Methyl bromide is a toxicant found in some fumigant pesticides and fire retardants. It has proven effective against common pests such as fungi, insects, rodents and spiders. MeBr is a colorless gas with a low boiling point( 4.5 degrees centigrade) and is odorless at low concentrations, but in high concentrations, has been described as a ‘sweet, chloroform-like odour’ [Bulathsinghala]. This compound has had its use monitored and reduced in the previous decade for its ability to affect the ozone layer. Methyl bromide has acute moderate toxicity when given to animals but is highly toxic in human exposure. There have been cases of human exposure to methyl bromide that resulted in adverse health effects, such as; headaches, nausea and vomiting, vision difficulty, confusion, slurred speech and skin, eye, and respiratory irritation. In more severe cases, the effects have proven lethal. This compound has not only been proven to pose an environmental risk, but also a human health hazard; causing not only concern for long term usage but also immediate exposure.
Methyl bromide is an alkyl halide, causing the carbon to have a partial positive charge and a partial negative bromine. The halide size determines the overall reactivity of the compound. Because of methyl bromide’s electronegativity (2.685 on Allen scale), it is less likely to dissociate into a carbonium ion.
In one case study, a patient (male, works in a fumigation company) presented to the hospital complaining of “sudden-onset slurred speech, confusion and imbalance while walking.” The patient reported the symptoms began two days prior, concurrent with a leak from a fumigation tube at work. There was no history of similar illness in the family. The patient was confused, but had a normal pulse rate (80/a minute) and blood pressure values within a normal range (130/90 mmHg). A neurological examination revealed “generalized hyporeflexia,” which is poor muscle response to stimuli. There were no abnormalities observed in the electrocardiogram, there were elevated levels of serum ALT (alanine aminotransferase) found in a liver function test. The patient did show a serum bromide level of 200 mg/dl upon admission and after administration of a chelator bromide levels decreased with repeated regular dosage over the course of 5 days. Treatment proved effective and the patient was discharged from care and he left with regular reflexes, liver serum levels normal, and the dysarthria improving. An MRI scan found a volume loss in the cortex and cerebellum. The combination of symptoms and results led to the diagnosis of “methyl bromide toxic encephalopathy.” After four months, the scans were repeated to show that the condition had resolved itself, and confirm the diagnosis.
In a second case, a family of four on vacation in the U.S. Virgin Islands presented to the hospital with life threatening illnesses after boarding in a condominium resort that had two days prior been fumigated with methyl bromide. The family all had the same symptoms of “weakness, severe myoclonus [muscle spasms – in groups], fasciculations [muscle fiber spasms], altered sensorium [inability to think clearly or concentrate], and word-finding difficulty.” [Kulkami] Three of the four had more severe symptoms of vomiting and diarrhea, and required respiratory assistance via mechanical ventilation. The room that the family was renting was quarantined and the air quality tested, confirming elevated levels of methyl bromide.
Studies in humans have proven that there is a correlation between methyl bromide inhalation exposure, both acute and chronic, and neurological symptoms. According to the article by Bulathsinghala in the journal of Human and Experimental Toxicology, the first reported case of methyl bromide poisoning basin 1893. This was a case of occupational exposure; albeit from poor transfer technique — transfer via oral suction through a pipe from one container to another. Prior to being admitted to the hospital the man suffered from dizziness, vision changes, and labored breathing. Although he was released from the hospital after a little over a month, the patient still suffered from dizziness upon returning to work. More recent cases have confirmed a symptomatic pattern following exposure to methyl bromide: nausea, vomiting, dizziness, tremors and convulsions. Acute exposure can affect the exposed locally via nausea or neurologically via tremors, whereas chronic exposure has shown ‘electroencephalogram abnormalities, peripheral neuropathy, and deficits in the Wechsler Memory Scale.’ [Bulathsinghala]