As was indicated to be the intention of the committee responsible for Update 2008, the committee for Update 2010 has removed chloracne, porphyria cutanea tarda (PCT), and early-onset peripheral neuropathy from the body of these Veterans and Agent Orange (VAO) reports. The three conditions that occur in temporal proximity to exposure have little relevance for new claims from Vietnam veterans, and there has been minimal new evidence since they were classified as having evidence of an association with herbicide exposure
The three conditions have long been recognized by the Department of Veterans Affairs as presumptively related to service in Vietnam. Consequently, the committee wants to provide easy access to the body of biomedical evidence on which these decisions were made by retaining the information distilled in this appendix and in the corresponding appendixes in future volumes in the VAO series.
Chloracne is a skin disease that is characteristic of exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and other diaromatic organochlorine chemicals. It shares some pathologic processes (such as the occlusion of the orifice of the sebaceous follicle) with more common forms of acne (such as acne vulgaris), but it can be differentiated by the presence of epidermoid inclusion cysts, which are caused by proliferation and hyperkeratinization (horn-like cornification) of the epidermis and sebaceous gland epithelium. Although chloracne is typically distributed over the eyes, ears, and neck, it can also occur on the trunk, genitalia, and buttocks of chemical-industry workers exposed to TCDD (Neuberger et al., 1998). It is resistant to acne treatments, but it usually regresses.
Chloracne has been used as a marker of exposure in epidemiologic studies of populations exposed to TCDD and related chemicals. It is one of the few findings in humans that are consistently associated with such exposure, and it is a well-validated indicator of high-dose exposure to TCDD and related chemicals (Sweeney et al., 1997/98). If chloracne occurs, it appears shortly after the chemical exposure, not after a long latent period; therefore, new cases of chloracne among Vietnam veterans would not be the result of exposure during the Vietnam War. It should be noted that absence of chloracne does not necessarily indicate absence of substantial exposure to TCDD, as is apparent from studies of people who had documented exposure to TCDD after the Seveso incident (Baccarelli et al., 2005a), nor is there necessarily a correlation between serum TCDD concentration and the occurrence or severity of chloracne. Susceptibility to the development of chloracne varies among individuals.
Conclusions from VAO and Previous Updates
The committee responsible for Veterans and Agent Orange: Health Effects of Herbicides Used in Vietnam (referred to as VAO; IOM, 1994) determined that there was sufficient evidence of an association between exposure to at least one chemical of interest (TCDD) and chloracne. Additional information available to the committees responsible for Veterans and Agent Orange: Update 1996 (IOM, 1996), Update 1998 (IOM, 1999), Update 2000 (IOM, 2001), Update 2002 (IOM, 2003), Update 2004 (IOM, 2005), and Update 2006 (IOM, 2007) has not modified that conclusion.
Even in the absence of full understanding of the cellular and molecular mechanisms that lead to the disease, several notable reviews (Panteleyev and Bickers, 2006; Sweeney and Mocarelli, 2000) have deemed the clinical and epidemiologic evidence of dioxin-induced chloracne to be strong. The occupational epidemiologic literature has many examples of chloracne in workers after reported industrial exposures (Beck et al., 1989; Bond et al., 1987, 1989a,b; Cook et al., 1980; Goldman, 1972; May, 1973, 1982; Oliver, 1975; Pazderova-Vejlupkova et al., 1981; Poland et al., 1971; Suskind and Hertzberg, 1984; Suskind et al., 1953; Zober et al., 1990). With relative-risk estimates as high as 5.5 in exposed workers compared with referent nonexposed workers, Bond et al. (1989a) identified a dose–response relationship between probable exposure to TCDD and chloracne. Not everyone exposed to relatively high doses develops chloracne, and some with lower exposure may acquire it (Beck et al., 1989).
Almost 200 cases of chloracne were recorded in those residing in the vicinity of the accidental industrial release of dioxin in Seveso, Italy. Most cases occurred in children, particularly in people who lived in the highest-exposure zone, and most cases resolved within 7 years (Assennato et al., 1989a,b; Caramaschi et al., 1981; Mocarelli et al., 1991). No cases of chloracne were identified in conjunc-
tion with the nonextreme environmental dioxin contamination at Times Beach, Missouri (Webb et al., 1987).
Exposures of Vietnam veterans were substantially lower than those observed in occupational studies and in environmental disasters, such as the one in Seveso. The long period since the putative exposure has imposed methodologic limitations on studies of Vietnam cohorts for chloracne. Nonetheless, the Vietnam Experience Study (CDC, 1988) found that chloracne was self-reported more often by Vietnam veterans than by Vietnam-era veterans (odds ratio [OR] = 3.9). An excess incidence was also found in Vietnam vs era veterans among subjects who were physically examined (OR = 7.3). In comparison with a nonexposed group, Air Force Ranch Hand personnel potentially exposed to Agent Orange reported a significant excess of acne (OR = 1.6) (Wolfe et al., 1990), but no cases of chloracne or postinflammatory scars were found on physical examination 20 years after possible herbicide exposure (AFHS, 1991b).
Previous updates have reported that chloracne-like skin lesions have been observed in several animal species in response to exposure to TCDD but not to purified phenoxy herbicides. Data accruing over the past several decades demonstrated that TCDD alters differentiation of human keratinocytes, and more recent studies have illuminated how. Geusau et al. (2005) found that TCDD accelerates the events associated with early differentiation but also obstructs completion of differentiation. Panteleyev and Bickers (2006) proposed that the major mechanism of TCDD induction of chloracne is activation of the stem cells in the basal layer of the skin to differentiate and inhibition of their ability to commit fully to a differentiated status. Ikuta et al. (2010) have investigated the expression of B-lymphocyte maturation protein 1 (Blimp1) in epidermal keratinocytes and sebocytes in mice after induction of the aryl hydrocarbon receptor (AHR). Recent work with a constitutively activated form of the AHR implicated additional inflammation-related mechanisms by which TCDD exposure may lead to chloracne (Tauchi et al., 2005). The data provide a biologically plausible mechanism for the induction of chloracne by TCDD.
No epidemiologic data in the past decade have refuted the conclusion of prior VAO committees that the evidence of an association between exposure to dioxin and chloracne is sufficient. The 2004 poisoning case of Ukrainian politician Victor Yuschenko has provided a high-profile instance that supports this condition as a response to high-level exposure to TCDD, and the careful monitoring of his case has demonstrated the course of chloracne’s resolution in conjunction with subsiding serum concentrations (Sorg et al., 2009). The formation of chlor-
acne lesions after administration of TCDD has been observed in some species of laboratory animals.
On the basis of numerous epidemiologic studies of occupationally and environmentally exposed populations and supportive toxicologic information, previous VAO committees have consistently concluded that there is sufficient evidence of an association between exposure to at least one chemical of interest and chloracne. Because TCDD-associated chloracne becomes evident shortly after exposure, there is no risk of new cases long after service in Vietnam. Given the established relationship of an association between TCDD and chloracne and the long period that has elapsed since service in Vietnam, the present committee concludes that the emergence of additional biologic or epidemiologic evidence that would merit review and deliberation by later VAO committees is unlikely.
PORPHYRIA CUTANEA TARDA
Porphyrias are uncommon disorders caused by deficiencies of enzymes involved in the pathway of biosynthesis of heme, the iron-containing nonprotein portion of the hemoglobin molecule. PCT, the most common of the porphyrias, is a heterogeneous group of disorders caused by a deficiency of a specific enzyme, uroporphyrinogen decarboxylase. It, can be inherited but usually is acquired. Type I PCT, which accounts for 80–90% of all cases, is an acquired disease that typically becomes evident in adulthood. It can occur spontaneously but usually occurs in conjunction with environmental factors, such as alcohol consumption, exposure to estrogens, or use of some medications.
The most important clinical finding in PCT is cutaneous photosensitivity. Sensitivity to sunlight is thought to result from the excitation of excess porphyrins in the skin by long-wave ultraviolet radiation, which leads to cell damage. Fluid-filled vesicles and bullae develop on sun-exposed areas of the face and on the dorsal surfaces of the hands, feet, forearms, and legs. Other features include hypertrichosis (excess hair) and hyperpigmentation (increased pigment), especially on the face. People with PCT have increased porphyrins in the liver, plasma, urine, and stools. Iron, estrogens, alcohol, viral hepatitis, and chlorinated hydrocarbons can aggravate the disorder. Iron overload is almost always present in people who have PCT.
Conclusions from VAO and Previous Updates
On the basis of strong animal studies and case reports demonstrating TCDD-induced PCT and resolution after cessation of exposure, the committee respon-
sible for VAO determined that there was sufficient evidence of an association between exposure to TCDD and PCT in genetically susceptible people.
Epidemiologic studies of occupational populations have indicated inconsistent associations between the chemicals of interest and increased urinary uroporphyrin. Bleiberg et al. (1964) reported increased urinary uroporphyrin in 11 of 29 workers in a factory that manufactured 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and the manifestation of some clinical evidence of PCT in three of them. In a follow-up study of the same facility 6 years later, no abnormalities in urinary porphyrins were observed (Poland et al., 1971). Calvert et al. (1992) reported no difference in porphyrinuria or the occurrence of PCT between 281 workers in the National Institute for Occupational Safety and Health (NIOSH) cohort who were involved in the production of trichlorophenol and were exposed to TCDD and 260 nonexposed workers. Serum TCDD concentration was not associated with uroporphyrin or coproporphyrin concentrations.
Among people who were exposed to TCDD as a result of the 1976 chemical-plant explosion in Seveso, Italy, clinical PCT was observed only in a brother and a sister who had a mutant enzyme that confers susceptibility in the heterozygous state. In 1977, 60 Seveso residents were tested for increased porphyrins, and 13 had secondary coproporphyrinuria; increased concentrations persisted in only three cases that were thought to be due to liver damage and alcohol consumption (Doss et al., 1984). In the Quail Run mobile-home park in Missouri, residents exposed to dioxin as a result of the spraying of waste oil contaminated with TCDD were found to have higher urinary uroporphyrins than controls, but no cases of clinical PCT were diagnosed (Hoffman et al., 1986; Stehr-Green et al., 1987).
The baseline study of the US Air Force Ranch Hands (AFHS, 1984) showed no difference in uroporphyrin or coproporphyrin concentrations in urine between Ranch Hands and controls. There were no indications of the clinical appearance of PCT in Ranch Hands. Followup studies of the Ranch Hand cohort revealed that mean uroporphyrin was greater in the comparison group than in the Ranch Hands, whereas mean coproporphyrin was higher in Ranch Hands. The clinical significance of the small differences between the Ranch Hands and the comparison groups was uncertain.
The committee responsible for Update 1996 considered three additional nonpositive citations of populations that had substantial exposure to TCDD. Jung et al. (1994) presented porphyrin data on former workers in a German pesticide plant that had manufactured 2,4-D and 2,4,5-T. Of 170 men tested, 27 had present or past chloracne. The study found no difference in porphyrin concentrations between subjects with and without chloracne. There was also no relationship between abnormal results of liver-function tests or porphyrin concentrations and the presence of chloracne. Additionally, there was no relationship between porphyrin concentrations in urine, red blood cells, or plasma and TCDD concentrations in adipose tissue. Three cases of chronic hepatic porphyria (none with overt PCT
and none with chloracne) were identified—a number that did not exceed the expected prevalence in this population. Von Benner et al. (1994) found no indication of clinical porphyria in self-referred workers at six other German chemical plants. Another report on the NIOSH cohort (Calvert et al., 1994) was negative. On the basis of the cumulative findings, the committee responsible for Update 1996 concluded that there was only limited or suggestive evidence of an association. The committees for later updates have not changed the revised conclusion.
Because PCT is manifested shortly after exposure to TCDD, new cases of PCT attributable to exposure during the Vietnam War are not expected to occur.
PCT has not been exactly replicated in animal studies on the effects of TCDD although other porphyrin abnormalities have been reported. Administration of TCDD to mice results in an accumulation of uroporphyrin that occurs in a manner that requires the AHR, cytochrome P450 1A1 (CYP1A1), and CYP1A2 (Robinson et al., 2002; Smith et al., 2001; Uno et al., 2004), but the underlying mechanism of action has not been fully illuminated (Smith and Chernova, 2009; Smith and Elder, 2010).
No epidemiologic data have emerged in the last decade that refute the conclusion of previous VAO committees that there is limited or suggestive evidence of an association between the chemicals of interest and PCT.
On the basis of the evidence reviewed here and in previous VAO reports, the committee concludes that there is limited or suggestive evidence of an association between exposure to at least one chemical of interest and PCT. The occurrence of PCT is rare and may be influenced by genetic predisposition in people who have low concentrations of protoporphyrinogen decarboxylase. Because TCDD-associated changes in porphyrin excretion become evident shortly after exposure, there is no risk that new cases will occur long after service in Vietnam. Given the recognized association between TCDD and porphyrin excretion and the long period that has elapsed since service in Vietnam, the committee concludes that the emergence of additional biologic and epidemiologic evidence that would merit review and deliberation by later VAO committees is unlikely.
EARLY-ONSET PERIPHERAL NEUROPATHY
Since Update 1996, VAO committees have partitioned their consideration of peripheral neuropathy into two categories: early-onset (implicitly transient)
peripheral neuropathy and chronic peripheral neuropathy. Primarily on the basis of reports of short-term health effects after industrial accidents, the committee concluded in 1996 that there was limited or suggestive evidence of an association between exposure to the chemicals of interest and “acute and subacute” neuropathy, which was redesignated early-onset transient peripheral neuropathy by the committee responsible for Update 2004. The present committee recognized the imprecision in the nomenclature that has been used to characterize the type of peripheral neuropathy that is regarded as service-connected. The diagnosis in question is, in fact, contingent on the proximity of its occurrence to the time of exposure, rather than on the transitory nature of the adverse outcome. Clinically, in cases of an immediate response of peripheral neuropathy after toxicant exposure, stabilization or improvement is the rule after exposure ends. However, recovery may not be complete; the degree of recovery can depend on the severity of the initial deficits and the particular exposure. Furthermore, there is a possibility of “subclinical” effects, and a person might be unaware of symptoms although evidence of nerve dysfunction can be found through detailed neurologic examination or electrodiagnostic testing. Thus, the committee chose to delete the word transient to recognize that symptoms of early-onset peripheral neuropathy may be protracted and that recovery from these symptoms may be incomplete.
The information about peripheral neuropathy presented in this appendix demonstrates that this outcome may occur soon after exposure to extremely high concentrations of dioxin. In addition, this appendix addresses the evidence that, in populations with members who experience early-onset peripheral neuropathy (that is, during or shortly after dioxin exposure), some may continue to manifest the problem long after exposure has ceased, and this would show that early-onset peripheral neuropathy is not necessarily transient.
Conclusions from VAO and Previous Updates
Several occupational studies have evaluated whether herbicide exposure or production may lead to early-onset neuropathy. In March 1949, an explosion occurred in a reactor vessel at a chemical plant in Nitro, West Virginia, where 2,4,5-T was being produced. Many workers reported health effects (toxic hepatitis, increased serum lipids, and central nervous system involvement), including a severe acute neuropathy in four workers with chloracne (Ashe et al., 1949, 1950). Thirty years later, an attempt was made to identify workers who had been exposed during that accident and workers who may have been chronically exposed from 1948 through 1969 (Suskind and Hertzberg, 1984). Neurologic examination and nerve-conduction studies did not demonstrate abnormalities compared with a cohort of unexposed controls; however, the procedure for obtaining controls did not ensure equivalence. It is unclear whether the four subjects who had acute neuropathy were included in this effort.
In April 1979, chlorinated dibenzo-p-dioxin contamination was found in a community in Arkansas that was close to a plant where 2,4,5-T and 2,4-D had
been produced since 1957. Fifty-five workers of that plant who had no history of diabetes or alcohol abuse were identified from the total workforce; these subjects underwent neurologic examination and nerve-conduction studies (Singer et al., 1982). Both median motor and sural sensory nerve-conduction studies showed significantly lower conduction velocity in the workers from the plant than in control subjects.
Other industrial accidents have also suggested a link between compounds of interest and early-onset neuropathic symptoms, which persisted in some people. Jirasek et al. (1974) studied 55 of 80 workers who complained of a variety of symptoms after chronic exposure to 2,4,5-T at a manufacturing facility in the Czech Republic; of the 55 workers, 17 had physical examinations suggestive of neuropathy that was said to have been confirmed with electromyographic abnormalities. Follow-up of 44 of the 55 poisoned workers was conducted 10 years after exposure had ceased; about 30% of them were reported to have continued neuropathic symptoms (Pazderova-Vejlupkova et al., 1981). More recently, Urban et al. (2007) evaluated the long-term sequelae of subjects who developed neuropathy after the original exposure. Subjects had increased serum TCDD concentrations more than 30 years after exposure, and evidence of continued neuropathy was noted in 9 of 15 subjects who were available for study.
Acute neuropathic symptoms were reported after the Seveso accident, and persistent signs were noted. Gilioli et al. (1979) evaluated 35 subjects who had been exposed during the accident and noted abnormalities in a variety of neurophysiologic measures compared with age-matched controls 2 years after the exposure. However, it is unclear how the exposed subjects were selected for study. In a more complete survey, Boeri et al. (1978) studied 470 subjects from two exposure zones about a year after the accident and found a higher incidence of neurophysiologic abnormalities than in unexposed controls; the residents of the zone of greater exposure were more severely affected than those of the less exposed zone. The same group (Filippini et al., 1981) found increased prevalence of peripheral neuropathy in residents who had indicators of exposure compared with those who did not (RR = 2.6, 95% CI 1.0–7.2, for those with choracne; RR = 3.6, 95% CI 1.3–10.2, for those with increased hepatic enzymes) when they were evaluated 21 months after the accident. Improvement may have occurred since the accident. Assennato et al. (1989a,b) studied 193 exposed residents of the area 9 years after the accident and did not find neurophysiologic abnormalities. However, the number of residents in the group who originally complained of neuropathic symptoms was not discussed. Similiarly, 6 years after the accident, Barbieri et al. (1988) examined 153 residents who had developed chloracne. World Health Organization critieria for neuropathy were not fulfilled for any subjects, but there was a statistically significant increase in neurophysiologic abnormalities compared with those in unexposed age-matched controls.
There have been a number of case reports of exposure-associated early-onset neuropathy. Goldstein et al. (1959) reported the cases of three patients seen at the Mayo Clinic who had acute weakness and sensory loss demonstrated to be due to
peripheral neuropathy; symptoms occurred within hours of an exposure to 2,4-D that included sufficient skin contact for clothes and skin to be wet. All three patients recovered incompletely: in one of the patients, a cerebrospinal fluid (CSF) examination was normal except for minimally increased protein. Todd (1962) reported another case of neuropathy that occurred about 4 days after 2,4-D exposure, again in sufficient quantities to cause large areas of skin to be wet from the herbicide. Clinical examination demonstrated a sensory motor polyneuropathy; CSF examination showed slightly increased protein but was otherwise normal. The patient recovered substantially but not completely over 2 years. Finally, Berkley and Magee (1963) reported a case of a 39-year-old man who had symptoms of acute neuropathy that progressed to inability to walk starting 4 days after 2,4-D exposure; CSF analysis was completely normal, including normal protein concentrations, and he recovered nearly completely over the course of 8 months.
Case reports do not provide conclusive evidence of causal relationships, but the cases discussed above showed a close temporal relationship between high exposure to 2,4-D and neuropathy. The most likely non–toxicant-related acute neuropathy is Guillain-Barré syndrome; however, this syndrome is associated with characteristic findings on clinical neurophysiologic examination and highly increased protein in CSF. In the three cases above that had CSF evaluation, protein concentrations were either normal or increased to a minimal extent not consistent with Guillain-Barré syndrome. In addition, patients who had clinical neurophysiologic studies also showed abnormalities not consistent with Guillain-Barré. Thus, it seems likely that the cases represent the results of 2,4-D exposure.
Neuronal cell cultures treated with 2,4-D showed decreased neurite extension associated with intracellular changes, including a decrease in microtubules, inhibition of the polymerization of tubulin, disorganization of the Golgi apparatus, and inhibition of ganglioside synthesis (Rosso et al., 2000a,b). Those mechanisms are important for maintaining synaptic connections between nerve cells and supporting the mechanisms involved in axon regeneration during recovery from peripheral neuropathy. Grahmann et al. (1993) and Grehl et al. (1993) reported observations of electrophysiologic and pathologic abnormalities, respectively, in the peripheral nerves of rats treated with TCDD. When the animals were sacrificed 8 months after exposure, there were pathologic evidence of axonal nerve damage and histologic findings typical of toxicant-induced injury. Those results constitute evidence of the biologic plausibility of an association between exposure to the chemicals of interest and peripheral neuropathy.
On the basis of studies of health effects after industrial accidents and the well-documented cases reported above, VAO committees since that responsible
for Update 1996 have concluded that there is limited or suggestive evidence of an association between exposure to the chemicals of interest and early-onset peripheral neuropathy. Inasmuch as new data on this subject, especially with regard to Vietnam veterans, are unlikely to emerge, the present committee reaffirms that finding.
AFHS (Air Force Health Study). 1984. An Epidemiologic Investigation of Health Effects in Air Force Personnel Following Exposure to Herbicides. Baseline Morbidity Study Results. Brooks AFB, TX: USAF School of Aerospace Medicine. NTIS AD-A138 340.
AFHS. 1991b. An Epidemiologic Investigation of Health Effects in Air Force Personnel Following Exposure to Herbicides. Mortality Update: 1991. Brooks AFB, TX: Armstrong Laboratory.
Ashe WF, Suskind RR. 1949, 1950. Reports on Chloracne Cases, Monsanto Chemical Co., Nitro, West Virginia, October 1949 and April 1950. Cincinnati, OH: Department of Environmental Health, College of Medicine, University of Cincinnati (unpublished).
Assennato G, Cervino D, Emmett E, Longo G, Merlo F. 1989a. Follow-up of subjects who developed chloracne following TCDD exposure at Seveso. American Journal of Industrial Medicine 16:119–125.
Assennato G, Cannatelli P, Emmett E, Ghezzi I, Merlo F. 1989b. Medical monitoring of dioxin cleanup workers. American Industrial Hygiene Association Journal 50:586–592.
Baccarelli A, Pfeiffer R, Consonni D, Pesatori AC, Bonzini M, Patterson DG Jr, Bertazzi PA. Landi MT. 2005a. Handling of dioxin measurement data in the presence of non-detectable values: Overview of available methods and their application in the Seveso chloracne study. Chemosphere 60(7):898–906.
Barbieri S, Pirovano C, Scarlato G, Tarchini P, Zappa A, Maranzana M. 1988. Long-term effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on the peripheral nervous system. Clinical and neurophysiological controlled study on subjects with chloracne from the Seveso area. Neuroepidemiology 7:29–37.
Beck H, Eckart K, Mathar W, Wittkowski R. 1989. Levels of PCDDs and PCDFs in adipose tissue of occupationally exposed workers. Chemosphere 18:507–516.
Berkley MC, Magee KR. 1963. Neuropathy following exposure to a dimethylamine salt of 2,4-D. Archives of Internal Medicine 111(3):351–352.
Bleiberg J, Wallen M, Brodkin R, Applebaum IL. 1964. Industrially acquired porphyria. Archives of Dermatology 89:793–797.
Boeri R, Bordo B, Crenna P, Filippini G, Massetto M, Zecchini A. 1978. Preliminary results of a neurological investigation of the population exposed to TCDD in the Seveso region. Rivista di Patologia Nervosa e Mentale 99:111–128.
Bond GG, Cook RR, Brenner FE, McLaren EA. 1987. Evaluation of mortality patterns among chemical workers with chloracne. Chemosphere 16:2117–2121.
Bond GG, McLaren EA, Brenner FE, Cook RR. 1989a. Incidence of chloracne among chemical workers potentially exposed to chlorinated dioxins. Journal of Occupational Medicine 31:771–774.
1 Throughout this report, the same alphabetic indicator after year of publication is used consistently for a given reference when there are multiple citations by the same first author in a given year. The convention of assigning the alphabetic indicators in order of citation in a given chapter is not followed.
Bond GG, McLaren EA, Lipps TE, Cook RR. 1989b. Update of mortality among chemical workers with potential exposure to the higher chlorinated dioxins. Journal of Occupational Medicine 31:121–123.
Calvert GM, Hornung RV, Sweeney MH, Fingerhut MA, Halperin WE. 1992. Hepatic and gastrointestinal effects in an occupational cohort exposed to 2,3,7,8-tetrachlorodibenzo-para-dioxin. Journal of the American Medical Association 267:2209–2214.
Calvert GM, Sweeney MH, Fingerhut MA, Hornung RW, Halperin WE. 1994. Evaluation of porphyria cutanea tarda in US workers exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin. American Journal of Industrial Medicine 25(4):559–571.
Caramaschi F, Del CG, Favaretti C, Giambelluca SE, Montesarchio E, Fara GM. 1981. Chloracne following environmental contamination by TCDD in Seveso, Italy. International Journal of Epidemiology 10:135–143.
CDC (Centers for Disease Control and Prevention). 1988. Centers for Disease Control Vietnam Experience Study. Health status of Vietnam veterans. II: Physical health. Journal of the American Medical Association 259(18):2708–2714.
Cook RR, Townsend JC, Ott MG, Silverstein LG. 1980. Mortality experience of employees exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Journal of Occupational Medicine 22:530–532.
Doss M, Sauer H, von Tiepermann R, Colombi AM. 1984. Development of chronic hepatic porphyria (porphyria cutanea tarda) with inherited uroporphyrinogen decarboxylase deficiency under exposure to dioxin. International Journal of Biochemistry 16(4):369–373.
Filippini G, Bordo B, Crenna P, Massetto N, Musicco M, Boeri R. 1981. Relationship between clinical and electrophysiological findings and indicators of heavy exposure to 2,3,7,8-tetrachlorodibenzodioxin. Scandinavian Journal of Work, Environment, and Health 7(4):257–262.
Geusau A, Khorchide M, Mildner M, Pammer J, Eckhart L, Tschachler E. 2005. 2,3,7,8-tetrachlorodibenzo-p-dioxin impairs differentiation of normal human epidermal keratinocytes in a skin equivalent model. Journal of Investigative Dermatology 124(1):275–277.
Gilioli R, Cotroneo L, Bulgheroni C, Genta PA, Rota E, Cannatelli P, Fereari E. 1979. Neurological monitoring of workers exposed to TCDD: Preliminary neurophysiological results. Activitas Nervosa Superior 21:288–290.
Goldman P. 1972. Critically acute chloracne caused by trichlorophenol decomposition products. Arbeitsmedizen Sozialmedizen Arbeitshygiene 7:12–18.
Goldstein NP, Jones PH, Brown JR. 1959. Peripheral neuropathy after exposure to an ester of dichlorophenoxyacetic acid. Journal of the American Medical Association 171:1306–1309.
Grahmann F, Claus D, Grehl H, Neundorfer B. 1993. Electrophysiologic evidence for a toxic polyneuropathy in rats after exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Journal of the Neurological Sciences 115(1):71–75.
Grehl H, Grahmann F, Claus D, Neundorfer B. 1993. Histologic evidence for a toxic polyneuropathy due to exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in rats. Acta Neurologica Scandinavica 88(5):354–357.
Hoffman RE, Stehr-Green PA, Webb KB, Evans RG, Knutsen AP, Schramm WF, Staake JL, Gibson BB, Steinberg KK. 1986. Health effects of long-term exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin. Journal of the American Medical Association 255:2031–2038.
Ikuta T, Ohba M, Zouboulis CC, Fujii-Kuriyama Y, Kawajiri K. 2010. B lymphocyte-induced maturation protein 1 is a novel target gene of aryl hydrocarbon receptor. Journal of Dermatological Science 58(3):211–216.
IOM (Institute of Medicine). 1994. Veterans and Agent Orange: Health Effects of Herbicides Used in Vietnam. Washington, DC: National Academy Press.
IOM. 1996. Veterans and Agent Orange: Update 1996. Washington, DC: National Academy Press.
IOM. 1999. Veterans and Agent Orange: Update 1998. Washington, DC: National Academy Press.
IOM. 2000. Veterans and Agent Orange: Herbicide/Dioxin Exposure and Type 2 Diabetes. Washington, DC: National Academy Press.
IOM. 2001. Veterans and Agent Orange: Update 2000. Washington, DC: National Academy Press.
IOM. 2003. Veterans and Agent Orange: Update 2002. Washington, DC: The National Academies Press.
IOM. 2005. Veterans and Agent Orange: Update 2004. Washington, DC: The National Academies Press.
IOM. 2007. Veterans and Agent Orange: Update 2006. Washington, DC: The National Academies Press.
Jirasek L, Kalensky J, Kubec K, Pazderova J, Lukas E. 1974. Chronic poisoning by 2,3,7,8-tetrachlorodibenzo-p-dioxin. Ceskoslovenska Dermatologie 49:145–157.
Jung D, Konietzko J, Reill-Konietzko G, Muttray A, Zimmermann-Holz HJ, Doss M, Beck H, Edler L, Kopp-Schneider A. 1994. Porphyrin studies in TCDD-exposed workers. Archives of Toxicology 68:595–598.
May G. 1973. Chloracne from the accidental production of tetrachlorodibenzodioxin. British Journal of Industrial Medicine 30:276–283.
May G. 1982. Tetrachlorodibenzodioxin: A survey of subjects ten years after exposure. British Journal of Industrial Medicine 39(2):128–135.
Mocarelli P, Needham LL, Marocchi A, Patterson DG Jr, Brambilla P, Gerthoux PM, Meazza L, Carreri V. 1991. Serum concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin and test results from selected residents of Seveso, Italy. Journal of Toxicology and Environmental Health 32:357–366.
Neuberger M, Kundi M, Jäger R. 1998. Chloracne and morbidity after dioxin exposure (preliminary results). Toxicology Letters 96-97:347–350.
Oliver RM. 1975. Toxic effects of 2,3,7,8 tetrachlorodibenzo 1,4-dioxin in laboratory workers. British Journal of Industrial Medicine 32:49–53.
Panteleyev AA, Bickers DR. 2006. Dioxin-induced chloracne—Reconstructing the cellular and molecular mechanisms of a classic environmental disease. Experimental Dermatology 15(9):705–730.
Pazderova-Vejlupkova J, Lukáš E, Nemcova M, Pickova J, Jirasek L. 1981. The development and prognosis of chronic intoxication by tetrachlorodibenzo-p-dioxin in men. Archives of Environmental Health 36:5–11.
Poland AP, Smith D, Metter G, Possick P. 1971. A health survey of workers in a 2,4-D and 2,4,5-T plant with special attention to chloracne, porphyria cutanea tarda, and psychologic parameters. Archives of Environmental Health 22:316–327.
Robinson SW, Clothier B, Akhtar RA, Yang AL, Latour I, Van Ijperen C, Festing MF, Smith AG. 2002. Non-ahr gene susceptibility Loci for porphyria and liver injury induced by the interaction of ‘dioxin’ with iron overload in mice. Molecular Pharmacology 61(3):674–681.
Rosso SB, Caceres AO, Evangelista de Duffard AM, Duffard RO, Quiroga S. 2000a. 2,4-dichlorophenoxyacetic acid disrupts the cytoskeleton and disorganizes the golgi apparatus of cultured neurons. Toxicologic Sciences 56:133–140.
Rosso SB, Garcia GB, Madariaga MJ, De Duffard AME, Duffard RO. 2000b. 2,4-dichlorophenoxyacetic acid in developing rats alters behaviour, myelination and regions brain gangliosides pattern. NeuroToxicology 21(1-2):155–164.
Singer R, Moses M, Valciukas J, Lilis R, Selikoff IJ. 1982. Nerve conduction velocity studies of workers employed in the manufacture of phenoxy herbicides. Environmental Research 29:297–311.
Smith AG, Chernova T. 2009. Chapter 6 disruption of heme synthesis by polyhalogenated aromatics. Advances in Molecular Toxicology 3(C):161–210.
Smith AG, Clothier B, Carthew P, Childs NL, Sinclair PR, Nebert DW, Dalton TP. 2001. Protection of the Cyp1a2 (-/-) null mouse against uroporphyria and hepatic injury following exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin. Toxicology and Applied Pharmacology 173(2):89–98.
Smith AG, Elder GH. 2010. Complex gene-chemical interactions: Hepatic uroporphyria as a paradigm. Chemical Research in Toxicology 23(4):712–723.
Sorg O, Zennegg M, Schmid P, Fedosyuk R, Valikhnovskyi R, Gaide O, Kniazevych V, Saurat J-H. 2009. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) poisoning in victor yushchenko: Identification and measurement of TCDD metabolites. Lancet 374(9696):1179–1185.
Stehr-Green P, Hoffman R, Webb K, Evans RG, Knutsen A, Schramm W, Staake J, Gibson B, Steinberg K. 1987. Health effects of long-term exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin. Chemosphere 16:2089–2094.
Suskind RR, Hertzberg VS. 1984. Human health effects of 2,4,5-T and its toxic contaminants. Journal of the American Medical Association 251(18):2372–2380.
Suskind R, Cholak J, Schater LJ, Yeager D. 1953. Reports on Clinical and Environmental Surveys at Monsanto Chemical Co., Nitro, West Virginia, 1953. Cincinnati, OH: Department of Environmental Health, University of Cincinnati (unpublished).
Sweeney MH, Mocarelli P. 2000. Human health effects after exposure to 2,3,7,8-TCDD. Food Additives and Contaminants 17(4):303–316.
Sweeney MH, Calvert GM, Egeland GA, Fingerhut MA, Halperin WE, Piacitelli LA. 1997/98. Review and update of the results of the NIOSH medical study of workers exposed to chemicals contaminated with 2,3,7,8-tetrachlorodibenzodioxin. Teratogenesis, Carcinogenesis, and Mutagenesis 17(4–5):241–247.
Tauchi M, Hida A, Negishi T, Katsuoka F, Noda S, Mimura J, Hosoya T, Yanaka A, Aburatani H, Fujii-Kuriyama Y, Motohashi H, Yamamoto M. 2005. Constitutive expression of aryl hydrocarbon receptor in keratinocytes causes inflammatory skin lesions. Molecular and Cellular Biology 25(21):9360–9368.
Todd RL. 1962. A case of 2,4-D intoxication. Journal of the Iowa Medical Society 52:663–664.
Uno S, Dalton TP, Sinclair PR, Gorman N, Wang B, Smith AG, Miller ML, Shertzer HG, Nebert DW. 2004. Cyp1a1(-/-) male mice: Protection against high-dose TCDD-induced lethality and wasting syndrome, and resistance to intrahepatocyte lipid accumulation and uroporphyria. Toxicology and Applied Pharmacology 196(3):410–421.
Urban P, Pelclová D, Lukas E, Kupka K, Preiss J, Fenclová Z, Smerhovsky Z. 2007. Neurological and neurophysiological examinations on workers with chronic poisoning by 2,3,7,8-TCDD: Follow-up 35 years after exposure. European Journal of Neurology 14(2):213–218.
Von Benner A, Edler L, Mayer K, Zober A. 1994. “Dioxin” investigation program of the chemical industry professional association. Arbeitsmedizin Sozialmedizin Praventivmedizin 29:11–16.
Webb K, Evans RG, Stehr P, Ayres SM. 1987. Pilot study on health effects of environmental 2,3,7,8-TCDD in Missouri. American Journal of Industrial Medicine 11:685–691.
Wolfe WH, Michalek JE, Miner JC, Rahe A, Silva J, Thomas WF, Grubbs WD, Lustik MB, Karrison TG, Roegner RH, Williams DE. 1990. Health status of Air Force veterans occupationally exposed to herbicides in Vietnam. I. Physical health. Journal of the American Medical Association 264:1824–1831.
Zober A, Messerer P, Huber P. 1990. Thirty-four-year mortality follow-up of BASF employees exposed to 2,3,7,8-TCDD after the 1953 accident. International Archives of Occupational and Environmental Health 62:139–157.