Regional measurements of PCDD/PCDF concentrations in Korean atmosphere and comparison with gas-particle partitioning models

The current investigation was aimed at determining the levels of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/PCDFs) in the Korean atmosphere along with their estimation using gas-particle partitioning. Samples collected from six cites showed that large cities were polluted with a concentration of 0.593 pg TEQ/m3. Samples were also collected from residential (nine sites), commercial (five sites), and industrial (seven sites) districts in each city. Higher levels of PCDDs/PCDFs were observed in industrial area than other areas, since it includes many sources. Higher chlorinated 2,3,7,8-substituted congeners were predominantly found in the particulate phase. HpCDD/Fs and OCDD/Fs shared 97-99% of the particulate phase, whereas TCDD/Fs, which dominated the gaseous phase, shared 34.8% and 42.8% in 2,3,7,8-substituted congeners. The regression dataset was transformed due to the relationship between log K(P) and log P(L)o. A wide variation was observed in the slopes for the residential areas when compared with the slopes for the commercial and industrial areas. The Junge-Pankow model and K(oa) adsorption model were both found to be helpful in describing the gas-particle partitioning in the current study.     

Modeling the atmospheric transport and deposition of polychlorinated dibenzo-p-dioxins and dibenzofurans in North America

The atmospheric fate of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) was simulated for the year 2000 in North America using a SMOKE/CMAQ-based chemical transport model that was modified for this purpose. The 1999 USEPA emission inventories of PCDD/Fs and criteria pollutants were used. The 1995 Canadian emission inventory of criteria pollutants and the 1995 Canadian area source emissions for PCDD/Fs were used with the 2000 Canadian point source emissions. Modifications to CMAQ involved coupling it with dual organic matter (OM) absorption and black carbon (BC) adsorption models to calculate PCDD/F gas–particle partitioning. The model satisfactorily reproduced the particle bound fractions at all rural sites for which there were measured data and across the whole domain, the modeled vs. measured differences in particle bound fractions were less than 20% for nearly all congeners. The model predicted ambient air PCDD/F concentrations were also consistent with measurements. Simulated deposition fluxes were within 58% of direct measurements. PCDD/F atmospheric depositions to each of the Great Lakes were estimated for the year 2000. The results indicate that approximately 76% of the total deposition of PCDD/Fs to the Great Lakes (in W-TEQ, or toxic equivalent units as defined by the World Health Organization) is attributed to PCDD/Fs absorbed into OM in aerosol. For all of the lakes, more than 92% of all deposition is particle phase wet deposition and only 5–8% is particle phase dry deposition. Wet deposition from the gas phase is negligible. Of the 17 toxic PCDD/F congeners, the Cl_4–5DD/F compounds contribute approximately 70% to the total atmospheric deposition to the Great Lakes. The seasonal changes in the PCDD/F deposition flux track variations in ambient temperature.     

Air-vegetation transfer of PCDD/PCDFs: an assessment of field data and implications for modeling

This study was designed to evaluate soil and air (gas and particle) transfer of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) to vegetation in residential and industrial areas. In a first part, soil-vegetation transfer was assessed. The levels of PCDD/Fs in 120 soil and 120 herbage samples collected from 1996 to 2002 in an industrial area of Montcada (Barcelona, Spain), near a municipal solid waste incinerator (MSWI), were determined. Some additional individual samples were also evaluated. It was concluded that high soil concentrations, which are not at steady state with the air layer above it, show a tendency for PCDD/Fs to escape via volatilization. In a second part of the study, air-vegetation transfer was examined. PCDD/F concentrations from 24 herbage samples were used, while PCDD/F concentrations were also measured in seven high-volume air samples and seven passive air-vapor samples. Scavenging coefficients (m3 air "sampled"/g grass d.m.) ranged from 1.9 to 11.3 m3/g. A good trend with K(OA) was observed for PCDDs (R=0.82), while it was lower for PCDFs (R=0.55). The current results corroborate that PCDD/F concentrations in vegetation are associated with atmospheric deposition. For the highest substituted PCDD/F congeners, the air-particle uptake from plants is the principal pathway. In regions impacted by combustion emission sources, PCDD/F gas-particle partitioning is influenced by a higher concentration of particles in the air. Particles and associated particle-bound PCDD/Fs would sorb to leaf surfaces, and are subject to removal via wash off. However, in areas where emissions to air are not very notable, vapor absorption would be the principal source of vegetation pollution. The results of this investigation can have a potential interest in risk assessment studies and environmental fate models.     

Exposure of arc-furnace-plant workers to polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs)

This study aimed to evaluate serum polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) levels in electric-arc-furnace workers according to their corresponding occupational exposure. In addition, the ambient PCDD/Fs of the work environment were measured to provide additional support for the exposure and accumulation inside the electric arc furnace. The ambient PCDD/F concentrations inside the electric arc furnace were 1.557-1.917 pg-TEQ/Nm(3), 5-24 folds higher than those outside (0.080-0.385 pg-TEQ/N m(3)). In addition, higher average serum levels were measured in the workers with high occupational dioxin exposure (24.0 pg WHO-TEQ/g lipid) than in those with lower occupational dioxin exposure (13.8 pg WHO-TEQ/g lipid). Higher PCDFs/PCDDs ratios were found in serum samples from high-exposure groups than in low-exposure groups. The higher ratio of PCDFs/PCDDs was also found in ambient samples consistent with other metallurgical processes reported previously. Our results suggest that PCDD/Fs exposure exits in the smelting process of electric arc furnace, and the occupational hygiene should be taken more seriously concern in that workplace.     

PCDD/Fs in sprat (Sprattus sprattus balticus) from the Gulf of Finland, the Baltic Sea

The concentrations and congeners pattern of the polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) were determined in sprat collected by the commercial catches in the Gulf of Finland, Baltic Sea. Based on the toxic equivalent concentrations 2,3,4,7,8-PeCDF prevailed among the congeners of PCDD/Fs. The significance of age- and season-specific relationship between the concentration of lipids and dioxins was demonstrated. On lipid weight basis the concentration of PCDDs was significantly higher in spring than in autumn. This difference was not statistically significant for PCDFs. On lipid weight basis the concentration of dioxins decreased with rising content of lipids. PCDD/Fs toxic equivalent concentration increased with the age of sprat exceeding the EU maximum limit value at more than 5-year-old fish.     

Analysis of polychlorodibenzo-p-dioxins and dibenzofurans (PCDDs/PCDFs) in baked-salt food additives in Korea

Thirty-one samples of baked-salt products used in commercial food additives were analyzed for the presence of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs). Dioxins were highly detected in 12 samples of baked salts. The amount of dioxins found in the samples ranged from 12.47 pg/g to 406.56 pg/g (0.71 pg TEQ/g to 23.51 pg TEQ/g, respectively). The most abundant congeners, as TEQ values, were 2,3,4,7,8-PeCDF; 1,2,3,7,8-PeCDF; and 1,2,3,4,7,8-HxCDF in PCDF congeners and 1,2,3,7,8-PeCDD; 1,2,3,6,7,8-HxCDD; and 1,2,3,7,8,9-HxCDD in PCDD congeners. Meanwhile, PCDDs/PCDFs were analyzed in high-temperature-treated samples of natural sea salt alone and natural sea salt to which di-(2-ethylhexyl)phthalate (DEHP) had been added. In the former case, PCDD/PCDF formation was most evident at temperatures near 450 degrees C, the total amount of dioxins was 90.07 pg/g (6.07 pg TEQ/g), and PCDD congeners comprised less than 50% of the total PCDDs/PCDFs. However, when the latter samples were heated, the total PCDD/PCDF concentration was 512.30 pg/g (21.53 pg TEQ/g), with PCDD congeners comprising over 87% of the total PCDDs/PCDFs.     

Simultaneous removal of PCDD/Fs and mercury by activated carbon from a full-scale MSW incinerator in southeast China

This study emphasized on the removal performance of polychlorinated-ρ-dibenzodioxins and dibenzofurans (PCDD/Fs) and mercury by different activated carbon injection (ACI) rates from a full-scale (700 t/d) MSW incinerator. The result exhibited that the emission standard of PCDD/Fs and mercury could be met when the ACI rate reached 50 mg/Nm³ and 30 mg/Nm³, respectively. Lower chlorinated PCDD/Fs and PCDFs showed higher removal efficiencies compared with highly chlorinated PCDD/Fs and PCDDs, which could be attributed to the larger competitiveness of highly volatile congeners in AC adsorption than the lower volatile ones. AC turned out to have different adsorption selectivity for CP-routes PCDD/Fs congeners, among which 1379-TCDD was preferred to be absorbed while others exhibited little or poor selectivity for AC adsorption. The removal efficiency of PCDD/Fs was positively correlated with ACI rate at 99% confidence interval with a linear relationship (R²?=?0.98). Also, the outlet concentration of mercury decreased with the increase of ACI rate in a nearly linear function (R²?=?0.96). These results will be meaningful for the rational use of AC for pollutants control.

     

Concentration of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and dioxin-like PCBs in human adipose tissue from Turkish men

There is no previous report from Turkey on chemically determined polychlorinated dibenzo-para-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and dioxin-like polychlorinated biphenyls (PCBs) in human tissues expressed as World Health Organization (WHO) toxic equivalents (TEQs). The objective of this study was to determine the occurrence of PCDDs/Fs, and dioxin-like PCBs in the general adult Turkish population. For this reason we measured adipose tissue concentrations of PCDDs/Fs and dioxin-like PCBs in 23 Turkish men living in Ankara,Turkey in 2004. PCDD/F concentrations ranged between 3.2 and 19.7 pg WHO-TEQ/g fat (5.34 and 42.7 WHO-TEQ/g fat, respectively, including dioxin-like PCBs). The mean concentrations of WHO(PCDD/F)-TEQ and WHO(PCB)-TEQ were 9.2 and 6.67 pg/g on a lipid basis , respectively. Samples were analyzed for PCDD/F and twelve dioxin-like PCB congeners using high resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS). This study is very important since it is the first report on PCDDs/Fs and dioxin-like PCB contamination in human adipose tissue from Turkey.     

Correlation coefficients between the dioxin levels in mother's milk and the distances to the nearest waste incinerator which was the largest source of dioxins from each mother's place of residence in Tokyo, Japan

BACKGROUND: To observe the relationship between the PCDD/F and Co-PCB levels in samples of human breast milk and nearby waste incinerators in Tokyo, Japan. METHODS: Breast milk was taken from 240 mothers residing in Tokyo, Japan to measure and analyze the concentrations of polychlorinated dibenzo-p-dioxins (PCDDs; 14 congeners), polychlorinated dibenzofurans (PCDFs; 15 congeners), and coplanar polychlorinated biphenyls (Co-PCBs; 12 congeners) contained in the fat. Individual milk samples (about 50 ml) were obtained from the mothers 30 days after delivery, between the months of June and September in 1999 and 2000. A map of Tokyo was used to measure the distances between each mother's place of residence and the closest public and industrial waste incinerators. RESULTS: The distances to the nearest waste incinerators bore no apparent correlations with the congeners of PCDD/Fs and Co-PCBs. The distances were also uncorrelated with the mean toxic equivalent quantities (TEQs) of PCDD/Fs (the sum of PCDDs and PCDFs), Co-PCBs, and the total PCDD/Fs and Co-PCBs. CONCLUSIONS: Although waste incinerators were the largest source of dioxins in Japan at the time of the study, the dioxins levels of mother's milk bore no apparent relationships with the distances between the mothers' domiciles and the nearest waste incinerators. In this study, several meaningful factors were not taken into account, namely, the wind direction, the level of dioxin emitted from each incinerator, the level of environmental pollution of dioxins, and the average time the mothers stayed at home each day. A full understanding of these points awaits future studies.     

Atmospheric concentrations of PCDDs/PCDFs in southern California.

A comprehensive air toxics measurements program designed to establish baseline concentrations of atmospheric polychlorinated dioxins and dibenzofurans (PCDDs/PCDFs) in the South Coast Air Basin has been completed. The program utilized state-of-the-art air sampling and laboratory analysis techniques (HRGC/HRMS) to quantify the fifteen 2,3,7,8-substituted PCDDs/PCDFs congeners of primary toxicological significance. This study, which included nine discrete sampling sessions between December 1987 and March 1989, provides the first systematic assessment of ambient PCDDs/PCDFs concentrations in the state of California. The highest PCDDs/PCDFs concentrations noted during this study occurred in December 1987. This period was dominated by off-shore air flows, suggesting a regional air mass and transport phenomena. Concentrations of the PCDDs/PCDFs were diminished markedly in subsequent sampling sessions where air flow patterns were primarily of on-shore or of coastal origin. Ambient PCDDs/PCDFs concentrations, expressed as toxic equivalents, were highest during the December 1987 sampling period. The El Toro monitoring site, located approximately 40 miles southeast of Los Angeles, consistently showed the lowest measured ambient PCDDs/PCDFs concentrations and toxic equivalents values. In the majority of the sessions and samples examined the PCDDs/PCDFs congener profiles strongly suggest combustion source influences. Typical of combustion source profiles, 1,2,3,4,6,7,8-HpCDD was the predominant 2,3,7,8-substituted species and most prevalent PCDD after OCDD. The congener of highest toxicological significance, 2,3,7,8-TCDD, was reported below the 10-20 fg/m3 detection limit for most of the ambient air samples selected for analysis.     

Levels and congener profiles of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and dioxin-like polychlorinated biphenyls in cow’s milk collected in Campania, Italy

Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and certain dioxin-like polychlorinated biphenyls (dl-PCBs) are a family of chemically-related lipophilic compounds characterized by similar toxicity. Due to their properties they are universally distributed in the environment and classified as persistent organic pollutants (POPs). From most of studies carried out to evaluate human dietary intake, milk and dairy products result as a major contributors of PCDD/Fs uptake. Of course the main source of milk contamination is animal feeds. Lactating ruminants, cows included, transfer these compounds to the food chain by ingestion of contaminated vegetables or soil. Their resistance to degradation and a high lipophilicity means that PCDD/Fs and dl-PCBs may be accumulated into fat tissues from which they are transferred to milk during lactation period.Seventy-nine cows milk samples, collected in the monitoring plan 2008, were analyzed for PCDD/Fs and dl-PCBs. Eleven milk samples were non-compliant corresponding to five breeding livestock located in Caserta province. The distribution of PCDD/Fs and dl-PCBs congeners in these samples was examined in order to determine the likely sources of dioxins. The results show that the congener profile is characterized by a prevalence of PCDFs in respect of PCDDs, that represents the typical pattern of thermal origin contamination.     

Differential uptake for dioxin-like compounds by zucchini subspecies

The zucchini (Cucurbita pepo) cultivars 'Patty Green', 'Black Beauty', and 'Gold Rush' were cultivated on weathered dioxin-contaminated soil in pots, and concentrations of the 29 dioxin-like compounds that were assigned WHO-TEFs, three non-toxic polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs), and two non-dioxin-like polychlorinated biphenyls (PCBs) were analyzed. Toxic equivalent (TEQ) values accumulated in 'Black Beauty' and 'Gold Rush' were about 180 times higher than those in 'Patty Green'. The bioconcentration factor (BCF) based on total mass concentration of the twelve dioxin-like PCBs was higher than those of the seven PCDDs and ten PCDFs in all the cultivars. The BCFs for PCDD and PCDF congeners were negatively correlated with octanol-water partition coefficients in all the plants. No correlations were observed in PCB congeners in the high accumulators, although in 'Patty Green' the BCFs for PCB congeners were significantly correlated with octanol-water partition coefficients. Our findings suggest that the high accumulators had unknown, unique mechanisms for uptake of PCBs, whereas PCDDs and PCDFs were absorbed based on their physicochemical properties.     

Black carbon-dominated PCDD/Fs sorption to soils at a former wood impregnation site

The influence of black carbon (BC) on the sorption of 17 native polychlorinated-p-dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) was studied in five soil samples from a sawmill site where wood used to be impregnated with chlorophenol preservatives. The presence of BC caused measured total organic carbon (TOC)-water distribution ratios (K(TOC)) to be a median factor of 51 (interquartile range 18-68, n=85) higher than modeled amorphous organic carbon (AOC)-water distribution ratios (K(AOC)). K(TOC) was a factor of 73+/-27 above K(AOC) for PCDFs (n=10) and a factor of 20+/-13 (n=7) for PCDDs. The reason for this difference is probably that attaining a planar configuration after sorption to BC is less thermodynamically favorable for PCDDs than for PCDFs. BC-water distribution ratios were calculated from K(TOC), K(AOC) and BC contents, and ranged from 10(9.9) (2,3,7,8-Tetra-CDD) to 10(11.5) l kg(-1) (Octa-CDF). More than 90% of the PCDD/Fs in the soil was calculated to be BC-sorbed. Dissolved organic carbon (DOC)-water distribution ratios were measured to be in the same order of magnitude as K(AOC). This study shows that strong sorption to BC should be included when assessing ecotoxicological risk or modeling transport to groundwater of PCDD/Fs in soil.     

Formation of PCDD/Fs and PCBs in the process of production of 1,4-dichlorobenzene

The occurrence and distribution of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) in a typical process of production of 1,4-dichlorobenzene (p-DCB) were investigated systematically in this study. P5CDFs and H6CDFs were the main congeners of PCDD/Fs, while only low levels of other PCDD/Fs were detected in the samples. The concentrations of PCBs were up to 4614 ng/g in the semi-manufactured products, and 1797 ng/g in the product p-DCB. It was also found that high chlorinated PCB congeners increased with the further chlorination. The levels of PCDD/Fs decreased obviously in the purification process, while PCBs could not be removed effectively. Polychlorophenols and other important dioxin precursors (1,4-dichloro-2-phenoxybenzene and 2-phenyl-2',5,5'-trichlorophenol) were also analyzed. Polychlorophenols which ortho- and para-positions of the hydroxyl were substituted by chlorine were the main congeners. In addition, a possible pathway of the formation of PCDD/Fs and PCBs in the production of p-DCB was presented. The results of this article suggest that re-estimation on the risk of using p-DCB products, especially the products for daily use such as mothballs, is expected.     

Levels and congener profiles of PCBs and PCDD/Fs in blue shark (Prionace glauca) liver from the South-Eastern Mediterranean Sea (Italy)

Liver of blue shark (Prionace glauca) specimens from the South-Eastern Mediterranean Sea were analyzed for the presence of polychlorinated biphenyls (PCBs), including coplanar congeners, polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs). PCBs were the dominant chemicals, followed by PCDFs and PCDDs. The pattern of PCB congener concentrations in the hepatic tissue was dominated by higher chlorinated compounds. The specific profile of toxic PCDD/F congeners was characterized mainly by 2,3,7,8-TCDF and 2,3,7,8-TCDD, followed by 1,2,3,6,7,8-HxCDD and 2,3,4,6,7,8-HxCDF. The total 2,3,7,8-TCDD toxic equivalent (TEQs) was 149 pg g⁻¹ lipid wt. The profile of TEQ shows that PCDDs present the greatest risk to this species contributing to total toxicity with a percentage approximately of 60%, while the contribution of PCDFs and DL-PCBs is almost the same being 22.4% and 21.6%, respectively. Further investigations are urgently needed to characterize the PCDD/Fs contamination levels not only in elasmobranch fish but in all Mediterranean marine biota.     

Formation behavior of PCDD/Fs in PVC pyrolysis with copper oxide

Formation and decomposition behaviors of PCDD/Fs during pyrolysis of polyvinyl chloride (PVC) with CuO have been investigated. These reactions proceed simultaneously, and the rate of decomposition exceeds that of formation with further retention. More 2,3,7,8-TCDD is formed when the dechlorination of PCDD/Fs proceeds significantly. Homologue profile patterns of PCDD/Fs show that the fractions of O8CDD and H6CDFs are relatively larger within PCDDs and PCDFs, respectively. Extremely large amounts of PCDD/Fs are obtained with the long retention time at 200 degrees C. The formation of PCDD/Fs decreases drastically with increase in the molar ratio of CuO/PVC. The acceptability of thermodynamic calculations on the formation of PCDD/Fs is also investigated. The thermodynamic calculated tendency of the effect of oxygen on the formation of PCDD/Fs agrees well with the experimental results, although absolute values of the amount of PCDD/Fs are much different.     

Distribution of PCDDs, PCDFs and dioxin-like PCBs in the blood, testis and adipose tissue of suckling beef calves

To determine the distribution of persistent organochlorine compounds in beef cattle, concentrations of 2,3,7,8-substituted PCDDs, PCDFs and dioxin-like PCBs were measured in the blood, testes and adipose tissue of four two-month-old Japanese Black calves. Of 29 congeners analyzed, 19, 20 and 28 were detected in the blood, testes and adipose tissue, respectively, of three or all calves. Total toxic equivalents (TEQs) were similar in the testes and adipose tissue, and approximately two times higher than in the blood on a lipid weight basis (P<0.05). More PCDDs and PCDFs had accumulated in the testes than in adipose tissue (P<0.01), but more dioxin-like PCBs were found in adipose tissue than in the testes (P<0.0001). Accumulation patterns in the testes and adipose tissue varied among the congeners of PCDD and PCDF, whereas the patterns were similar in dioxin-like PCBs. In particular, highly substituted PCDD congeners were detected at high concentrations in the testes but at lower concentrations in adipose tissue compared with other congeners. By contrast, accumulation levels of highly substituted PCDFs were lower in both those tissues than the other congeners. In conclusion, it was demonstrated that PCDDs, PCDFs and dioxin-like PCBs leave the circulation and accumulate in the testes and adipose tissue in bovine calves. It was suggested that congeners of PCDD, especially highly substituted PCDDs, and PCDFs have a tendency to accumulate in the testis and dioxin-like PCB congeners accumulate readily in adipose tissue.     

Emission characteristics of PCDD/Fs in diesel engine with variable load rate

Emission characteristics of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in diesel engine were studied with variable load rate of the diesel engine with the emission test cycles, US D-13 mode. The load rate is changed from 25% to 50% and 75% at constant speed of 2400 rpm. PCDD/Fs concentration and phase distribution of PCDD/Fs with the isokinetic sampling of exhaust gas is obtained in this study. The average PCDD/Fs concentrations per unit of exhaust gas with 25%, 50% and 75% load rate are 14.5, 6.9 and 6.4 pg-TEQ/N m3, respectively. In all diesel engine runs, PCDFs are more prevalent than PCDDs. As a load rate is increased, the ratio of PCDDs is gradually decreased. The amount of high-chlorinated PCDDs emitted in diesel engine is larger than that of low-chlorinated PCDDs. The significant emission form of PCDD/Fs produced from diesel engines exhaust is a gas phase.     

Precipitation scavenging of particle-bound contaminants – A case study of PCDD/Fs

Precipitation scavenging of particles is a major mechanism for atmospheric deposition of organic contaminants, but there have been few field studies. We studied precipitation scavenging of PCDD/Fs with the aim of deepening understanding of environmental variables influencing this process. Bulk deposition of PCDD/Fs and their concentrations in ambient air measured at a background site in Sweden were used to calculate precipitation scavenging ratios. Contrary to expectations, increasing scavenging ratios with decreasing degree of chlorination of the PCDD/F congeners were observed when the particle-associated PCDD/F concentrations in air were used for the calculation. This was attributed to differences in temperature and thereby in the gas – particle partitioning of the PCDD/Fs between ground level and clouds where much of the particle scavenging occurs. When the particle-associated PCDD/F concentrations were recalculated for a 10–20 °C lower temperature, the scavenging ratios of the different PCDD/F congeners were similar. Hence differences between ground level and in-cloud temperature should be considered when calculating scavenging ratios from field observations and when modeling this process. The scavenging ratios averaged ～200 000, with lower values when the particle-associated PCDD/F concentration in air was lower. The soot concentration in air was a good predictor of bulk deposition of PCDD/Fs.     

PCDDs/PCDFs in ambient air (<1 fg m(-3)) - the CTDEP long term sampling (30 d) method

The Connecticut Department of Environmental Protection (CTDEP) commenced monitoring for PCDDs/PCDFs (polychlorinated dibenzodioxins and polychlorinated dibenzofurans) in ambient air in 1987 and adopted the long term (30 d) sampling approach in 1993. The CTDEP method represents the first use of isotopically labeled PCDDs/PCDFs as field surrogates to monitor the behavior of native PCDDs/PCDFs present in actual ambient air samples. This feature first introduced in 1987 was later adopted by US EPA in revisions to sampling methods for PCDDs/PCDFs in ambient air (EPA Method TO9A) as well as development of EPA Reference Method 23 for measurement of PCDDs/PCFDs in stationary source emissions. Results are provided here for a total of twenty-three (23) samples (reported as pairs) representing twelve (12) 30 d sampling events conducted at a site located in metropolitan Hartford CT. Samples were collected in winter months during calendar years 2002-2008. PCDDs/PCDFs concentration data (pg m⁻³) are reported as both congener sums (Cl₄-Cl₈) and 2378-substitued congeners. Total PCDDs/PCDFs concentrations for these twelve (12) sampling events ranged from 0.68 pg m⁻³ (2003) to 4.18 pg m⁻³ (2004) with a mean concentration of 2.04 pg m⁻³.Method performance was monitored through use of collocated samples, in field isotopically labeled compounds, isotopically labeled laboratory applied internal standards and field blank samples. Method performance consistently exceeded goals established in USEPA Method TO9A for these same parameters. Average recoveries of in field labeled PCDDs/PCDFs ranged from 97.5% to 104.2%. Average (mean) recoveries for each of the ten (10) isotopically labeled internal standards ranged from 77.0% (¹³C-OCDF) to 95.5% (¹³C-2,3,7,8-TCDF). Method precision defined as % RPD data for collocated sampler pairs ranged from 8% to 14% for PCDDs and from 5% to 12% for PCDFs. The mean RPD for all PCDDs/PCDFs combined is 9.6%. Field monitoring results demonstrate method sensitivity for all PCDDs/PCDFs congeners and 2378-substituted congeners to be well below concentrations typically found for these compounds in ambient air (all reported data represent measured concentrations). Quantities (pg) found in field blanks represent the major determinant to achieving further enhancements in method sensitivity for selected congeners (OCDD < 42 fg m⁻³; 1,2,3,4,6,7,8-HpCDD < 5.7 fg m⁻³; and 1,2,3,4,6,7,8-HpCDF < 2.1 fg m⁻³). The CTDEP method represents a highly sensitive and reliable technique for monitoring of PCDDs/PCDFs congeners and other persistent organic pollutants (POPs) at ultra trace levels in ambient air (fg m⁻³).