Environmental Medicine Integrating a Missing Element into Medical Education (1995) / Chapter Skim
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Case Study 13: Dioxin Toxicity
Case Study 13: Dioxin Toxicity
Pages 332-348
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From page 332... ...
This monograph is one in a series of self-instructional publications designed to increase the primary care provider's knowledge of hazardous substances in the environment and to aid in the evaluation of potentially exposed patients. The Agency for Toxic Substances and Disease Registry (A TSDR)
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Two days ago, worl |
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. They are believed to produce similar health effects and are known to coexist as unwanted contaminants in various matenals.
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Several human populations exposed to dioxin-contaminated compounds have been studied extensively for health effects. Some Vietnam veterans were potentially exposed to dioxins through the military use of the defoliant Agent Orange (a mixture of 2,4,5-trichlorophenoxyacetic acid [2,4,5-~ and 2,4-dichlorophenoxyacetic acid [2,4-D]
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From page 336... ...
Municipal and waste incineratorworkers may encounter dioxins in smoke, gases, or fly ash formed during combustion processes. Major industrial accidents have been the source of most overt clinical effects from dioxins.
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Because of the lipophil~ nature of milk, nursing females decrease their body burden of TCDD through lactation. Dioxins distribute to organs according to lipid content and readily accumulate in body fat.
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Only two clinical effects have been repeatedly observed in exposed populations: chloracne and transient hepatic effects. Soft-tissue sarcomas, Iymphomas, peripheral neuropathy, birth defects, and reproductive effects have been studied but remain unconfirmed.
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From page 339... ...
No case of peripheral neuropathy was found; however, subclinical peripheral nerve impairment was reported in 16 victims. A study of railroad workers exposed to TCDD during cleanup of a tank car spill reported that 43 of 45 workers had findings suggestive of peripheral neuropathy 6 years after exposure, but the validity of the study has been questioned and numerous other epidemiologic studies have found no evidence of necrologic impairment due to dioxin exposure.
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From page 340... ...
Reproductive and Developmental Effects Studies of Vietnam servicemen possibly exposed to Agent Orange revealed no overall increase of debilitating birth defects in progeny. A study of the Missouri incident encompassing 410 births reported no statistically significant increase in risk ratios for infant, fetal, and perinatal death, low birthweight, orfor several subcategories of birth defects.
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The category of Probable human carcinogen. ind Gates that EPA considers animal evidence of carcinogen~ity suff~ient.
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From page 342... ...
Since exposureto TCDD always involves mixed exposures, it is impossible to state with certainty that dioxins caused these effects. Laboratory Tests Direct Biologic Indicators Adipose tissue and blood serum analyzed for the presence of TCDD by gas chromatography-mass spectrometry (GC-MS)
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From page 343... ...
In 50 persons exposed in the Missouri incident, the mean ratio of the TCDD level in adipose tissue to that in serum was 1.09 after adjusting both samples for lipid content. Some of the exposed people in the Seveso, Italy, accident had TCDD levels athousand times greaterthan the average found in the general unexposed population and did not experience illness.
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NIOSH considers TCDD a Probable" human carcinogen and recommends that workplace exposure be reduced to the lowest feasible level.
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Dioxins readily adsorb to aquatic sediment, and can be ingested by bottom-feeding organisms that are subsequently ingested by predatoryfish, thereby bioconcentrating these substances.
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Cohort mortality study of chemical workers with potential exposure to the higher chlorinated dioxins. J Occup Med 1987:29:422-9.
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An evaluation of reports of dioxin exposure and soft tissue sarcoma pathology among chemical workers in the United States. Scand J Work Environ Health 1984;10:299-303.
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From page 348... ...
(4) The primary human health effects of dioxin exposure are chloracne, and secondarily, hepatomegaly, elevated liver enzyme levels, and possibly peripheral neuropathy (subclinical changes in nerve conduction velocity)
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