Dietary intake of PCDD/F by small children with different food consumption measured by the duplicate method

The dietary intake of PCDD/F by 42 small children, 21 boys and 21 girls in the age range 14-47 months, with different food consumption behaviour living in urban and rural areas of Germany was measured by the duplicate method with a 7 day sampling period from May to September 1998. The PCDD/F-levels in the food duplicates were in the range 39.2-325 fg I-TEq/g(dry weight) (median: 90.7; arithmetic mean: 96.6) and the doses were in the range 0.681-5.43 with a median of 1.56 and an arithmetic mean (AM) of 1.60 pg I-TEq/(kg(body weight) x d). Children living in an urban industrialized area with food consumption including products from the family owned vegetable gardens or the surrounding area and/or products from domestic animals showed no statistically significant different concentrations in the food duplicates or in the dietary intake of PCDD/F, calculated as I-TEq, than children living in a rural area with similar food consumption behavior or than children consuming exclusively food from the supermarket.     

Decrease of PCDD/F levels in human blood from Germany over the past ten years (1989-1998)

744 whole blood samples of normal subjects from Germany collected in 1989-1998 have been analyzed for polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF) by capillary gas chromatography/high resolution mass spectrometry. Over the examined time period a continuous decrease of the PCDD/F concentrations in human blood was observed. The mean levels found were 43.7 pg I-TEq/g (lipid basis) in 1989 and 20.7 pg I-TEq/g (lipid basis) in 1996/98 [median: 42.2 and 19.4]. The reduction to about the half was found for most congeners. Each one-year subset of the collective and the entire collective shows a positive correlation of the PCDD/F blood levels with age for most of the congeners, the sum values and the calculated toxicity equivalents. For statistical evaluation a multiplicative model was used: Concentration = A x Age(B). The correlation is mostly pronounced for lower chlorinated PCDD and for 2,3,4,7,8-PentaCDF. The PCDD/F concentrations in human blood in relation to the year of examination and the age of the subjects can be described by a linear model: I-TEq [pg/g (lipid basis)] = 6176 - 3.097 x Year + 0.6482 x Age or by a multiplicative model: I-TEq [pg/g(lipid basis)] = 10(89.08-0.04415 x Year + 0.008468 x Age).     

Bioavailable DDT residues in sediments: laboratory assessment of ageing effects using semi-permeable membrane devices

We describe the reduction in bioavailability of DDT in contaminated soil after it was incubated as sediment for 365 d. Bioavailability was assessed using semi-permeable membranes. Contaminated soils from three cattle dip sites, one spiked paired uncontaminated site, and one spiked OECD standard soil were studied. Sandy soil with residues of 1880 mg/kg summation operator DDT incurred since 1962, initially had 4.6% of summation operator DDT available, reducing to 0.6% following 365 d. Clay soil (1108 mg summation operator DDT/kg) had 4.1% initially available, reducing to 0.3% after 365 d. Freshly spiked soils had a greater amount of DDT initially available (10.9%), but this reduced to 1.5% by the end of the incubation. Of the DDT congeners, both o,p'-DDD and p,p'-DDD were most bioavailable in the soils, but also had the most significant decrease following incubation.     

Correlation of PCDD/F and PCB concentrations in soil samples from the Swiss soil monitoring network (NABO) to specific parameters of the observation sites

Concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) and polychlorinated biphenyls (PCB) were determined in 23 soil samples collected at reference sites of the Swiss national soil monitoring network (NABO). Total PCDD/F and PCB concentrations are well correlated and proportional (R2=0.720). The total PCDD/F levels were between 72 and 703 ng/kg corresponding to 1.1-11 ng I-TEQ/kg, total PCB concentrations (sum of seven congeners IUPAC no. 28, 52, 101, 118, 138, 153, and 180) were from 1.1 to 12 microg/kg. In all samples, the PCDD/F and PCB concentrations were in the range of background levels for these contaminants in Central Europe. Ninteen samples revealed PCDD/F levels below the guide value of 5 ng I-TEQ/kg set by the Swiss ordinance relating to impacts on the soil (OIS); concentrations for the remaining four samples were below the trigger value (20 ng I-TEQ/kg). All PCB concentrations were below the guide value of 100 microg/kg. The elevated PCDD/F and PCB levels in some of the samples originating from forested sites could be attributed to the scavenging effect of forest canopies for semivolatile organic compounds. This interpretation could be substantiated by the observed distortion of the congener and homolog patterns of PCDD/F and PCB which is characteristic for forested sites.     

The use of ultrasound-assisted anaerobic compost tea washing to remove poly-chlorinated dibenzo-p-dioxins (PCDDs), dibenzo-furans (PCDFs) from highly contaminated field soils

The remediation of dioxin-contaminated soil of a specific coastal area previously employed for the manufacture of pentachlorophenol (PCP) in southern Taiwan’s Tainan City has attracted much attention of researchers there. This work addresses the possibility of providing an effective and environmentally friendly option for removing PCDD/Fs from soil in that field. Soil screening/sieving was first conducted to assess particle distribution. Fine sand was observed to be the major component of the soil, accounting for more than 60% of the total mass. A combination of ultrasonification and mechanical double-blade agitation was used to facilitate the washing of the soil using the biosurfactant anaerobic compost tea. More than 85 and 95% of total removal efficiencies were achieved for moderately and highly contaminated soils after 6 and 10 washing cycles, respectively, under ambient temperature, a soil/liquid ratio 1:2.5, 700 rpm, and over a relatively short duration. These results were achieved through the collision and penetration effects of this combined treatment as well as PCDD/F partitioning between the particles and anaerobic compost tea. This study represents the first to report the use of anaerobic compost tea solvent to wash soil highly contaminated by dioxin. It was concluded that anaerobic compost tea, rich in non-toxic bio-surfactants (e.g., alcohols, humic acids), can be used to improve bioavailability and bioactivity of the soil making bio-attenuation and full remediation more efficient.     

Photodegradation of polychlorinated dibenzo-p-dioxins and dibenzofurans in soil with vegetable oil

GOAL, SCOPE AND BACKGROUND: This study was carried out to investigate the effect of olive oil on the photodegradation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in contaminated sawmill soil. Previous studies had shown that the solubility of PCDD/Fs in olive oil is high and a rapid photodegradation of PCDD/Fs takes place in olive oil when irradiated with ultraviolet (blacklight) lamps. The efficiency of this treatment method was evaluated under more practical conditions. These included the use of sunlight irradiation and a lower-grade olive oil, without a preliminary extraction of soil with olive oil. METHODS: A 1-cm layer of contaminated sawmill soil was blended with 20 weight-% of olive oil and exposed to sunlight for four weeks. In another experiment, a new dose of olive oil was added at the middle of the exposure period. The PCDD/F concentrations of the soils were monitored periodically. RESULTS AND DISCUSSION: A reduction in the concentration of 2,3,7,8-chlorinated PCDD/Fs by 59% and in WHO-TEQ in contaminated sawmill soil by 48% was attained after blending the soil with two doses (20 + 20%) of olive oil and exposing the mixture to sunlight for four weeks. Photodegradation with only one dose of olive oil was less efficient. This suggests that periodical additions of olive oil would be needed to maintain a proper degradation rate. After the oil additions, the WHO-TEQ content of the soil declined with first order reaction half-lives of 19.2 to 19.7 d. The overall half-life during the four-week treatment, however, was 30 d. CONCLUSION: A significant reduction in the PCDD/F concentration of aged sawmill soil can be achieved with a relatively simple olive oil-sunlight treatment. RECOMMENDATIONS AND OUTLOOK: Some theoretical and technological questions need to be solved before using the investigated soil decontamination method in larger-scale applications. The functions of vegetable oils in photodegradation processes should be studied in more detail. The amount of oil that is needed for a proper solubilisation and photodegradation of PCDD/Fs should be minimised. Moreover, special care should be taken to prevent mobilisation of PCDD/Fs to the surrounding environment and to avoid leaving bioavailable residuals of PCDD/Fs in soil.     

Congener profiles of PCBs and PCDD/Fs in Yucheng victims fifteen years after exposure to toxic rice-bran oils and their implications for epidemiologic studies

In 1978-1979, a mass poisoning occurred in central Taiwan from rice-bran oil contaminated by heat-degraded PCBs was later called the Yucheng (oil disease in Chinese). Only a few studies have so far investigated the levels of specific polychlorinated biphenyl (PCB) or polychlorinated dibenzodioxin/furan (PCDD/F) congeners in the Yucheng victims. This study aimed to investigate the serum residual levels of thirty-three PCBs and seventeen 2,3,7,8-substituted PCDD/F congeners in the Yucheng victims 15 years after the exposure. Forty-one blood samples were collected from individual Yucheng victims in 1994-1995. The mean levels of total 33 PCBs and 17 PCDD/Fs were 2468 ng/g lipid (13.3 ng/g sample) and 6550 pg/g lipid (30.9 pg/g sample) respectively. The higher levels were found in PCBs #99, #138, #153, #156, #170, #179, and #180 among 33 PCB congeners, while 2,3,4,7,8-PeCDF, 1,2,3,4,7,8-HxCDF, and OCDD had the higher concentrations among 17 PCDD/F congeners. The total TEQ was contributed in decreasing order by 10 PCDFs (44%), three non-ortho-PCBs (24%), six mono-ortho-PCBs (20%), and seven PCDDs (12%). The mean total PCB levels and TEQ value of the 17 PCDD/Fs in the Yucheng victims 15 years after the toxic exposure were still 9 and 46 times higher than those in the general population in Taiwan. Principle component analysis (PCA) indicated that seven PCB congeners, PCBs #99, #138, #153, #156, #170, #179, and #180, accounted for 73% of the total variances in PCBs. On the other hand, six PCDD/F congeners, 2,3,4,7,8-PeCDF, 1,2,3,4,7,8-HxCDF, 1,2,3,6,7,8-HxCDF, 1,2,3,6,7,8-HxCDD, 1,2,3,4,6,7,8-HpCDF, and OCDD, accounted for 97% of the total variances in PCDD/Fs. In addition, PCA revealed that at least three characteristic patterns of congener profiles for PCBs were observed among the Yucheng victims. Similar trend was also observed for PCDD/Fs. These patterns may reflect distinctive exposure scenarios and/or different metabolizing capabilities among the Yucheng victims. We suggest that these patterns, in contrast to total PCB and PCDD/F levels, may be valuable for the future epidemiologic studies when linking exposure with specific health effect.     

Levels of PCDDs, PCDFs and PCBs in Belgian and international fast food samples

Congener-specific analyses of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) were performed on twenty-eight non-pooled fast food samples collected in Belgium, Switzerland, Czech Republic, United States of America and Australia. PCDD/F and PCB concentrations for the four investigated types of meals were very low. PCDD/F values ranged from non-detected to 1.40 pg WHO-TEQ/g fat and from 0.79 to 2.08 pg WHO-TEQ/g fat for lower and upper bound, respectively. Major contributors to the PCDD/F TEQ were 1,2,3,4,7,8-HxCDD, 1,2,3,6,7,8-HxCDD, 2,3,7,8-TCDF and 2,3,4,7,8-PeCDF. The relative contribution of PCBs to the total TEQ was 68%. For adults, an average estimated intake was 6.7 pg WHO-TEQ/kg bw/month, including consumption of all types of analyzed meals, representing 9.5% of the PTMI. For child, a value of 14.5 pg WHO-TEQ/kg bw/month was obtained, representing 20.6% of the PTMI.     

Concentration changes for 5 PCDD/F congeners after administration in beef cattle

Ten cattle were treated with daily doses of five PCDD/F congeners, over a 4 week period. Four control animals were not treated. They were subsequently slaughtered as three groups, at 5, 18 and 31 weeks after the first dose. All congeners showed an increase in concentration within animal tissues when sampled at 5 weeks post-dosing. Concentrations had reduced after 18 weeks and there was a further small reduction after 31 weeks. Halflives for each congener were calculated at 13-21 weeks (93-148 days). Concentrations of congeners were different in the various tissues analysed. At 5 weeks after dosing commenced, concentrations in sub-cutaneous fat and in perirenal fat were close to 40 ng/kg (a predicted level based on 50% absorption of the dosed compounds). Concentrations on a fat basis in muscle tissue and liver were, however, about 5 and 10 times higher, respectively. The concentrations found in muscle tissue and liver samples taken at 18 and 31 weeks were approximately twice that found in fat deposits, thus the differences were still apparent, but at a reduced level. It is possible that the distribution phase was incomplete and that PCDD/Fs remained predominantly in association with circulating blood lipids rather than in equilibrium with depot fat. It follows that if livestock were recently exposed to PCDD/Fs (for example, through the consumption of contaminated feed), the analysis of depot fats would not necessarily provide a reliable indicator of the concentrations of PCDD/Fs in edible tissues.     

PCDD/F in waste water discharges from flue gas scrubbers of waste incinerators and coal operated power plants

Scrubber water samples from different combustion plants and gypsum samples as obtained in the flue gas washing with lime water were analyzed for PCDD/F. Three of the investigated nine scrubber water samples showed PCDD/F contents between 0,4 and 11,5 ng I-TEq/1 where as in the 17 gypsum samples examined only in a few cases very low levels of HpCDD and OCDD could be detected.     

Reduction of dioxin emission by a multi-layer reactor with bead-shaped activated carbon in simulated gas stream and real flue gas of a sinter plant

A laboratory-scale multi-layer system was developed for the adsorption of PCDD/Fs from gas streams at various operating conditions, including gas flow rate, operating temperature and water vapor content. Excellent PCDD/F removal efficiency (>99.99%) was achieved with the multi-layer design with bead-shaped activated carbons (BACs). The PCDD/F removal efficiency achieved with the first layer adsorption bed decreased as the gas flow rate was increased due to the decrease of the gas retention time. The PCDD/F concentrations measured at the outlet of the third layer adsorption bed were all lower than 0.1 ng I-TEQ Nm⁻³. The PCDD/Fs desorbed from BAC were mainly lowly chlorinated congeners and the PCDD/F outlet concentrations increased as the operating temperature was increased. In addition, the results of pilot-scale experiment (real flue gases of an iron ore sintering plant) indicated that as the gas flow rate was controlled at 15 slpm, the removal efficiencies of PCDD/F congeners achieved with the multi-layer reactor with BAC were better than that in higher gas flow rate condition (20 slpm). Overall, the lab-scale and pilot-scale experiments indicated that PCDD/F removal achieved by multi-layer reactor with BAC strongly depended on the flow rate of the gas stream to be treated.     

A probabilistic model for the carry-over of PCDD/Fs from feed to growing pigs

When food producing animals are contaminated with PCDD/F congeners, information on the contaminant’s concentration in the bodies of the animals at time of slaughter is needed for risk management purposes. We have developed a mathematical model for the kinetics of PCDD/Fs in growing pigs in case of contaminated feed fed for a limited duration of time. This model allows the prediction of concentrations in body fat. It considers absorption fractions of PCDD/Fs, clearance by metabolism, dilution by growth and excretion through fecal fat. The model parameters were calibrated by fitting the model to experimental data. On the basis of this toxicokinetic model a probabilistic model has been constructed. The probabilistic model handles the parameters with appropriate probability distributions and Monte-Carlo simulation technique, providing for realistic situations with many animals and a range of contaminations and feeding intervals. We applied the new model to describe the German dioxin incident of winter 2010/2011 and discuss its viability as decision tool. The approach demonstrated here is a showcase how a risk assessment in the case of contaminated feeding can be performed.     

Evaluation of the leachability of polychlorinated dibenzo-p-dioxins and dibenzofurans in raw and solidified air pollution control residues from municipal waste incinerators

Leachability of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from raw and solidified air pollution control (APC) residues with selected solvents, including acetic acid, simulated acid rain, humic acid, linear alkylbenzene sulfonate (LAS) and n-hexane was investigated. High-chlorinated PCDD/F congeners were observed in all leachates of raw APC residue samples, with the largest total leaching concentration (61.60 ngm(-3); 0.30 ngI-TEQm(-3)) from treatment with humic acid. Low-chlorinated congeners were mainly leached with LAS and n-hexane. Solidification and stabilization (S/S) processes with cement and sulfur-containing chelating agent decreased the leachability of PCDD/Fs by up to 98% with humic acid and LAS as solvents. However, S/S processes enhanced the leachability of both high- and low-chlorinated PCDD/F congeners with n-hexane as the solvent, which largely increased the toxic equivalent quantity of leachates. These results suggest that conventional S/S processes may effectively restrain the release of PCDD/Fs when APC residues are leached with rain water or natural organic compounds (e.g., humic acid), but may have a deteriorated effect when APC residues are leached with nonpolar organic solvents (e.g., n-hexane) coexisting in the landfill sites.     

Dietary exposure to polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and polychlorinated biphenyls of the French population: Results of the second French Total Diet Study

Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) bioaccumulate through the food chain and are therefore of public health concern. Exposure to these compounds was assessed in the second French Total Diet Study (TDS). Food samples (n=583) were collected to be representative of the whole diet of the population, prepared as consumed, and analyzed. Contamination data were combined with national individual food consumption data. Mean exposure (95th percentile) to PCDD/F+DL-PCBs was assessed to be 0.57 (1.29) pg TEQ(WHO-98) (kg bw)(-1) d(-1) in the adult population and 0.89 (2.02) pg TEQ(WHO-98) (kg bw)(-1) d(-1) in the child and teenager population. Less than 4% of the population exceeded the health-based guidance value for PCDD/F+DL-PCBs. Mean exposure (95th percentile) to the six indicator PCBs (PCB 28, 52, 101, 138, 153, 180) was estimated at 2.71 (7.90) ng (kg bw)(-1) d(-1) in the adult population and 3.77 (11.7) ng (kg bw)(-1) d(-1) in the child and teenager population. Only 2.6% of the adults [CI(95%): 1.9; 3.3] and 6.5% of the children and teenagers [5.2; 7.8] exceeded the health-based guidance value for total PCBs. These results show that the contamination levels in food and therefore the exposure of the general French population to PCDD/Fs and PCBs have declined (by a factor of 3.2 for PCDD/F+DL-PCBs and about three for total PCBs) since the last evaluation, which was conducted using another methodology in 2005 and 2007, and show the efficiency of the European risk management measures which came into force after these evaluations.     

Atmospheric PCDD/F and PCB levels implicated by pine (Cedrus deodara) needles at Dalian, China

Dalian is a seaside city situated in the northeastern monsoon area of China. For the first time, levels of PCDD/F and PCB congeners in pine (Cedrus deodara) needles of Dalian urban areas were investigated. Two sampling campaigns with 17 sampling points were performed in 2002. The summation of tetra- to octachlorinated PCDD/Fs and summation of 209 PCB congeners in Dalian pine needles averaged 127+/-40 ng/kg (dry) and 4389+/-1575 ng/kg (dry), respectively. Average toxic equivalence (TEQ) for PCDD/Fs and PCBs are 2.1 and 0.4 ng/kg (dry), respectively. The pine needles can differentiate spatial variation of the pollutants. The PCDD/F and PCB levels in Dalian pine needles are low or comparable with other international regions that were not impacted by evident point sources. The data can serve as a base for long-term spatial and temporal studies of PCDD/Fs and PCBs in China.     

PCBs and PCDD/Fs in lake sediments of Grosser Arbersee, Bavarian Forest, South Germany

Despite their environmental importance, there are still relatively few historical studies of the environmental occurrence of polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), especially in middle Europe. Trends in PCBs and PCDD/Fs were, therefore, assessed in lake sediments of the Grosser Arbersee over the past 130 years (1860-1990). Ballschmiter-PCB concentrations (congeners # 28, 52, 101, 138, 153, 180) increased between 1946 and 1972 from 4.2 to 32.0 microg kg(-1) dry wt, but have since decreased to 25.6 microg kg(-1) dry wt. High chlorinated PCB congeners reached their maxima earlier (1968-1972) than low chlorinated congeners (1985-1991). These trends were consistent with patterns expected from the production and use of PCBs and their precursors. PCDD/F concentrations increased between 1950 from 0.6 microg kg(-1) dry wt to 2.3 microg kg(-1) dry wt in 1977, falling to 1.7 microg kg(-1) dry wt by 1993. PCDF concentrations exceeded those of PCDD until 1968, but afterwards PCDDs (especially OCDD) were predominant. These patterns suggest that domestic heating and waste combustion were the most likely sources, but pollution from local industries, such as metal smelting and glass production, might also have been involved. The data provide a valuable case study from central Europe which confirms the overall declining trends of PCB and PCDD/F contamination shown elsewhere.     

Destruction of PCDD/Fs by SCR from flue gases of municipal waste incinerator and metal smelting plant

Partitioning of PCDD/F congeners between vapor/solid phases and removal and destruction efficiencies achieved with selective catalytic reduction (SCR) system for PCDD/Fs at an existing municipal waste incinerator (MWI) and metal smelting plant (MSP) in Taiwan are evaluated via stack sampling and analysis. The MWI investigated is equipped with electrostatic precipitators (EP, operating temperature: 230 degrees C), wet scrubbers (WS, operating temperature: 70 degrees C) and SCR (operating temperature: 220 degrees C) as major air pollution control devices (APCDs). PCDD/F concentration measured at stack gas of the MWI investigated is 0.728 ng-TEQ/Nm(3). The removal efficiency of WS+SCR system for PCDD/Fs reaches 93% in the MWI investigated. The MSP investigated is equipped with EP (operating temperature: 240 degrees C) and SCR (operating temperature: 290 degrees C) as APCDs. The flue gas sampling results also indicate that PCDD/F concentration treated with SCR is 1.35 ng-TEQ/Nm(3). The SCR system adopted in MSP can remove 52.3% PCDD/Fs from flue gases (SCR operating temperature: 290 degrees C, Gas flow rate: 660 kN m(3)/h). In addition, the distributions of PCDD/F congeners observed in the flue gases of the MWI and MSP investigated are significantly different. This study also indicates that the PCDD/F congeners measured in the flue gases of those two facilities are mostly distributed in vapor phase prior to the SCR system and shift to solid phase (vapor-phase PCDD/Fs are effectively decomposed) after being treated with catalyst. Besides, the results also indicate that with SCR highly chlorinated PCDD/F congeners can be transformed to lowly chlorinated PCDD/F congeners probably by dechlorination, while the removal efficiencies of vapor-phase PCDD/Fs increase with increasing chlorination.     

Bioaccumulation and bioavailability of polybrominated diphynel ethers (PBDEs) in soil

Earthworms were exposed to artificially contaminated soils of DE-71 and DE-79 to investigate the bioaccumulation and bioavailability of PBDEs in soil. All major congeners were bioavailable to earthworms. The uptake and elimination rate coefficients of PBDEs decreased with their logK_ows. The biota soil accumulation factors of PBDEs also declined with logK_ow. These may be due to the large molecular size and the high affinity of PBDEs to soil particles. The concentrations extracted by Tenax for 6 h correlated very well with those found in earthworms, suggesting that the bioavailability of PBDEs in soil is related to the fraction of rapid desorption from soil. This also indicates that 6 h Tenax extraction is a good proxy for the bioavailability of PBDEs to earthworms in soil. The BSAFs of PBDEs in aged soil decreased 22-84% compared to freshly spiked soil, indicating that aging may diminish the bioavailability of PBDEs in soil significantly.     

Influence of temperature on PCDD/PCDF desorption from waste incineration flyash under nitrogen

A municipal solid waste incinerator flyash was heated to between 200 and 400 degrees C under nitrogen in a bench-scale, static bed reactor for 4 days soak time. The influence of temperature on the levels of PCDD and PCDF remaining in and desorbed from the ash were investigated using GC-MS/MS. PCDD and especially PCDF formation was seen on the flyash between 225 and 300 degrees C. Large increases in the I-TEQ of the treated ash relative to the increase in its overall PCDD/PCDF content indicated that the formation of 2378-substituted congeners was favoured over that of other substitution patterns. In the absence of a source of gaseous oxygen, formation was mainly attributed to de novo reactions involving solid phase oxygen. Dechlorination of the PCDD/PCDF in flyash became increasingly important above 275 degrees C. Maximum desorption was seen at 325 degrees C, with the equivalent of 35 wt% of the PCDD/F in the original flyash being recovered from the exhaust traps at this temperature. The desorbed species were mainly M(1)CDD/CDDF-T(3)CDD/CDDF resulting from dechlorination of higher chlorinated PCDD/PCDF, with consequently low I-TEQ values.     

Distribution of polychlorinated dibenzo-p-dioxins and dibenzofurans in suspended sediments, dissolved phase and bottom sediment in the Houston Ship Channel

Spatial distributions of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) in the water column and bottom sediments of the Houston Ship Channel in Texas were measured three times over a 1-year period. Total TEQ concentrations in water ranged from 0.01 to 0.25 pg/l for the dissolved phase and from 0.09 to 2.91 pg/l for the suspended phase, while TEQ concentrations in bottom sediments varied from 0.9 to 139.8 ng/kg dry wt. The dissolved concentrations were lower than their respective suspended concentrations, with average dissolved/suspended ratios between 0.11 and 0.59 for individual congeners. More than 89% of the total concentration of 2378-substituted PCDD/PCDFs was attributable to OCDD but 2378-TCDD was the major contributor to total TEQ for the three sampled media. Average logs of organic carbon-normalized suspended sediment-dissolved partitioning coefficients (logK(oc)(obs)) varied between 4.92 and 8.59 l/kg-oc; while in the bottom sediment-dissolved interface, logK(oc)(obs) values ranged from 5.48 to 8.48 l/kg-oc. Observed logK(oc)values varied within a factor of 0.64-1.26 from equilibrium logK(oc) values, suggesting fluxes of PCDD/PCDFs across the interfaces. It was found that in the HSC, on average, the tendency of a compound to move from the particulate phase to the dissolved phase decreases with increasing K(ow).