Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants Volume 2 (1996) / Chapter Skim
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B7 Mercury
B7 Mercury
Pages 251-276
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From page 251... ...
Kaplan, Ph.D. Johnson Space Center Toxicology Group Biomedical Operations and Research Branch Houston, Texas PHYSICAL AND CHEMICAL PROPERTIES Elemental mercury is a heavy, silvery-white, slightly volatile liquid at room temperature (Stokinger, 1981; ACGTH, 19861.
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From page 252... ...
Human subjects retained approximately 70-80% of inhaled mercury vapor, retention occurring almost entirely in the alveoli (Nielsen-Kudsk, 1965; Hursch et al., 19761. Oxidation of elemental mercury to the mercuric ion is the primary metabolic pathway (Hursch et al., 1976~.
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From page 253... ...
The mercuric ions, which traverse the blood-brain barrier less freely than elemental mercury, bind to sulfhydryI-containing ligands and are retained within the brain. Because of this greater diffusibility of the vapor, the mercury content in the brains of animals exposed to the vapor was ten times greater than that of arsenals injected with an equivalent dose of mercuric salts (Berlin et al., 1969~.
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The clearance of inhaled mercury vapor from tissues of the body follows a complicated pattern; biological half-times differ according to the tissue and the time after exposure (WHO, 19911. Tracer studies on human volunteers and animals indicate that, after a short exposure to mercury vapor, the first phase of elimination from blood has a half-time of approximately 2-4 d and accounts for about 90% of the retained mercury (WHO, 19911.
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From page 255... ...
In rabbits, a 1-h exposure at 28.8 mg/m3 caused moderate histopathological changes to the kidneys and brain and mild changes to the lungs and heart (Ashe et al., 19531. With 2-, 4-, or 6-h exposures, damage to the kidneys and brain was severe (extensive cellular degeneration and necrosis)
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From page 256... ...
Recovery of operant behavior began at 14 d postexposure and was almost complete at 45 d. Histopathological changes were not evident in the kidneys, liver, or lungs; but in the brain, two of three rats had lymphocytic cuffing around capillaries of the medulla
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Peak or time-integrated average urinary mercury levels in workers were reported to be associated with neurological dysfunction, increased tremor, impaired psychomotor performance, decreased coordination,
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These subtle effects include impaired psychomotor performance, measurable tremor, impaired nerve conduction velocity, fatigue, irritability, loss of appetite, and possibly proteinuria. Continuous low-level exposure to mercury vapor also occurs as a result of the release of vapor from amalgam fillings in the mouth (WHO, 1991~.
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From page 259... ...
The potential for developmental toxicity is high because elemental mercury readily crosses the placenta and accumulates in many fetal organs, but at concentrations below those typically found in the mother (CIarkson et al., 1972; Khayat and Dencker, 19821. The reproductive toxicity of mercury has been evaluated in both male and female industrial workers exposed to concentrations that were often incompletely characterized.
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From page 260... ...
In a questionnaire study of nearly 60,000 dental workers divided into two groups according to the frequency of amalgam restorations performed? there was no significant increase in the rate of spontaneous abortion or congenital malformations with the presumed increase in exposure to mercury vapor (Brodsky et al, 1985~.
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or aminotriazole (rat) caused decreased mercury retention in most organs and in the whole body, increased blood concentrations of elemental mercury, and increased retention of mercury in most liver and adrenal cells (Khayat and Dencker, 1984~.
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262 an X ._ =m .= "s .3 ~= ~ .= ~ 3 ~ O O =: O V, ~ ~ ~ U)
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264 .S red au Cal C)
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265 oo ~ - , C - ~Cal ~t ~ A I=\ A ~is;, ~ _ ~C;:^ _ _ Ct Ct Ct so ~1 ~ ~ ~ ~ - ~D ~ ~e _ ~ ~ ~, ~2 ~.
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0.2, 24 ha 0.01, 90 da TABLE 7-3 Spacecraft Maximum Allowable Concentrations Duration ppm 1 h mg/m3 Target Toxicity 0.01 0.08 Respiratory tract 24 h 0.002 0.02 Respiratory tract 7 d 0.001 0.01 CNS, kidney 30 d 0.001 0.01 CNS, kidney 180 d 0.001 0.01 CNS, kidney RATIONALE FOR ACCEPTABLE CONCENTRATIONS In setting SMAC values for mercury vapor, the toxic effects on the respiratory tract, the brain and CNS, and the kidney must be considered. Few well-controlled animal studies have been conducted with observations and measurements of toxic end points in adequate numbers of animals and at more than one concentration of vapor.
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In another report of accidental human exposures at 1-3 mg/m3 for 2.5-5 h, similar respiratory symptoms were reported in three-fourths of the exposed workers and one-fourth of the workers reported minimal respiratory symptoms (MiIne et al., 1970~. Authors of the first study assert that all nine workers had approximately equal exposures to mercury vapor even though there was a wide range in apparent lung injury.
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From page 268... ...
Nephrotoxicity Data were available for subchronic and chronic exposures of animals to mercury vapor. No more than mild histopathological changes were seen in the kidneys of rabbits exposed at 0.86 mg/m3, 7 in/d, 5 d/w, for up to 4 w, and no histopathological changes were seen in the kidneys of rabbits, rats, and two dogs exposed at 1 mg/m3 for 83 w (Ashe et al., 19531.
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From page 269... ...
A large epidemiological study reported no significant toxic effects below 0.1 mg/m3 in workers chronically exposed to mercury vapor, but there were some complaints of symptoms (Smith et al., 1970~. A few much smaller studies suggest occasional complaints, symptoms, or subclinical effects at exposures below 0.1 mg/m3 and even possibly below 0.05 mg/m3 (Bidstrup et al., 1951; Fawer et al., 1983; Verberk et al., 1986~.
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1989. Occupational mercury exposure and male reproductive health.
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Possick 1973. Metallic mercury exposure in scientific glassware manufacturing plants.
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1971. Metallic mercury induced tremor in rabbits and mercury content of the central nervous system.
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1978. Evaluation of workers exposed to elemental mercury using quantitative tests of tremor and neuromuscular functions.
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1982. Comparison of renal function and psychomotor performance in workers exposed to elemental mercury.
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1987. Effects of elemental mercury vapor exposure on pregnant Sprague-Dawley rats [abstract]
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