-TEQ/m3. Ultimately, the PCDD/F exposure would be associated to a cancer risk (2.5 × 10−6) for the population living in the surrounding area. Globally, this information indicates that the MSWI of Sant Adrià de Besòs could have had a negative impact on the environment and potentially on public health, being an example of a possible inappropriate management for years. The application of Best Available Techniques to minimize the emission of PCDD/Fs and other chemicals is critical.

Unintentional persistent organic pollutants in cremation process: Emissions, characteristics, and inventory

Pollutants produced by cremation furnaces have gradually caused concern because of the increasing rate of cremation around the world. In this study, the levels, patterns, and emission factors of unintentional persistent organic pollutants (UPOPs) from cremation were investigated. The toxic equivalent (TEQ) concentrations (11 % O2 normalized) of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in flue gas ranged from 0.036 to 22 ng TEQ/Nm3, while the levels of polychlorinated biphenyls (PCBs) and polychlorinated naphthalenes (PCNs) in flue gas samples ranged from 0.0023 to 1.2 ng TEQ/Nm3 and 0.17–44 pg TEQ/Nm3, respectively. The average concentrations of UPOPs in flue gas from car-type furnaces were higher than those from flat-panel furnaces. Secondary chambers and air pollution control devices were effective for controlling UPOPs emissions. However, heat exchangers were not as effective for reducing UPOPs emissions. It was observed that the UPOPs profiles exhibited dissimilarities between fly ash and flue gas samples. HxCDF, OCDD, and PeCDF were the dominant homologs of PCDD/Fs in flue gas, while HxCDF, PeCDF, and HpCDF were the dominant homologs in fly ash. The fractions of MoCBs and MoCNs in fly ash were higher than those in flue gas. Finally, we conducted an assessment of the global emissions of UPOPs from cremation in the years of 2019 and 2021. The total emission of UPOPs in 47 countries was estimated at 239 g TEQ in 2021, which was during the peak period of the COVID-19 pandemic worldwide. The emissions in 2021 increased by approximately 24 % compared to 2019, with the impact of COVID-19 being a significant factor that cannot be disregarded.

Formation behavior of PCDD/Fs during waste pyrolysis and incineration: Effect of temperature, calcium oxide addition, and redox atmosphere

The clean and efficient utilization of municipal solid waste (MSW) has attracted increasing concerns in recent years. Pyrolysis of MSW is one of the promising options due to the production of high-value intermediates and the inhibition of pollutants at reducing atmosphere. Herein, the formation behavior of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) during MSW pyrolysis and incineration was experimentally investigated and compared. The influence of reaction temperature, CaO addition, and redox atmosphere on PCDD/Fs formation were compared and discussed. The results showed as the pyrolysis temperature increased, the mass concentration and international toxicity equivalence quantity of PCDD/Fs initially peaked at ∼750 °C before declining. Most of the generated PCDD/Fs were concentrated in the liquid and gaseous products, accounting for ∼90% of the total. Among liquid products, octachlorodibenzo-p-dioxin (O8CDD), 2,3,4,7,8-pentachlorodibenzofuran and 1,2,3,4,6,7,8-heptachlorodibenzofuran (H7CDF) were the most crucial mass concentration contributors, while in gas products, high-chlorinated PCDD/Fs, such as O8CDD, octachlorodibenzofuran (O8CDF) and 1,2,3,4,6,7,8-H7CDF were predominant. Compared to incineration, the formation of PCDD/Fs was 7–20 times greater than that from pyrolysis. This discrepancy can be attributed to the hydrogen-rich and oxygen-deficient atmosphere during pyrolysis, which effectively inhibited the Deacon reaction and the formation of C–Cl bonds, thereby reducing the active chlorine in the system. The addition of in-situ CaO additives also decreased the active chlorine content in the system, bolstering the inhibiting of PCDD/Fs formation during MSW pyrolysis.

A novel, low-cost, and efficient separation strategy based on S-doped C3N4 for the analysis of PCDD/Fs and dioxin-like PCBs

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (dl-PCBs) are widespread and highly toxic persistent organic pollutants with similar chemical structure. The popular process for the separation of PCDD/Fs and dl-PCBs in one sample often relies on imported and expensive activated carbon, giving rise to an urgent need of inexpensive and efficient separation method. Herein, a novel, simple, and low-cost separation strategy based on sulfur-doped carbon nitride (S-C3N4) is reported. The S-C3N4 material was synthesized through simple thermal annealing with precursor of thiocyanuric acid. After recovery experiments, the optimal addition ratio of S-C3N4 was determined to be 40% mixed with silica gel. The recoveries for PCDD/Fs and dl-PCBs congeners are 32% - 105% and 60% - 70% respectively, which not only meets USEPA and Chinese standards but also shows comparable performance to activated carbon. Moreover, the proposed S-C3N4 strategy exhibits excellent performance for the analysis of PCDD/Fs and dl-PCBs in real complex samples (sediment and fish liver) in terms of detected concentrations and toxic equivalents. Overall, this study puts forward a new and low-cost avenue for the separation of PCDD/Fs and dl-PCBs, which is of remarkable meaning for motivating the development of detection techniques and domestic equipment for dioxins and other pollutants in the environment.

Distribution of PCDD/Fs and PCBs at different locations in a circulating fluidised bed municipal solid waste incinerator.

This study investigates a circulating fluidised bed (CFB) incineration plant to examine the concentrations and fingerprints of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs) at five locations downstream of the post-combustion zone. Sampling encompassed both flue gas and ash, spanning from the high-temperature superheater to the outlet of the baghouse filter, thus covering a wide range of flue gas temperatures. The analysis reveals a continuous increase in PCDD/F and PCB concentrations in the flue gas from the superheater to the inlet of the air pollution control system (APCS). The maximum concentrations observed were 75.8ng/Nm3 for PCDDs, 219ng/Nm3 for PCDFs, and 763ng/Nm3 for PCBs. These values represent 9.14, 11.5, and 6.37 times their respective concentrations at the outlet of the high-temperature superheater. Concurrently, the levels of PCDD/Fs and dioxin-like PCBs (dl-PCBs) in the ash steadily increased along the cooling path of the flue gas within the plant. Comparing dl-PCBs to the total amount of 209 PCB congeners, it was evident that dl-PCBs exhibited a trend more akin to that of PCDD/Fs. A robust linear correlation was observed between dl-PCBs and PCDD/Fs (R2 = 0.99, p < 0.001), surpassing that between PCBs and PCDD/Fs (R2 = 0.92, p < 0.01), suggesting that dl-PCBs share closer formation pathways with PCDD/Fs. Additionally, elemental composition analysis of fly ash samples aimed to explore potential links between fly ash characteristics and PCDD/F and PCB formation. The Cl/S ratio increased from 1.58 to 5.13 with decreasing flue gas temperature. Principal component analysis (PCA) was employed to visualise the concentrations of PCDD/Fs and PCBs in the flue gas alongside elemental contents in the fly ash. With the exception of PCBs in ash, all other PCDD/Fs and PCBs in fly ash exhibited positive correlations with both carbon (C) and chlorine (Cl). Furthermore, a positive relationship between C/Cl and PCDD/Fs-PCBs in fly ash implies that fly ash serves as the primary reaction surface for dioxin generation during low-temperature heterogeneous catalytic reactions.

Characteristics of the pyrolytic products and the pollutant emissions at different operating stages from a pilot waste tire pyrolysis furnace

Pyrolysis is considered a highly practical, cost-effective, and environment-friendly technology for waste tires disposal. In this study, pyrolysis processes of waste tires were conducted in a pilot scale furnace feeding at 30 kg/h. The properties of pyrolytic products and the distribution patterns of pollutants generated in different operating stages (start-up, steady, and shut-down) were investigated. The pyrolytic gas in the steady state had a high caloric value of 10799 kJ/Nm3, valuable as heating source for pyrolysis. The elements of sulfur and zinc were effectively fixed as ZnS in the pyrolytic carbon. The basic properties of pyrolytic oil were in line with commercial diesel oil except for the lower flash point. Heavy metals were mainly concentrated in the pyrolytic carbon, with slightly higher concentrations in the steady state. Moreover, polycyclic aromatic hydrocarbons (PAHs) and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) were mainly concentrated in the pyrolytic oil, with predominated low-ring PAHs and high chlorinated PCDD/Fs. The concentrations of PAHs and PCDD/Fs in the gas phase were higher during the start-up stage due to the memory effect, whereas were effectively reduced during the steady stage. The concentration of PAHs in the solid phase was highest during the furnace start-up and lowest in the shut-down stage. In contrast to PAHs, the PCDD/Fs in the solid phase reached their highest concentration during the shut-down stage, which was mainly affected by temperature. The results provide guidance for the reducing of pollutant emissions and the recycling of pyrolytic products.

Levels, patterns and risk assessment of PCDD/Fs and dl-PCBs through dietary exposure in the Valencian Region (Spain)

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and dioxin like polychlorinated biphenyls (dl-PCBs) levels were measured in representative vegetable oils and animal origin foodstuffs collected in a Total Diet Study carried out in the Valencian Region (Spain). A total amount of 3,300 food samples were collected and grouped into 5 main food groups: vegetable oils, meat and meat products, eggs, milk and dairy products and fish and sea products. The samples were analysed using gas chromatography coupled to high-resolution mass spectrometry (GC-HRMS). The food group which presented the highest concentration in wet weight (ww) for the sum of PCDD/Fs and dl-PCBs was fish and sea products (0.5 pg TEQ g−1 ww), whereas meat and meat products (0.6 pg TEQ g−1 lipid) showed the highest levels expressed in lipid terms. Occurrence data of PCDD/F and dl-PCBs were combined with consumption data to estimate the dietary exposure of adults (>15 years) and children (6–15 years). Finally, the estimated weekly intake (EWI) was calculated using a deterministic approach and considering the food consumption of the population, with fish and sea products being the main food group contributor. Likewise, considering the worst-case scenario (Upper Bound, UB), average EWI were 1.8 and 3.4 pg TEQ kg−1 body weight (bw) week−1 for adults and children, respectively. For children, the average EWI was almost twice above the tolerable weekly intake (TWI) of 2 pg TEQ kg−1 bw week−1 set by EFSA in 2018. In terms of risk characterisation, the overall obtained results showed that 19 % of adults and 43 % of children may exceed the TWI when using UB.