Quantification of polycyclic aromatic hydrocarbons and polychlorinated dibenzo-p-dioxins in human serum by combined micelle-mediated extraction (cloud-point extraction) and HPLC

Quantification of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated dibenzo-p-dioxins (PCDDs) usually requires preconcentration and cleanup prior to analysis. These procedures often involve using large amounts of toxic organic solvents. The sample preparation from serum is even more complex because of the coextraction of lipids and other nonpolar serum components. We describe the unprecedented use of cloud-point extraction to preconcentrate, extract, and clean up PAHs and PCDDs from human serum using the nonionic surfactant Triton X-100. The samples were analyzed by high-performance liquid chromatography with ultraviolet detection. The phase separation was induced by the addition of salt to the micellar serum solutions. The surfactant-rich phase was treated with acetonitrile and water to precipitate and remove some of the unwanted substances in the serum sample extract without significantly affecting the recoveries of the analytes. The favorable characteristics of cloud-point extraction discussed here strengthen its potential use as an alternative to other techniques of separation.

Selected analytical methods used at the Centers for Disease Control and Prevention for measuring environmental pollutants in serum

Blood serum is one of the more viable matrices used in assessing exposure to persistent environmental contaminants or their metabolites, especially those that are lipophilic. Analytic methods currently in use for this matrix usually involve liquid/liquid extraction followed by adsorption chromatography as a cleanup step, and low- or high-resolution gas chromatography with either electron-capture or mass spectrometric detection. The traditional analytic methods are labor intensive, have low sample throughput, and use excessive amounts of solvents and reagents. Two analytic approaches that address the requirements of modern laboratories more effectively are: 1) solid-phase extraction (SPE), used to analyze serum for several classes of compounds of environmental concern (e.g., polychlorinated biphenyls [PCBs], persistent pesticides, dioxins, furans, and coplanar polychlorinated biphenyls [CPCBs]), and 2) fast chromatography with a two-dimensional gas chromatographic system, which can be used in the determinative step for these types of analytes.

Reference range data for assessing exposure to selected environmental toxicants

We analyzed blood and urine specimens from 32 charter boat captains, anglers, and spouses from both groups, who reportedly ate fish from Lakes Michigan, Huron, or Erie, for selected environmental toxicants. The toxicants measured in serum were polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), coplanar polychlorinated biphenyls, other polychlorinated biphenyls (PCBs), and persistent pesticides. Nonpersistent pesticides and elements were measured in urine; and elements were measured in blood. Internal dose levels of these toxicants will be compared to reference range data that we have compiled. These reference range data will be used to ascertain the exposure status of individuals or groups within this study.

Quantification of polycyclic aromatic hydrocarbons and polychlorinated dibenzo-p-dioxins in human serum by combined micelle-mediated extraction (cloud-point extraction) and HPLC

Quantification of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated dibenzo-p-dioxins (PCDDs) usually requires preconcentration and cleanup prior to analysis. These procedures often involve using large amounts of toxic organic solvents. The sample preparation from serum is even more complex because of the coextraction of lipids and other nonpolar serum components. We describe the unprecedented use of cloud-point extraction to preconcentrate, extract, and clean up PAHs and PCDDs from human serum using the nonionic surfactant Triton X-100. The samples were analyzed by high-performance liquid chromatography with ultraviolet detection. The phase separation was induced by the addition of salt to the micellar serum solutions. The surfactant-rich phase was treated with acetonitrile and water to precipitate and remove some of the unwanted substances in the serum sample extract without significantly affecting the recoveries of the analytes. The favorable characteristics of cloud-point extraction discussed here strengthen its potential use as an alternative to other techniques of separation.

Pharmacokinetics of TCDD in veterans of Operation Ranch Hand: 10-year follow-up

Using multiple measurements from serum collected over 10 yr (1982, 1987, and 1992), we estimated the half-life of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in 213 veterans of Operation Ranch Hand, the Air Force unit responsible for the aerial spraying of Agent Orange in Vietnam. The potential influences of age, percent body fat, and changes in percent body fat on the half-life estimate were also examined. The mean decay rate of TCDD for these veterans is 0.0797 per year with 95% confidence interval 0.0727 to 0.0868 per year; the corresponding half-life estimate is 8.7 yr with 95% confidence interval 8.0-9.5 yr. Half-life increased significantly with increasing body fat, but not with age or relative changes in percent body fat.

Case studies of the use of biomarkers to assess exposures

Because many environmental toxicants are ubiquitous, humans are continuously exposed to them. At other times, certain populations may be more highly exposed to these toxicants from point sources. The evaluation of the degree of the exposure to either a population or an individual is frequently based on indirect surrogates of exposure, such as questionnaire data on time-activities and/or concentrations measured in environmental media. We prefer to assess the degree of the exposure to a given toxicant by measuring the concentration of the toxicant, its metabolite(s), or reaction product(s) in human specimens. Then by applying pharmacokinetic information for that toxicant, we can best reconstruct the exposure scenario. These data are then compared to reference range levels of these toxicants in the preferred biologic specimen. The development and uses of the reference range data are exemplified by case studies including potential exposure to dioxin and solvents.

Photodecomposition of 1,2,3,4- and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in water-alcohol media on a solid support

We used a hydrophobic solid support, octadecylsilylated silica gel (C18), packed in a quartz column as a reaction medium for the photolysis of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) and 1,2,3,4-tetrachlorodibenzo-p-dioxin (1,2,3,4-TCDD). When we exposed the column to a 450 W UV lamp, the adsorbed 1,2,3,4-TCDD or 2,3,7,8-TCDD in 10% 2-propanol/water decomposed completely in 20 minutes and 5 minutes, respectively. The large estimated partition coefficient of 1,2,3,4-TCDD in 10% 2-propanol/water (> 1000) indicates that on the C18 stationary phase, both the saturated hydrocarbon chains and the absorbed 2-propanol may act as proton donors and accelerate the photolysis. In direct sunlight, the adsorbed 1,2,3,4-TCDD in 10% 2-propanol/water decomposed much faster than in a nonaqueous solvent (50% 2-propanol/methanol). This solvent effect is advantageous for the practical use of the C18 photolysis process in aqueous waste treatment. We have demonstrated that complete C18 trapping with continuous photodecomposition of TCDD contained in an aqueous alcohol waste is possible.

Relation of a seafood diet to mercury, selenium, arsenic, and polychlorinated biphenyl and other organochlorine concentrations in human milk

Human transition milk was sampled from 88 mothers at the Faroe Islands, where the seafood diet includes pilot whale meat and blubber. Milk mercury concentrations (median, 2.45 micrograms/liter) were significantly associated with mercury concentrations in cord blood and with the frequency of pilot whale dinners during pregnancy. Milk selenium concentrations (mean, 19.1 micrograms/liter) correlated significantly with concentrations in cord blood but not with seafood consumption. Arsenic concentrations were very low. Twenty-four of the milk samples were separated into four pools based on fish intake and milk mercury concentrations. The polychlorinated biphenyl (PCB) concentrations (1.8-3.5 micrograms/g lipid) were high and mainly due to congener numbers 153, 180, and 138. One pool contained a congener 77 concentration of 1380 ppt, which is the highest ever reported in a human specimen for a coplanar PCB. The highest PCB concentrations were seen in the pools from women who had eaten frequent whale dinners and whose milk contained high mercury concentrations. The concentrations of chlorinated dibenzo-p-dioxins and furans were not similarly elevated. Given the advantages associated with breast-feeding, advice to nursing mothers in this population should take into regard the possible risks associated with long-term exposure to milk contaminants.

PCDD/PCDF levels in the blood of workers at a pulp and paper mill

Blood samples from 34 workers at a pulp and paper mill and from 14 control persons were analysed for 2,3,7,8-substituted PCDDs and PCDFs. There were no statistically significant differences in total lipid-adjusted PCDD/PCDF concentrations, expressed as toxic equivalents, in blood plasma between the potentially exposed bleaching plant or paper mill workers and the controls. The mean level was 61 pg/g I-TEQ in bleaching plant workers, 60 pg/g I-TEQ in paper mill workers and 49 I-TEQ pg/g in controls. Regarding the concentrations of individual isomers, however, there was an indication that the blood plasma concentrations might be affected by the living and working environment.

A remote method for simultaneous measurement of corneal thickness and curvature at a single point

Advances in refractive surgery have been limited by the measurement technology for determining corneal thickness and curvature. A measurement technique is needed that can provide a detailed corneal thickness and curvature model without contacting the cornea or obstructing the view of the surgeon or surgical equipment. The authors present preliminary results of a method to remotely measure the thickness and curvature of the human cornea at a single point. The method combines ray tracing and interferometry to estimate thickness and curvature in two orthogonal planes in an area less than 100 microns in diameter. This technique has been successfully used to provide very accurate estimates of several thin-shelled test objects. Based upon these results, recommendations are given for further improvement of the technique and extension to a multipoint cornea-modeling system.

Using biological monitoring to assess human exposure to priority toxicants

Scientifically valid exposure assessment is crucial to risk assessment, risk management, and prevention of environmental disease. Scientists have used three tools to assess exposure: exposure history/questionnaire, environmental monitoring (including personal monitoring), and biological monitoring. Combinations of these tools usually provide the exposure information needed to meet objectives of human studies evaluating the exposure-health effect relationship. Biological monitoring is a capable exposure assessment tool that has provided important information used in public health decisions. We briefly describe how risk assessment and risk management decisions for lead, dioxin, and volatile organic compounds have substantially benefited from exposure information obtained from biological monitoring.

Paternal serum dioxin and reproductive outcomes among veterans of Operation Ranch Hand

We studied whether paternal exposure to Agent Orange and its dioxin contaminant (2,3,7,8-tetrachlorodibenzo-p-dioxin) during the Vietnam War is related to adverse reproductive outcomes after service in Southeast Asia. The index cohort comprises conceptions and children of veterans of Operation Ranch Hand, the unit responsible for aerial spraying of herbicides in Vietnam from 1962 to 1971. The comparison cohort comprises conceptions and children of Air Force veterans who served in Southeast Asia during the same period but who were not involved with spraying herbicides. We found no meaningful elevation in risk for spontaneous abortion or stillbirth. In analyses of birth defects, we found elevations in risk in some organ system categories, which, after review of the clinical descriptions, were found to be not biologically meaningful. There was an increase in nervous system defects in Ranch Hand children with increased paternal dioxin, but it was based on sparse data. We found no indication of increased birth defect severity, delays in development, or hyperkinetic syndrome with paternal dioxin. These data provide little or no support for the theory that paternal exposure to Agent Orange and its dioxin contaminant is associated with adverse reproductive outcomes.

Comprehensive two-dimensional gas chromatography for the fast separation and determination of pesticides extracted from human serum

A comprehensive two-dimensional gas chromatograph with flame ionization detection was constructed and evaluated for the fast separation and analysis of pesticides. A two-stage thermal desorption modulator served as an interface between the two capillary GC columns. By controlling the temperature of the modulator chamber, all sample substances covering a wide polarity and volatility range were modulated without sample breakthrough. Orthogonal separations were achieved with a nonpolar first column and a moderately polar second column. The system allows fast separations of complex mixtures. When we used the method to analyze pesticides extracted from human samples, we achieved complete separation of 15 pesticides in less than 4 min. The flame ionization detector gave detection limits for particular pesticides that ranged from 1.8 to 3.8 pg on-column. The relative standard deviations were from 6.2% to 8.8% over the linear dynamic range.

Field-amplified sample stacking in micellar electrokinetic chromatography for on-column sample concentration of neutral molecules

On-column concentration of neutral molecules was achieved for the first time in micellar electrokinetic chromatography by means of field-amplified sample stacking. The stacking process was accomplished by dissolving the neutral analytes in a low-concentration micellar solution that was still above the critical micelle concentration. The lower total ionic strength in the sample buffer compared to the electrophoresis buffer allowed the negatively charged micelles to migrate rapidly into the boundary between the sample and the running buffer where they slow down. This field-amplified sample stacking was achieved by using normal or reversed electrode polarity and produced a 75-85-fold increase in sensitivity for 1,2,4,7- and 1,2,4,8-tetrachlorodibenzo-p-dioxins. The peak area counts obtained from the sample stacking process were proportional to the sample volume injected, and the stacking efficiency was dependent on the micellar concentration. The best stacking efficiency was obtained when the micelle concentration was slightly higher than the critical micelle concentration. When the injection volume was relatively small, the normal-polarity stacking procedure produced a higher stacking efficiency. However, when the injection volume was large, reversed polarity produced a higher stacking efficiency because the non-uniform distribution of the electrical field strength had been eliminated.

Technical and scientific developments in exposure marker methodology

Recent advances in techniques to measure markers of exposure to environmental toxicants in humans are changing the ways in which environmental scientists, epidemiologists, and policymakers characterize and interpret such exposure. In this article we review some major technical and scientific developments in exposure marker methodology for estimating internal dose, with special reference to studies conducted at the US Centers for Disease Control and Prevention. We consider important characteristics of laboratory methods, advances in laboratory technology, analytical standards, and quality assurance of laboratory measurements; comparisons with indirect methods for estimating exposures, such as exposure indices and questionnaires; human pharmacokinetic data; sampling problems; surveillance of human exposures to toxicants; and interpretation of measurements. With a view to increasing the reliability of exposure assessment, we make recommendations for obtaining more data on human exposure to toxicants.

Determinants of TCDD half-life in veterans of operation ranch hand

The half-life of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) changed significantly with body fat and age in 337 members of Operation Ranch Hand, the Air Force unit responsible for the aerial spraying of Agent Orange in Vietnam. Using paired TCDD measurements derived from serum collected in 1982 and in 1987, we investigated how TCDD half-life varied with percent body fat (PBF), relative changes in PBF, and age. We found that half-life increased significantly with increasing PBF and decreased significantly with increasing relative change in PBF and with age. The median observed half-life of TCDD for these 337 veterans is 11.3 yr with a nonparametric 95% confidence interval of 10.0-14.1 yr.

Chemical characterization and disposition studies with 1,2,7,8-tetrabromodibenzofuran in the rat

Polybrominated dibenzo-p-dioxins and dibenzofurans have been identified as potential environmental contaminants. The present studies were designed to characterize the chemical disposition of a tetrabrominated dibenzofuran. The isomer-specific pattern of 1,2,7,8-tetrabromodibenzofuran (TBDF) was chemically characterized using high-pressure liquid chromatography, gas chromatography/mass spectrometry, infrared absorption, and proton nuclear magnetic resonance techniques. The absorption, distribution, and elimination of 1,2,7,8-[4,6-3H]-TBDF were examined in the rat following a single oral, dermal, or intravenous dose of 1 nmol/kg. The 1,2,7,8-TBDF was rapidly excreted in the bile (approximately 50% of the dose in 8 h). Likewise, over half of the administered dose was found in the feces and intestine contents 24 h after iv administration and in feces 72 h after oral administration. Thus, the half-life of 1,2,7,8-TBDF is approximately 1 d. Major tissue depots included the liver, adipose tissue, and skin. The decline in hepatic concentrations observed in the iv and bile studies occurred in conjunction with metabolic elimination as well as a slight accumulation in adipose tissue. Dermal absorption of 1,2,7,8-TBDF, quantified as the amount contained in tissues (excluding the skin site) and excreta at 72 h, was estimated to be 29% of the administered dose. Thus, the general disposition profile of 1,2,7,8-TBDF in the rat is similar to that of other polyhalogenated aromatic hydrocarbons. Due to its rapid elimination, which is consistent with its predicted susceptibility to metabolic elimination, acute exposure to 1,2,7,8-TBDF would not be expected to result in the degree of toxicity associated with other more persistent congeners.

Levels of non-ortho-substituted (coplanar), mono- and di-ortho-substituted polychlorinated biphenyls, dibenzo-p-dioxins, and dibenzofurans in human serum and adipose tissue

We have measured non-ortho-substituted (coplanar) polychlorinated biphenyl (PCB) levels as well as polychlorinated dibenzo-p-dioxin (PCDD) and polychlorinated dibenzofuran (PCDF) levels in human adipose tissue and serum collected in Atlanta, Georgia. The results show that the concentrations of the coplanar PCBs can be more than an order of magnitude higher than the concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin. Our measurements in pooled serum collected in 1982, 1988, and 1989 show a decrease in coplanar PCB levels from 1982 to 1989. We found that the pattern of relative amounts of coplanar PCBs in adipose tissue varied greatly from person to person unlike the PCDD and PCDF patterns, which were more nearly the same. Age was significantly correlated with the concentrations of 2,3,7,8-TCDD,3,3'4,4'-PCB, 3,3',4,4',5-PCB, and 3,3'4,4',5,5'-PCB in adipose tissue. We also measured levels of the mono- and di-ortho chlorine-substituted PCBs in human serum. The levels for some of these PCB congeners were three orders of magnitude higher than the coplanar PCBs, PCDDs, and PCDFs. We used the international toxicity equivalency factors (TEFs) for PCDDs and PCDFs and the TEFs proposed by Safe for PCBs to calculate the 2,3,7,8-TCDD equivalents. Four PCBs (3,3',4,4',5-; 2,3',4,4',5-;2,3,3',4,4'-;2,3,3',4,4',5-) make a larger contribution than 2,3,7,8-TCDD, while four other PCBs (3,3',4,4'5,5'-; 2,2',3,4,4',5'-;2,2',4,4',5,5'-;2,2',3,4,4',5,5'-) make nearly the same contribution as 2,3,7,8-TCDD. The mono-ortho-chlorine-substituted 2,3',4,4',5-PCB, however, is the major contributor to the total 2,3,7,8-TCDD equivalents in general population samples from the United States, Sweden, and Japan.(ABSTRACT TRUNCATED AT 250 WORDS)

Current serum levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin in phenoxy acid herbicide applicators and characterization of historical levels

BACKGROUND

Workers who sprayed phenoxy acid herbicides, especially those who sprayed before 1975, may have been exposed to significant amounts of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a potent animal carcinogen present in herbicide preparations as a contaminant.

PURPOSE

The aims of this study were (a) to determine serum levels of TCDD in a representative sample of workers occupationally exposed to the agent during the spraying of phenoxy acid herbicides; (b) to compare serum levels in workers exposed before 1965, when concentrations in herbicide products were unregulated and high, with levels in workers exposed after 1974, when concentrations were lower as a result of government regulations worldwide; and (c) to examine the correlation, if any, between serum levels and duration of employment in spraying.

METHODS

Thirty-seven subjects were randomly selected from a group of 654 men who had sprayed the herbicides 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and 2,4-dichlorophenoxyacetic acid (2,4-D) in Australia for at least 12 months. The workers were classified as follows: eight who sprayed only before 1965, nine who sprayed only during the period after 1964 and before 1975, and 20 who sprayed during the period after 1974 and before 1991. Serum from the workers was analyzed for TCDD by high-resolution gas chromatography and high-resolution mass spectrometry at a detection limit of 0.6 parts per trillion (ppt) on a lipid-weight basis. In addition, rates of exposure to TCDD were estimated, as were TCDD serum concentrations at termination of employment and intensity of herbicide use.

RESULTS

Only one worker, with a serum TCDD level of 34 ppt, had a serum level higher than the maximum level of 26 ppt reported for the general population. Assuming a half-life of 7.1 years, we estimated the mean exposure rates to be 2.7, 2.3, and 0.06 ppt/mo for the three epochs, respectively. We found the highest serum level of TCDD at the time of cessation of employment to be 329 ppt. Calendar period and intensity of use of 2,4,5-T and 2,4-D were statistically significant determinants of rate of exposure to TCDD, but 2,4-D was associated with exposure rate only for the pre-1975 periods. Estimated rates prior to 1965 were more than an order of magnitude higher than those after 1974.

CONCLUSION

The highest estimated exposure rate was 20.7 ppt/mo, which suggests that some sprayers may have been exposed to levels comparable with those that produce cancer in laboratory animals.

Importance of enhanced mass resolution in removing interferences when measuring volatile organic compounds in human blood by using purge-and-trap gas chromatography/mass spectrometry

The number of volatile organic compounds (VOCs) that can be purged from human blood is so great that they cannot be separated completely by capillary gas chromatography. As a result, the single-mass chromatograms used for quantitating the target compounds by mass spectrometry have many interferences at nominal (integer) mass resolution of a quadrupole mass spectrometer. The results of these interferences range from small errors in quantitation to completely erroneous results for the target VOCs. By using a magnetic sector mass spectrometer, these interferences at nominal mass can be removed at higher resolution by lowering the ion chromatogram windows around the masses of interest. At 3000 resolution (10% valley definition), unique single-ion chromatograms can be made for the quantitation ions of the target VOCs. Full-scan mass data are required to allow the identification of unknown compounds purged from the blood. By using isotope-dilution mass spectrometry, most target VOCs can be detected in the low parts per trillion range for a 10-mL quantity of blood from which the VOCs have been removed by a purge-and-trap method.

Determining volatile organic compounds in human blood from a large sample population by using purge and trap gas chromatography/mass spectrometry

Volatile organic compounds (VOCs) are a major public health concern, because of their ubiquitous nature and the possible health effects associated with exposure to them. An analytical method has been developed that enabled the determination of parts per trillion levels of 32 VOCs in 10 mL of blood. Special efforts toward reducing blank levels and improving measurement sensitivity have resulted in an analytical method that shows excellent reproducibility and recovery even at these ultratrace levels. Results on normal human blood indicate that quantifiable levels of eleven VOCs can be found in virtually all whole blood samples. In a fraction of the samples, six other VOCs can also be determined at levels above detection limits. This method shows promise as a technique for estimating the normal baseline level of VOCs in human blood and may have future applications in cases of exposure.

Serum 2,3,7,8-tetrachlorodibenzo-p-dioxin levels of New Zealand pesticide applicators and their implication for cancer hypotheses

BACKGROUND

The phenoxyherbicide 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) has been widely used by professional pesticide applicators in New Zealand since before 1950. Epidemiologic studies of the risk of cancer and birth defects have been conducted in this group of workers, but little is known about the extent of their exposure to the 2,4,5-T contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a potent carcinogen in animals.

PURPOSE

The objective of this study was to determine whether the blood serum levels of TCDD in a group of professional 2,4,5-T applicators in New Zealand were greater than those of a matched control group not involved in 2,4,5-T spraying.

METHODS

Of 548 men employed as professional pesticide applicators in New Zealand from 1979 through 1982, nine were selected who had sprayed pesticides, although not necessarily 2,4,5-T, for at least 180 months. These applicators had sprayed 2,4,5-T for a range of 83-372 months. We measured the blood serum levels of polychlorinated dibenzo-p-dioxins and dibenzofurans, which were substituted with chlorine at the 2,3,7,8 position, in the nine pesticide applicators and in a matched group of nine control subjects.

RESULTS

The average serum level of TCDD for applicators was almost 10 times that for the matched control subjects, while the average levels of all other congeners and isomers measured in the two groups did not differ substantially. TCDD levels in eight of the nine applicators were higher than those in the control subjects (mean difference, 47.7 parts per trilion). The variation in TCDD levels among the applicators was related to their duration of work exposure to 2,4,5-T.

CONCLUSIONS

On the basis of our findings in these subjects in New Zealand, we conclude that increased risks of cancer from brief exposure to phenoxyherbicides reported in other countries are probably not attributable to the TCDD that contaminates 2,4,5-T. We cannot determine from these results, however, whether TCDD exposure from prolonged use of 2,4,5-T poses significant health risks.

Serum concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin and test results from selected residents of Seveso, Italy

2,3,7,8-Tetrachlorodibenzo-p-dioxin levels (TCDD) were measured in serum specimens from Seveso, Italy, residents, who were potentially highly exposed to the 1976 explosion, and in controls. The residents were chosen so as to represent those who did and did not develop chloracne. Levels of TCDD as high as 56,000 parts per trillion (ppt) were found in these serum specimens that were collected in 1976. These TCDD levels are the highest ever reported, and yet almost all clinical laboratory tests on these individuals were normal; any abnormal test result was only transitory in nature. These findings are unique in linking clinical histories to TCDD levels following an acute exposure.

Medical evaluation of subjects with known body levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin

Forty-one persons with a history of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure and measured adipose tissue TCDD levels were evaluated for potential health effects. No pattern of clinical abnormalities emerged related to TCDD levels.