Tetrachlorodibenzodioxin in the environment: sources, fate, and decontamination

The aryl hydrocarbon receptor interacts with ATP5α1, a subunit of the ATP synthase complex, and modulates mitochondrial function

Dioxins, including 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD), produce a wide range of toxic effects in mammals. Most, if not all, of these toxic effects are regulated by the aryl hydrocarbon receptor (AHR). The AHR is a ligand activated transcription factor that has been shown to interact with numerous proteins capable of influencing the receptor's function. The ability of secondary proteins to alter AHR-mediated transcriptional events, a necessary step for toxicity, led us to determine whether additional interacting proteins could be identified. To this end, we have employed tandem affinity purification (TAP) of the AHR in Hepa1c1c7 cells. TAP of the AHR, followed by mass spectrometry (MS) identified ATP5α1, a subunit of the ATP synthase complex, as a strong AHR interactor in the absence of ligand. The interaction was lost upon exposure to TCDD. The association was confirmed by co-immunoprecipitation in multiple cell lines. In addition, cell fractionation experiments showed that a fraction of the AHR is found in the mitochondria. To ascribe a potential functional role to the AHR:ATP5α1 interaction, TCDD was shown to induce a hyperpolarization of the mitochondrial membrane in an AHR-dependent and transcription-independent manner. These results suggest that a fraction of the total cellular AHR pool is localized to the mitochondria and contributes to the organelle's homeostasis.

Long overlooked historical information on Agent Orange and TCDD following massive applications of 2,4,5-T-containing herbicides, Eglin Air Force Base, Florida

BACKGROUND

From 1961-1971, The Air Development Test Center, Eglin Air Force Base (AFB), Florida, developed, tested, and calibrated the aerial spray systems used in support of Operation RANCH HAND and the US Army Chemical Corps in Vietnam. Twenty major test and evaluation projects of aerial spray equipment were conducted on four fully instrumented test grids, each uniquely arrayed to match the needs of fixed-wing, helicopter, or jet aircraft. Each of the grids was established within the boundary of Test Area 52A of the Eglin Reservation.

METHODS

The tests, conducted under climatic and environmental conditions similar to those in Vietnam, included the use of the military herbicides (Agents) Orange, Purple, White, and Blue. Approximately 75,000 kg of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and 76,000 kg of 2,4-dichlorophenoxyacetic acid (2,4-D) were aerially disseminated on an area of less than 3 km2 during the period 1962-1970. Data from the analysis of archived samples suggested that an estimated 3.1 kg of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), present as a contaminant, were aerially released in the test area. Because most of the vegetation had been removed before establishing the test site in 1961, there was an opportunity to follow ground-based residues independent of canopy interception, and the resulting high solar exposure of initial residues. Studies of the soils, fauna, flora, and aquatic ecosystems of the test grids and associated perimeters of Test Area C-52A (an area totally more than 8 km2) were initiated in 1969 and concluded in 1984.

RESULTS AND DISCUSSION

Data from soil samples collected from 1974 through 1984 suggested that less than one percent of the TCDD that was present in soil when sampling began persisted through the ten-year period of sampling. More than 340 species of organisms were observed and identified within the test area. More than 300 biological samples were analyzed for TCDD and detectable residues were found in 16 of 45 species examined. Examination of the ecological niches of the species containing TCDD residues suggested each was in close contact with contaminated soil. Indepth field studies, including anatomical, histological and ultrastructural examinations, spanning more than 50 generations of the Beachmouse, Peromyscus polionotus, demonstrated that continual exposure to soil concentrations of 0.1 to 1.5 parts-per-billion (ng/g) of TCDD, had minimal effects upon the health and reproduction of this species.

CONCLUSIONS

Since Agent Orange with its associated TCDD contaminant was aerially disseminated on the test grids, Test Area C-52A provided a 'field laboratory' for what may have happened in Vietnam, had there been no intercepting forest cover. However, in Vietnam a 'typical' mission would have disseminated 14.8 kg of 2,4,5-T/ha, most of which was intercepted by the forest canopy, versus the 876 kg 2,4,5-T/ha on the test grid at Eglin. Moreover, each hectare on the Eglin test grid received at least 1,300 times more TCDD than a hectare sprayed with Agent Orange in Vietnam. The disappearance or persistence of TCDD is dependent upon how it enters the ecosystem. Spray equipment test and evaluations missions at Eglin were generally scheduled and conducted with environmental conditions that were optimal for spray operations. This suggests that conditions favorable for dissemination of herbicide were the same conditions favorable for photodegradation of TCDD. It was likely that 99 percent of the TCDD never persisted beyond the day of application. No long-term adverse ecological effects were documented in these studies despite the massive quantities of herbicides and TCDD that were applied to the site. Reviews by the US Environmental Protection Agency and the National Academy of Sciences' Institute of Medicine did not address the fate of Agent Orange and TCDD as described in these studies from Eglin AFB, Florida.

Depression of rat testicular 17-hydroxylase and 17,20-lyase after administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

Toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), such as chloracne, hirsutism, and skin hyperpigmentation, suggest endocrine involvement, however, little is known about the effects of TCDD on steroidogenic organs. It is known that TCDD can cause decreases in testicular heme, testicular microsomal cytochrome P-450, and serum testosterone in the rat. This study was designed to examine the activities of the testicular hemoprotein microsomal cytochrome P-450-dependent enzymes, 17-hydroxylase and 17,20-lyase, following a single, oral dose of either 12.5, 25, or 50 micrograms/kg TCDD. TCDD caused dose- and time-dependent decreases in the activity of the 17-hydroxylase enzyme. Significant decreases were observed at 3, 7 and 14 days at the lowest dose of 12.5 micrograms/kg TCDD. The 17,20-lyase enzyme seemed to be less sensitive to the toxic effects of TCDD with significant decreases in enzyme activity being observed at days 3, 7 and 14 only after treatment with 50 micrograms/kg TCDD. Both microsomal cytochrome P-450 and serum testosterone levels decreased in a dose- and time-dependent manner following 12.5, 25 and 50 micrograms/kg doses of TCDD. These results indicate that decreased testosterone production following treatment with TCDD is related to decreased activities of the testicular microsomal cytochrome P-450-dependent enzymes 17-hydroxylase and 17,20-lyase.

2,3,7,8-Tetrachlorodibenzo-p-dioxin-mediated depression of rat testicular heme synthesis and microsomal cytochrome P-450

Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) produces hirsutism, alopecia, and chloracne, symptoms that suggest a possible alteration of endocrine function. Therefore, the effects of TCDD on rat testicular cytochrome P-450 content were investigated. Forty-eight hours after a single, oral dose of TCDD (25 microgram/kg) testicular microsomal cytochrome P-450 levels were depressed by approximately 24%. Microsomal cytochrome P-450 continued to decrease to 62% of control levels at 4 days and remained at approximately the same levels 7 days following treatment. Testicular microsomal heme content exhibited a similar pattern after administration of TCDD. No alterations in testicular delta-aminolevulinic acid (ALA) synthase were detected. The incorporation of [14C]ALA into microsomal heme was decreased to approximately 36% of control values at 24 hr after TCDD administration. Testicular weights were not altered during the 7-day experimental period. These data suggest that TCDD depresses cytochrome P-450 levels in the rat testis through an inhibition of the synthesis of testicular heme.

Review of the dioxin problem. Mass spectrometric analyses of tetrachlorodioxins in environmental samples

Major concern over the chemical group of chlorodioxins has arisen since 2,3,7,8-tetrachlorodibenzo-p-dioxin with its extremely toxic and teratogenic properties has been found in widely distributed pesticides such as the herbicide 2,4,5-trichlorophenoxy acetic acid. Because of its chemical stability and lipophilic nature, 2,3,7,8-tetrachlorodibenzo-p-dioxin released into the environment has the potential of accumulation in the food chain. Mass spectrometry in its various forms has been the method of choice to detect and confirm low parts per billion of 2,3,7,8-tetrachlorodibenzo-p-dioxin. Recently, a Consensus Forum held at the National Center for Toxicological Research amongst the various United States Government agencies (Food and Drug Administration, Environmental Protection Agency, US Department of Agriculture and National Institute of Environmental Health Sciences), eloquently demonstrated the potential, as well as the shortcomings, of the various techniques applied. In particular, the availability of a stable 13C labeled 2,3,7,8-tetrachlorodibenzo-p-dioxin has proved to be an essential component to achieve low level quantitation. A brief review of the findings of the Consensus Forum is presented together with a detailed survey of the application of atmospheric pressure ionization mass spectrometry to TCDD analysis at the National Center for Toxicological Research/Food and Drug Administration.

Biological degradation of TCDD in rats

Apart from its high toxicity, the chemical stability and persistence of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the environment bring about additional hazards. However, until now there has been no evidence for degradation of this dioxin in biological systems, and it is considered unusual that a compound which is insusceptible to biological attack should be so extremely toxic. In in vitro studies with microsomal preparation from mouse, rat and rabbit liver, as well as in vivo, no metabolite of TCDD has been detected by several workers. Recent data, showing a lower toxicity of TCDD in rats after stimulation of the hepatic mixed-function oxidase, suggested possible metabolic transformation of this compound. In the present study, we used tritiated TCDD to search for metabolites in the bile of rats and found marked changes in lipophilicity and mobility in TLC of the excreted radioactivity. Treatment with diazomethane yielded at least two new compounds. These observations hinted at the formation of phenolic hydroxyl groups in the dioxin molecule.

Multinationals and health: reflections on the Seveso catastrophe

On July 10, 1976, a cloud of vaporized products containing dioxin escaped from a deposit of a plant of the Icmesa firm in the northern suburbs of Milan. The fallout was deposited on a vast zone in the municipalities of Desio, Seveso, Meda, and Cesano. Dioxin was not the desired product of the industrial process, but rather an impurity which generally accompanies trichlorophenol, and, to a smaller extent, the products synthesized from trichlorophenol. Among these there are hexachlorophene and the herbicide 2,4,5-trichlorophenoxyacetic acid, which was used as a defoliant in the Vietnam War. After describing toxicological properties of dioxin, this paper examines the role of multinational corporations and of capitalist governments in exploiting not only the people of underdeveloped lands, but also workers of developed countries, transforming into capital not only the increased value of man, but also the conditions, harmfulness, and risks of work.