Partitioning of dioxins and dibenzofurans: Whole blood, blood plasma and adipose tissue

It has become relatively common to estimate human dioxin body burden and to document dioxin exposures by measuring dioxin and dibenzofuran congeners in adipose tissue, whole blood or blood plasma, and reporting these values on a lipid basis. It has not been determined whether these three types of specimens contain identical dioxin and dibenzofuran levels. This paper compares paired plasma and adipose tissue and paired whole blood and adipose tissue in analyses from two groups of patients. The first group consists of twenty U.S. veterans with paired plasma and adipose specimens. The second group consists of four German adults with whole blood compared to adipose tissue. Forty-eight analyses were performed. The results suggest that for some higher chlorinated compounds, such as OCDD, plasma lipid values may be higher than adipose lipid values, but whole blood lipid values for the higher as well as lower chlorinated PCDD/Fs may be relatively similar. On the other hand, the values for the lower chlorinated PCDD/Fs, such as TCDD, are similar in blood plasma, adipose tissue and whole blood. Total PCDD/F dioxin “toxic equivalents” are similar within each of the two series reported here, using the current “International Dioxin Toxic Equivalent” system.     

Apportionment of TEQs from four major dioxin sources in Japan on the basis of five indicative congeners

The major sources of dioxins (polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and dioxin-like polychlorinated biphenyls (DL-PCBs)) in the environment in Japan have been considered to be combustion by-products, pentachlorophenol (PCP) formulations, chlornitrofen (CNP, 4-nitrophenyl-2,4,6-trichlorophenyl ether) formulations, and PCB products. Data on PCDDs, PCDFs and DL-PCBs from the four sources were analyzed, and indicative congeners whose concentrations were highly correlated with WHO-2006 toxic equivalencies (TEQs) were identified for each source sample. The indicative congeners for combustion by-products, PCP formulations, and CNP formulations were 2,3,4,7,8-pentachlorodibenzofuran, 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin, and 1,2,3,7,8-pentachlorodibenzo-p-dioxin, respectively; for PCB products, the indicative congeners were IUPAC Nos. #126- and #105-pentachlorobiphenyls. Moreover, using the data on PCDDs, PCDFs and DL-PCBs, we developed a set of equations for estimating the apportionment of TEQs from the four sources by using only the concentrations of the above-mentioned five indicative congeners. The equations were used along with the analysis results of different types of environmental samples collected from Japan, to determine the TEQ contributions of the four sources. The obtained values of TEQ contributions seemed to be reasonable. The estimation method was developed by using the data on major dioxin sources in Japan, and therefore, it is generally adaptable to environmental samples from any part of Japan. The method may be usable for regions outside Japan if source identification is carried out and the estimation equations are modified appropriately.     

Dioxin and dibenzofuran concentrations in blood of a general population from Tarragona, Spain

The concentrations of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) were determined in plasma samples of 20 nonoccupationally exposed subjects living in the vicinity of a new hazardous waste incinerator (HWI), now under construction in Tarragona (Catalonia, Spain). The mean PCDD/F value was 27.0 pg I-TEQ/g lipid with a range from 14.8 to 48.9 pg I-TEQ/g lipid. All samples showed higher PCDD than PCDF levels. Although PCDD/F concentrations were higher in women (27.7 pg I-TEQ/g lipid) than in men (25.2 pg I-TEQ/g lipid), the difference was not statistically significant. While a significant correlation (r = 0.565, p < 0.01) between the age of the subjects and the levels of PCDD/F in plasma could be observed, no significant differences were found in relation to the specific residential area. The plasma concentrations of PCDD/F obtained in the current study are discussed and compared with the results of similar investigations reported in the last two years.     

Partitioning and removal of dioxin-like congeners in flue gases treated with activated carbon adsorption

Activated carbon adsorption is commonly used to control dioxin-like congener (PCDD/Fs and PCBs) emissions. Partitioning of PCDD/Fs and PCBs between vapor and solid phases and their removal efficiencies achieved with existing air pollution control devices (APCDs) at a large-scale municipal waste incinerator (MWI) and an industrial waste incinerator (IWI) are evaluated via intensive stack sampling and analysis. Those two facilities investigated are equipped with activated carbon injection (ACI) with bag filter (BF) and fixed activated carbon bed (FACB) as major PCDD/F control devices, respectively. Average PCDD/F and PCB concentrations of stack gas with ACI+BF as APCDs are 0.031 and 0.006ng-TEQ/Nm(3), and that achieved with FACB are 1.74 and 0.19ng-TEQ/Nm(3) in MWI and IWI, respectively. The results show that FACB could reduce vapor-phase PCDD/Fs and PCBs concentrations in flue gas, while the ACI+BF can effectively adsorb the vapor-phase dioxin-like congener and collect the solid-phase PCDD/Fs and PCBs in the meantime. Additionally, the results of the pilot-scale adsorption system (PAS) experimentation indicate that each gram activated carbon adsorbs 105-115ng-PCDD/Fs and each surface area (m(2)) of activated carbon adsorbs 10-25ng-PCDD/Fs. Based on the results of PAS experimentation, this study confirms that the surface area of mesopore+macropore (20-200A) of the activated carbon is a critical factor affecting PCDD/F adsorption capacity.     

Mono- to tri-chlorinated dibenzodioxin (CDD) and dibenzofuran (CDF) congeners/homologues as indicators of CDD and CDF emissions from municipal waste and waste/coal combustion

Total homologue concentrations and select congener concentrations from amongst the mono- to tri-chlorinated dibenzodioxins (CDDs) and dibenzofurans (CDFs) are used to model both Total (mono- to octa-) CDD + CDF emissions and the toxicity equivalent (TEQ) of the 2,3,7,8-chlorine-substituted emissions. Analysis of emission data from two facilities indicates that use of total homologue concentrations shows limited, facility-specific correlations with Total CDDs/CDFs and TEQ. Concentrations of select mono- to tri-CDD/CDF congeners show promising correlation with CDD/CDF TEQ across facilities, suggesting that these compounds can act as TEQ indicators.     

Assigning concentration values for dioxin and furan congeners in human serum when measurements are below limits of detection: an observational approach

Concentrations of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) in dietary sources for humans have been declining over the previous two decades. These declines have been accompanied by decreases in concentrations of these compounds in humans, as evidenced by measurements in blood and milk. Because of the decreasing concentrations of PCDD/PCDFs in the environment and in humans, measuring PCDD/PCDF congeners in humans has become increasingly difficult, despite advances in analytic methods. An observational approach was recently described to address the quandary of non-detectable results in determining toxic equivalents. This approach, called the congener ratio approach, is specifically for cases where concentrations of 2,3,7,8-TCDD (TCDD) are below the limit of detection (LOD), and where concentrations of 1,2,3,7,8-pentachlorodibenzo-p-dioxin (PeCDD) are equal to or above the LOD. Development of this approach relied on evaluating data on measured concentrations of TCDD and PeCDD in human serum from the general population. The congener ratio approach for TCDD and PeCDD was based on the concentration of TCDD being approximately 40% that of PeCDD in serum from the general population. Additional analyses presented here reveal that when concentrations of both congeners are above the LOD, the data appear to generally support the congener ratio approach for TCDD and PeCDD, with the caveat that gender may affect the ratio. However, the TCDD/PeCDD relation is less clear when TCDD is less than the LOD; in this situation, the relation overpredicts levels of TCDD approximately 80% of the time for the 2001-2002 NHANES database. Using the congener ratio approach for other PCDD/PCDF congeners requires assessing the correlation and the frequency of detection for both TCDD and PeCDD.     

热等离子体处理前后垃圾飞灰中重金属浸出浓度的变化及二恶英分布特性的差异

为探究热等离子体处理飞灰工艺工业应用的潜力,分析处理前后飞灰中9种重金属浸出浓度变化及二恶英的分布特性,基于处理量为5 t·d⁻¹的中试规模的热等离子体熔融系统,在1 550 ℃的处理温度下进行了飞灰处理实验。结果表明,不宜使用硫酸硝酸法检测玻璃态渣中As浸出浓度,硫酸根离子会与As在熔融过程中形成的砷酸钙和亚砷酸钙中的钙离子结合,导致As的浸出浓度增加;熔融处理后,除As外的其他重金属的浸出浓度均降至国家标准浓度限值以下;就太原地区而言,其垃圾飞灰中PCDFs的含量高于PCDDs,且低氯代呋喃含量高于高氯代呋喃;熔融处理后的垃圾飞灰中,二恶英毒性当量减少率为99.96%,降至0.546 6 ng·kg⁻¹,远低于填埋标准中二恶英排放限值,说明该中试系统能够满足飞灰处理要求。该研究结果可为热等离子体熔融飞灰中试系统的工业应用提供参考。     

Influence of the chemical structure on mobility of PCB congeners in female and male sardine (Sardina pilchardus) from Portuguese coast

Concentrations of 30 polychlorinated biphenyl congeners (CBs) were determined in muscle, liver and gonad tissues of female and male sardines (Sardina pilchardus) collected in February-May 2000 and September-January 2001 from purse seine vessels operating around Peniche, Portugal. The determined CBs were aggregated in four groups (I, II, III and IV), according to similarities of their chemical structures. Muscle and liver of males contained significantly higher concentrations of groups I and II than females during the final period of spawning (February-April). A less contrast was observed for the groups III and IV. This seasonal fluctuation associated with the spawning indicates that female sardines regulate the excess of CBs sequestrated during fatten period. On the contrary, levels of groups I and II were higher in males than in females indicating slower mobility of these compounds as lipids were consumed during the final period of spawning. The deficient regulation of those CBs in muscle of male sardines can not be attributed to selective transfer to gonads and subsequent excretion. Although the full explanation was not found for the different mobility of PCBs with the gender, the results provide evidence of slower elimination of group I and II congeners in male sardines.     

Depletion of selected polychlorinated biphenyl, dibenzodioxin, and dibenzofuran congeners in farmed rainbow trout (Oncorhynchus mykiss): a hint for safer fish farming

Farmed fish can be exposed to persistent organic contaminants--such as polychlorinated biphenyls (PCBs), dibenzodioxins (PCDDs), and dibenzofurans (PCDFs)--via feed, this eventually resulting in accumulation levels of health concern. To study the correlation between feed contamination, chemical accumulation in fish muscle (fillet), and chemical depletion, an all-vegetal base (or blank) feed was prepared and fortified with a commercial PCB mixture (Aroclor 1254) and six PCDD and PCDF congeners (namely, 2,3,7,8-T(4)CDD, 2,3,7,8-T(4)CDF, 1,2,3,7,8-P(5)CDD, 1,2,3,7,8-P(5)CDF, O(8)CDD, and O(8)CDF) to reproduce realistic low, medium, and high contamination levels. After a 1-month exposure, trout (Oncorhynchus mykiss) were fed with the blank feed and sacrificed every 0.5 months over a 3-month period from exposure end; fillet specimens were sampled at each time. In all groups, the average fish weight increased linearly through the observation period. The chemical diminishing patterns observed were due to the combined effect of clearance and growth dilution: for 10 PCB and four PCDD and PCDF congeners, patterns were described with an empirical one-compartment (fish muscle) model. The canonical pseudo-first-order kinetic equation used was also modified into the form C=[C(0)exp(-k(C)t)] (m(W)t+1)(-1) to distinguish between the contributions to depletion from clearance, exp(-k(C)t), and growth dilution, (m(W)t+1)(-1). Most mean clearance half-life (HL(C)) estimates appear to be greater than 4 months, in a number of cases reaching magnitudes well over 10 months or even negative, thus clearly indicating a non-negligible contribution from a second compartment. Based on means and their 95% confidence intervals, the depletion HL(D) estimates of the 14 selected congeners seem to be comprised between 1.2-3.4 and 1.0-5.0 months, respectively: these values, accounting for both clearance and growth dilution, provide an indication of the relevance of a blank feed as a management option to reduce the overall PCB, PCDD, and PCDF content in farmed trout. Due to a lack of bioaccumulation, O(8)CDD and O(8)CDF yielded no results for evaluation, whereas for many PCB congeners results were insufficient for empirical modelling.     

Dioxin and dibenzofuran concentrations in adipose tissue of a general population from Tarragona, Spain

Polychlorinated dibenzo-p-dioxin (PCDD) and polychlorinated dibenzofuran (PCDF) levels were determined in adipose tissue of 15 autopsied subjects who at the time of death had lived in the city of Tarragona (Catalonia, Spain) and surroundings during at least the last 10 years. PCDD/F concentrations ranged between 13.37 and 69.37 ng I-TEQ/kg fat, with mean and median values of 30.98 and 26.30 ng I-TEQ/kg fat, respectively. PCDD/F concentrations were higher (p < 0.01) in women (mean value: 44.95 ng I-TEQ/kg fat) than in men (mean value: 24.00 ng I-TEQ/kg fat). Although individuals living in industrial areas showed higher PCDD/F levels than those living Tarragona downtown the difference was not statistically significant. When Principal Component Analysis was applied to the concentrations of PCDD/Fs found in the 15 adipose tissue samples together with those found in 20 blood samples collected in a previous study, a single two-dimensional model was obtained, which would explain 62.9% of the variance in the data. The PCDD/F concentrations in adipose tissue found in the current study are of the same order of magnitude than those reported for most industrialized countries.     

The reduction of dioxin emissions from the processes of heat and power generation

The first reports that it is possible to emit dioxins from the heat and power generation sector are from the beginning of the 1980s. Detailed research proved that the emission of dioxins might occur during combustion of hard coal, brown coal, and furnace oil as well as coke-oven gas. The emission of dioxins occurs in wood incineration; wood that is clean and understood as biomass; or, in particular, wood waste (polluted). This paper thoroughly discusses the mechanism of dioxin formation in thermal processes, first and foremost in combustion processes. The parameters influencing the quantity of dioxins formed and the dependence of their quantity on the conditions of combustion are highlighted. Furthermore, the methods of reducing dioxin emissions from combustion processes (primary and secondary) are discussed. The most efficacious methods that may find application in the heat and power generation sector are proposed; this is relevant from the point of view of the implementation of the Stockholm Convention resolutions in Poland with regard to persistent organic pollutants.     

The relation between levels of selected PCB congeners in human serum and follicular fluid

Individual congener and total PCB concentrations were determined in serum and follicular fluid obtained from women undergoing assisted reproductive technologies (in-vitro fertilization and embryo replacement). Although the mean individual PCB levels revealed varying degrees of contamination, the results fall in the same range as that observed by other investigators. Except for PCB 118, correlations between levels in serum and follicular fluid were strong, and statistically significant at p < 0.05. Moreover PCB 153, a major and very stable PCB congener has been shown to correlate to the total amount of PCBs (r = 0.994, and r = 0.987, for serum and follicular fluid, respectively). The same accumulation patterns of PCBs for serum and follicular fluid have been observed.     

Effects of dietary habits and CYP1A1 polymorphisms on blood dioxin concentrations in Japanese men

The major source of dioxin impurities in Japan in the past was agrochemical formulations; more recently, it has been exhaust from waste incinerators. To examine the environmental and genetic factors that influence blood dioxin concentration, we investigated the relationship among dioxin concentrations, dietary habits and cytochorome P450 1A1 (CYP1A1) polymorphisms (MspI type and Ile-Val type) in Japanese fishermen and farmers, including also a group of office workers as controls. The mean dioxin concentrations in the fishermen, the farmers and the controls were 161369, 79079 and 100500 pg/g fat, respectively. The elevated dioxin concentration with polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and coplanar-PCBs found in the fishermen may be due to the frequent consumption of fish; no such relationship was found both in the farmers and the controls. We found that the concentrations of congeners found as impurities in certain chemicals such as those previously used in agriculture showed no significant differences among the three groups; we consider it unlikely that the farmers would be directly exposed to dioxins from such chemicals. Thus, it is probable that the primary route of dioxin exposure in the Japanese population is through the food chain via fish consumption, regardless of occupation. No meaningful relationship between blood dioxin concentration and CYP1A1 polymorphisms was found in this study, although there was a significant difference between the concentration of total non-ortho-PCBs in genotypes A and B. Further studies on more subjects, including those of genotype C, are needed to confirm the relationship between blood dioxin concentrations and MspI polymorphisms.     

Elimination of 10 polybrominated diphenyl ether (PBDE) congeners and selected polychlorinated biphenyls (PCBs) from the freshwater mussel, Elliptio complanata

Mussel biomonitors are widely used as screening tools for polybrominated diphenyl ethers (PBDEs) in marine and aquatic environments. This study determined elimination rate coefficients (k(tot)) for eight PBDE and five PCB congeners in the freshwater mussel, Elliptio complanata, over a 120d depuration period. Elimination of BDE 15, 28, 47, 75 and 100 was similar to PCBs of equivalent hydrophobicity and negatively related to chemical K(OW). Rapid elimination of BDE 190 and an inferred rapid elimination of BDE 183 indicate mussels are capable of biotransformation of certain highly brominated PBDEs. Time to 90% steady state ranged from 48 to 66d for di- and tribromoDE congeners and from 91 to >250d for tetra- to hexabromoDE congeners. Given the long time periods required for steady state, mussel accumulated PBDE residues should be interpreted in the context of calibrated bioaccumulation models.     

Relations between PM10 composition and cell toxicity: a multivariate and graphical approach

Previous studies have used particle mass and size as metrics to link airborne particles with deleterious health effects. Recent evidence suggests that particle composition can play an important role in PM-toxicity; however, little is known about the specific participation of components (individually or acting in groups) present in such a complex mixture that accounts for toxicity. This work explores relationships among PM(10) components in order to identify their covariant structure and how they vary in three sites in Mexico City. Relationships between PM(10) with cell toxicity and geographical location were also explored. PM(10) was analyzed for elemental composition, organic and elemental carbon, endotoxins and the induction of inhibition of cell proliferation, IL-6, TNFalpha and p53. PM(10) variables were evaluated with principal component analysis and one-way ANOVA. The inhibition of cell proliferation, IL-6 and TNFalpha were evaluated with factorial ANOVA and p53 with the Welch test. The results indicate that there is heterogeneity in particle mass, composition and toxicity in samples collected at different sites. Multivariate analysis identified three major groups: (1) S/K/Ca/Ti/Mn/Fe/Zn/Pb; (2) Cl/Cr/Ni/Cu; and (3) endotoxins, organic and elemental carbon. Groups 1 and 3 showed significant differences among sites. Factorial ANOVA modeling indicated that cell proliferation was affected by PM concentration; TNFalpha and IL-6 by the interaction of concentration and site, and p53 was different by site. Radial plots suggest the existence of complex interactions between components, resulting in characteristic patterns of toxicity by site. We conclude that interactions of PM(10) components determine specific cellular outcomes.     

Concentrations and distribution of 3,3'-dichlorobenzidine and its congeners in environmental samples from Lake Macatawa

Release of 3,3'-dichlorobenzidine (DCB), an intermediate in dye manufacturing processes, is of environmental concern due to its carcinogenic nature. An 11-year field study has been conducted to elucidate the fate and behavior of DCB and its congeners in the Lake Macatawa (Holland, MI, USA) sediment-water system. The sediments were variable in composition, ranging from sandy sediments with 1-8.7% total organic carbon (OC) to silty-clay sediments with 7.5-20.6% total OC. The pH ranged from 6.3 to 7.4. The findings from this field study confirmed that DCB and its congener, benzidine, are transported over long distances. The concentration of DCB in the water phase was found to be from non-detectable to approximately 1300 times greater than the water quality criteria established for DCB (0.021 microg/l). Its congener, benzidine, which is substantially more toxic for humans than its parent compound has been found up to approximately 12300 times higher levels than the EPA guidelines suggest (0.000086 microg/l). Both DCB and benzidine were found in the sediment phase. DCB was observed at almost 70 mg/kg in a sample collected in 1993. The concentrations in both phases have declined in recent years. To assess the threat of the released pollutants, it is necessary to understand how pollutants tend to behave in various media. Therefore, it is crucial to identify and quantify all sources of the chemical and its congeners in order to meaningfully predict the fate (and transport) of a hydrophobic organic compound (HOC) in the environment.     

Assessment of polychlorinated dibenzo-p-dioxin and dibenzofuran emissions from a hazardous waste incineration plant using long-term sampling equipment

The aim of this work is to evaluate the performance of a continuous monitoring system for the analysis of the mass concentration of PCDD/Fs from stationary sources. Data was acquired from a modern, state of the art, hazardous waste thermal treatment plant for a period of more than 2 years using a commercial available continuous monitoring system. The study consisted of a total of 16 samples, collected in periods from 1 week to 2 months resulting in an average of 360 m³ sampled flue gas per sample. The study showed the system was able to confirm that for a period of more than 2 years the plant was complying with the limit of 0.1 ng I-TEQ/Nm³. In addition, the data showed the typical fingerprint of such installations which is useful for example in impact studies. Long-term samples were compared to five short-term samples (6 h) collected every 6 months during the study period. Principal component analysis was applied to PCDD/Fs obtained data as useful statistical tool to find out trends and similarities between different samples. Improvement in terms of representativeness of data was achieved through continuous assessment since the starts of the project. The obtained data was further used to determine the emission factor for this activity and the total annual PCDD/Fs release to the atmosphere.     

Partitioning of Cd and Pb in the blood of European blackbirds (Turdus merula) from a smelter contaminated site and use for biomonitoring

Blood composition is commonly measured to assess exposure to and effects of metals on birds. In most of passerine species, only small volumes of blood may be sampled safely (<500 μL), which limit the measure of several markers of health status and chemical residues. Here, we documented the partitioning of Cd and Pb in the blood of European Blackbirds Turdus merula in order to propose usable relationships between whole blood concentrations (for which toxicological benchmarks exist) and those measured in the erythrocytes. Sixty-two blackbirds were trapped along a pollution gradient (smelter of Metaleurop Nord, Northern France). Blood was sampled and Cd and Pb concentrations were measured both in whole blood and in the erythrocytes only. Birds coming from the most contaminated sites exhibited high residues for both Cd and Pb. We assessed that 73% and 99% of Cd and Pb, respectively, were associated to erythrocytes. Strong linear relationships, that were not influenced by neither the age nor the sex, were established between whole blood residues and those of erythrocytes for Cd and Pb (adj-R² = 0.78 and 0.93, respectively). Present findings are promising to optimize the use of small blood samples in order to investigate several responses relative to wildlife health status.     

Atmospheric oxidation mechanisms of polychlorinated dibenzo-p-dioxins are different from those of benzene and dibenzofuran: a theoretical prediction

The reaction mechanisms of dibenzo-p-dioxin (DD) and 2,3,7,8-TCDD with OH radical have been studied using density functional theory calculations. Under the atmospheric conditions, ca 42% of DD + OH reaction proceeds as formation of DD − OH-β adduct, which will react with O₂ slowly; while the rest will proceed as formation of DD − OH-γ adduct, which will decompose to the substituted phenoxy radical P1 by the fused-ring C-O bond cleavage. For 2,3,7,8-TCDD + OH, the reaction will predominantly form the substituted phenoxy radical P2. The reaction mechanisms are drastically different from the peroxy mechanism for the atmospheric oxidations of benzene and dibenzofuran.     

Chlorinated dibenzo-p-dioxin and dibenzofuran levels in human adipose tissue and milk samples from the north and south of Vietnam

Although 2,3,7,8-TCDD has been found to be extremely toxic to a variety of laboratory aminals, human epidemiology studies, where exposure to 2,3,7,8-TCDD has been less well characterized than in animal toxicologic studies, have been less conclusive in characterizing the extent of toxicity. In order to determine whether the newly refined techniques of human adipose tissue biopsy including isomer specific and sensitive measurement of PCDDs and PCDFs might be able to assist in finding populations within the same country with high and low levels of dioxins, adipose tissue samples were taken and levels analyzed from the north and south of Vietnam. It seemed reasonable, based on previous work, that high levels of 2,3,7,8-TCDD might still be found in adipose tissue in selected patients living in areas sprayed with Agent Orange and other 2,3,7,8-TCDD containing herbicides, and that lower levels should be found in patients not exposed to 2,3,7,8-TCDD from herbicides or other sources, such as persons who had always resided in the north of Vietnam. Of 9 specimens from patients hospitalized in Hanoi who had never been south, none had detectable adipose tissue levels of 2,3,7,8-TCDD at a detection limit of 2 or 3 ppt on a wet weight basis. Of 15 specimens from Ho Chi Minh City hospitalized patients the mean of positive specimens (12 of 15) was 28 on a lipid basis. The mean of the positive values from the south is about 2 to 3 times higher than found in the North American Continent control patients where the mean is about 6–10 ppt and much higher than in the north of Vietnam. In the northern specimens, the levels were non-detectable with a sensitivity of between 2 and 3 ppt. Other PCDD and PCDF isomers not found in Agent Orange, the penta- through octachlorinated dibenzo-dioxins and dibenzofurans, were similar in isomer type and quantity in the south of Vietnam to what we previously reported in North America. Adipose tissue from the north of Vietnam contained the lowest levels of four through eight chlorinated dioxins and furans thus far reported. The initial data suggests that populations exist in the south of Vietnam with elevated levels of 2,3,7,8-TCDD at the present time, fourteen years after the last known 2,3,7,8-TCDD (Agent Orange) application, superimposed on a preexisting body burden of dioxins and dibenzofurans from sources other than Agent Orange such as technical grade pentachlorophenol or products of incineration contaminated with higher chlorinated PCDDs or PCDFs. In light of the recent finding that unexpected levels of PCDDs and PCDFs exist in the general adult population of industrialized countries, ca. 1,000 to 1,200 ppt, wet weight of total dioxin and furan isomers in adipose tissues, it seems reasonable that the extent of human toxicity of dioxins may be more readily characterized in Vietnam than in industrialized countries. Because 2,3,7,8-TCDD was applied in 1962–1970, although not yet cleaned up, the levels of 2,3,7,8-TCDD in the environment, the food chain, and in humans, would be expected to decrease with time. Therefore, if studies are not initiated in a timely fashion, the opportunity to better characterize the extent of the toxicity of TCDD to humans as well as the persistence of TCDD in the environment in Vietnam may be lost.