Influence of solvents and adsorbents on dermal and intestinal absorption of TCDD

Bioaccessibility of polychlorinated dioxins and furans in soil from a Superfund site

Bioaccessibilities of PCDD/PCDF congeners contributing to cancer risk were determined in twelve soil samples from the American Creosote Works Superfund site in Florida. Based upon sample locations, congener profiles (i.e., the same dominant congeners), and total (Toxic Equivalent; TEQ) concentrations, each of these samples has PCDD/PCDF contamination reasonably attributable to the site. Bioaccessibility was determined using a 2-phase in vitro extraction method that included both simulated gastric and intestinal conditions of the human GI tract. Measured congener-specific bioaccessibility values ranged from 34.3 to 62.1%. There was no apparent relationship between the extent of chlorination of PCDD/PCDF congeners and their bioaccessibility. TEQ-weighted bioaccessibility values varied among individual soil samples, which is not unexpected based upon the literature. This variability could not be explained by differences in soil pH, composition, or organic carbon content. The average TEQ-weighted bioaccessibility value of 59% for the twelve samples was accepted as representing site-specific bioavailability of PCDD/PCDFs. This value is higher than most dioxin/furan bioaccessibility values reported in the literature and at the upper end of the range of relative oral bioavailability (RBA) values reported for PCDD/PCDFs from in vivo bioavailability studies. This study used a finer fraction of soil particles (<150 microns versus the more typical <250 microns) to better represent soil that is incidentally ingested. This finer fraction would be expected to have a greater surface area available for extraction of PCDD/PCDFs per unit mass, which might account for the greater than expected bioaccessibility.

Sequestration of 2,3,7,8-tetrachlorodibenzo-p-dioxin by activated carbon eliminates bioavailability and the suppression of immune function in mice

The effectiveness of activated carbon in reducing the bioavailability of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was examined from the context of using in situ sorbent amendments to remediate soils/sediments contaminated with polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs). This technology has gained rapid acceptance based on observations that activated carbon amendments predictably lower PCDD/F concentrations in water and bioaccumulation by simple aquatic organisms and earthworms; it has been assumed that bioavailability to mammals is similarly reduced, although this has been disproven for other sorbent materials. In the present study TCDD was absorbed to a microporous activated carbon (TCDD-AC) using the incipient wetness method. An aqueous suspension of TCDD-AC and an equivalent dosage of TCDD in corn oil were administered by oral gavage to B6C3F1 mice. The relative bioavailability of TCDD-AC was determined by quantifying and comparing the hepatic induction of cyp1A1 (messenger ribonucleic acid) and suppression of the immunoglobulin M antibody-forming cell immune response by the 2 forms of TCDD. A concentration-dependent response was observed for both assays when TCDD in corn oil was administered to mice. However, when equivalent masses of TCDD were administered as TCDD-AC, no induction of cyp1A1 or suppression of the immunoglobulin M antibody-forming cell response was observed. The absence of these 2 sensitive aryl hydrocarbon receptor-mediated responses in mice provides the first direct evidence that activated carbon can sequester TCDD in a form that eliminates its bioavailability to mammals. These results support the premise that activated carbon can be used to reduce the bioeffective dose of TCDD delivered to mammals and that activated carbon amendments may provide a low-cost alternative to traditional remediation technologies. Environ Toxicol Chem 2017;36:2671-2678. © 2017 SETAC.

A review of the current state of the art of physiologically-based tests for measuring human dermal in vitro bioavailability of polycyclic aromatic hydrocarbons (PAH) in soil

Polycyclic Aromatic Hydrocarbons are classed as Persistent Organic Pollutants, a large group of compounds that share similar characteristics. They are lipophilic, resistant to degradation in the environment and harmful to human and environmental health. Soil has been identified as the primary reservoir for Polycyclic Aromatic Hydrocarbons in the United Kingdom. This study reviews the literature associated with, or is relevant to, the measurement and modelling of dermal absorption of Polycyclic Aromatic Hydrocarbons from soils. The literature illustrates the use of in vivo, in vitro and in silico methods from a wide variety of scientific disciplines including occupational and environmental exposure, medical, pharmaceutical and cosmetic research and associated mathematical modelling. The review identifies a number of practical shortcomings which must be addressed if dermal bioavailability tests are to be applied to laboratory analysis of contaminated soils for human health risk assessment.

Biological responses to activated carbon amendments in sediment remediation

Sorbent amendment with activated carbon (AC) is a novel in situ management strategy for addressing human and ecological health risks posed by hydrophobic organic chemicals (HOCs) in sediments and soils. A large body of literature shows that AC amendments can reduce bioavailability of sediment-associated HOCs by more than 60-90%. Empirically derived biodynamic models can predict bioaccumulation in benthic invertebrates within a factor of 2, allowing for future scenarios under AC amendment to be estimated. Higher AC dose and smaller AC particle size further reduce bioaccumulation of HOCs but may induce stress in some organisms. Adverse ecotoxicity response to AC exposure was observed in one-fifth of 82 tests, including changes in growth, lipid content, behavior, and survival. Negative effects on individual species and benthic communities appear to depend on the characteristics of the sedimentary environment and the AC amendment strategy (e.g., dose and particle size). More research is needed to evaluate reproductive end points, bacterial communities, and plants, and to link species- and community-level responses to amendment. In general, the ability of AC to effectively limit the mobility of HOCs in aquatic environments may outshine potential negative secondary effects, and these outcomes must be held in comparison to traditional remediation approaches.

Dermal absorption of environmental contaminants from soil and sediment: a critical review

Risk assessment of hazardous wastes sites may require characterization of the dermal availability of chemical contaminants in soil and/or sediment. Current U.S. Environmental Protection Agency guidance for assessment of dermal exposures to contaminants in water and soil was finalized in 2004 as a supplement (Part E) to the Risk Assessment Guidance for Superfund (RAGS). The soil protocol presented in RAGS Part E is less sophisticated than the water protocol and is supported by less empirical data. Investigations of dermal absorption of soil and sediment-borne contaminants that have been conducted to date include in vitro and in vivo experiments using both human and surrogate skin. A review of that literature was conducted with attention to relevant criteria including consideration of layering effects, degree of chemical saturation of soil, appropriateness of particle size distribution employed, soil-chemical contact time, and continuity of soil-skin contact (in in vivo studies). Most studies published to date are deficient by virtue of execution or reporting on one or more of the selected criteria. In addition the lack of methodological standardization evident in the literature hinders systematic evaluation of results. Since additional experimental work is needed, general agreement on acceptable approaches would be useful. Recommendations for good practice are presented.

Percutaneous absorption of 3,3',4,4'-tetrachlorobiphenyl (PCB 77) from soil

Six dermal absorption experiments (one in vivo, five in vitro) were conducted using 3,3',4,4'-tetrachlorobiphenyl (TCB) either neat at 141 microg/cm2 or sorbed on a low organic (LOS) or high organic (HOS) soil at 6-10 microg/cm2. All soil experiments were conducted at 1000 ppm and soil loads of 6-10 mg soil/cm(2). After 96 h the percentage of applied dose absorbed (PADA) for TCB sorbed on LOS was 49.7 (rat, in vivo), 31.9 (rat, in vitro), and 7.4 (human, in vitro). The 96-h PADA for TCB sorbed on HOS was 9.6% (rat, in vitro). Generally, rat skin was observed to be four- to ninefold more permeable to TCB than human skin (in vitro). At steady state, the dermal flux of TCB on LOS at 1000 ppm and on HOS at 1000 ppm (both in vitro, rat) was 33 and 10 ng/cm2/h, respectively (ratio = 3.3).

Percutaneous absorption of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) from soil

Eight dermal absorption experiments (two in vivo; six in vitro) and one intravenous experiment were conducted using 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) either neat (high dose at approximately 250 microg/cm(2) and low dose at 10 ng/cm(2)) or sorbed on a low organic soil (LOS) or high organic soil (HOS) at 1 ppm (10 ng TCDD/10 mg soil/cm(2)). After 96 h the percent of applied dose absorbed (PADA) for the neat low dose was 78% in vivo (rat) and 76% in vitro (rat). PADA for the equivalent TCDD dose sorbed on LOS were 16.3% (rat in vivo), 7.7% (rat in vitro) and 2.4% (human in vitro). The PADA for TCDD sorbed on HOS (1 ppm) was 1.0% (rat in vitro). Generally, rat skin was observed to be three to four times more permeable to TCDD than human skin. At steady state, the dermal flux of TCDD in neat form, sorbed on LOS at 1 ppm, and sorbed on HOS at 1 ppm (all in vitro, rat) was 120, 0.007, and 0.0007 ng/cm(2)/h, respectively (ratio = 1.7 x 10(5):10:1). Making adjustments to account for differences between in vitro and in vivo results and adjusting for application to monolayer loads, the 24-h TCDD absorption for human skin is estimated as 1.9% from LOS (1 ppm) and 0.24% from HOS (1 ppm).

Bioavailability of PCDD/F from contaminated soil in young Goettingen minipigs

For the general population the intake of food of animal origin is the main route of human exposure to polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F). Besides this the ingestion of contaminated soil might be an important exposure path for small children. For risk assessment the knowledge of the bioavailable fraction of soil bound contaminants is important. In a balance study with young Goettingen minipigs the oral bioavailability of PCDD/F from contaminated soil was estimated by determination of the retention of PCDD/F from soil in different organs and tissues. Relative bioavailability was estimated by comparing the retention from soil to the retention of PCDD/F in organs and tissues after oral administration of a PCDD/F mixture extracted from the same soil by solvent. The soil had a PCDD/F-contamination of 5.3 microg I-TEq/kg and originated from a former arable land that had been treated with sludge from the port of Hamburg some years ago. Two groups of each four animals were exposed daily for 28 days via their diet either to 0.5 g soil per kg body weight and day (2.63 ng I-TEq/(kg(bw).d)) or to a daily dose of 1.58 ng I-TEq/(kg(bw).d) given to the diet by solvent. Five unexposed animals were used as a control group. Liver, adipose tissue, muscle, brain and blood were analyzed for their PCDD/F content. Accumulation of PCDD/F from soil or solvent in comparison to control animals was only observed for congeners with 2378-chlorosubstitution and predominantly took place in the liver. Bioavailability of 2378-chlorosubstituted congeners was in the range of 0.64%-21.9% (mean: 10.1%) from soil and 2.8%-59.8% (mean: 31.5%) when administered by solvent. The soil matrix reduced the bioavailability by about 70%. Expressed as I-TEq only 13.8% of the PCDD/F contamination were bioavailable from soil. The relative bioavailability of 2378-chlorosubstituted congeners from soil in relation to administration by solvent was in the range of 2%-42.2% (mean: 28.4%). When not considering the bioavailability, the risk by oral uptake of PCDD/F contaminated soil might be overestimated.

Identifying soil cleanup criteria for dioxins in urban residential soils: how have 20 years of research and risk assessment experience affected the analysis?

This article reviews the scientific evidence and methodologies that have been used to assess the risks posed by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and presents a probabilistic analysis for identifying virtually safe concentrations of TCDD toxicity equivalents (TEQ) in residential soils. Updated data distributions that consider state-of-the-science cancer and noncancer toxicity criteria, child soil ingestion and dermal uptake, bioavailability in soil, and residential exposure duration are incorporated. The probabilistic analysis shows that the most sensitive determinants of dose and risk are childhood soil ingestion, exposure duration, and the selected TCDD cancer potency factor. It also shows that the cancer risk at 1 per 100,000 predicted more conservative (lower) soil criteria values than did the noncancer hazard (e.g., developmental and reproductive effects). In this analysis, acceptable or tolerable soil dioxin concentrations (TCDD TEQ) ranged from 0.4 to 5.5 ppb at the 95th percentile for cancer potency factors from 9600 to 156,000 (mg/kg/d)(-1) with site-specific adjustments not included. Various possible soil guidelines based on cancer and noncancer risks are presented and discussed. In the main, the current toxicology, epidemiology, and exposure assessment data indicate that the historical 1 ppb TEQ soil guidance value remains a reasonable screening value for most residential sites. This analysis provides risk managers with a thorough and transparent methodology, as well as a comprehensive information base, for making informed decisions about selecting soil cleanup values for PCDD/Fs in urban residential settings.

Bioavailability of 2,3′,4,4′,5-pentachlorobiphenyl (PCB118) and 2,2′,5,5′-tetrachlorobiphenyl (PCB52) from soils using a rat model and a physiologically based extraction test

The bioavailability of coplanar 2,3',4,4',5-pentachlorobiphenyl (PCB118) and nonplanar 2,2',5,5'-tetrachlorobiphenyl (PCB52) from soils representing a range in organic carbon (OC), clay content and pH were investigated using an in vivo rat model and an in vitro physiologically based extraction test (PBET) to assess the role of soil and chemical properties on bioavailabilty. Affinity to soil and persistence of PCBs have been shown to increase with increasing soil organic carbon (OC) content, PCB chlorination, and PCB coplanarity. In the in vivo tests for both PCB118 and PCB52, the AUCs following iv injection were significantly higher than the AUCs for all soil groups, indicating that the soil matrix can reduce the absolute bioavailability of PCB118 and PCB52. However, no significant differences were detected between soils of different properties. In the in vitro PBET, significant differences in the mobilization of PCB118 and PCB52 were observed among soils, and PCBs had the least mobilization from the soil with the highest OC content consistent with hydrophobic partitioning theory. Also, significantly less PCB118 was mobilized relative to PCB52 in the PBET assay, showing the potential impact of spatial orientation and chlorine content on bioavailability. No correlation between the in vitro PBET and the in vivo rat model was observed for the PCBs. Although the in vitro PBET and related assays may serve as an indicator of bioavailability, it is likely to underestimate what can be released from a soil in an in vivo assay.

Environmental fate and bioavailability of Agent Orange and its associated dioxin during the Vietnam War

BACKGROUND

In 1996, the Committee on the Assessment of Wartime Exposure to Herbicides in Vietnam of the National Academy of Sciences' Institute of Medicine (IOM) issued a report on an exposure model for use in epidemiological studies of Vietnam veterans. This exposure model would consider troop locations based on military records; aerial spray mission data; estimated ground spraying activity; estimated exposure opportunity factors; military indications for herbicide use; and considerations of the composition and environmental fate of herbicides, including changes in the TCDD content of the herbicides over time, the persistence of TCDD and herbicides in the environment, and the degree of likely penetration of the herbicides into the ground. When the final report of the IOM Committee was released in October 2003, several components of the exposure model envisioned by the Committee were not addressed. These components included the environmental fate of the herbicides, including changes in the TCDD content over time, the persistence of TCDD and herbicides in the environment, and the degree of likely penetration of herbicides into the ground. This paper is intended to help investigators understand better the fate and transport of herbicides and TCDD from spray missions, particularly in performing epidemiological studies.

METHODS

This paper reviews the published scientific literature related to the environmental fate of Agent Orange and the contaminant, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and discusses how this affected the potential exposure to TCDD of ground troops in Vietnam. Specifically, the mechanisms of dissipation and degradation as they relate to environmental distribution and bioavailability are addressed.

RESULTS

The evaluation of the spray systems used to disseminate herbicides in Vietnam showed that they were capable of highly precise applications both in terms of concentrations sprayed and area treated. Research on tropical forest canopies with leaf area indices (a measure of foliage density) from 2 to 5 indicated that the amount of herbicide and associated TCDD reaching the forest floor would have been between 1 and 6% of the total aerial spray. Studies of the properties of plant surface waxes of the cuticle layer suggested that Agent Orange, including the TCDD, would have dried (i.e., be absorbed into the wax layer of the plant cuticle) upon spraying within minutes and could not be physically dislodged. Studies of Agent Orange and the associated TCDD on both leaf and soil surface have demonstrated that photolysis by sunlight would have rapidly decreased the concentration of TCDD, and this process continued in shade. Studies of 'dislodgeable foliar residues' (DFR, the fraction of a substance that is available for cutaneous uptake from the plant leaves) showed that only 8% of the DFR was present 1 hr after application. This dropped to 1% of the total 24 hrs after application. Studies with human volunteers confirmed that after 2 hrs of saturated contact with bare skin, only 0.15-0.46% of 2,4,5-T, one of the phenoxy acetic acid compounds that was an active ingredient of Agent Orange, entered the body and was eliminated in the urine.

CONCLUSIONS

The prospect of exposure to TCDD from Agent Orange in ground troops in Vietnam seems unlikely in light of the environmental dissipation of TCDD, little bioavailability, and the properties of the herbicides and circumstances of application that occurred. Photochemical degradation of TCDD and limited bioavailability of any residual TCDD present in soil or on vegetation suggest that dioxin concentrations in ground troops who served in Vietnam would have been small and indistinguishable from background levels even if they had been in recently treated areas. Laboratory and field data reported in the literature provide compelling evidence on the fate and dislodgeability of herbicide and TCDD in the environment. This evidence of the environmental fate and poor bioavailability of TCDD from Agent Orange is consistent with the observation of little or no exposure in the veterans who served in Vietnam. Appreciable accumulation of TCDD in veterans would have required repeated long-term direct skin contact of the type experienced by United States (US) Air Force RANCH HAND and US Army Chemical Corps personnel who handled or otherwise had direct contact with liquid herbicide, not from incidental exposure under field conditions where Agent Orange had been sprayed.

Inhibition of Human Polymorphonuclear Cell Oxidative Burst by 17-β-estradiol and 2,3,7,8-tetrachlorodibenzo-p-dioxin

PROBLEM

Polymorphonuclear cell (PMN) function may be directly influenced by 17-beta-estradiol and the endocrine disruptor, 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD). This may have significant consequences on PMN function within the female reproductive tract. This study evaluated the effects of 17-beta-estradiol and TCDD on PMN oxidative burst.

METHOD OF STUDY

Peripheral blood PMN were isolated from normal male donors. Following treatment with 17-beta-estradiol, TCDD or both, PMN were stimulated with phorbol 12-myristate 13-acetate. Superoxide production was measured by lucigenin-enhanced chemiluminescence.

RESULTS

Following 24-hr culture with either 17-beta-estradiol or TCDD, PMN superoxide production was significantly reduced, however, no such inhibition was observed when PMN were cultured with both estradiol and TCDD. Using antagonists, the estradiol and TCDD effects on PMN superoxide production was shown to be estrogen and aryl hydrocarbon receptor mediated.

CONCLUSIONS

Estradiol and TCDD influence PMN oxidative burst through receptor mediated events. Such altered PMN function may have profound effects upon the normal endometrial cycle.

Oral bioavailability of pentachlorophenol from soils of varying characteristics using a rat model

Evidence accumulated during the last two decades suggests that only a fraction of any chemical in soil is available to organisms, and soil-related effects on bioavailability should be considered in optimizing soil remediation cleanup levels. In the current study, the absolute and relative bioavailabilities of pentachlorophenol (PCP) from freshly spiked and environmentally aged soils varying in organic carbon content, clay content, and pH were examined using a rat model. PCP is a broad-spectrum biocide widely used as a wood preservative, and thus is ubiquitous in the environment. Soils and corn oil containing equivalent levels of PCP were administered to male Sprague-Dawley rats by gavage at 2 dose levels: 100 and 200 microg/kg body weight. Equivalent doses were also given intravenously. The areas under the plasma concentration of PCP versus time curves were calculated, and absolute and relative bioavailabilities of PCP from each soil were determined. At a dose of 100 microg/kg body weight, the absolute bioavailabilities of PCP across soils ranged from 36% to 65%, and the relative bioavailabilities ranged from 48% to 82%. At the higher dose level (200 microg/kg body weight), absolute and relative bioavailability ranges were somewhat higher at 46% to 77% and 52% to 87%, respectively. All soils decreased absolute PCP bioavailability significantly at both dose levels and relative bioavailability at the lower PCP dose level. At the higher dose level, only one of the two field-contaminated soils decreased the relative PCP bioavailability. The data indicate that PCP-soil interactions do significantly decrease the oral bioavailability of PCP from soil, but no obvious correlation was observed between soil properties and bioavailabilities.

Oral bioaccessibility of dioxins/furans at low concentrations (50-350 ppt toxicity equivalent) in soil

Animal studies have indicated that the oral bioavailability of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in environmentally contaminated soil could range from 0.5 to 60%. To estimate the oral bioavailability of TCDD, and the 16 other 2,3,7,8-substituted dioxin/furan congeners, this study used a physiologically based extraction test, designed around the anatomic and physiologic characteristics of the human digestive tract. This test measures the fraction of dioxins/furans in soil that would be solubilized in the gastrointestinal tract (i.e., that would be bioaccessible) and therefore available for absorption. Eight soils from Midland, MI, were evaluated in this study and exhibited TCDD concentrations of 1.7-139 pg/g (ppt) and total TEQ concentrations of 6-340 ppt. Bioaccessibility of dioxins/furans from these soils ranged from 19 to 34% averaged across the 17 2,3,7,8-substituted dioxin/furan congeners), with an average of 25%. The total organic carbon in these soils was low--ranging from 1 to 4%--particularly for the soil series from which they were collected. Bioaccessibility of individual congeners did not appear to be correlated with degree of chlorination. Even though these dioxin/furan concentrations are much less than studied previously, these results are consistent with those from animal studies at other sites, which have generally yielded values of 20-60% relative bioavailability for TCDD in soil.

Kinetics and organotropy of some polyfluorinated dibenzo-p-dioxins and dibenzofurans (PFDD/PFDF) in rats

While polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/PCDF) and the corresponding polybrominated congeners must be considered as animal teratogens and carcinogens, little information is available on corresponding polyfluorinated compounds (PFDD/PFDF). Kinetic studies on a few fluorinated dibenzo-p-dioxins and dibenzofurans revealed a rapid elimination, suggesting a much lower toxicity than the corresponding polychlorinated and polybrominated congeners. In order to obtain further clues on the possible toxicity, the kinetics and organ distribution (in liver, thymus and adipose tissue) of a PFDD/PFDF-mixture were studied in Wistar rats after intravenous application. The congeners investigated included four of the 2,3,7,8-substituted, and four of the not-2,3,7,8-substituted dibenzo-p-dioxins, as well as two dibenzofurans. The main result of our studies is the finding that the concentration in the thymus of several of the 2,3,7,8-substituted PFDD/PFDF greatly exceeded that in hepatic tissue. An organotropy quite different from that of the other polyhalogenated congeners must be expected, immunosuppressive effects presumably being the predominant ones. Overall, the elimination half-life of all the PFDD/PFDF studied is considerably shorter than that of the corresponding polychlorinated or polybrominated congeners, in the rat, suggesting a much lower toxicity in this species. No information is available for other species, e.g. nonhuman primates or humans.

Dermal absorption in rhesus monkeys of polychlorinated biphenyls from soil contaminated with Aroclor 1260

Human health risk assessments involving contaminated soil include dermal absorption as a potential pathway contributing to the total exposure burden. For PCB-contaminated soil, the U.S. Environmental Protection Agency uses a dermal absorption factor of 14%, based on a 1993 study of dermal absorption in rhesus monkeys. The current study examined several parameters that can influence the dermal absorption of lipophilic hydrocarbons, including soil organic content, particle size, skin residence time, and contaminant "aging" in the soil. Four groups of four female rhesus monkeys each were exposed to radiolabeled Aroclor 1260 either intravenously (100% absorption) or dermally with PCB-spiked soil. Groups exposed for 12 or 24 h to PCBs aged in soil exhibited percutaneous absorption values of 3.43 +/- 0.35 and 4.26 +/- 0.52%, respectively, while a group exposed for 24 h to soil freshly spiked with PCBs exhibited a dermal absorption value of 4.07 +/- 0.46%. Evidence strongly suggests that the factor most responsible for modulating the percutaneous absorption of highly lipophilic compounds from soil is its organic content. The base soil used in the current study with Aroclor 1260 had an organic content of 5-6% (< or =2 mm particle fraction), a value typical for U.S. soil. The organic content of the soil applied to the skin was 8.7% (<150 microm particle fraction), a value that contrasts sharply with the soil containing 0.9% organics used in the 1993 study with Aroclors 1242 and 1254 that produced a dermal absorption value of 14% for PCBs.

Cutaneous elimination of 2,3,7,8-tetrachlorodibenzo-p-dioxin

BACKGROUND

After exposure, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is excreted via the faeces, breast milk and epidermal lipids.

OBJECTIVES

To determine to what extent TCDD is eliminated via the skin and to evaluate whethe cutaneous elimination can be accelerated by the application of petrolatum.

METHODS

In two patients severely intoxicated with TCDD, material obtained from the skin surface and, in one patient, cerumen and the content of epithelial cysts, was analysed for TCDD.

RESULTS

The TCDD concentration in the initial blood sample taken was 144 000 pg g(-1) blood fa in patient 1, and 26 000 pg g(-1) blood fat in patient 2. Six months later, when the skin tests were performed, the blood TCDD levels had decreased to 80 900 and 16 100 pg g(-1) blood fat, respectively. In the two samples of pooled cyst contents from patient 1, TCDD levels of 34 400 an 18 600 pg g(-1) fat were found. A cerumen sample contained TCDD at 20 500 pg g(-1) fat. In the material collected from the skin surface we observed a linear increase of the amount of TCD measured per test field with time, indicating a continuous elimination of TCDD via the skin. Th daily amount of TCDD eliminated via the skin was 1.51 pg cm(-2) in patient 1 and 0.57 pg cm(-2) in patient 2. Application of petrolatum led to a twofold increase in the amount of TCDD measured in patient 1, but had no significant effect in patient 2.

CONCLUSIONS

In our patients, elimination of TCDD via the skin, most probably through desquamating scales, represented 1-2% of the overall daily TCDD elimination rate, with regard to the body surface and when calculated on the basis of the half-life of TCDD at the time of the skin test. If a more typical overall elimination half-life of 7 years is used as the basis for the calculatio the skin would account for 9% (patient 1) and 15% (patient 2) of the overall elimination. Although we observed an increase in TCDD in material derived from the skin surface of up to 100% after application of petrolatum in patient 1, such an approach appears not to be a feasible means to increase elimination. Owing to the small amount of TCDD measured in skin-surface material, as well as in the cyst contents and cerumen obtained from one patient, contamination of the environment and other persons appears highly unlikely.

Comparison of different digestive tract models for estimating bioaccessibility of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) from red slag 'Kieselrot'

'Kieselrot' (red slag), a highly PCDD/F-contaminated leaching residue from a copper production process, has been used as surface layer for more than 1,000 sports fields, playgrounds and pavements in Germany and neighbouring countries. Children can ingest this material directly by hand-to-mouth activities or soil-pica behaviour. Furthermore secondary contamination of farm land or kitchen gardens by drift of red slag dust may lead to an enrichment of PCDD/F within the food-chain. PCDD/F can be mobilized from contaminated materials by digestive juices and thus become bioaccessible for intestinal absorption. Two different digestive tract models were used to estimate the bioaccessibility of PCDD/F from red slag and to study the influence of food material on the mobilization of the contaminants. The bioaccessibility of PCDD/F from red slag depends on the charge of red slag material used, the bile content of the intestinal juice and on the presence of lipophilic foodstuffs. A low bioaccessibility of less than 5% was found when using a digestive tract model with a low bile content and in absence of food material. The bioaccessibility was estimated to be more than 60% when using a model with a higher bile content and in the presence of whole milk powder. A low bioaccessibility of PCDD/F from red slag in general--as assumed until now and mentioned in legal provision--was not confirmed by our study. Considering observations for the different homologue groups it is obvious that bioaccessibility is the first of several important steps to estimate human health risks arising from contaminated materials. In case red slag contaminated with PCDD/F their absorption rate in the digestive tract and/or metabolism might be at least just like important.

Reproductive toxicity and tissue concentrations of low doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin in male offspring rats exposed throughout pregnancy and lactation

The effects of low doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the reproductive system of male offspring rats were examined. The dams were treated subcutaneously 2 weeks prior to mating and throughout mating, pregnancy, and lactation. They received an initial loading dose of 25, 60, or 300 ng TCDD/kg body wt, followed by a weekly maintenance dose of 5, 12, or 60 ng TCCD/kg body wt (TCDD 25/5, TCDD 60/12, and TCDD 300/60). Three dams per group were killed on Gestation Day 21 and the fetuses were removed. The concentration of TCDD in the maternal liver and fat was measured. After birth, developmental landmarks in male rats were monitored. At weaning, the concentration of TCDD in the offspring liver and testis was determined. Effects on male reproduction were studied on Postnatal Days (PND) 70 and 170. At weaning, the concentration of TCDD in the offspring liver was 0.24, 0.39, and 1.78 ng/g in the TCDD 25/5, TCDD 60/12, and TCDD 300/60 groups, respectively. In the testes, the concentration of TCDD was 0.25 ng/g in the TCDD 25/5 and TCDD 60/12 groups and 0.28 ng/g in the TCDD 300/60 group. The number of sperm per cauda epididymis was reduced in TCDD groups at puberty and at adulthood. Daily sperm production was permanently decreased as was the sperm transit rate in the TCDD-exposed male rats, thus increasing the time required by the sperm to pass through the cauda epididymis. Moreover, the male rats of the TCDD groups showed an increased number of abnormal sperm when investigated at adulthood. Similarly, mounting and intromission latencies were significantly increased in the TCDD 25/5 and TCDD 300/60 groups. In the highest dose group, serum testosterone concentration was decreased at adulthood. Likewise, in this dose group permanent changes including pyknotic nuclei and the occurrence of cell debris in the lumen were revealed. The lowest adverse effect level and the no observed effect level can be estimated to be substantially lower than the estimated daily dose of the lowest dose which is 0.8 ng/kg body wt/day. Sperm parameters were more susceptible than the other end points investigated. However, the question as to whether such doses exposed throughout gestation and lactation induce subtle changes in humans remains to be determined.

Ingestion of sludge applied organic chemicals by animals

Intake of sludge-borne chemicals is related to the crop and animal management systems, the species and physiological status of animals, and the properties of the chemicals. The greatest intake occurs when sludge is applied to established crops and animals have immediate access. Intake is reduced when access is delayed to allow losses by weathering and dilution by plant growth, or when sludge is incorporated into soil because vapour transport from soil to plants and lower concentrations at the surface reduce intake via soil ingestion. Animals that consume forage are the most subject to contaminant exposure, which is maximized when pasture is the major component of the diet because soil ingestion is an additional exposure pathway. Of the many organic contaminants in sludges, only lipophilic halogenated hydrocarbons accumulate in animal tissues and products. Compounds like phthalate esters, PAHs, acid phenolics, nitrosamines, volatile aromatics, and aromatic surfactants are metabolized and do not accumulate. Among halogenated hydrocarbons, compounds with low degrees of halogenation are metabolized and do not accumulate, but higher degrees of halogenation block metabolism, and concentrations in milk and tissue fat may be several-fold greater than in the diets.

The form and bioavailability of non-ionic organic chemicals in sewage sludge-amended agricultural soils

The application of sewage sludges to agricultural land may increase the concentrations of many toxic organic chemicals in soils which could have adverse effects on wildlife and human health if these compounds enter foodchains. Chlorobenzenes (CBs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) are amongst those compounds currently receiving most attention. The "form' in which these, and other organic chemicals, are present in soils and their potential to be lost by various processes including leaching, volatilisation and (bio)degradation is shown to be dependent on the physicochemical characteristics of the soil and sewage sludge, environmental conditions and the properties of the chemicals themselves. The distinction is made between those compounds that are labile, reversibly sorbed and irreversibly sorbed by sewage sludge-amended soils. The implications of the form in which the chemicals are present in soil for their "availability' to transfer from the soil to bacteria, fungi, earthworms, grazing livestock and food crops followed by the potential for further transfers, metabolism or bioaccumulation are discussed. The importance of the timing and method of sewage sludge application to soil on "form' and "availability' are also considered.

Public health assessment for dioxins exposure from soil

Dioxins are among the most toxic anthropogenic chemicals in the environment. Their toxicity has been extensively studied in both humans and animals. Dioxin-contaminated soil may result in dioxins occurring in a food chain. This is especially important for the general population. It has been estimated that about 98% of exposure to dioxins is through the oral route. In the 1980s, a concentration level of 1 ppb 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in soil was specified as "a level of concern," based on cancer effects. However, recent studies indicate that end points other than cancer are also of concern. A health risk analysis scenario based on health effects of TCDD other than cancer is discussed and compared with the projected intake from 1 ppb TCDD in soil.

Comparison between oral and dermal bioavailability of soil-adsorbed phenanthrene in female rats

Phenathrene is a major coal tar component found in hazardous waste disposal sites. The purpose of this study was to evaluate the extent to which phenanthrene adsorption to either of 2 different soils affects the manner in which phenanthrene is subsequently handled in orally and dermally exposed adult female rats. Absorption from the gastrointestinal tract was relatively rapid for all treatments with maximum plasma concentration of radioactivity occurring within 1 h following oral administration. After dermal application, the time to reach maximum plasma concentration (12 h) was the same in all 3 phenanthrene treatment groups although sandy soil lowered the area under the plasma concentration time curve (AUC) compared to the pure and clay soil groups. Dermal exposure increased absorption half-lives 8-fold compared to oral exposure in the pure group and 15-fold in each of the soil groups. After oral or dermal treatment with phenanthrene alone or adsorbed to soil, the urine represented the primary excretion route of 14C activity. Ileum contained the highest tissue concentration of radioactivity in all oral treatment groups. However, the skin application site contained the highest concentration of radioactivity followed by ileum after dermal exposure. Phenanthrenequinone and 9,10-phenanthrene dihydrodiol were the major urinary metabolites detected in the 0-12-h urine of all treatment groups in both routes of administration. The data suggest that the oral exposure route for phenanthrene is a greater health risk than the dermal route. However, the presence of sandy or clay soil tends to delay the elimination of phenanthrene from the plasma.

Transport of organic environmental contaminants to animal products

A large number of chemical contaminants potentially may be present in agricultural environments, leading to exposure of animals and potential residues in animal products. The contamination may be either widespread, as a result of aerial transport of industrial emissions, or localized, as a result of accidental emissions and spills, improper waste disposal, contaminants in useful products, and areas of past use of products now banned. The halogenated hydrocarbons, including the polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), and persistent organochlorine insecticides remaining from past use, are the contaminants of most concern. Depending on the degree and pattern of chlorine substitution, these compounds are resistant to degradation and tend to accumulate in the fat of animals and their products. Other classes of environmental contaminants as exemplified by the PAHs, phthalate esters, acid phenolics, and nitrosamines also may occur widely in the environment. These compounds are unlikely to be transported to animal products because the compounds are water-soluble or can be metabolized to water-soluble products, which are excreted in the urine and thus do not bioaccumulate in products such as milk and meat. The points of entry of environmental contaminants into agricultural environments usually are plants and soils. Lipophilic compounds such as the halogenated hydrocarbons are not taken up and translocated by plants. Contamination of plants is mainly a surface phenomenon resulting from aerial deposition of emissions or deposition of compounds volatilized from the surface of contaminated soil. Thus, fibrous roughages used primarily in feeding cattle and other ruminants will be the most important pathway of animal exposure and transport to human foods. The second pathway of animal exposure is by ingestion of contaminated soil while grazing or when confined to unpaved facilities. As in the case of feed sources, cattle is the species most vulnerable to exposure by the soil ingestion pathway under most commercial management systems, but poultry and swine are more vulnerable in those infrequent situations in which these species have access to contaminated soil.

Parameter values to model the soil ingestion pathway

Soil ingestion is an important exposure pathway for contaminants that are not otherwise very mobile in the environment. Health of both humans and animals can be affected. This paper summarizes the literature and recommends models and probabilistic parameter values for risk assessment applications. Models of the pathway require estimates of the amounts of soil ingested, the concentration of contaminants relative to the original soil, and the bioavailability in the gut of the contaminants ingested with soil. Using a lead-contaminated sandbox as an example, the modelling recommendations suggest that a child typically may consume 50 mg d(-1) of the sandbox soil, the soil ingested will have a tenfold higher lead concentration than the original soil, and the lead will be as bioavailable as if ingested as inorganic lead in water.

The toxicokinetics and metabolism of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) and their relevance for toxicity

This article reviews the present state of the art regarding the toxicokinetics and metabolism of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs). The absorption, body distribution, and metabolism can vary greatly between species and also may depend on the congener and dose. In biota, the 2,3,7,8-substituted PCDDs and PCDFs are almost exclusively retained in all tissue types, preferably liver and fat. This selective tissue retention and bioaccumulation are caused by a reduced rate of biotransformation and subsequent elimination of congeners with chlorine substitution at the 2,3,7, and 8 positions. 2,3,7,8-Substituted PCDDs and PCDFs also have the greatest toxic and biological activity and affinity for the cytosolic arylhydrocarbon (Ah)-receptor protein. The parent compound is the causal agent for Ah-receptor-mediated toxic and biological effects, with metabolism and subsequent elimination of 2,3,7,8- substituted congeners representing a detoxification process. Congener-specific affinity of PCDDs and PCDFs for the Ah-receptor, the genetic events following receptor binding, and toxicokinetics are factors that contribute to the relative in vivo potency of an individual PCDD or PCDF in a given species. Limited human data indicate that marked species differences exist in the toxicokinetics of these compounds. Thus, human risk assessment for PCDDs and PCDFs needs to consider species-, congener-, and dose-specific toxicokinetic data. In addition, exposure to complex mixtures, including PCBs, has the potential to alter the toxicokinetics of individual compounds. These alterations in toxicokinetics may be involved in some of the nonadditive toxic or biological effects that are observed after exposure to mixtures of PCDDs or PCDFs with PCBs.

The penetration of 2,3,7,8-tetrachlorodibenzo-p-dioxin into viable and non-viable porcine skin in vitro

Freshly harvested, full thickness porcine skin was kept metabolically viable at 4 degrees C in a minimal essential medium for at least 48 h, as judged by the formation of lactate or 14CO2 from 14C-labeled glucose. In vitro topical exposure to the environmental contaminant, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, 65 ng/cm2) for up to 1000 min did not affect the viability of skin. The penetration and distribution of TCDD into porcine skin was studied in an in vitro system under a variety of conditions, such as viability status, different vehicles or concentrations, or artificial removal of the stratum corneum. Loss of viability of the skin increased the rate of penetration of TCDD by about 60%. Removal of the stratum corneum to mimic lesioned skin increased the rate of dermal penetration of TCDD about 3-fold. The use of acetone as the vehicle, simulating dermal exposure to TCDD as a dust or from a volatile solvent, resulted in higher rates of penetration than the use of mineral oil as the vehicle, which simulates the situation of industrial accidents. The percentage of dose absorbed was independent of the dose of TCDD (65 or 6.5 ng/cm2) administered to the surface of skin. Rates of dermal penetration of TCDD ranged form 14 to 985 pg/cm2 skin per h, or 0.2-1.5% of the dose/h, depending on the conditions of exposure. These rates of penetration are comparable with results obtained by others in several other species, with both in vitro and in vivo systems including human skin in vitro. Full thickness porcine skin, viable or previously frozen, is therefore a valid in vitro model to estimate dermal penetration of TCDD in humans.

Decontamination of human skin exposed to 2,3,7,8-tetrachlorodibenzo-p-Dioxin (TCDD) in vitro

Human post-mortem skin was exposed in vitro to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) at 32 degrees C, under controlled humidity. In one-half of the samples, damage to the surface of the skin was simulated by stripping of the stratum corneum. After incubation with TCDD for 100 min, four different decontamination protocols were performed: (1) the sample was wiped with dry, adsorbent material (cotton balls); (2) a 10-min topical treatment with mineral oil was followed by dry wiping with cotton balls; (3) a 10-min topical treatment with mineral oil was followed by wiping with acetone-soaked cotton balls; and (4) the sample was washed with water and soap. After decontamination, skin samples were incubated (up to 300 min) again at 32 degrees C. One set of both intact and stripped TCDD-exposed skin samples was incubated for 300 min--absent decontamination--and was used as a control. Mineral oil treatment and acetone wipes, or water and soap, were effective in reducing (i.e., about two-fold) the amount of TCDD in the stratum corneum of intact skin. Mineral oil plus dry wipes reduced the amount of TCDD in the stratum corneum by about one-third, whereas dry wiping alone was ineffective. All protocols, however, were similarly effective in reducing the amount of TCDD in the epidermis and upper dermis; TCDD concentrations were decreased locally by factors of up to ten. In the lower dermis, a minimal effect of the decontamination procedures was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Recent developments on the hazards posed by 2,3,7,8-tetrachlorodibenzo-p-dioxin in soil: implications for setting risk-based cleanup levels at residential and industrial sites

Since the publication of the Times Beach risk assessment in 1984, which suggested that residential soils were of concern when the level of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was in excess of 1 ppb, there has been continued interest in this topic. Studies conducted within the past 5 yr on the environmental and toxicological behavior of TCDD, as well as refinement of parameters regarding human exposure, indicate that previous assessments of the risk to humans posed by TCDD-contaminated soil were overestimated. In this paper, recent information drawn from nearly 100 recently published articles regarding the histopathology interpretation of the Kociba bioassay, environmental fate and half-life of TCDD in soil, and estimates of human exposure via soil ingestion, dermal contact, inhalation, surface runoff, and the consumption of fish were incorporated into a risk assessment. Cleanup levels for TCDD in residential and industrial soils were calculated based on most likely exposure scenarios. Probability distributions of key exposure parameters were incorporated into a Monte Carlo uncertainty analysis to predict the range and probability of TCDD uptake and corresponding cleanup levels in soil. This analysis demonstrated that the most significant route of human exposure to TCDD is through dermal contact with soil, followed by soil ingestion, fish consumption, and inhalation of airborne particulates. At residential sites, soils containing 20 parts per billion (ppb) of TCDD were found to pose a lifetime cancer risk no greater than 1 in 100,000 (10(-5) risk) under typical exposure conditions. Based on the Monte Carlo analysis, soil concentrations for the 75th and 95th percentile person were 12 and 7 ppb (10(-5) risk), respectively. In industrial soils, TCDD concentrations ranged between 131 and 582 ppb (10(-5) risk), depending on the amount of time spent outdoors under typical exposure conditions. Industrial soil concentrations of approximately 93 and 46 ppb (10(-5) risk) were calculated for the 75th and 95th percentile worker, respectively, engaged in outdoor activities. The range of TCDD concentrations in industrial soils was not reduced significantly when the consumption of fish from a neighboring waterway by off-site receptors was considered. While cleanup levels for TCDD should be derived on a site-specific basis, this analysis indicated that soil cleanup standards can be generally higher than those implemented over the past 8 yr.

Penetration, distribution and kinetics of 2,3,7,8-tetrachlorodibenzo-p-dioxin in human skin in vitro

The in vitro penetration of 3H-labeled 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) into human cadaver skin was studied at concentrations of 65 and 6.5 ng TCDD per cm2 of skin surface. Vehicles used were acetone to simulate exposure to TCDD as a dry material, and mineral oil to simulate exposure to TCDD in an oily medium. Penetration was performed for 30, 100, 300, and 1000 min in improved Franz cells. Skin was used either intact, or with stripped horny layer. Skin was sectioned along its natural layers and radioactivity determined in epidermis and dermis. TCDD did not readily penetrate into human skin in vitro. The vehicle of exposure to TCDD played an important role in dermal penetration. The rapidly evaporating acetone allowed TCDD to penetrate deeply into the loose surface lamellae of the horny layer, but then appeared to be poorly available for further penetration. Mineral oil as the vehicle, on the other hand, represented a lipophilic compartment which competed with lipophilic constituents of the stratum corneum for TCDD and hence slowed its penetration even more. The stratum corneum acted as a protective barrier, as its removal increased the amount of TCDD absorbed into layers of the skin. Hourly rates of absorption of TCDD per unit area of skin were calculated in two ways: a worst case scenario where TCDD absorbed into any layer of skin including the stratum corneum was used for regression analysis; and a physiological approach where only that amount of TCDD was considered absorbed which had penetrated beyond the epidermis into the region of dermal vascularization.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of potential transmission of 2,3,7,8-tetrachlorodibenzo-p-dioxin-contaminated incinerator emissions to humans via foods

Interest in the potential sources of human exposure to TCDD (dioxins, TCDD and equivalents, or 2,3,7,8-tetrachlorodibenzo-p-dioxin) via foods has recently shifted from phenoxy herbicides to products of combustion and waste disposal. Proposals to locate municipal waste combustors in rural areas have raised concerns that emissions, which could contain TCDD, could contaminate animal feeds and such human foods as milk, meat, and vegetables. Important factors that can affect the results of an assessment of incinerator emissions include (1) the emission and deposition rates of TCDD from the source, (2) the fractional retention and half-life of fly ash on plants, (3) the environmental half-life of TCDD, (4) the animal feeding and management systems, (5) the bioavailability of TCDD and related compounds, (6) the metabolism and pharmacokinetics of TCDD in farm animals, (7) food consumption levels, (8) the half-life of TCDD in humans, and (9) the model selected to estimate cancer risk. For persons living in the area of highest deposition near an incinerator, a possible uptake of TCDD from foods of animal origin was estimated to be about 10-40 fg/kg.d, which was much greater than the 1-5 fg/kg.d uptake estimated for foods of plant origin. The total uptake of TCDD from foods by the maximally exposed population will usually be about 500- to 1000-fold greater than that due to inhalation. Although milk was assumed to be the most important food pathway in several previous assessments that evaluated the hazards of airborne emissions, we determined that the deposition-forage-cattle-beef pathway was the more important route of exposure. The previous assessments appear to have used inappropriate pharmacokinetic models for TCDD and to have overestimated pasture use for dairy cows. The amount of TCDD accumulated in soil from airborne emissions was found to be less important than the amount deposited in forage, a finding that is the opposite of the usual conclusions drawn for other routes of TCDD introduction into agricultural environments. Based on the assumption and parameters used in this assessment, the potential human health risks due to TCDD emissions from incinerators are insignificant compared to other background sources of TCDD. It would be desirable to measure TCDD in soil and crops around existing facilities to better evaluate this assessment, but it is likely that concentrations would be too low to reliably quantitate.

Important recent advances in the practice of health risk assessment: implications for the 1990s

Health risk assessments have been so widely adopted in the United States that their conclusions are a major factor in many environmental decisions. The procedure by which these assessments are conducted is one which has evolved over the past 10-15 years and a number of short-comings have been widely recognized. Unfortunately, improvements in the process have often occurred more slowly than advancements in technology or scientific knowledge. Recent significant advances for more accurately estimating the risks posed by environmental chemicals are likely to have a dramatic effect on the regulation of many substances. Each of the four portions of risk assessment (hazard identification, dose-response assessment, exposure assessment, and risk characterization) has undergone significant refinement since 1985. This paper reviews some of the specific changes and explains the likely benefits as well as the implications. Emphasis is placed on the improved techniques for (a) identifying those chemicals which may pose a human cancer or developmental hazard, (b) using statistical approaches which account for the distribution of interindividual biological differences, (c) using lognormal statistics when interpreting environmental data, (d) using physiologically based pharmacokinetic models for estimating delivered dose and for scaling up rodent data, (e) using biologically based cancer models to account for the seven or more apparently different mechanisms of chemical carcinogenesis, (f) describing the severity of the public health risks by considering those portions of the population exposed to various concentrations of a contaminant, and (g) reviewing how criteria for acceptable risk have been influenced by the number of exposed persons. The net benefit of these improvements should be a reduction in the uncertainty inherent in current estimates of the health risks posed by low level exposure to carcinogens and developmental toxicants.

Pharmacokinetics and biological activity of 2,3,7,8-tetrachlorodibenzo-p-dioxin. 2. Pharmacokinetics in rats using a loading-dose/maintenance-dose regime with high doses

Wistar rats were treated initially with very high single doses of 14C-2,3,7,8-TCDD (either 75 or 25 micrograms/kg body wt) followed by weekly maintenance doses of 15 and 5 micrograms/kg body wt, respectively. 14C-radioactivity was measured in various organs over a period of 22 weeks. 1) 75 micrograms TCDD/kg body wt (followed by the maintenance doses) was lethal for all the rats within a period of 9 weeks. While the concentration of 14C-TCDD equivalents in liver and thymus stayed reasonably constant during this period in the surviving rats, the concentration in adipose tissue and kidneys clearly increased in the same animals. 2) The dose of 25 micrograms TCDD/kg body wt (followed by weekly doses of 5 micrograms/kg body wt) proved to be a just tolerable dose over a period of 22 weeks for our strain of rats. 3) Within the individual variabilities the TCDD concentrations in the investigated organs showed no clear-cut decline, indicating that the animals were exposed to fairly constant levels of TCDD throughout the study. Thus, this dosing regime is suitable for maintaining constant TCDD exposure during long-term studies.

Effects of soil on percutaneous absorption of toluene in male rats

Previous assessments of health risks from soil-adsorbed chemical exposures relied on extrapolations from data derived with pure compounds. However, interactions between chemical and soil can alter the rate, amount, and form of chemical that enters the body, resulting in effects that are different from those that occur after exposures to chemical alone. In this study, male rats were treated dermally with [14C]toluene alone or adsorbed to either a sandy or a clay soil. Both soils produced a higher plasma concentration compared to pure toluene, with a statistical decrease in half-life of absorption observed after sandy soil-adsorbed treatment. The time to reach peak plasma concentration, half-life of elimination, and area under the plasma concentration-time curve (AUC) were similar for all groups. Skin and fat contained the highest concentration of radioactivity 48 h after all treatments. Pure and soil-adsorbed toluene were primarily metabolized and excreted via the kidney rather than exhaled. Furthermore, soil treatment did not alter the percentages of the metabolic products.

Comparative dermal absorption of 2,3,7,8-tetrachlorodibenzo-p-dioxin and three polychlorinated dibenzofurans

Polychlorinated dibenzodioxins (PCDDs) and dibenzofurans (PCDFs) are toxic environmental contaminants which have the potential to accumulate in human tissues. In order to examine the potential for systemic exposure following dermal exposure, the absorption, distribution, and elimination of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,7,8-tetrachlorodibenzofuran (TCDF), 1,2,3,7,8-pentachlorodibenzofuran (1PeCDF), and 2,3,4,7,8-pentachlorodibenzofuran (4PeCDF) were evaluated in male F344 rats. TCDD (0.00015, 0.001, 0.01, 0.1, 0.5, and 1.0 mumol/kg) and the three PCDFs (0.1, 0.5, and 1.0 mumol/kg) were applied to a preclipped region on the back of the rat and covered with a perforated cap. The rats were held in individual metabolism cages for 3 days. In animals administered 0.1 mumol/kg, the absorption of TCDF was greater than that of 4PeCDF, 1PeCDF, and TCDD. Relative absorption (percentage of administered dose) declined with increasing dose while the absolute absorption (microgram/kg) increased nonlinearly with dose. Absorption of TCDF at 0.1 mumol/kg was 48% of the administered dose which was significantly greater than that of the other compounds. At this dose, absorption of 4PeCDF was greater than that of TCDD. Absorption at the higher doses was similar for all four compounds. Maximum relative absorption of TCDD (approximately 40% of the administered dose) was obtained at 0.001 and 0.00015 mumol/kg. Major tissue depots for these four chemicals included liver, adipose, skin, and muscle tissue; however, the liver:fat ratio for 4PeCDF was approximately fourfold higher than that for the other three compounds. When normalized to 100% of dose absorbed, the distribution of 4PeCDF-derived radioactivity in liver and adipose tissue was similar to that previously observed after oral and iv administration. In animals administered 0.1 mumol TCDF or 1PeCDF/kg, 56 and 32% of the respective absorbed dose was excreted as polar metabolites within 3 days. Very little of the absorbed dose of either TCDD (approximately 10%) or 4PeCDF (approximately 2%) was eliminated. Results indicate that the dermal absorption of these compounds is incomplete and that systemic toxicity following acute dermal exposure to levels found in the environment is unlikely.

Pharmacokinetics and biological activity of 2,3,7,8-tetrachlorodibenzo-p-dioxin. 1. Dose-dependent tissue distribution and induction of hepatic ethoxyresorufin O-deethylase in rats following a single injection

Concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in rat liver and adipose tissue, and hepatic ethoxyresorufin O-deethylase (EROD) activity were studied subsequent to a single subcutaneous injection of TCDD. Two types of experiments were performed to study: (a) time-dependent changes following a single injection of 300 ng TCDD/kg body wt (points 1-4), and (b) dose-dependent changes measurable after 7 days following a single injection (points 5-7). 1. Absorption of TCDD following a single subcutaneous injection was about 90% after 3 days and 98% after 5 days. 2. Following a single dose of 300 ng TCDD/kg body wt peak concentrations were: liver (after 3 days): 4.7 +/- 0.9 ng/g wet wt, and adipose tissue (after 7 days): 0.82 +/- 0.07 ng/g wet wt. 3. T1/2 of TCDD in liver was 13.6 days over the total experimental period (from day 10 to 91 of the study), apparently with an initial faster phase: 11.5 days (from day 10 to 49), and a slower period at the end of the experiment: 16.9 days (from day 49 to 91); in adipose tissue the t1/2 was 24.5 days (from day 14 to 91 of the study). 4. Maximum induction of EROD in the liver was observed (14-fold at 300 ng TCDD/kg body wt) 3-7 days following the injection; the activity was decreased to about one third of the maximum 3 weeks after the injection; increase in total cytochrome P-450 at this dose was only about 1.4-fold at the induction maximum. 5. The ratio of the TCDD concentrations in liver and adipose tissue increased considerably between doses of 3 ng TCDD/kg body wt (ratio: about 0.74) and 3000 ng TCDD/kg body wt (ratio: about 7.7). 6. The extent of EROD induction in the liver increased dose dependently. A significant effect was first observed with a dose of 3 ng TCDD/kg body wt (activity about +32% above control activity). The corresponding tissue concentration was about 10 pg TCDD/g liver wet wt. 7. An almost perfect linear relationship exists (when using a double-log plot) between the hepatic TCDD concentration and the EROD activity for tissue concentrations ranging from 40 to 30,000 pg TCDD/g wet wt.

Landspreading dioxin-contaminated papermill sludge: a complex problem

Assessing the potential for human exposure and resultant health risk from applying dioxin-contaminated papermill sludge to agricultural and silvicultural lands in Central Wisconsin is a complex issue. This is an intricate problem with many facets to consider. Among the exposure and risk assumption issues discussed are application of dioxin and furan equivalency factors; acceptable daily intake levels; cancer risk levels; and exposure scenarios including food, air, dermal, and soil ingestion. The range of regulatory options run from banning any application of dioxin-contaminated sludge to establishing acceptable or tolerable contamination limits. A preliminary assessment of potential human exposure scenarios found a many thousand-fold range of risk.

Bioavailability and cytochrome P-450 induction from 2,3,7,8-tetrachlorodibenzo-P-dioxin contaminated soils from Times Beach, Missouri, and Newark, New Jersey

Bioavailability of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) from contaminated soils from Times Beach, Missouri and Newark, New Jersey, was examined using liver concentrations and toxicity in guinea pigs observed up to 60 days following a single oral administration, and induction of cytochrome P-450 in rats sacrificed 24 hours after a single oral dose as endpoints. Both soils are contaminated with several chlorinated dioxins and numerous other compounds. Times Beach soil resulted in greater TCDD concentration in liver and TCDD was considerably more bioavailable from Times Beach soil than from Newark soil. However, both soils induced cytochrome P-450 activity to approximately the same extent. Moreover, similar banding patterns of microsomal proteins were seen on polyacrylamide electrophoretic gels. The many other compounds present in the soils, particularly in Newark, may account for the similar protein bands and levels of cytochrome P-450 observed.

A critical examination of assumptions used in risk assessments of dioxin contaminated soil

Environmental standards for 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin, TCDD) are currently being considered by regulatory agencies worldwide. Among these are limits for tap water, soil at industrial sites, residential soil, fish, ambient air, and fly ash. Thus far, in the United States, no standards have been promulgated but a few have been suggested. This paper critically evaluates several aspects of previously proposed approaches to setting limits for TCDD in residential soil and soil within industrial sites. Factors and assumptions which significantly affect the predicted degree of hazard associated with exposure to soil contaminated with low levels of dioxin are discussed. This paper shows how different, more justifiable assumptions than those used by the Centers for Disease Control (CDC) regarding the quantities of soil typically consumed by children, TCDD's nongenotoxicity, dermal exposure to soil, the concentration of airborne soil particles, dioxin's bioavailability in soil, and extrapolation of the dose response curve can profoundly affect the results of the risk assessment and, subsequently, the magnitude of the recommended limits. Two case studies which quantitatively illustrate the effect of these assumptions on the risk estimates are presented. Non-U.S. regulatory agencies have considered TCDD's nongenotoxicity in estimating that the virtually safe dose (VSD) or acceptable daily dose for dioxin is approximately 10 pg/kg/day (10,000 fg/kg/day). These approaches are compared and contrasted with the method used by the United States EPA whose risk estimates are higher and whose VSD is approximately 1,000-fold lower. Alternative approaches to interpreting the cancer data indicate that a VSD of 130 pg/kg/day is more scientifically justified than risks estimated using standard approaches. This assessment indicates that a soil concentration of TCDD considerably in excess of 1 ppb should be acceptable for residential and nonresidential areas.

Bioavailability of dioxin in soil from a 2,4,5-T manufacturing site

Dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin, TCDD) is a highly toxic contaminant produced in the manufacture of phenoxy herbicides. Despite its high TCDD content, soil from a contaminated area associated with a 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) manufacturing site in Newark, New Jersey, did not induce acute toxicity when administered to guinea pigs (the most sensitive species) by gavage. Analysis of liver samples demonstrated low bioavailability of TCDD from this soil. A comparative analysis of soils showed that Soxhlet extraction was necessary for the determination of TCDD on Newark soil, whereas solvent extraction was sufficient for soil from Times Beach, Missouri. The difference in the bioavailability of TCDD from these soils is correlated with TCDD extractability and may be related to the different compositions of the soils.

Assessment of health risk from exposure to contaminated soil

The risk to human health posed by contaminated soil in a residential area depends on the potential extent of exposure to soil and on the toxic properties of the contaminants. A detailed soil exposure analysis is presented for young children, older children, and adults living in a house surrounded by contaminated soil. From this analysis, a lifetime exposure model is derived and used to assess chronic health risks.

Bioavailability of soil-borne polybrominated biphenyls ingested by farm animals

Concentrations of polybrominated biphenyl (PBB) were measured in the fat of livestock on several farms on which soil-borne PBB in confinement areas was the only source of residue. Ratios of concentrations in fat to concentrations in soil were 0.37 for dairy heifers, 0.27 for primaparous dairy cows, 0.10 for multiparous dairy cows, 0.27 for beef cows, 0.39 for beef calves, 0.37 for ewes, and 1.86 for swine. Multiparous dairy cows had lower ratios because of the excretion of PBB in milk during long-term lactation, and swine had higher ratios because they ingest greater amounts of soil than other species. Diets containing 5% PBB-contaminated soil, or 5% contaminated soil amended with activated carbon, were fed to lambs for 56 d. Accumulation of soil-borne PBB in fat, when adjusted for intake, did not differ significantly from accumulation of PBB from a diet in which PBB was added to cornmeal. Amending soil with activated carbon had no effect on residue accumulation. About 70% of PBB in a control diet with PBB added to cornmeal was absorbed, as measured by using titanium as an unabsorbed marker. Absorption of soil-borne PBB was 65% from unamended soil, 57% from soil amended with 0.3% activated carbon, and 56% from soil amended with 0.6% activated carbon. The differences were not great enough to be of practical importance. These results with PBB may be useful in assessing and managing risks of other soil-borne contaminants that have chemical characteristics similar to those of PBB.

Cutaneous signs of systemic toxicity due to dioxins and related chemicals

The controversy about dioxin effects on human health received a great deal of attention recently when the State of Missouri was declared to have a dioxin crisis. However, dioxin and several related chemicals are widespread throughout the world. Cutaneous signs play an important part in evaluating toxicity of dioxin and similar chemicals. Chloracne is the most sensitive indicator of significant dioxin exposure. Porphyria cutanea tarda and hyperpigmentation are other known cutaneous effects, and malignant fibrous histiocytomas of the skin may possibly be associated, although data are inconclusive on this point. The AMC Council on Scientific Affairs recommended that all physicians become familiar with chloracne and other toxic effects of dioxin. Dermatologists, especially, should be aware of the problem and may discover early cases of previously unsuspected exposure to this group of chemicals.

Dioxin in soil: bioavailability after ingestion by rats and guinea pigs

Soil environmentally contaminated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was given by gavage to guinea pigs and rats. The development of a characteristic clinicopathologic syndrome in guinea pigs, the induction of aryl hydrocarbon hydroxylase in rats, and the presence of TCDD in the livers of both species show that TCDD in soil exhibits high biological availability after ingestion.

The influence of soil particle adsorption on 2,3,7,8-tetrachlorodibenzo-p-dioxin biological uptake in the rabbit

A comparative study on the biological uptake in the rabbit of 2,3,7,8-tetrachloridibenzo-p-dioxin (TCDD) in different formulations, including accident-contaminated Seveso soil, was attempted. On the whole, these results indicated that soil-borne TCDD had a bioavailability lower than that of free (solvent-borne) TCDD.

Health implications of 2,3,7,8-tetrachlorodibenzodioxin (TCDD) contamination of residential soil

Extrapolations from animal toxicity experiments (including carcinogenicity and reproductive effects) to possible human heath effects can be used to estimate a reasonable level of risk for 2,3,7,8-tetrachlorodibenzodioxin (2,3,7,8-TCDD). Extrapolations are derived from: (1) review of published studies, (2) a complex set of assumptions related to human exposure to contaminated soil, and (3) estimates of (a) a dose response curve, (b) appropriate margins of safety, and/or (c) applicable mechanisms of action. One ppb of 2,3,7,8-TCDD in soil is a reasonable level at which to begin consideration of action to limit human exposure for contaminated soil.