Methyl bromide

Methyl Bromide . Halogenated organic compound whose chemical formula is CH3Br. It is a colorless gas, with a mild , flammable chloroform aroma . Its chemical properties are similar to those of chloromethane. Better known commercially by Bromomethane, and Terabol. It is extremely toxic, classified by the World Health Organization in category 1A. It is a product that degrades with difficulty. It is used as a fungicide / herbicide / insecticide.

Summary

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• 1 General
• 2 Progressive elimination of methyl bromide
• 3 Mechanism of action
• 4 Toxic dose
• 5 Clinical manifestations
  • 1 Diagnosis
  • 2 Laboratory
  • 3 Treatment
• 6 Carcinogenicity
• 7 Recommendations for handling
• 8 Sources

General

Used since the 1930s, it is a halogenated derivative of methane (aliphatic hydrocarbon); It can also be produced by hydrobromination from methanol . The gas is odorless, colorless and extremely toxic. It is used as a pesticide applied in the soil, before planting strawberries, grapes, almonds, carrots, ornamental plants and other crops; it also has fungicidal, acaricidal, nematocidal, rodenticidal and herbicidal effects ( germinating seeds ); it is also used as a coolant in the disinfection of trucks, ships and planes; in the protection of stored merchandise (grains and flour ) and because it is a powerful alkylating agent , it is used in the chemical industry.

Methyl Bromide molecule

It can be condensed to liquid at cold temperatures (38.5ºF or 3.6ºC) and then vaporize when temperatures rise.

It is also called bromomethane, monobromomethane, perfume. Methyl bromide is a very insidious chemical. Since the odor threshold is much higher than the toxic concentration, its presence is not noticed (no warning); for this reason 2% chloropicrin , which is a tear substance, is added as a reporting agent. Methyl bromide reacts violently or even explosively with alkalis, with alkaline earth metals and with metal powders .

For use as a fumigant, land or buildings are evacuated and covered with large plastic or canvas.

In 1992 , methyl bromide was officially recognized in Copenhagen as being responsible for the deterioration of the ozone layer , also contributing to the increase in the average temperature of the earth . This compound has a half-life of two years in the atmosphere. The European Union has adopted legislation (EC Regulation 3093/94 of 23 December of 1994 ) requiring a reduction of 25% in production and supply of methyl bromide in 1998 , compared to the levels of 1991 , with the exception of use for quarantine and pre-shipment.

Phasing out of methyl bromide

According to the Montreal Protocol ( 1997 ), it had been agreed that in 2001 in developed countries the use of methyl bromide would be 50% of the use in 1995 , 70% reduction for 2003 and elimination for 2005 except for critical uses. For developing countries, a freeze was agreed in 2002 according to the average use from 1995 to 1998 , revision of the level of reduction in 2003, 20% reduction in 2005, the year 2011 is set to reduce the use of methyl bromide and its elimination in 2015 except for critical uses.

All these efforts to reduce and eliminate the use and production of methyl bromide have prompted the generation of alternatives to replace it in its different applications.

Mechanism of action

It is a powerful non-specific alkylating agent, with a special affinity for sulfhydryl and amino groups. It binds to amino groups of amino acids, interfering with protein synthesis and function.

Limited data indicates that its toxicity may be the result of both direct alkylation on cellular components (glutathione, proteins, RNA or DNA ) and the formation of toxic metabolites from methylated glutathione. Animal data indicate that its toxicity is not due to the bromide ion.

The most important route of exposure is inhalation. Inhaled methyl bromide is rapidly distributed to all tissues. Dermal contact with liquid methyl bromide can cause irritation and its absorption produces burning and systemic toxicity. Gas and liquid retention in rubber clothing and boots can be a prolonged route of dermal exposure as it can penetrate clothing and some protective elements.

Upon entering the body, it is metabolized by hydrolysis to the bromide and methanol ion with great reactivity in the nervous system (gray matter and peripheral axons) and in the liver.

Sublethal studies in animals indicate that approximately 50% is excreted as carbon dioxide , 25% is excreted in the urine and faeces, and 25% is bound to the tissues as a methyl group. The elimination half-life of the bromide ion is 9 – 15 days.

Toxic dose

Methyl bromide is three times heavier than air and can accumulate. After being applied to the ground, the vapors can dissipate in the air, affecting nearby people and causing injury to the ozone layer. The Lethal Dose in rats is 214 mg / kg, inhalation CL100 6 hours, for rats 0.53 mg / L of air.

The American Conference of Government Industrial Hygienists (ACGIH) recommends an airborne workplace exposure limit of 1 ppm, for an average exposure time of 8 hours. The toxic effects are generally seen at levels greater than 200 ppm and the level in air considered imminently dangerous to humans is 250 ppm.

The Food and Agriculture Organization of the United Nations (FAO) specifies the tolerance level in human nutrition at 0.3 mg of bromide per kilogram of body weight.

The Environmental Protection Agency (EPA) classifies methyl bromide in toxic category I, being the most toxic.

Clinical manifestations

The latency time is between 30 minutes and 48 hours. Acute irritating effects on the eyes (tearing), mucous membranes, and upper respiratory tract are attributed to the tear chloropicrin (lethal exposures can occur without warning if chloropicrin has not been added). Moderate dermal exposure can result in dermatitis and in severe cases deep chemical burns, blisters (blistering gas) and necrosis.

Acute systemic effects are the result of many hours of exposure. These may include general malaise, visual disturbances (blurred vision, diplopia, strabismus, and possible transient blindness), impaired language, headache, nausea, vomiting, pulmonary disturbances (chest pain, dyspnea, cyanosis, chemical pneumonitis, pulmonary hemorrhage, pneumonia), kidney damage (distal convoluted tubule, oliguria and anuria), liver damage, gonadal disorders (seminiferous tubules), myocardial irritability, tremor, seizures, depression of the Central Nervous System and coma.

Death can be caused by fulminant respiratory failure with non-cardiogenic pulmonary edema or complications of epileptic status. Sublethal exposures can result in flu-like symptoms, respiratory disturbances, or chronic effects.

Chronic neurological sequelae can result from chronic or acute sub-lethal exposures. A wide spectrum of neurological (central and peripheral nervous system) and psychiatric problems can occur reversible or irreversible. These include agitation, delirium, dementia, psychoneurotic symptoms, psychosis, visual disturbances, vertigo, nystagmus, aphasia, ataxia, peripheral neuropathies, myoclonus, speech difficulties, tremors, and seizures.

Possible sequelae include axonal neuropathies, chemical pneumonitis, renal tubular necrosis, and gonadal abnormalities. After exposure, convalescence can last for weeks or months.

Diagnosis

Diagnosis is based on a history of exposure to the compound and on the clinical presentation. People at risk are employees of fumigation companies, people who handle the plastic where methyl bromide is contained, and fruit and vegetable packers who have been fumigated.

Laboratory

Recognizing methyl bromide levels are not routine tests; however, it is estimated that normal blood bromide levels are between 0.2-10 mg / L, showing a good correlation with air levels; In urine normal bromide levels are 6.3 2.5 mg / L. Despite this, it is considered not a very good correlation between bromide levels and symptoms.

Treatment

1. Remove victims from the contaminated area to a better ventilated area and administer supplemental oxygen, treat bronchospasm, pulmonary edema, seizures, and coma if they occur.
2. Optimize patient hydration.
3. If contact was dermal with liquid methyl bromide, contaminated clothing should be removed and the affected area washed with soap and water.
4. In eye contact, irrigate with plenty of water or saline.
5. Patient monitoring for at least 6 – 12 hours, to detect unfavorable symptoms, including seizures or non-cardiogenic pulmonary edema.
6. N-acetylcysteine ​​offers reactive sulfhydryl groups to bind to free methyl bromide and is therefore recommended for treatment. See chapter on antidotes.
7. Intractable seizures usually predict a fatal outcome. Inducing barbituric coma with short-acting agents such as pentobarbital and evaluation by a neurologist as soon as possible may be considered.
8. Order electrolytes, glucose, BUN, creatinine, arterial gases, oximetry and chest radiography.
9. Rapid decontamination measures have no action on methyl bromide.

Carcinogenicity

The damage produced in the ozone layer leads to an increase in type B ultraviolet radiation reaching the earth’s crust, being harmful to man as it increases the risk of skin cancer and the appearance of eye diseases.

Due to its methylating action, it is described as a weak mutagen. The International Agency for Research on Cancer (IARC) indicates limited evidence in animals and inadequate in humans as carcinogens or potential carcinogens. Methyl bromide is considered a potential occupational carcinogen by the United States National Institute for Occupational Safety and Health (NIOSH).

It can cause alterations in the birth of calves of pregnant animals. The US National Cancer Institute links methyl bromide to increased prostate cancer in farmworkers and others involved in pesticide manipulation. Mutagenic effects have been described.

Recommendations for handling

Personal protection elements are always recommended in work or contaminated areas. The absence of chloropicrin does not guarantee safety when entering the contaminated area without protection.

Among the precautions to take into account after 12 to 24 hours are: removing the plastic, ventilating the area and evaluating methyl bromide residues, before reoccupying the land. The plastic should not be removed until completing 5 days of application of methyl bromide. The area should not be entered within 24 hours of removing the plastics or having cut them with holes to sow.

A minimum space of 30 feet is required between the fumigated field and the field with workers and 100 feet with schools and the community. These spaces are effective for 24 hours up to one week after application, requiring warning signs in each fumigated field.