THE DEVELOPMENT OF A HIGH-RESOLUTION MASS SPECTROMETRY METHOD FOR ULTRA-TRACE ANALYSIS OF CHLORINATED DIOXINS IN ENVIRONMENTAL AND BIOLOGICAL SAMPLES INCLUDING VIET NAM ERA VETERANS.

Chlorinated dioxins are labeled and recognized by both the World Health Organization and the United Nations Environmental Programme (UNEP) as "persistent organic pollutants". Their potential for high toxicity is one of the primary factors behind intense public and regulatory scrutiny and the need to measure the compounds at very low limits, specifically the isomer 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD). This article highlights the early mass spectrometry methods to investigate, detect, confirm, and quantify chlorinated dioxins and the initial applications involving human biomonitoring, as attempts were made to attribute health effects to TCDD exposure. This effort represented a complex and difficult scientific response to the pressing need to investigate expected exposures and alleged subsequent medical effects, which in the case of the Viet Nam veterans was being attempted a decade or more after their exposure. It is noteworthy that this method and its development touched on delicate issues involving human subjects, war veterans, environmental contamination, and was difficult not only scientifically, but for ethical and political reasons as well. Stable-isotope dilution with analysis by gas chromatography/high-resolution mass spectrometry (GC/HRMS) became the method of choice because of its ability to monitor characteristic ions and isotope ratios to quantify and qualify/confirm the analyte in the presence of coextracting and coeluting interferences at these low levels with the highest possible confidence. This method was rigorously tested and validated before it was used to discover and monitor levels in the environment and in various populations at then unprecedented low levels. These early studies demonstrated the feasibility of monitoring dioxins in humans even decades after exposure, and led to the detection of 2,3,7,8-TCDD in the general population as well as specific overexposed populations. These studies also provided strong evidence regarding the origins of the 2,3,7,8-isomer in the environment. © 2020 John Wiley & Sons Ltd. Mass Spec Rev.

Identifying Phlorofucofuroeckol-A as a Dual Inhibitor of Amyloid-ß25-35 Self-Aggregation and Insulin Glycation: Elucidation of the Molecular Mechanism of Action.

Both amyloid-ß (Aß) and insulin are amyloidogenic peptides, and they play a critical role in Alzheimer's disease (AD) and type-2 diabetes (T2D). Misfolded or aggregated Aß and glycated insulin are commonly found in AD and T2D patients, respectively, and exhibit neurotoxicity and oxidative stress. The present study examined the anti-Aß25-35 aggregation and anti-insulin glycation activities of five phlorotannins isolated from Ecklonia stolonifera. Thioflavin-T assay results suggest that eckol, dioxinodehydroeckol, dieckol, and phlorofucofuroeckol-A (PFFA) significantly inhibit Aß25-35 self-assembly. Molecular docking and dynamic simulation analyses confirmed that these phlorotannins have a strong potential to interact with Aß25-35 peptides and interrupt their self-assembly and conformational transformation, thereby inhibiting Aß25-35 aggregation. In addition, PFFA dose-dependently inhibited d-ribose and d-glucose induced non-enzymatic insulin glycation. To understand the molecular mechanism for insulin glycation and its inhibition, we predicted the binding site of PFFA in insulin via computational analysis. Interestingly, PFFA strongly interacted with the Phe1 in insulin chain-B, and this interaction could block d-glucose access to the glycation site of insulin. Taken together, our novel findings suggest that phlorofucofuroeckol-A could be a new scaffold for AD treatment by inhibiting the formation of ß-sheet rich structures in Aß25-35 and advanced glycation end-products (AGEs) in insulin.

Physiologically based pharmacokinetic toolkit to evaluate environmental exposures: Applications of the dioxin model to study real life exposures.

Chlorinated dibenzo-p-dioxins (CDDs) are a series of mono- to octa-chlorinated homologous chemicals commonly referred to as polychlorinated dioxins. One of the most potent, well-known, and persistent member of this family is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). As part of translational research to make computerized models accessible to health risk assessors, we present a Berkeley Madonna recoded version of the human physiologically based pharmacokinetic (PBPK) model used by the U.S. Environmental Protection Agency (EPA) in the recent dioxin assessment. This model incorporates CYP1A2 induction, which is an important metabolic vector that drives dioxin distribution in the human body, and it uses a variable elimination half-life that is body burden dependent. To evaluate the model accuracy, the recoded model predictions were compared with those of the original published model. The simulations performed with the recoded model matched well with those of the original model. The recoded model was then applied to available data sets of real life exposure studies. The recoded model can describe acute and chronic exposures and can be useful for interpreting human biomonitoring data as part of an overall dioxin and/or dioxin-like compounds risk assessment.

Dynamic Transgenerational Fate of Polychlorinated Biphenyls and Dioxins/Furans in Lactating Cows and Their Offspring.

We report on two farms in Switzerland heavily contaminated by polychlorinated biphenyls (PCBs) and dioxins (PCDD/Fs), occurring in the first case from diffuse sources and in the second case from PCB-containing wall paint. Extensive measurements of PCBs and PCDD/Fs on site (soil, forage, and paint) and in cattle (blood, fat, and milk) allowed validation of our novel dynamic toxicokinetic model, which includes the transfer of contaminants from the mother cows to their suckling calf and the uptake of soil by grazing cattle. We show that for calves, the mother milk is the main uptake route of contaminants. For both cows and calves, ingestion of contaminated soil, although often overlooked, is an appreciable uptake path. The remediation of the contaminated stable lead to a 2-3 fold reduction of the PCB levels in animals within one year. The transfer of animals to an uncontaminated mountain site during summer proved to be an effective decontamination procedure with up to 50% reduction of the levels within three months. Our study calls for a rapid removal of PCB-containing materials in animal husbandry farms and shows that the diffuse contamination of soils will remain a source for PCBs and PCDD/Fs in our food chain for decades to come.

Comparison of intake and systemic relative effect potencies of dioxin-like compounds in female rats after a single oral dose.

Risk assessment for mixtures of dioxin-like compounds uses the toxic equivalency factor (TEF) approach. Although current WHO-TEFs are mostly based on oral administration, they are commonly used to determine toxicity equivalencies (TEQs) in human blood or tissues. However, the use of "intake" TEFs to calculate systemic TEQs in for example human blood, has never been validated. In this study, intake and systemic relative effect potencies (REPs) for 1,2,3,7,8-pentachlorodibenzo-p-dioxin (PeCDD), 2,3,4,7,8-pentachlorodibenzofuran (4-PeCDF), 3,3',4,4',5-pentachlorobiphenyl (PCB-126), 2,3',4,4',5-pentachlorobiphenyl (PCB-118) and 2,3,3',4,4',5-hexachlorobiphenyl (PCB-156) were compared in rats. The effect potencies were calculated based on administered dose and liver, adipose or plasma concentrations in female Sprague-Dawley rats 3 days after a single oral dose, relative to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Hepatic ethoxyresorufin-O-deethylase activity and gene expression of Cyp1a1, 1a2, 1b1 and aryl hydrocarbon receptor repressor in liver and peripheral blood lymphocytes were used as endpoints. Results show that plasma-based systemic REPs were generally within a half log range around the intake REPs for all congeners tested, except for 4-PeCDF. Together with our previously reported systemic REPs from a mouse study, these data do not warrant the use of systemic REPs as systemic TEFs for human risk assessment. However, further investigation for plasma-based systemic REPs for 4-PeCDF is desirable.

In utero and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin modulates dysregulation of the lipid metabolism in mouse offspring fed a high-calorie diet.

Exposure to environmental chemicals, including dioxins, is a risk factor for type 2 diabetes mellitus in humans. This study explored the hypothesis that in utero and lactational exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most toxic congener among dioxins, aggravates this disease state later in adulthood. Pregnant C57Bl/6 J mice were administered either a single oral dose of TCDD (3.0 µg kg(-1) body weight) or corn oil on gestational day 12.5. The male pups born to these two groups of dams were given either a regular diet or a high-calorie diet, after postnatal day (PND) 28. The four groups of investigated offspring were thus termed T-R (TCDD regular diet), T-H (TCDD high-calorie diet), V-R (vehicle regular diet), and V-H (vehicle high-calorie diet). The mice were regularly monitored for body weight, blood pressure and glucose, until they reached 26 weeks of age. Mice in the V-H group were significantly obese at weeks 15 and 26, but they exhibited no diabetes-associated signs of insulin resistance or hypertension. However, metabolic syndrome-related alterations with marginal signs of liver damage were found at week 26. Pronounced signs of dysregulated lipid metabolism with altered gene expression and liver inflammation were already present at week 15, whereas such alterations were suppressed in the T-H group. Although the mechanism is unclear, this study showed that in utero and lactational exposure to low-dose TCDD does not aggravate obesity-induced disease states, such as adult-onset diabetes, but instead attenuates the dysregulation of lipid metabolism brought on by a high-calorie diet.

Synthesis and evaluation of novel 2,3-dihydrobenzo[b][1,4]dioxin- and indolealkylamine derivatives as potential antidepressants.

A series of 2,3-dihydrobenzo[b][1,4]dioxin- and indolealkylamine derivatives were synthesized and the target compounds were evaluated for their binding affinities at the 5-HT1A receptor and serotonin transporter. Antidepressant-like activities of the compounds were screened using the tail suspension and forced swim tests in mice. Preliminary results indicated that the target compounds exhibited high binding affinities at the 5-HT1A receptor and serotonin transporter, and produced marked antidepressant-like effects. The best example from this study, compound 5, exhibited high binding affinities for the 5-HT1A receptor (Ki = 96 nM) and serotonin transporter (Ki = 9.8 nM). The intrinsic activity of compound 5 showed agonistic property to the 5-HT1A receptor and inhibition of the 5-HT transporter. Furthermore, compound 5 exhibited greater antidepressant efficacy than fluoxetine and showed acceptable pharmacokinetic properties.

The importance of problem formulations in risk assessment: a case study involving dioxin-contaminated soil.

The need to remediate contaminated soils is typically accomplished by applying standard risk assessment methods followed by risk management to select remedial options. These human health risk assessments (HHRAs) have been largely conducted in a formulaic manner that relies heavily on standard deterministic exposure, toxicity assumptions and fixed mathematical formulas. The HHRA approach, with its traditional formulaic practice, does not take advantage of problem formulation in the same manner as is done in ecological risk assessment, and historically, has generally failed to emphasize incorporation of site-specific information. In response to these challenges, the National Academy of Sciences recently made several recommendations regarding the conduct of HHRAs, one of which was to begin all such assessments with problem formulation. These recommendations have since been extended to dose response assessment. In accordance with these recommendations, a group of experts presented and discussed findings that highlighted the importance and impact of including problem formulation when determining the need for remediation of dioxin contamination in soils, focusing in particular on exposure assessment is described.

Effect of chitosan intake on fecal excretion of dioxins and polychlorinated biphenyls in healthy men.

Six healthy male subjects were treated with 0 g, 1 g, 3 g, and 0 g of chitosan for the first, second, third, and fourth of four weeks, respectively. They were administered chitosan before breakfast on the second, third, and fourth days of the week, and fecal specimens were collected corresponding to the prescribed diet consumed for breakfast on the second day to breakfast on the fourth day. Fecal excretion of dioxins and polychlorinated biphenyls (PCBs) was promoted by intake of 3 g of chitosan (p=0.0589 and p<0.05 respectively), and was positively correlated with that of fat (p<0.01 for both). We found that chitosan intake increased the fecal excretion of dioxins and PCBs, as well as that of fat, suggesting that it might be useful for reducing the adverse effects of lipophilic endocrine-disrupting chemicals.

[Associations of exposure to dioxins and polychlorinated biphenyls with diabetes: based on epidemiological findings].

Persistent organic pollutants (POPs) are a group of chemical substances that have the common properties of resistance to biodegradation, wide-range transportation, high lipophilicity, bioaccumulation in fat, and biomagnification in the food chain. POPs are persistent in the environment worldwide and have potential adverse impacts on human health and the environment. Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs) are well known chemicals that are considered as POPs. The association between high-level exposure to dioxins and type 2 diabetes among U.S. Air Force veterans who had been exposed to Agent Orange contaminated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) during the Vietnam War was reported in the late 1990s. This association has been supported by similar epidemiologic studies, whose subjects were exposed to high doses of dioxins in their places of work involving phenoxyacid herbicide production and spraying, and in the industrial accident in Seveso, Italy. Recently, low-level exposure to dioxins and PCBs has been reported to be linked to type 2 diabetes. Cross-sectional studies in the U.S. general population and Japanese general population showed that body burden levels of some dioxins and PCBs were strongly associated with the prevalence of type 2 diabetes. Very recently, following these cross-sectional studies, several prospective studies have suggested that low-level exposure to some PCBs predicted the future risk of type 2 diabetes in the general population. Environmental exposure to some dioxins and PCBs, which mainly accumulate in adipose tissue, may play a role in the development of type 2 diabetes.

[Human biomonitoring and variation of haematic parameters in a population exposed to PCB and dioxin near a steel plant in the lower Susa Valley]. / Biomonitoraggio umano e variazione dei parametri ematici in una popolazione esposta a PCB e diossine presso un'acciaieria in bassa Val di Susa.

OBJECTIVE: to evaluate the degree of exposure to PCB in a population resident in the lower Susa Valley and its effects on general and endocrine homeostasis. DESIGN, SETTING, PARTICIPANTS AND MAIN OUTCOME MEASURES: in the lower Susa Valley (Piedmont, Italy), there is a steel secondary casting plant (i.e. by fusion of scrap iron), active since the '50s. The emissions of PCB and dioxin coming from the furnace were found in samples of herb, pulse and ground in a preliminary environmental characterisation study. During 2005-2006 we run an epidemiologic study of biomonitoring (measuring as outcome common haematochemical parameters, hormonal parameters, haematic PCB) on a sample of subjects resident in the municipalities with higher levels of PCB and dioxin contamination (exposed subjects), that was compared with another sample (unexposed) of subjects residing in other areas of the Susa Valley. RESULTS: the final sample consisted of 244 subjects (119 unexposed and 125 exposed), balanced by gender, age, education and representative of the Susa Valley population. The greater part of hormonal and toxic parameters showed worse values among exposed than among unexposed, including PCB median value (2.30 µg/l among exposed vs. 1.90 µg/l among unexposed). The difference however was not statistically significant and the values were lower than the population reference values (7.2 µg/l). Haematic PCB values were significantly and positively correlated with age and alcohol consumption and not significantly with male gender. The distribution of the principal haematochemical parameters (hemochrome, total, LDL and HDL cholesterol, triglycerides, glucose, creatinine, bilirubin, transaminases, gamma-glutamiltranspeptidase, proteine electrophoresis) showed also, on the whole, worse values among exposed compared to unexposed, even if the difference was not statistically significant for single values. CONCLUSIONS: the exposed population showed higher values of PCB haematic values and alterations of the hormonal and common heamatochemical parameters compared to unexposed population, even if within reference limits.

Engineered membrane superchannel improves bioremediation potential of dioxin-degrading bacteria.

Sphingomonas sp. A1 possesses specialized membrane structures termed 'superchannels' that enable the direct incorporation of macromolecules into the cell. We have engineered two related sphingomonads, the dioxin-degrading S. wittichii RW1 and the polypropylene glycol-degrading S. subarctica IFO 16058(T), to incorporate this superchannel into their cell membranes. In both cases the bioremediation capability of the organisms was substantially increased pointing at the potential of this approach as a general strategy to improve bacterial degradation of hazardous compounds in the environment.

Model estimates bioaccumulation of total PCBs, dioxin-furan TEQs, and total mercury in mink liver based on concentrations in Lake Ontario water.

We used stable isotope analysis and a bioaccumulation model to estimate concentrations of total polychlorinated biphenyls (PCBs), dioxin-furan toxic equivalents (TEQs), and total mercury (Hg) in mink and to compare predicted ranges with their chemical concentrations in mink liver (PCB, TEQ) and brain (Hg). Actual concentrations were within predicted bounds for total PCB, dioxin-furan TEQ, and Hg except in two cases (lowest PCB and highest Hg) which were very close to predicted bounds. Based on (15)N analysis, the trophic level of mink ranged from 3.4 to 3.9. Animals at the upper end of the range were exposed to Lake Ontario water and its food web, whereas those at the lower end were captured at inland locations. Because of the complexity of wetland (an important habitat for mink in this study) food webs with pelagic, littoral, and terrestrial carbon sources and overlapping (13)C signatures, whether the origins of mink diets were aquatic or terrestrial could not be determined. We have established a nondestructive biomonitoring tool to reasonably estimate concentrations of total PCBs, TEQs and total Hg in mink tissues as concentrations of these chemicals change in their water supply.

Total PCBs, dioxin-furan TEQs, and total mercury concentrations in mink in and out of the Rochester Embayment area of concern near and inland from the shore of Lake Ontario.

In terms of reproductive and other adverse outcomes after exposure to polychlorinated biphenyls (PCBs), dioxins, and furans, the mink (Mustela vison) is one of the most sensitive mammals. Our objective was to determine if there are differences in the concentrations of total mercury (Hg), total PCBs, and dioxin-furan toxic equivalents (TEQs) between mink living in and out of the Rochester Embayment of Lake Ontario (RELO) Area of Concern (AOC) and between mink living near the shore of Lake Ontario and inland. Concentrations of total Hg in the brain, total PCBs and dioxin-furan TEQs in adipose, and total PCBs in liver were significantly higher for mink living near the shore of Lake Ontario than inland. For mink living in and out of the AOC, differences in total PCBs and dioxin-furan TEQs in adipose and the liver were substantial but not significant. Correlations among concentrations of total Hg, total PCBs, and dioxin-furan TEQs in mink were high. Our results suggest that contamination of mink living near the southern shore of Lake Ontario primarily comes from contact with the Lake Ontario food web, not from sources in the RELO AOC.

Impact of environmental pollution on PCDD/F and PCB bioaccumulation in game animals.

Elucidation of the relationship between the levels of 35 individual dioxins and polychlorinated biphenyl congeners in environmental samples (pine needles, leaves, grass and soil), and their bioaccumulation in the muscles of two game animal families (Cervidae and Suidae) was the aim of the research. Comparative studies were performed in four industrially degraded regions with various types of heavy industry and in an agricultural region with a tourism industry. The content of pollutants was determined by the isotopic dilution method using high resolution gas chromatography coupled with high resolution mass spectrometry. The polychlorinated dibenzodioxins/furan and PCB profiles in plants, soil and animal tissues varied by region and were related to the indigenous industry. The presence of characteristic congeners of particular industrial sectors was found. The animal tissue congeners were a reflection of the types and levels found in soil and plants. Independently of the region, deer tissue had almost twice the concentration of PCDD/F/DL-PCBs compared to boars, but the converse was true for NDL-PCBs. Spearman's statistical test showed strong correlations between pine needle, leaf, grass and soil dioxin and dioxin-like PCB levels and concentrations of these in the tissues of both species. Coefficients of bioaccumulation in deer muscles (BAF) calculated for all regions varied considerably and they were significantly higher for wild boars. BAF decreased with increasing number of chlorine atoms in the dioxin and furan molecule. The highest congener values were for 2,3,7,8-tetrachlorodibenzodioxin, 1,2,3,7,8-pentachlorodibenzodioxin, 2,3,7,8-tetrachlorodibenzofuran and 2,3,4,7,8-pentachlorodibenzofuran in both kinds of muscle regardless of the region. The levels of pollutants, types of pollutants, and their relative abundance in tissues of deer and boar reflected their surrounding environment and local pollutant emitters.

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.

Persistent organic pollutants in 9/11 world trade center rescue workers: reduction following detoxification.

Exposure to toxins following the September 11, 2001 attack on and collapse of the World Trade Center (WTC) is of particular concern given the ultra fine particulate dust cloud, high temperature combustion, and months-long fire. Firefighters, paramedics, police and sanitation crews are among the approximately 40000 personnel who labored for weeks and months on rescue and cleanup efforts. Many of the rescue workers have subsequently developed symptoms that remain unresolved with time. This study characterizes body burdens of polychlorinated biphenyls (PCBs), polychlorinated dibenzofurans (PCDFs), and polychlorinated dioxins (PCDDs) in rescue workers and citizens exposed following the WTC collapse. Our research includes a pilot evaluation of a detoxification method aimed at reducing toxic burden. Many congeners were found at elevated levels, in ranges associated with occupational exposures. Post-detoxification testing revealed reductions in these congeners and despite the small study size, some reductions were statistically significant. Health symptoms completely resolved or were satisfactorily improved on completion of treatment. These results argue for a larger treatment study of this method and an overall treatment approach to address toxic burden.

Concentration and distribution of dioxins and related compounds in human tissues.

Polychlorinated dibenzo-p-dioxin, polychlorinated dibenzofuran and dioxin-like polychlorinated biphenyl concentrations in human blood, lung, liver, bile, pancreas, spleen, kidney and mesentery fat were determined to assess the concentrations and distribution of these chemicals in human tissues from 20 donors. The mean TEQ concentrations in blood, lung, liver, bile, spleen, pancreas, kidney and mesentery fat were 119, 178, 228, 50, 113, 163, 138 and 139 pg TEQ/g lipid, respectively. Parallel levels were seen in the blood, spleen, kidney and mesentery fat; in the lungs and pancreas, the levels were somewhat higher. Among the organ tissues samples, the highest concentration was observed in the liver and the lowest in the bile. Mean total-TEQ concentration of the liver was about 4.5 times higher than that of bile. Positive correlations were observed among the concentrations of dioxins in various tissues. However, the concentrations in bile were not correlated with any tissues. It is suggested that the distribution behavior of dioxin-like congeners in human tissues varies among tissues and the kinds of congeners ingested. To evaluate the relationship between the accumulation levels of dioxins and their pathophysiological significance or risk, data must be accumulated from a more extensive group of human samples.

Dose- and time-dependent effects of 2,3,7,8-tetrabromodibenzo-p-dioxin on rat liver.

Dose- and time-dependent effects of 2,3,7,8-tetrabromodibenzo-p-dioxin (TBDD) on the liver were examined by single administration of TBDD by gavage to male and female rats. Fifteen Wistar rats of each sex per group received 0, 10, 30, 100 or 300 microg TBDD/kg body weight. Rats surviving to scheduled necropsy on Day 2, 7 or 36 after the TBDD administration were examined for hepatic histopathology, activities of hepatic microsomal enzymes and serum levels of lipids, total cholesterol and transaminases and hepatic concentrations of TBDD. Tigroid basophilic cytoplasm and hepatocellular hypertrophy were observed at 10 microg/kg on Day 2 or 7 through 36, whereas degenerative and aggressive lesions such as necrosis, fibrosis, multinucleated hepatocytes and disarrangement of hepatocytes occurred later at higher dose levels. Persistently increased activities of hepatic aryl hydrocarbon hydroxylase (AHH), ethoxycoumarin O-deethylase (ECOD) and ethoxyresorufin O-deethylase (EROD), increased serum levels of total cholesterol and phospholipid and increased relative liver weight were observed in all groups dosed 10 mug/kg and above, suggesting that hepatic microsomal monooxygenases and basophilic cytoplasm of hepatocytes were early and sensitive indicators among those TBDD-induced effects. A dose-dependent increase in liver concentrations of TBDD on Day 2 was followed by logarithmic decreases in TBDD concentrations against the days elapsed after the TBDD administration. An elimination half-life (t(1/2)) of TBDD from the liver was estimated to range from 12 to 16 days. It was suggested that females were more susceptible to TBDD than males, and that acute hepatotoxicity of TBDD was as potent as that of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD).