Traditionally, food safety issues associated with alcoholic beverages focus on chemical or physical hazards from the processing line. Intoxication with alcoholic beverages, as it relates to food safety, is less reported in the literature. However, there occasionally arise incidents where the adulteration of an alcoholic product leads to severe illness or death upon consumption or intoxication. The addition of cheap methanol to illicitly produced liquor—a rising issue in Asia—is increasingly being studied as a food safety and food adulteration issue.
In this case study, seven people were hospitalized with alcohol poisoning from October to November 2020. Two victims suffered from methanol poisoning, one person died, and four others suffered eye and brain damage. All of the cases stemmed from consumption of the same commercial liquor produced by a local company in Vietnam.
One victim reported drinking liquor bought from a grocery store, along with three other people. The next day, the victim suffered from headache, blurred vision, and fatigue. He was taken to the Poison Control Center Hospital and hospitalized for alcohol poisoning; shortly thereafter, the victim entered a coma. The test result of the liquor in this victim's system showed a methanol content of 20.21 percent, with an additional ethanol level of 11.42 percent. The three others who drank the same liquor were hospitalized and diagnosed with methanol poisoning; fortunately, however, all of them recovered after treatment.
One of the other three patients, a 22-year-old male, registered a very high level of blood-methanol after drinking the same liquor over three consecutive days. Although this patient had a toxic level of methanol in his system, hospital medical professionals were able to detoxify him. Another patient, a 32-year-old male, was diagnosed with industrial methanol poisoning at a lower level. The patient was hospitalized in a state of deep coma, with dilated pupils and low blood pressure. Test results showed a blood-methanol level of 141 mg/dL. He recovered gradually, due to the administration of timely treatment.
Methanol Poisoning from Adulterated Liquor
In some countries where the official sale of alcoholic drinks is prohibited, people may buy alcohol that is produced under dubious conditions and sold on the black market. These products are sometimes adulterated. The most serious poisoning cases involve liquor containing industrial methanol instead of ethanol as a basic ingredient. Methanol negatively affects mental and physical health and may result in death.
These cases, known as industrial methanol poisoning, happen due to the consumption of adulterated liquor that contains a high concentration of methanol. This type of product comes with its own name and label, registration, and source information, which makes it appear authentic. This enhances the danger, because consumers can be misled by the appearance of a regular commercial product.
Methanol, commonly known as industrial alcohol, is the simplest alcohol with the formula CH3OH. In distilled spirits, methanol is derived from the breakdown of macromolecules, such as hemicellulose, pectin, lignin, and xylan, during fermentation. Methanol itself is less toxic, although its metabolites are very toxic. When entering the body, methanol is metabolized by alcohol dehydrogenase—an enzyme that metabolizes alcohol in the liver, producing formaldehyde, which is 33 times more toxic than methanol and causes clinical symptoms. Formaldehyde is then rapidly converted to formic acid (which is six times more toxic than methanol) by formaldehyde dehydrogenase, which inhibits cytochrome oxidase in the optic nerve and disturbs axonal conduction. Finally, formic acid is converted to carbon dioxide and water.
Methanol affects mainly the central nervous system with symptoms of intoxication, somnolence, stupor, convulsions, and/or coma. A concentration of methanol in excess of the permissible limit can lead to poisoning for users. The Vietnamese standard (TCVN 7043: 2013) stipulates that the methanol content in 1 liter of 100-percent-proof ethanol is not more than 2,000 mg.
Difference between Ethanol and Methanol
Ethanol is alcohol produced by the distillation of starches from grains, rice, etc. Ethanol is used as a main ingredient in alcoholic beverages, perfumes, and mouthwashes. At regulated levels, it is not harmful to the human body. Traditional methods for the distillation of liquor from grains do not cause poisoning. Products with a high methanol concentration, as in the above-mentioned cases, come from mixing traditional liquor with industrial alcohol and bottling it for sale as low-priced, adulterated liquor.
Methanol is produced from materials containing cellulose and is used to dissolve inorganic or organic substances for non-drinking or antiseptic purposes. When it is misused as an ingredient in adulterated alcoholic beverages, it can be highly toxic and cause serious poisoning. The allowable methanol content in liquor is 0.1 percent, but the percentage of methanol in adulterated liquor is often much higher.
Due to differences in anatomy and physical health, people will have different reactions when drinking liquor containing methanol. Some people experience normal alcohol intoxication and may not show any symptoms of poisoning until a day or two later. Methanol is metabolized and eliminated from the body very slowly, so if the patient is not affected immediately, methanol can be dangerous since it remains at a detectable level in the body up to eight days after ingestion. However, if methanol is allowed to exist in the body for many hours, then the toxin will gradually convert into formic acid, which can lead to eye and brain damage.
Risks of Methanol Poisoning
Those who are poisoned by methanol usually show signs of intoxication within 30 minutes of consumption or possibly later, depending on how much liquor they consume. Usually, methanol poisoning includes two stages:
- Insidious stage (within the first few hours to 30 hours): Symptoms are initially subtle, mildly inhibiting nerves, sedation, and apathy, so they often go ignored or undetected.
- Poisoning stage (can manifest within hours or up to two days after consumption): Symptoms include vomiting, abdominal pain, impaired vision and eye pain, headache, slow reaction time, limping, impaired senses of taste and smell, impaired memory, muscle stiffness, and lack of motor control or convulsions. Severe poisoning can lead to unconsciousness (coma), hypotension, heart failure, and death.
Trace amounts of methanol are present in natural fruit juices, which are a nontoxic source of methanol due to its low content. Methanol is also a nontoxic product of alcoholic fermentation. When ethanol and methanol are both added to alcoholic beverages, however, the toxic metabolism of methanol appears to be slower and manifests as contamination. At a late stage of intoxication, patients and physicians may notice the symptoms of ethanol poisoning and miss the indications of methanol poisoning. For all clinical cases of suspected general alcohol intoxication, simultaneous testing of both ethanol and methanol should be performed.
Avoiding Liquor Adulterated with Methanol
Adulterated liquor is a public health issue because it is produced without regulatory or market oversight, and the addition of high percentages of industrial methanol poses a serious public health threat to consumers. To avoid liquor adulterated with methanol, only liquor of origin with clear labels and stamps certified by authorities should be sold at a retail establishments and consumed by end users. No liquor with a methanol content greater than 0.1 percent should be sold or consumed.
To detect the presence of high levels of methanol in adulterated liquor, researchers in 2020 reported the development of a palm-sized, sensor–smartphone system for the on-demand analysis of beverages. The sensor system was reported to quantify methanol concentrations in 89 pure and methanol-contaminated alcoholic beverages from six continents, performing accurate analyses for 107 consecutive days.1 This device, and other technologies under development, could be used to assist distillers, regulatory authorities, public health workers, and even consumers in easily screening for methanol in alcoholic beverages.
- Abegg, Sebastian, Leandro Magro, Jan van den Broek, Sotiris E. Pratsinis, and Andreas T. Güntner. "A pocket-sized device enables detection of methanol adulteration in alcoholic beverages." Nature Food 1 (2020): 351–354. https://doi.org/10.1038/s43016-020-0095-9.