By Noor Hasani Hashim
The Sun, November 21, 1995
The word arsenic is derived from the Greek word arsenikon, meaning potent. As early as 2000BC, the word become synonymous with poison.
In fact, it was considered "the perfect poison" for many reasons. These included its physical qualities (odourless and nearly tasteless with a sugar-like appearance), its ability to cause a slow painful death and the inability to detect it in the body.
Arsenic poisoning is thought to be responsible for the deaths of some well known historical figures such as Britanicus, Pope Pius III and Clemente XIV, Charles Francis Hall, and Napoleon Bonaparte.
Historically, arsenic was used for medical purposes and such functions were described by Hippocrates, Aristotle, Pliny the Elder and Paracelsus. It was used to treat dietary deficiencies (pellagra, anorexia), neuralgia, rheumatism, asthma, chorea, tuberculosis, diabetes, fever, skin disoders, malaria and syphilis. In Third World countries, it is still being used for the treatment of some protozoal infections.
Chemically, arsenic is classified as a transition element or metalloid and it usually exists in the form that is bonded to other elements such as carbon, hydrogen and oxygen. Arsenic may exist in three different oxidation or valence states, namely the metalloid, arsenite and arsenate states.
Knowing the state of the arsenic compound is important as they vary substantially in their toxicity to mammals. The most toxic of all arsenic compounds is arsine gas. This is followed by inorganic trivalent mercuric compounds, organic pentavalent compounds and finally elemental arsenic.
Some arsenic compounds are apparently non-toxic at any dose. Toxicity, however, may also depend on other factors such as the physical state (gas, solution or powder), particle size, the rate of absorption into cells, the rate of elimination, the presence of impurities and the nature of the chemical constituents in the compound.
Among the most important poisonous arsenic compounds used commercially are the arsenious oxide and the arsenic pentoxide. The arsenious oxide, which is known as white arsenic, is used in the making of pesticides, in the manufacture of glass and the preservation of animal hides. Arsenic pentoxide is a major ingredient in the production of insectisides, herbicides, weed killers and metal adhesives.
Besides these, arsenic acid, lead arsenate and calcium arsenate are other forms of arsenic being used in agriculture for sterilizing soils and controlling pests.
Arsenic exists in both yellow and grey crystalline forms. Grey arsenic is more stable than the softer yellow form. It sublimes when heated and turns directly from a solid state to vapour without passing through the liquid state. Upon cooling, it goes straight from vapour to the solid state. In nature, it is found in areas where silver or antimony are deposited.
Arsenic is a ubiquitous heavy metal found in fossil fuel, water, air and marine animals. Sea water ordinarily contains 0.006 to 0.03 parts per million (ppm) of arsenic. In active geothermal areas, arsenic is naturally present in soil in amounts as high as 20 ppm, and levels of several hundred ppm may occur after years of use of pesticide.
Arsenic is present in all living organisms. The average daily human intake is 0.5 to 1 mg, most of which is in the form of food and water. The highest concentrations are found in fish and crustaceans, and urinary arsenic concentrations can increase 10 fold after a large seafood meal.
In 1984, the American Association of Poison Control Centres received information on 5,000 cases of heavy metal ingestion. Arsenic was the heavy metal most commonly involved in these poisonings.
Of 1,200 reported cases of arsenic ingestion, 847 occurred in children less than six years old. Fortunately, the majority of these cases were not serious. These poisonings, however, were preventable. This is because the most common cause of these poisonings were from over-the-counter preparations. These sweet syrupy solutions are as attractive to toddlers as they are to ants or rodents.
Clinical manifestations of arsenic poisoning may vary greatly depending on the chemical compound, dose, rate of ingestion and patient characteristics. Multiple organ involvement seems to be the norm for both acute and chronic poisoning.
A dose of 20 mg arsenic trioxide may be life-threatening while doses ranging from 200mg to 300mg has always been associated with death.
Arsenic poisoning usually manifests itself within 30 to 60 minutes following ingestion. However, this may be delayed if arsenic is taken together with food. The severity of symptoms depends on the amount and form of arsenic ingested.
With arsenic dioxide, as little as 1mg has been reported to cause severe toxicity. The clinical presentation of acute arsenic toxicity occurs in two distint forms; acute gastrointestinal and acute paralytic forms.
The acute gastrointestinal form is the most common presentation of arsenic poisoning. Initially, the patient may experience a metallic or garlic-like taste associated with dry mouth, burning lips and/or dysphagia (difficulty swallowing).
Violent vomiting ensues and this may progress to frank vomiting of blood. Diarrhea is often profuse, with stools ranging from "rice water" in consistency to hematochezia.
These gastrointestinal symptoms are usually the result of injury to the gastrointestinal tract. Severe gastrointestinal symptoms often result in dehydration and electrolyte imbalance and may lead to a state of low blood pressure and oxygen deprivation. A number of organs may fail to function normally because of this.
Acute massive arsenic ingestion on the other hand can result in the acute paralytic syndrome. This is characterised by cardiovascular collapse, central nervous system depression and death within hours.
Chronic arsenic exposure can occur from working in the smelter industry. The smelting of non-ferrous ores, particularly copper and gold, is one example of this.
To protect children from accidental arsenic poisoning, restriction of the toxin source must be considered. Since insecticides and rodenticides are the most common sources, it is reasonable that such subtances be sold in amounts sufficient to kill rodents or ants but not in quantities that would endanger the lives of children.
This step can be expected to reduce the number of serious accidental poisonings and might reduce the number of serious intentional poisonings as well. Other measures to be considered include the use of childproof containers and registration of purchases.
In general, accidental poisonings involving arsenic have been diminished by campaigns to increase social awareness, by the use of childproof containers for toxic substances and by the practice of reporting suspected cases of child neglect, abuse or endangerment to the social services or relevant authorities.
The writer is a chemist at the National Poison Centre, Universiti Sains Malaysia, Penang.
