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<br />• Acute toxicity: Since bromomethane is a gas at ambient temperatures, the most significant route of
<br />exposure is inhalation [ 1881. The reported 1 -hour inhalation LC50 in rats is 4.5 mg/L, and the
<br />1 I -hour LC50 in rabbits is 8 mg/L [8]. Inhalation of 6 mg/L for 10 to 20 hours, or 30 mg/L for 1.5
<br />hours is lethal to humans [8]. The compound is readily absorbed through the lung alveoli (gas
<br />exchange regions). Methyl bromide can be highly irritating to the mucous membranes of the eyes,
<br />ainvays, and skin with contact [ 17]. About 1000 human poisoning incidents caused by methyl
<br />bromide exposure have been documented, with effects ranging from skin and eye irritation to death
<br />[ 17]. Most fatalities and injuries occurred when methyl bromide was used as a fumigant. The lowest
<br />inhalation level found to cause toxicity in humans is 0.14 mg/L in air [17]. A typical delay in onset
<br />Of symptoms following exposure combined with an odor threshold (level at which most people can
<br />smell it) well -above the level at which toxic effects occur, means that the victim may not realize a
<br />harmful exposure is occurring until it is too late [17]. Initial acute effects may include headache.
<br />dizziness, nausea or vomiting, chest and abdominal pain, and irritated eyes, nose, and throat [188].
<br />With sufficient exposure, symptoms of slurred speech, blurred vision, temporary blindness, mental
<br />confusion, and sweating may occur [188]. More severe symptoms at even higher doses may include
<br />lung swelling; congestion; hemorrhaging of the brain, heart, and spleen; severe kidney damage; and
<br />numbness, tremors, and convulsions [188]. The nervous effects observed in lab animals included
<br />degeneration of key nerve cells in various portions of the brain and peripheral nervous system
<br />[188]. Death may occur from respiratory failure [188]. The rat oral LD50 (bromomethane
<br />administered as a liquid, or in solution) is 214 mg/kg [1], also indicating moderate to high toxicity.
<br />• Chronic toxicity: Chronic exposure to methyl bromide can cause extensive damage to neurons
<br />(nerve cells) involved in cognitive processes and physical coordination or muscular control [188].
<br />These effects were seen in rats exposed to 0.51 to 1.3 mg/L 6 hours per day for 5 days [ 1881. Rats
<br />exposed to 65 ppm over 4 weeks for an average of 7 hours per day for 4 to'5 days did not show
<br />neurological effects, but this level of exposure did result in severe, in some cases irreversible,
<br />neurological effects in rabbits over a similar time period [ 188]. Exposure levels of 0.1 mg/L over 8
<br />months (7.5 hours per day, 4 days/week) did not produce observable neurotoxicity [ 188]. The
<br />symptoms of chronic exposure may include dizziness, vision and hearing disturbances, depression.
<br />confusion, hallucinations, euphoria, personality changes, and irritability [8]. A chronic
<br />pneumonia -like syndrome may become apparent after repeated exposure to sufficient levels [8].
<br />Other targets of the fumigant identified through long-term animal studies are the heart, adrenal
<br />gland, and the testis [ 189].
<br />• Reproductive effects: No reproductive efffects were seen in rats exposed to up to 0.3 mg/L for 7
<br />hours/day, 5 days a week, for 3 weeks prior to mating and during gestation [ 188]. This suggests that
<br />methyl bromide does not cause reproductive effects.
<br />• Teratogenic effects: No teratogenic efffects were seen in rats exposed to up to 0.3 mg/L for 7
<br />hours/day, 5 days a week, for 3 weeks prior to mating and during gestation [188]. This evidence
<br />indicates that bromomethane is unlikely to cause teratogenic effects.
<br />• Mutagenic effects: Mutagenic effects were seen in mouse cell cultures, mutagenicity assays with
<br />bacteria, and in in human white blood cells [190]. Rat liver cells did not display increased rates of
<br />mutation after exposure to methyl bromide [190]. Methyl bromide is considered to be weakly
<br />mutagenic [ 188].
<br />• Carcinogenic effects: In one study of industrial workers exposed to various brominated
<br />compounds, exposure to methyl bromide was suggested as the possible common factor in two fatal
<br />cases of testicular cancer, but other exposures could not be ruled out [189]. In a rat study, methyl
<br />bromide given at 50 mg/kg/day by stomach tube for 90 days (gavage) induced stomach tumor
<br />increases [188,190]. It appeared that the cancerous growth was due to severe localized cellular
<br />injury,, with subsequent increased cell reproduction to repair tissue damage amplifying the natural
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