Characterization of PCDD/Fs and dioxin-like PCBs in flue gas from thermal industrial processes in Vietnam: A comprehensive investigation on emission profiles and levels

Degradation and regeneration inhibition of PCDD/Fs in incineration fly ash by low-temperature thermal technology

Low-temperature thermal degradation of PCDD/Fs for incineration fly ash (IFA), as a novel and emerging technology approach, offers promising features of high degradation efficiency and low energy consumption, presenting enormous potential for application in IFA resource utilization processes. This review summarizes the concentrations, congener distributions, and heterogeneity characteristics of PCDD/Fs in IFA from municipal, medical, and hazardous waste incineration. A comparative analysis of five PCDD/Fs degradation technologies is conducted regarding their characteristics, industrial potential, and applicability. From the perspective of low-temperature degradation mechanisms, pathways to enhance PCDD/Fs degradation efficiency and inhibit their regeneration reactions are discussed in detail. Finally, the challenges to achieve low-temperature degradation of PCDD/Fs for IFA with high-efficiency are prospected. This review seeks to explore new opportunities for the detoxification and resource utilization of IFA by implementing more efficient and viable low-temperature degradation technologies.

A Comprehensive Evaluation of Dioxins and Furans Occurrence in River Sediments from a Secondary Steel Recycling Craft Village in Northern Vietnam

This first study investigated the presence of dioxins and furans in river sediments around a craft village in Vietnam, focusing on Secondary Steel Recycling. Sediment samples were collected from various locations along the riverbed near the Da Hoi Secondary Steel Recycling village in Bac Ninh province. The analysis was conducted using a HRGC/HRMS-DFS device, detecting a total of 17 dioxin/furan isomers in all samples, with an average total concentration of 288.86 ng/kg d.w. The concentrations of dioxin/furan congeners showed minimal variation among sediment samples, ranging from 253.9 to 344.2 ng/kg d.w. The predominant compounds in the dioxin group were OCDD, while in the furan group, they were 1,2,3,4,6,7,8-HpCDF and OCDF. The chlorine content in the molecule appeared to be closely related to the concentration of dioxins and their percentage distribution. However, the levels of furan isomers did not vary significantly. The distribution of these compounds was not dependent on the flow direction, as they were mainly found in solid waste and are not water-soluble. Although the hepta and octa congeners had high concentrations, when converted to TEQ values, the tetra and penta groups (for dioxins) and the penta and hexa groups (for furans) contributed more to toxicity. Furthermore, the source of dioxins in sediments at Da Hoi does not only originate from steel recycling production activities but also from other combustion sites. The average total toxicity was 10.92 ng TEQ/kg d.w, ranging from 4.99 to 17.88 ng TEQ/kg d.w, which did not exceed the threshold specified in QCVN 43:2017/BTNMT, the National Technical Regulation on Sediment Quality. Nonetheless, these levels are still concerning. The presence of these toxic substances not only impacts aquatic organisms in the sampled water environment but also poses potential health risks to residents living nearby.

Source characteristics of polycyclic aromatic hydrocarbons and polychlorinated biphenyls in surface soils of Shenyang, China: A comparison of two receptor models combined with Monte Carlo simulation

The surface soil concentrations of 16 PAHs and 15 PCBs were simultaneously determined by gas chromatography-tandem mass spectrometry in 21 locations of urban areas of Shenyang. The average concentrations of PAHs and PCBs were 26.40 ± 34.68 mg/kg and 48.03 ± 27.47 μg/kg, respectively. Factor analysis with nonnegative constraints (FA-NNC) and absolute principal component score with multiple linear regression (APCS-MLR) model were used to explore and evaluate the sources of PAHs and PCBs in the study area. The results of FA-NNC showed that PAHs in soils were mainly from traffic emissions (49.64%), coal combustion (46.88%) and petrogenic source (3.49%). The PCBs in soils were mainly from commercial and high temperature combustion mixed sources (20.3%), combustion and industry emission mixed sources (21.1%), electrical equipment sources (22.2%) and traffic emission sources (36.4%). The results of APCS-MLR were consistent with those of FA-NNC. The uncertainty of FA-NNC and APCS-MLR model was analyzed by Monte Carlo simulation method. The results revealed the reliability of the two receptor models on source apportionment. The estimated carcinogenic risks indicated that the risks of PAHs in soils exceed the acceptable range (10-6-10-4), while the risks of PCBs were below the acceptable risk level of 10-6.

Polychlorinated dibenzo-p-dioxins, dibenzofurans and dioxin-like polychlorinated biphenyls in bivalve molluscs. Risk to Polish consumers?

Introduction

Concentrations of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (DL-PCBs) were investigated in six species of bivalve mollusc purchased on the Polish retail market. The risk to consumers was calculated as a percentage of the tolerable weekly intake (TWI) (2 pg World Health Organization toxic equivalent (WHO-TEQ) kg-1 body weight (b.w.)).

Material and Methods

Altogether 32 samples were analysed using an isotope dilution technique with high resolution gas chromatography coupled with high resolution mass spectrometry.

Results

Low levels of all analysed compounds were found. The range of PCDD/Fs was 0.08-0.37 pg WHO-TEQ g-1 of wet weight (w.w.) and 0.04-0.41 pg WHO-TEQ g-1 w.w. for DL-PCBs. The highest concentrations of all analysed compounds were found in Pacific oysters, at 0.30 pg WHO-TEQ g-1 w.w. for the sum of PCDD/Fs and 0.19 pg WHO-TEQ g-1 for the sum of DL-PCBs. These concentrations were 2-4 times higher than those detected in the other analysed mollusc species. Different species-dependent congener profiles were observed for PCDD/F concentrations, while PCB congener concentration profiles were species independent. The risk to consumers was assessed relating theoretical intakes of PCDD/Fs and DL-PCBs per 25, 50 and 100 g of consumption of molluscs per week to the TWI.

Conclusion

Taking into account the low consumption of molluscs in Poland and low concentrations of analysed compounds, neither adults nor children are likely to exceed the TWI by ingestion of food in this category.

Utility of an alternative method (to USEPA Method 1613) for analysis of priority persistent organic pollutants in soil from mixed industrial-suburban areas of Durban, South Africa

This study evaluates the adequacy of a USEPA Method 1613 alternative analytical method for analysis of persistent organic pollutants (POPs) in soil from the immediate vicinity of industrialized areas in the eThekwini municipal area in South Africa. The objective of this study is in line with the Stockholm Convention Article 11 on research, development, and monitoring. Furthermore, it became imperative to find an alternative analytical procedure to USEPA Method 1613 that could cater to studies conducted in Africa where recent reviews have indicated that most African countries lack the technical and instrumental capacity for performing analysis of dioxin-like compounds according to USEPA Method 1613, which entails the use of high-resolution chromatography and high-resolution mass spectrometry instrumentation. The study aimed to ascertain the utility of an alternative two-dimensional gas chromatography-time of flight mass spectrometry method for analysis of trace-level priority POPs in soil, along with a fast single quadrupole gas chromatography-mass spectrometry method. The analytical methods were applied to the analysis of POPs on soil samples from industrial areas with oil refineries and a pulp and paper manufacturing company, while other samples were collected near the electricity substations and a landfill site. Analytical results showed BDE 209 as the dominant contaminating polybrominated diphenyl ether (concentration ranges from 0.006 to 5.71 ng g^-1 ). Polybrominated biphenyls (PBBs) 9, 10, and 49 were the dominant PBBs detected in 78% of the sites tested, although their concentrations were below the limit of quantification (LOQ). Polychlorinated dibenzo-p-dioxins and furans and dioxin-like polychlorinated biphenyls detected could not be quantified above their respective LOQs, indicating that the Durban area has low priority pollutant contamination levels compared to other regions around the world. The methods developed are a starting point that will inform considerations for routine evaluation and management of soil contamination, which plays a vital role in environmental management. Integr Environ Assess Manag 2023;19:749-762. © 2022 SETAC.

Emission characteristics of dioxin during solid waste co-processing in the Chinese cement industry

Development of co-processing technology in the cement industry in China is important for environmentally sound disposal and recycling of waste, and contributes to sustainable development of the cement industry. However, dioxin pollution could negatively affect promotion of this technology. Therefore, it is necessary to study the emission characteristics of dioxins in cement kilns. In this study, the emission characteristics of dioxins and factors influencing their generation during co-processing solid wastes were studied in 14 new dry cement kilns. The dioxin concentrations were very similar regardless of whether solid wastes were fed into the kiln. In blank runs without co-processing, the average dioxin concentration was 0.0097 ng international toxic equivalents (I-TEQ)/Nm³. By comparison, that for co-processing solid wastes was 0.012 ng I-TEQ/Nm³. These values meet the relevant emission standards. The type of co-processed solid wastes had almost no effect on the dioxin concentration. At larger production scales, the concentration of dioxin emitted in the flue gas decreased. The dioxin concentrations in kiln dust were obviously higher than those in clinker and raw materials. The average emission factor of dioxin per ton of cement was 30 ng I-TEQ/t, which is equivalent to that in cement kilns in other countries.

Suppression on PCDD/Fs formation by a novel inhibition system consisting of phosphorous-based compounds coupled with a chlorine-deactivation material

The SN-containing inhibitors are effective for suppressing the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the post-combustion zone of municipal solid waste incineration systems, but the industrial application of the SN-containing inhibitors is restricted by the high cost and the generation of corrosive by-products (e.g., SOx). To develop cost-effective and environmentally friendly inhibitors, a new inhibition system consisting of P-based compounds (i.e., NH₄H₂PO₄ (ADP) and KH₂PO₄ (PDP)) and a chlorine-deactivation material (CaO) was proposed in this study. Also, the performance of this inhibition system in terms of suppressing PCDD/Fs formation was evaluated in an experimental system which simulated PCDD/Fs generation in the post-combustion zone. Generally, the formation of PCDD/Fs was effectively suppressed by over 95 % by the mixed inhibitors (ADP/CaO and PDP/CaO) and the individual inhibitor of ADP. Based on the observation on PCDD/F-fingerprints and the chemical speciation of Cl and Cu, the mechanisms of inhibitors were identified as: (i) passivating metal catalyst by converting the speciation of Cu from chlorides and Cu²⁺ with high reactivities to phosphates, oxides, and Cu⁺ with low reactivities, and (ii) deactivating Cl by CaO to prevent the formation of organic Cl which was critical for PCDD/Fs formation. In addition, both mechanisms were supported by (i) the better performance of inhibitors on suppressing the PCDD/F-congeners formed via de novo pathway than congeners synthesized from chlorophenols and (ii) lower degrees of chlorination of PCDD/Fs for reaction systems with CaO involved than other systems.

Feed as a source of dioxins and PCBs

Dioxins (PCDD/PCDF) and polychlorinated biphenyls (PCBs) are a group of undesirable chemicals classified as persistent organic pollutants (POPs). The main route of human exposure to these compounds is through the diet (about 80%), with food of animal origin being the predominant source. For this reason, animal feed can contribute significantly to the presence of these compounds in food. The aim of this study was to present the concentrations of dioxins and PCBs as well as congener profiles in feed exceeding the acceptable limits (277/2012/EU). In addition, an attempt was made to identify the source of contamination for the different types of contaminated feedstuffs. Among a total of 743 samples of feed materials from the Polish market tested between 2013 and 2021, exceedances of the maximum levels of dioxins and PCBs were found in 21 samples (2.8%). The largest group among the non-compliant feed samples were feed materials of plant origin (43%) followed in decreasing order by vegetable oils and fats of animal origin (24%), materials of mineral origin (9%), and fish oils and meals (5%). The exceedances of the dioxin limits in the category feed materials of plant origin were only caused by dried materials (pulp, dried alfalfa, dried apple). Furthermore, for 8 (1%) samples, the concentrations of test substances exceeding the Action Levels (AL) were recorded.

Dioxins and PCBs in freshwater fish and sediments from Polish lakes

PCDD/F and PCB concentrations were analysed in sediments, fish muscles, and livers collected from four lakes in Poland. In general, the fish and sediments had low levels of dioxins and PCBs. The total TEQ in the sediments was 0.12-0.47 pg WHO-TEQ g^-1 dry matter (dm), the NDL-PCB content was at 0.05-0.36 ng g^-1 dm. The muscles contained PCDD/F/DL-PCBs levels of 0.03-3.19 pg WHO-TEQ g^-1 wet weight (ww) while the NDL-PCB content was 0.08-27.30 ng g^-1 ww. The livers contained 0.73-8.74 pg WHO-TEQ g^-1 ww and the NDL-PCB content was 1.52-88.84 ng g^-1 ww. The potential health risk for fish consumers was assessed using the Tolerable Weekly Intake (2 pg WHO-TEQ/kg bw). The consumption of 200 g of fish containing an average PCDD/D/DL-PCB content results in an intake of 43-455% TWI and 14-150% TWI for children and adults, respectively, depending on fish species and sampling point.

Investigation on Pollution Control Device (PCD) in iron foundry industry to reduce environmental chemicals

Right from the olden days, many products have been made according to foundry practices in order to generate prosperity in the societies in which they operate while reaping these types of benefits through the operation of foundries. It is alarming that the emissions released by foundries affect human health. Therefore, foundries installed Pollution Control devices (PCDs), in accordance with this development; researchers examined the effectiveness of these PCDs in controlling emissions from foundries in different parts of the world. The emission control obtained by installing these PCDs is explained in this article based on the data gathered from the survey. The cartridge filter equipped with an induction furnace reduced the concentration of SPM to less than 20 mg/Nm³. This result of the investigation indicates that the cartridge filter built into the induction furnace achieves the best efficiency in controlling contaminants from iron foundries. Interestingly, the operation of the cartridge filter has yet to be documented. Therefore, the construction operation, the performance of the cartridge filter, and its efficiency in achieving contaminations control in foundries are described. This will provide useful information on the use of cartridge filters in an induction furnace to reduce Iron foundry emissions.

Occurrence, partitioning, and bioaccumulation of an emerging class of PBT substances (polychlorinated diphenyl sulfides) in Chaohu Lake, Southeast China

Polychlorinated diphenyl sulfides (PCDPSs) represent an emerging group of constituents that are persistent, bioaccumulative and toxic (PBT) substances of great concern in terms of human health and ecological integrity. However, little is known about the occurrence, environmental behaviour and ecological risks of PCDPSs in lake environments. In this study, the concentrations of 21 PCDPSs were determined in surface water, suspended particulate matter (SPM), sediments, and 8 fish species from Chaohu Lake, China. Eighteen PCDPS congeners were prevalently detected in the samples, with concentrations ranging from 0.272-1.69 ng/L (water), 0.477-2.03 ng/g d.w. (SPM), 0.719-4.07 ng/g d.w. (sediment) and 0-0.131 ng/g w.w. (fish), respectively. Medium- and high-chlorinated PCDPSs in SPM and sediment were significantly higher than those in water samples. Increased PCDPS concentrations were found in higher trophic level fishes and those with a demersal habitat preference, indicating their bioaccumulation and biomagnification potential. The logBCFs, BSSAFs, and BSAFs of PCDPS congeners in fishes were determined to be 3.91-5.18, 0.0500-2.33, and 0.0360-4.94 L/kg, respectively. The organic carbon normalized partition coefficients (logK_oc) of PCDPSs in surface water-SPM (4.61-5.54 L/g) and surface water-sediment (4.38-5.69 L/g) systems were determined, and it was found that highly chlorinated PCDPSs were more prone to migrate from water to sediment and SPM. The toxic equivalent (TEQ) values of PCDPSs in the samples (lower than 10^-1 pg/g or pg/L) and daily intake via fish consumption (0.180-0.340 μg/kg/day) were estimated for humans, and cumulative risk quotients (RQs) after correction at ten sampling sites (0.065-0.66) were calculated for green algae. The findings elucidated the environmental behaviour of PCDPSs in Chaohu Lake.

PCDD/Fs and Dioxin-like PCBs in Chicken Eggs and Soils in Dong Nai Province, Southern Vietnam: Impacts of Raising Methods and Nearby Pollution Sources

Polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) and dioxin-like PCBs (DL-PCBs) were examined in chicken egg and soil samples collected from Dong Nai Province, southern Vietnam. PCDD/F and DL-PCB levels in egg samples ranged from 5.74 to 1320 (median 350) and from 120 to 51,200 (median 1470) pg/g lipid weight (lw), respectively. Toxic equivalents to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TEQ) in egg samples ranged from 0.817 to 245 (median 10.8) pg TEQ/g lw. Higher dioxin levels were found in free-range eggs than non-free-range ones. We found significant correlation between TEQ levels in paired egg and soil samples collected from the Bien Hoa Airbase and some communities adjacent to industrial areas (Spearman's ρ = 0.671; p < 0.05), suggesting the co-occurrence of legacy and current dioxin emission sources in these areas.

Emissions of PAHs, PCDD/Fs, dl-PCBs, chlorophenols and chlorobenzenes from municipal waste incinerator cofiring industrial waste

Concentrations and distributions of PAHs and chlorinated aromatic compounds including PCDD/Fs, dl-PCBs, chlorophenols (CPs), and chlorobenzenes (CBz) in the municipal waste incinerator are investigated to characterize their formation and emission via intensive stack sampling. In addition, the toxicity of fly ash contribution by PCDD/Fs and dl-PCBs is evaluated in this study. The results reveal that concentrations of PCDD/Fs and dl-PCBs in flue gas are significantly lower than those of CPs, CBz, and PAHs. Additionally, the removal efficiencies of PAHs and chlorinated aromatic compounds achieved with existing air pollution control devices are evaluated, indicating that the removal efficiencies achieved with activated carbon injection + baghouse (95-99%) are higher than those with semi-dry scrubber (SDS). Besides, PCDD/Fs and PCBs TEQ concentrations in SDS and BH ashes are within 1.61-2.66 WHO-TEQ/g and 0.09-0.19 WHO-TEQ/g, respectively. Furthermore, the calculated mass flow rates suggest that the input rate of PCDD/Fs and dl-PCBs of SDS are 60.24 mg/h and 59.74 mg/h, respectively. The mass flow rates of PCDD/Fs and dl-PCBs after SDS in flue gas are 32.47 mg/h and 49.73 mg/h, respectively. However, the discharge rates of PCDD/Fs and dl-PCBs from SDS are 120.60 mg/h and 27.05 mg/h, respectively, indicating that PCDD/Fs are significantly formed within the SDS. PCDD/Fs formation is attributed to the operating temperature of SDS (240 ± 11.5 °C), which is within the temperature window for de novo synthesis. Thus, operating parameters of the APCDs should be optimized to reduce the formation of PAHs and chlorinated aromatic pollutants from MWI.

Characterization of unsubstituted and methylated polycyclic aromatic hydrocarbons in settled dust: Combination of instrumental analysis and in vitro reporter gene assays and implications for cancer risk assessment

Concentrations of 34 unsubstituted and methylated polycyclic aromatic hydrocarbons (PAHs and Me-PAHs) and AhR-mediated activities in settled dust samples were determined by a combination of gas chromatography-mass spectrometry and an in vitro reporter gene assay (PAH-CALUX). The levels of Σ34PAHs and bioassay-derived benzo[a]pyrene equivalents (CALUX BaP-EQs) were significantly higher in workplace dust from informal end-of-life vehicle dismantling workshops than in common house dust and road dust. In all the samples, the theoretical BaP-EQs of PAHs (calculated using PAH-CALUX relative potencies) accounted for 28 ± 19% of the CALUX BaP-EQs, suggesting significant contribution of aryl hydrocarbon receptor (AhR) agonists and/or mixture effects. Interestingly, the bioassay-derived BaP-EQs in these samples were significantly correlated with not only unsubstituted PAHs with known carcinogenic potencies but also many Me-PAHs, which should be included in future monitoring and toxicity tests. The bioassay responses of many sample extracts were substantially reduced but not suppressed with sulfuric acid treatment, indicating contribution of persistent AhR agonists. Cancer risk assessment based on the CALUX BaP-EQs has revealed unacceptable level of risk in many cases. The application of bioassay-derived BaP-EQs may reduce underestimation in environmental management and risk evaluation regarding PAHs and their derivatives (notably Me-PAHs), suggesting a consideration of using in vitro toxic activity instead of conventional chemical-specific approach in such assessment practices.

Concentrations, profiles, emission inventory, and risk assessment of chlorinated benzenes in bottom ash and fly ash of municipal and medical waste incinerators in northern Vietnam

Concentrations and congener profiles of seven di- to hexachlorinated benzenes (CBzs) were characterized in bottom ash and fly ash samples collected simultaneously from one medical waste incinerator (MEWI) and one municipal waste incinerator (MUWI) in northern Vietnam. Total concentrations of seven CBzs in the fly ash samples ranged from 6.98 to 34.4 (median 19.1) ng g^-1 in the MEWI, and ranged from 59.1 to 391 (median 197) ng g^-1 in the MUWI. Concentrations of CBzs in the bottom ash samples of the MEWI (median 1.95; range 1.53-5.98 ng g^-1) were also lower than those measured in the MUWI samples (median 17.4; range 14.5-42.6 ng g^-1). Levels of CBzs in the fly ash samples were significantly higher than concentrations measured in the bottom ash samples, partially indicating the low-temperature catalytic formation of these pollutants in post-combustion zone. In general, higher chlorinated congeners (e.g., hexachlorobenzene, pentachlorobenzene, and 1,2,4,5-tetrachlorobenzene) were more abundant than lower chlorinated compounds. However, compositional profiles of CBzs were different between the ash types and incinerators and even between the same sample types of different sampling days, suggesting that the formation of CBzs in these incinerators is complicated and influenced by many factors. Emission factors and annual emission amounts of CBzs were estimated for the two incinerators by using actually measured data of CBz concentrations in the ash. Daily intake doses and cancer risks of ash-bound CBzs estimated for workers in the two incinerators were generally lower than critical values, but cancer risks caused by other relevant pollutants (e.g., polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and dioxin-related compounds) were not considered.

Emission and migration of PCDD/Fs and major air pollutants from co-processing of sewage sludge in brick kiln

The annual output of sewage in China is increasing rapidly and continues to grow, so there is an urgent need for a treatment other than landfills. Among various treatment methods, brick production coprocessing of sewage sludge is technically and economically advantageous. The emission characteristics of typical brick kiln coprocessing of sewage sludge with an annual production of 60 million bricks were studied. The major air pollutants and PCDD/Fs in gas and soil were determined. Particulate matter and SO₂ contributed most before treatment, with concentrations of (1.017 ± 0.089) × 10⁴ mg/Nm³ and (2.770 ± 0.251) × 10³ mg/Nm³, respectively. After cleaning, the average emitted concentrations of major air pollutants were permissive and homogeneous: 58.13 ± 5.51 mg/Nm³ for NO_x, 30.15 ± 9.12 mg/Nm³ for HCl, 28.63 ± 14.33 mg/Nm³ for SO₂, 23.76 ± 3.31 mg/Nm³ for particulate matter, and 356.8 ± 99.1 for odor. The PCDD/Fs in the exhaust gas and ambient air showed similar distributions and fingerprint characteristics. The annual emission amounts of the PCDD/Fs were 0.265 g/year and 0.0393 g TEQ/year. Moreover, correlation analysis indicated that PCDD/Fs were most relevant to HCl, and particulate matter might be important to SO₂ and fluoride. Further relativity studies showed that the brick kiln was a source of PCDD/Fs but not a main source of major air pollutants to the surrounding environment. All the above pollutants from the brick kiln were permissive with relevant national standards. The results could help with pollution inventories for the brick and tile industry and sewage sludge disposal process.

Process tracing of PCDD/Fs from economizer to APCDs during solid waste incineration: Re-formation and transformation mechanisms

The emission of PCDD/Fs is a crucial factor for the aggravation of the Not-In-My-Back-Yard (NIMBY) syndrome, especially for the incineration plants that fail to meet the emission standard. It is well known that physicochemical processes in the boiler can notably affect the discharge of dioxins, especially under transient, non-steady conditions. However, few studies paid attention to the important operational parameters that influence PCDD/Fs formation and transformation in the boiler when an incinerator is in its daily steady operation. In this study, 36 samples were analyzed to achieve process tracing of PCDD/Fs. The concentration, congener profile and vapor/solid partitions of PCDD/Fs from the economizer to air pollution control devices (APCDs) under two typical steady conditions were investigated. Results indicated that increasing air supply aggravated the formation of PCDD/Fs, disturbed the vapor/solid partitions, and triggered a substandard emission. Quantitative structure-activity relationship (QSAR) modeling was firstly performed for the formation mechanism and orbital energy factors were identified as dominating factors. Besides, the removal rates of PCDD/Fs significantly correlated with the saturated vapor pressure and proportions of different isomers. This study is beneficial for operators to optimize relevant operational parameters of the incineration plants so as to get rid of substandard problems.

Concentrations and profiles of persistent organic pollutants unintentionally produced by secondary nonferrous metal smelters: Updated emission factors and diagnostic ratios for identifying sources

Secondary nonferrous metal smelters are important sources of unintentionally produced persistent organic pollutants (UPOPs) including polychlorinated biphenyls (PCBs), polychlorinated naphthalenes, pentachlorobenzene, and hexachlorobenzene. Quantifying UPOP emissions by the main sources is an important step when evaluating UPOP emissions and establishing an inventory. In this study, field investigations were performed to allow UPOP emissions and distributions in stack gases emitted by secondary nonferrous metal smelters to be compared. A total of 25 stack gas samples were collected from secondary copper smelters (SCus), secondary zinc smelters, and secondary lead smelters in China. The mean toxic equivalent concentrations (TEQs) and mass concentrations of most of the UPOPs were highest in the secondary zinc smelter stack gas samples, next highest in the SCu stack gas samples, and lowest in the secondary lead smelter stack gas samples. The mean dioxin-like PCB and polychlorinated naphthalene TEQs were ∼8.9 and ∼6.6 times higher in stack gases from a SCu equipped with an oxygen-enriched smelting furnace than in stack gases from a SCu with a converter furnace. The mean PCB-118 to PCB-123 ratios and CN-10 to CN-35 ratios varied strongly and could be used as diagnostic ratios for apportioning the sources of UPOPs in the environment. Emission factors for dioxin-like PCBs, polychlorinated naphthalenes, pentachlorobenzene, and hexachlorobenzene in stack gases from secondary nonferrous metal smelters were derived and updated. The results improve our understanding of UPOP emission and provide data for establishing UPOP emission inventories for secondary nonferrous metal smelters.

Sources and health risks of PM2.5-bound polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in a North China rural area

Polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) are typical persistent organic pollutants (POPs), which have high toxicity, bioaccumulation and long-distance transfer capability. Daily variation, sources of PCBs and OCPs in PM_2.5 are rarely explored in polluted rural area. Here, the sources and health risks of the PCBs and OCPs were evaluated for 48 PM_2.5 samples collected in winter 2017 in Wangdu, a heavy polluted rural area in the North China Plain. The average diurnal and nocturnal concentrations of Σ₁₈PCBs and Σ₁₅OCPs were 1.74-24.37 and 1.77-100.49, 11.67-408.81 and 16.89-865.60 pg/m³, respectively. Hexa-CBs and penta-CBs accounted for higher proportions (29.0% and 33.6%) of clean and polluted samples, respectively. Hexachlorobenzene (HCB) was the dominant contributor to OCPs with an average concentration of 116.17 pg/m³. Hexachlorocyclohexane (ΣHCHs) and dichlorodiphenyltrichloroethane (ΣDDTs) were the other two main classes in OCPs with the average concentrations of 4.33 and 15.89 pg/m³, respectively. β-HCH and p,p'-DDE were the main degradation products of HCHs and DDTs, respectively. The principal component analysis and characteristic ratio method indicated both waste incineration and industrial activities were the main sources of PCBs, contributing 76.8% and 12.7%, respectively. The loadings of OCPs were attributed to their application characteristics and the characteristic ratio method reflected a current or past use of OCPs. Health risk assessment showed that the respiratory exposure quantity of doxin-like PCBs (DL-PCBs) and the lifetime cancer risk from airborne OCPs exposure was negligible, while the other exposure modes may pose a risk to human bodies.

Long-term monitoring of PCDD/Fs in soils in the vicinity of a hazardous waste incinerator in China: Temporal variations and environmental impacts

Campaigns from 2008 to 2016 are carried out to study temporal variations and environmental impacts of polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/Fs) in soils in the vicinity of a new hazardous waste incinerator (HWI) in China. Results indicate that after 8-year operation of HWI, the geometrical means of both the total concentrations and the TEQ values of PCDD/Fs in soils decrease from 1280 ng·kg^-1 and 3.08 ng WHO-TEQ·kg^-1 to 568 ng·kg^-1 and 2.70 ng WHO-TEQ·kg^-1, respectively, showing generally limited impact on soils within 7.5 km. Temporal changes of PCDD/Fs congener profiles trend to profiles in combustion sources. Considering the whole studied area, results of principal component analysis between soils and emission sources show that instead of HWI, other sources including open burning, traffic, and cement plant are more responsible for PCDD/Fs accumulation. The modeling results of AERMOD indicate the dominant roles of wind velocities and directions on the deposition of PCDD/Fs emitted from HWI. The largest PCDD/Fs increase value in soils predicted by integrating AERMOD and a reservoir model is very limited after 25 years (2.03 × 10^-5 ng WHO-TEQ·kg^-1), indicating relatively minor impacts of HWI on surrounding soils, but the noticeable impact on area downwind from the stack in short distance (e.g., within 0.5 km) should be recognized.

Bioaccumulation of PCDD/Fs in foodstuffs near Bien Hoa and Da Nang airbases: assessment on sources and distribution

In this survey, food items were collected from vicinities of Bien Hoa and Da Nang airbase and determined for polychloro-dibenzo-dioxins and polychloro-dibenzo-furans (PCDD/Fs) to assess their accumulation, distribution in the local food items, and risk of PCDD/F exposure through consumption of the local foods. Dioxin compounds were determined using isotope dilution method which is slightly modified from US-EPA method 1613B. The dioxin concentration was the highest in fish followed by eggs, chicken, meat (pork and beef), and vegetables. Particularly, in Bien Hoa airbase, the mean concentrations of dioxin on TEQ and lipid basis (except for vegetables) were 26 pg/g for fish, 13 pg/g for eggs, 20 pg/g for chicken, 4.5 pg/g for meat, and 0.34 pg/g fresh wt for vegetables. In Da Nang airbase, the mean levels of dioxin on TEQ and lipid basis were slightly lower, 12.9 pg/g for fish, 8.7 pg/g for eggs, 5.9 pg/g for chicken, 6.7 pg/g for meat, and 0.17 pg/g for vegetables. It has been interesting to observe that free-range chicken expose to higher level of dioxin than caged chicken. In some free-range chicken, the portion of 2,3,7,8-TCDD was relatively high and implying recent exposure to dioxin.

Experimental and Numerical Simulation Study on Co-Incineration of Solid and Liquid Wastes for Green Production of Pesticides

A large amount of solid and liquid waste is produced in pesticide production. It is necessary to adopt appropriate disposal processes to reduce pollutant emissions. A co-incineration scheme for mixing multi-component wastes in a rotary kiln was proposed for waste disposal from pesticide production. According to the daily output of solid and liquid wastes, the proportion of mixing was determined. An experiment of the co-incineration of solid and liquid wastes was established. Experimental results showed that the mixed waste could be completely disposed at 850 °C, and the residence time in the kiln exceeded 1 h. A model method for mixture and diesel oil-assisted combustion was proposed. Numerical simulation was performed to predict the granular motion and reveal the combustion interactions of the co-incineration of mixed wastes in the rotary kiln. Simulation results reproduced movements, such as rolling and cascading, and obtained the optimum rotational speed and diesel oil flow for the rotary kiln incineration operation. The simulation showed that the temperature in the kiln was maintained at 850 °C, and the mass fraction of CO and O2 at the outlet reached the standard for the complete combustion of the waste. Finally, the rotary kiln incineration and flue gas treatment processes were successfully applied in engineering for green production of pesticides.

Residue concentrations and profiles of PCDD/Fs in ash samples from multiple thermal industrial processes in Vietnam: Formation, emission levels, and risk assessment

The residue concentrations and congener profiles of polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) were examined in fly ash and bottom ash released from different thermal industrial processes in Vietnam. PCDD/F concentrations and toxic equivalents (TEQs) in the ash samples varied greatly and decreased in the following order: steel making > aluminum recycling > medical waste incinerator > boilers > municipal waste incinerator > tin production > brick production > coal-fired power plant. Both the precursor and de novo synthesis were estimated as possible formation mechanisms of dioxins in the ash, but the latter pathway was more prevalent. The highest emission factors were estimated for the ash released from some steel-making plants, aluminum-recycling facilities, and a medical waste incinerator. The emission factors of PCDD/Fs in ash released from some steel plants of this study were two to six times higher than the UNEP Toolkit default value. The annual emission amount of ash-bound dioxins produced by 15 facilities in our study was estimated to be 26.2 to 28.4 g TEQ year^-1, which mainly contributed by 3 steel plants. Health risk related to the dioxin-containing ash was evaluated for workers at the studied facilities, indicating acceptable risk levels for almost all individuals. More comprehensive studies on the occurrence and impacts of dioxins in waste streams from incineration and industrial processes and receiving environments should be conducted, in order to promote effective waste management and health protection scheme for dioxins and related compounds in this rapidly industrializing country.